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SD 2 Documentation - Department of Electrical Engineering and

1. ee Re ee ee ee ee RR ee ee ee ee ee ee RR ee ee ee 117 PAO User Mandala AA A n de AAA ord 118 A EE We eee 118 TL Operaatio ass sin A IA A nae A De GE OAS 118 7 3 Monitoring and Log iia ESE BERGE RAS EE AR Se RR GR Se RR DR Re GR ee Se Ee Se 119 APPLESANA AAA AAA Ge 120 Appendix A Copyright PerMisSi0NS ooooooooooooooooooooonnnnnnnnnnononnnnnononnnnnnnonnnnnnnns 120 Appendix B Works Cited rd Re si ved ee ee Ge Ee eect 125 Appendix Eist of FigUrES sais SS ee an EG ta lo ed Ee dE 128 Appendix D Listof tables SE se Ee N eg ER se eo EE ed 129 Appendix E List of Equal A ge ee we Ge GE ER Ge nn 130 1 0 Executive Summary The Group 7 South Africa Project G7 SAP is a power system intended to make energy from renewable fuel to help the Pomolong Township of South Africa power their community center The power system will also store any power generated and provide interfaces to the community center that allows for easy practical use of the power The main purpose of The G7 SAP is to allow an impoverished village to be able to be entirely energy sufficient by giving them the tools to help sustain themselves through the means of a green energy solution The power system is user friendly and easy to monitor and maintain because it is intended to be used by individuals with little to no technical background The ultimate goal of this project was to create an off the grid stand alone photovoltaic PV system that utilizes m
2. R108 R109 R110 R111 R112 2 2k 1 20k 5 20k 5 100 1 100 1 100 1 0 2 2 2k 1 20 5k 1 100 5 100 1 12 4k 1 47k 5 10k 5 1M 5 1M 5 100k 1 10k 1 15k 1 10k 1 22k 1 1M 5 20 5k 1 10k 5 1M 5 SMO805 SMO805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SMO805 SM0805 SMO805 SM0805 SM0805 SM0805 SM0805 SM0805 SMO805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 MCR10EZPF2201 RK73B2ATTD203J RK73B2ATTD203J MCR10EZHF1000 MCR10EZHF1000 MCR10EZHF1000 MCR10EZHFLR200 MCR10EZPF2201 MCR10EZHF2052 MCR10EZPJ101 MCR10EZHF1000 MCR10EZHF 1242 MCR10EZPJ473 RK73B2ATTD103J MCR10EZPJ105 MCR10EZPJ105 MCR10EZPF1003 MCR10EZPF1002 MCR10EZHF 1502 MCR10EZPF1002 MCR10EZHF2202 MCR10EZPJ105 MCR10EZHF2052 RK73B2ATTD103J MCR10EZPJ105 102 Semiconductor ROHM Semiconductor KOA Speer KOA Speer ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor KOA Speer ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor KOA Speer ROHM 0 08 0 08 0 05 0 05 0 05 0 37 0 10 0 05
3. 0 05 0 05 0 08 0 05 0 05 0 05 0 05 0 05 0 05 0 05 0 05 0 08 0 05 R113 R114 R115 R116 R117 R118 R119 R120 R121 R122 R123 R124 SW2 U3 U4 U5 U6 U9 U10 U11 U12 U14 U15 X1 Total 47k 5 2M 1 47k 5 15k 1 15k 1 4 7k 5 4 7k 5 1M 5 100k 5 33 5 100k 1 1k 5 RESET SW IRS21171 LPV324M LPV324M LPV324M MC33063 A TPS73018 LPV324M 74LVC1G 332GW INA194AI SM0805 SM1206 SM0805 SM0805 SM0805 SM0805 SM0805 SMO805 SM0805 SM0805 SM0805 SM0805 con headers jp SIP 100 02 SOIC8 avr 4 SOIC14 avr 4 SOIC14 avr 4 SOIC14 SOIC8 SOT23 avr 4 SOIC14 SOT363 P HILIPS SOT23 LQFP48 HC 49V MCR10EZPJ473 MCR18EZPF2004 MCR10EZPJ473 MCR10EZHF 1502 MCR10EZHF1502 RK73B2ATTDD472J RK73B2ATTDD472J MCR10EZPJ105 RK73B2ATTED104J ERJ 6GEYJ330V MCR10EZPF 1003 RK73B2ATTDD102J 1825027 5 IRS21171STRPBF LPV324M NOPB LPV324M NOPB LPV324M NOPB MC33063ADR2G TPS73018DBV LPV324M NOPB 74LVC1G332GW INA194AIDBVT MPT612FBD48 151 ECS 120 20 4XDN 103 Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor KOA Speer KOA Speer ROHM Semiconductor KOA Speer Panasonic Corp ROHM Semiconductor KOA Speer TE Connectivity International Rectifier Texas Instruments Texas Instrument
4. to the system with no load 2 Connect Multi meter to battery to check for voltage 3 Connect Multi meter to battery to check for current 4 Monitor the time it takes for the battery to reach the Float charging state Expected Results Battery should start to Charge The Multi meter should read a voltage that coincides with the charging stage The Multi meter should read a current that coincides with the charging stage According to the battery and charge controller ratings it should take 8 hrs Table 29 Battery Discharge Time Steps Procedure 1 Connect the battery to the inverter with a predetermined load 2 Connect Multi meter to battery to check for voltage 3 Connect Multi meter to battery to check for current 4 Monitor the time it takes for the battery to reach the Float charging state 111 Expected Results Battery should start to discharge The Multi meter should read battery full voltage that will gradually decrease The Multi meter should read a current that is being drawn According to the battery and load ratings it should take 8 Hrs at a 5Ah load rate 6 3 Inverter Testing First we tested if the inverter outputs an AC voltage of 120V from a 24V DC power source The output waveform should be a modified sine wave with no distortion The maximum power should be 500W and the surge power should be 600W If any of the specifications above were not accomplished then the group had
5. 2381 640 63152 PSMN8R2 80YS PSMN1R3 30YL PSMN8R2 80YS PSMN1R3 30YL PBSS8110Z PMBT2222A PMBT2222A PBSS4160T PBSS4160T PMBT2222A PBSS4160T 99 Panasonic Corp Panasonic Corp Panasonic Corp EPCOS Panasonic Corp NXP Semiconductors NXP Semiconductors NXP Semiconductors EPCOS Vishay BC Components NXP Semiconductors NXP Semiconductors NXP Semiconductors NXP Semiconductors NXP Semiconductors NXP Semiconductors NXP Semiconductors NXP Semiconductors NXP Semiconductors NXP Semiconductors NXP 0 30 0 30 0 30 2 09 0 30 0 42 0 42 0 42 0 39 1 30 1 30 1 30 1 30 0 43 0 12 0 12 0 17 0 17 0 12 0 17 R1 R2 R3 R4 R5 R6 R7 R8 R10 R16 R21 R22 R23 R24 R25 R26 R27 R28 R29 R30 R31 R32 R33 R35 R36 R37 R38 OT 15 5 15 5 68 1k 1 27 4k 1 3 9k 1 0 010 1 4 1k 1 0 005 1 0 01 1 33 5 10k 5 20k 5 10k 1 10k 1 68 1k 1 10k 1 1k 1 10k 5 68 1k 1 68 1k 1 10k 5 20k 5 10k 1 5 1k 1 10k 1 68 1k 1 SM0805 SM0805 SM0805 SMO805 SM0805 R2512 SM0805 R2512 R2512 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SMO805 SM0805 SM0805 SM0805 SM0805 SM0805 SMO805 SM0805 SM0805 SM0805 SMO805 SM0805 ESR10EZPJ150 ESR10EZPJ150 MCR10EZHF6812 MCR10EZHF2742 MCR10EZHF3901
6. Controller SM72442 Programmable MPPT controller also by Texas Instruments and the NXP Semiconductor MPT612 Maximum Power Point Tracking IC 3 1 2 3 Texas Instruments BQ24650 The BQ24650 offers a highly integrated charge controller with MPPT capability by input voltage regulation three phase charge profile as well as charge status LED indicator outputs The MPPT algorithm is implemented slightly differently in this chip compared to the Arduino solution In this setup the input voltage is monitored in the feedback loop not the input output ratio This is known as the Constant Voltage algorithm and is considered by Texas Instruments to be the simplest MPPT method The BQ24650 automatically reduces charge current to maintain MPP behavior If the solar panel cannot provide the power required to run the charge controller then the input voltage begins to drop If the sensed voltage drops below a certain threshold the controller will reduce charge current to attempt to maintain the voltage If the sensed voltage drops further charging is disabled entirely While the BQ24650 has a lot of the features required for this project specifically the MPPT algorithm and basic protection and monitoring it was not chosen because of the lack of flexibility and documentation It did not quite compare to the other two chips with regard to availability of reference designs application and design notes and software programmability 3 1 2 4 Texas In
7. SM0805 SM0805 SM0805 SM0805 SMO805 SM0805 SMO805 SMO805 SM0805 SM0805 SM0805 SM0805 SMO805 SM0805 SMO805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 MCR10EZHF5101 MCR10EZHF 1001 MCR10EZHJ000 MCR10EZHF6812 MCR10EZHF6812 MCR10EZPF2741 MCR10EZPF1002 MCR10EZPF1002 MCR10EZPF2741 RK73B2ATTD103J MCR10EZPF1003 MCR10EZPF1002 RK73B2ATTDD472J RK73B2ATTDD102J MCR10EZPJ222 MCR10EZPF1802 MCR10EZPF1003 MCR10EZPF1002 RK73B2ATTDD472J MCR10EZPF1002 RK73B2ATTD103J MCR10EZPJ473 MCR10EZPJ222 RK73B2ATTDD102J MCR10EZPF1003 MCR10EZPF1002 101 Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor KOA Speer ROHM Semiconductor ROHM Semiconductor KOA Speer KOA Speer ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor KOA Speer ROHM Semiconductor KOA Speer ROHM Semiconductor ROHM Semiconductor KOA Speer ROHM Semiconductor ROHM 0 05 0 05 0 05 0 10 0 10 0 10 0 05 0 05 0 10 0 08 0 05 0 05 0 08 0 08 0 10 0 10 0 05 0 05 0 08 0 05 0 08 0 05 0 10 0 08 0 05 0 05 R79 R81 R82 R84 R86 R87 R93 R94 R96 R97 R98 R99 R100 R101 R102 R103 R104 R105 R106 R107
8. anks 123 Genesh Chen Shue Your Email ge5485 1 8 knights ucf edu Please ensure that your email address is correct Topic Select y Subject images in magazine Your Message Hi Homepower lam an engineering student from the University of Central Florida For our senior design project we are designing a solar power based power generation system for an impoverished African village In designing our battery bank we wanted to describe battery topologies and wanted to use an image in one of your magazine The image can be found on http www thecollaboratoryonline org w images Choosing_the_Best_Batteries pdf Please let me know if we can use the image for strictly academic and information purposes in our research documentation Thank you for your help in these issues Genesh Chen Shue 124 Appendix B Works Cited 1 2 3 4 5 6 7 8 9 Central Intelligence Agency The World Factbook 2009 2009 Online Available https www cia gov library publications the world factbook index html Accessed 26 November 2012 Wholesale Solar Wholesale Solar Online Available http www wholesalesolar com Information SolarFolder celltypes html Accessed 26 November 2012 B Burleigh A Calhoun E Eiermann and P Neely The Green Box 2009 Online Available http eecs ucf edu seniordesign su2009fa2009 g05 Accessed 26 November 2012 A Scheurer E Ago S
9. usc R37 S 30 DBAT volt sense 9 af LPVS24M GNDPWR 0 04uF GNOPWR BAT voltage sense circuit D BAT_overvoltage SSA R55 R59 isk 17 GNDPWR For the battery voltage sense the input signal comes from a voltage divider on the secondary side of the DC DC converter The signal enters on the left U5A operates as a battery overvoltage indicator If the overvoltage level is reached PWM to the battery is cut off Op amps U5B and U5C comprise the main voltage sense circuit U5B amplifies the signal with a gain of 1 1 and USC is a low pass filter to remove noise from the signal 65 Figure 15 Battery Current Sense Circuit T i 3 c3 mages O 1uF Ter D A BAT current sense circuit een But Ja BAT current ref AD O 12 AE P spel ves C34 as f lt i PVS24M al ion E tochar am 0 33uF 0 33uF GNOPWR GNDPWE agi mn GNDPWR BAT RLG 260 r B m a al sb al File BAT volt current sense sch ra GNDPWR Sheet BAT voltage and current sense ide Title GNDPWR Size A4 Date 3 dec 2012 m KiCad E D A eeschema 2012 01 19 BZR 3256 stable For the battery current sense the input signals enter the circuit on the left They come from a sense resistor located on the high current path of the secondary side of the DC DC converter Op amps U6A and U6B comprise a two stage amplifier to enhance the signal The first stage operates with a gain of
10. 110 07 T S 282856 2 282856 2 282856 2 282856 2 RB6132 50 0M2 EXC 3BP121H EXC 3BP121H 98 NXP Semiconductors Fairchild Semiconductor NXP Semiconductors Everlight Everlight Everlight NXP Semiconductors AVX KOA Speer KOA Speer KOA Speer KOA Speer Cooper Bussmann Cooper Bussmann Schurter Schurter Samtec Inc Samtec Inc TE Connectivity AMP TE Connectivity AMP TE Connectivity AMP TE Connectivity AMP Schaffner Panasonic Corp Panasonic Corp 0 34 0 46 1 44 0 25 0 24 0 22 0 30 0 06 0 08 0 08 0 08 0 08 0 72 0 72 0 50 0 50 2 24 0 75 0 87 0 87 0 87 0 87 26 49 0 30 0 30 L4 L5 L7 L8 M1 M5 M6 MOV1 NTC1 Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q11 Q13 d 121E_bea d 121 BEAD 121 BEAD 47uH 121E_bea d PMV65XP PMV65XP PMV65XP VR RVAR PSMN8R2 80YS PSMN1R3 30YL PSMN8R2 80YS PSMN1R3 30YL PBSS811 0Z 2N2222A 2N2222A PBSS416 OT PBSS416 OT 2N2222A PBSS416 SMO0603 SM0603 SM0603 140CLH 1010 SMO0603 SOT23 SOT23 SOT23 R3 LARGE_PA DS R3 LARGE_PA DS transistor power SOT669 transistor power SOT669 transistor power SOT669 transistor power SOT669 SOT223 SOT23 SOT23 SOT23 SOT23 SOT23 SOT23 EXC 3BP121H EXC 3BP121H EXC 3BP121H B82464G4473M EXC 3BP121H PMV65XP PMV65XP PMV65XP SIOV CN2220K25G
11. 30 Modified Pure Sine Wave ee ee ee RR ee ee ee ee Re RR Re ee ee ee 82 Figure 31 Commercial Power Inverter ees ee ee EE ee ee ee ee AR EE Ee ee ee ee ee 82 Figure 32 Pulse Width Modulation ees ss ee ee RR ee ee ee ee ee AR EE ee ee 83 Figure 33 Block Diagram for PWM InverteF ee ee ee ee ee RR ee ee ee ee ee 84 Figure 34 Bubba Oscillator Diagram ees ee ee RR ee ee ee ono RR RR ee ee ee ee ee 85 Figure 3S TE TESDAEN se GE LE EE ES Ge EG DLE 85 Figure 36 Example of Inverter Monitoring Display iese ee ee ee 87 Figure 37 Proposed Enclosure Design ee ee ee ee RR Re ee ee ee ee 90 Figure 30 Power Cables ES 91 EQU PCB aisla 104 Figure 40 Warning Label Sample ie ee ee ee RR ee ee ee ee ee ee ee ee RR 114 128 Appendix D List of Tables Table 4 bEaliEAUORS tit Bee A GR ah allan ias 8 Table 2 Senior Design 1 Project MilestonesS ee ee ee ee ee 10 Table 3 Research Milestone usus lg a Rd AG kg 12 Table 4 Design Milestone ee RR ER Ee ee ee ee AR EE Ee ee ee ee ee 13 Table 5 Acquisition Milestone us E Se ie se ee ee 14 Table 6 Prototype Milestone ee Ge ee ee Ve ee n 15 Table 7 Testing Milestone ii ee RR ee RR Ee ee ee ee ee ee AR EE Ee ee ee ee ee 16 Table E Budget du SAA AAA AAA AA AAA 17 Table 9 Factors for Choosing Battery ee ee ee ee ee ee ee ee ee ee 36 Table 10 Sample Battery Specs ie ee ee RR EE ee ee ee ee ee AR EE ee ee ee 39 Table 11
12. Availability Easy to find Internationally Maintenance Add water 3 1 4 Inverter The inverter will enable the system to deliver power stored in the batteries to the user efficiently and safely This is the final part of the project and is the final major section of the system The main function of the inverter is to convert direct current to alternating current similarly found in a household power outlet Inverters are not only used in off grid power systems but also inside electronic devices such as computers as small switching power supplies There are many Gel UB GC2 6V 225 AH is 280 90 charge discharge efficiency Hazardous 6V 12V 24V Hard to Find Internationally No Maintenance needed AGM UB GC2 6V 225 AH is 265 98 charge discharge efficiency Non hazardous 6V 12V 24V Hard to Find Internationally No Maintenance needed types of inverters the following is a table of the different kind of inverters 18 44 Table 15 Different Inverter Types Inverter Type Description Square Wave Square wave output arrived with the first inverters They have a high distortion level and cannot power most AC loads Modified Sine Also called guasi sguare these waves are similar to sguare Wave waves However the output goes to zero for a time before switching This is done to closer simulate a sine wave Most AC loads will work with this signal however at a lower efficiency Multilevel These inverte
13. Commercial Inverters As stated before there are many power inverters out there in the market today They range with wide varieties of characteristics prices and sizes The most well known brand for power inverters is Power Bright A close second would be the Cobra power inverters For the purpose of this section three of both brands of power inverters with similar characteristics are compared in the following table 51 Table 19 Commercial Power Inverters Comparison 22 Power Bright Power Inverter Cobra Power Inverter Continuous Power 900W BOOW Input 12V DC 12V DC Output 110V AC 110V AC Peak Power 1800W 1600W Number of Outlets 2 2 Price 58 00 80 00 Continuous Power 1100W 1000W Input 12V DC 12V DC Output 110V AC 110V AC Peak Power 2200W 2000W Number of Outlets 2 2 Price 90 00 120 00 Continuous Power 900W 1500W Input 12V DC 12V DC Output 220V AC 220V AC Peak Power 1800W 3000W Number of Outlets 1 3 Price 84 00 135 00 To conclude it can be seen that the input seems to be pretty standard throughout commercial inverters Also since the group is located in North America the output seems to be 110V AC standard However some brands offer European standard power which is 210 220V AC Another thing to note is that the Peak Power is usually two times as much as the Continuous Power As for price the power inverters above seem to range from 50 to 150 However 52 it is very crucial to remember that all of the power inve
14. The columns shown are described respectively PV voltage mV PV current mA PV power uW battery voltage mV battery current mA ambient temperature Celsius Load current mA PWM duty cycle The controller output will say TRACKING when it is tracking for the maximum power point MPP Once the MPP has been found the following will be displayed in the terminal MPP LATCHED Vmpp mV 17067 Wmpp UW 18483561 PW 261 This means the maximum power point has been achieved and the battery is being charged at optimum efficiency In the event that the controller output freezes or stops responding the software can be reset by momentarily pushing the red reset button located on the side of the charge controller This will restart the system and should begin tracking for MPP again 119 Appendices Appendix A Copyright Permissions Hi Rockwell Automation My name is Genesh Chen Shue am an engineering student at the University of Central Florida For our senior design project we are designing a solar power based power system for an impoverished african village In designing our inverter we wanted to describe pulse width modulation would like to use images describing pulse width modulation and its output in the document found at http www ab com support abdrives documentation techpapers PWMDrives01 pdf Please let me know if we can uselthe image for strictly academic and information p
15. converter is fixed at 20kHz to optimize both the switching loss and the inductor size The inductor eguation is given by Equation 2 lay lo 6 Where lo is the output current and 6 is the duty cycle In buck boost mode the maximum duty cycle is 60 The input bulk capacitor calculation is below The parameter to keep in mind for this application is the Effective Series Resistance or ESR and RMS current rating Low ESR is desired to minimize input voltage ripple and high current changes on the output Placing two capacitors in parallel will also further reduce the ESR Equation 3 Cr min Ii x ton AV Equation 4 ESR AV 1 0 The efficiency of the converter in buck boost mode depends on the diode forward voltage drop Vr so a diode with low V is desired Schottky diode STPS40L45CG has a forward voltage drop V 0 45V With the V parameter calculated the output filter capacitors can now also be calculated Equation 5 Co 2 leeg X Vo Vp Ven Yaw Vo Y7 NM 71 Where fosc is the switching frequency 20kHz AVoc 200mV and Vi 0 4V 4 2 6 Power Supply The power supply module is responsible for creating the 3 3v and 1 8v power rails which are used to power all of the integrated circuits and other externally powered components in the charging system The power supply circuit consists of two voltage regulators and three standby switches for energy savings and circuit protection Figure 21
16. ee ee ee RR RR ee ee ee ee ee 47 Figure 9 General Power Bright Inverter ee ee ee ee RR ee ee ee ee ee 53 Figure 10 Cobra Power Inverter iese ee se ee ee ee RR ee ee ee ee ee ee AR EE ee ee ee n 54 Figure 11 Battery Bank Connected to Power Inverter iese esse ee ee ee ee ee 54 Figure 12 MPPT Graph Ll id eo io GE e Li 59 Figure 13 Charge Controller Root Sheet ee RR RR ee ee ee ee 64 Figure 14 Battery Voltage Sense CircuIt iiiee ee RR Re ee RR RR RR Re ee ee ee ee 65 Figure 15 Battery Current Sense Circuit EE ee RE Ee ee ee ee ee 66 Figure 16 Solar Panel Voltage Sense Circuit ee ee Re Re ee 66 Figure 17 Solar Panel Current Sense Circuit RR RR ee ee 67 Figure 18 JTAG UART Connector and GPIO Connector 68 NO A 68 Figure 20 DC DC Converter ee ee ee ee ee ee RR ono no ke ee ee dee ee ee ee ee ee ee ee 70 Figure 21 Power SUDDIV ii AAA AAA N de le 72 Figure 22 JTAG UART Add on Board ee ee ee ee ee RR ee ee Re ee ee ee ee ee 74 Figure 23 Charge Controller Application ee ee RR RR ee ee ee ee ee ee 75 Figure 24 Series Wiring sede ese A A REG Eg we GE tai 78 Figure 25 Parallel Wiring a Se GR A RO BEE EG ER eN 78 Figure 26 Series Parallel Example ie ee ee RR ee ee ee ee AR EE ee ee ee 79 Figure 27 Single Series SING Error Bookmark not defined Figure 28 Two Series String ee Error Bookmark not defined Figure 29 Three Series SING ese Error Bookmark not defined Figure
17. is very important for the G7 SAP project The approach to the products Casing component was a progressive debate amongst the group members continually evolving and building upon itself throughout the whole of the design process The group all had justifiably envisioned the product In their individual ways when they came into this and had to gradually compromise and merge all different visions to reach a consensus yielding a product of increased functionality by summing the best of all parts We break up the casing design of the G7 SAP into two enclosure due to the high danger that the batteries can cause We have a casing for the battery bank and another one for all the other small component such as the inverter and charge controller We have seen a variety of materials used successfully such as plastic storage totes and coolers fiberglass reinforced plastic sheet PVC and even old refrigerators We ended up using an old computer chassis and modified it for use for our project It s familiar attractive versatile dimensionally stable and strong Most owner builders and building crews can make a good box and it is adaptable to specific sites and needs For insulation we used plywood The best plywood material we have used is called Baltic Birch available through wholesale lumber and hardwood suppliers We obtained ours from Home Depot It is 1 2 inch thick with nine plies and comes in various sheet sizes including our preferred 60 by 6
18. metal Variable Controls speed of an AC motor by controlling the AC source Frequency drives frequency and voltage Electric Vehicle Motors used in electric vehicles use inverters Also they Drives are used in regenerative braking technology which takes energy from heat to charge batteries Also the gas engine charges the batteries Air Conditioning Uses a variable frequency drive to control the speed of the motor and activation of compressor 3 1 4 2 Basic and Advanced Inverter Circuit Design At the basic level an inverter circuit consists of a DC power source connected to a transformer A transformer is a power converter that transfers AC power so it is effectively an AC to AC converter These are used widely for electronic appliances that work with 110V AC in a place where there is only 210V AC available In order to prevent damage for the electronic appliance a transformer must be used So the transformer is switched rapidly back and forth to allow current to flow back and forth thus creating AC in the circuit Back in the day when inverters were first used an electromechanical device had to be used to perform the switching So this device consisted of two stationary contacts and a spring moving contact The spring is used to hold one contact to a stationary one then a electromagnetic force pulls it to the other stationary contact Once it reaches the other contact the electromagnetic force is interrupted by the contact of the spri
19. system for low cost and high reliability is not practical Furthermore the 555 timer based circuit is just too simplistic It does not have any sort of charge profile to maximize the battery life circuit protection logging and monitoring support nor does it implement any maximum power point tracking algorithm for efficiency With a lack of these essential features the 555 timer based charge controller was not chosen for this project 3 1 2 2 Arduino PPT Solar Charger The next charge controller implementation which was considered during research was built around the Arduino platform The Arduino PPT Solar Charger is a small circuit board module which piggybacks on top of the Arduino board It uses the Arduino s microcontroller to implement the maximum power point tracking algorithm control the DC DC converter and provide optional logging and data output In this sense the charge controller is modularized This is the first implementation found during research which contains the required MPPT algorithm Since the maximum power point is not fixed for any solar panel the feedback loop for the DC DC converter differs than that of converter found in a traditional power supply While a DC DC converter for power supply applications uses a fixed input output voltage ratio for a solar charge controller the ratio is constantly in flux due to the constantly changing maximum power point Thus MPPT controllers typically use software algorithms to
20. that AGM was superior in almost every way The final sway in the decision to go with flooded Deep Cycle Lead Acid Batteries was there cost and availability It was considered that the part of the system most likely to be damaged or be in need of replacement would be the Batteries so it would be ideal to choose batteries that could be easily obtained in almost any place in the world With the price for the battery being lower it allows for more room in the budget to make irreplaceable parts in the project more robust and stable The charge controller was introduced as the component in the solar system that sits in between the PV panels and the battery bank and provides protection and monitoring capabilities aside from increasing the efficiency of the charging process using the MPPT algorithm Several different charge controller implementations were looked at varying from the simplicity of a 555 timer or an Arduino but these were too simplistic in the sense that they did not employ the use of a DC DC converter for increasing efficiency In the case of Arduino it freed up the computer engineer from doing any real computer engineering The more sophisticated charge controller ICs all required some form of DC DC 93 converter and thus were more complex however also far more efficient They were specifically geared toward renewable energy applications so all featured an MPPT algorithm The ICs from Texas Instruments and NXP have sophisticated featu
21. the two photovoltaic cell terminals Crystalline or first generation photovoltaic cells are usually protected from the outside elements with a protective layer of glass or clear plastic cover A clear layer of silicone is used to attach the rest of the cell to the glass An antireflection coat covers the n type terminal The n type terminal is then connected to the n type silicon Below the n type silicon layer is the p type layer needed to form the p n junction in between them The p type terminal is beneath the n type layer and lies on top of a conductive contact The entire structure and process can be seen in the image below 25 Figure 2 Silicon Solar Cell Structure and Mechanism 14 Reproduced with Permission under the CCLA 3 0 Antireflection layer SiO2 Solar panels in all sorts of various makes and models are not very efficient at converting solar energy noting that the highest efficiency made is 30 which is not even available for general consumer use Due to this solemn realization panel performance and any means to increase it are very important to this project All solar panels suffer from naturally caused issues that may decrease performance such as temperature electron hole recombination rate and light absorption efficiency How these different factors affect performance were addressed The first factor that was addressed was electron hole recombination The rates of electron hole recombination for Mono crystalline p
22. these ideas are unique to this project because this project will be used for an actual group of people who actually need power in reality This project is turning efficient but abstract ideas into tangible tools that render assistance to those most in need 3 1 1 Solar Panels With the knowledge that the goal of this project is to produce power it became necessary to find a reliable energy source to be utilized as fuel Using energy from the sun through the use of photovoltaic panels was an obvious idea to think about because South Africa is known for being sunny The object of this research section on energy production due to the conversion of solar radiation into electricity using semiconductors that exhibit the photovoltaic effect is to display the current status of solar technologies and to discuss the best options that can be used for this project This can be shown by an exhibition of the latest improvements in photovoltaic cell technology price comparisons of current 19 models of PV panels and climate conditions of the Pomolong Township that may affect the final decision making processes 3 1 1 1 Photovoltaic Cell Technology The first way to obtain solar energy is with Concentrated Solar Power This way involves the use of mirrors and lenses to intensify sunlight The thermal energy from the intensified sunlight is used to heat up water to produce steam The steam is used to turn steam turbines connected to a generator which then p
23. they do not lose as much efficiency as their temperature increases compared to their crystalline counterparts giving them an edge in warmer climates To top that off the CIGS compound has a panel efficiency of around 10 to 15 with a peak of 19 9 9 Because of these impressive numbers increases in the production of CIGS panels are projected to increase in the future The only downside to using these panels currently are that they are expensive and scarce due to being relatively new being in low supply and having an expensive fabrication process The next Thin film that will be discussed will be the Cadmium Telluride Thin film panel also known as CdTe panels They were one of the first semiconductors that were used in Thin film technology to improve the low efficiency experienced with amorphous silicon CdTe panels are produced similarly to CIGS panels They are the most common type of Thin film solar panel on the market due to being the most cost effective Thin film solar panel to manufacture Similarly to CIGS panels CdTe panels also perform better in higher temperatures and low light conditions compared to crystalline panels As for efficiency Cadmium Telluride Thin film panel range in efficiency from 7 to 12 with a peak of 16 5 10 The major disadvantages of these panels are that they are dangerous to the environment because Cadmium is toxic and they are expensive because Tellurium is rare 23 The final panel that will be dis
24. to go back to designing and building because without these specifications than the inverter could not be able to accomplish its goal of powering AC loads at the groups specifications When testing new equipment it is important to note what the equipment is meant to do thus having an idea of what kind of testing to perform not only to check if it is in proper working condition but also meets safety standards and will not endanger its users So if one looks at the purpose of the projects inverter the device is used to convert DC power to AC power Therefore this device works with high voltage and current which will cause high temperatures coming from the device The high temperatures can potentially cause a fire if there are no cooling properties for the device So for the first part of testing we wanted to make sure that the inverter is safe to use for long periods of times without anything catching fire Also we had to take note that the system would be used in a non air conditioned room So to take this into account we did temperature testing outside As far as stress tests for the inverter the group plans on running the inverter for 8 hours straight powering a low demanding AC load which is no more than 150 W and monitor the temperatures Next we will run the inverter at its max AC load for as long as the batteries can hold and monitor the temperatures Depending on the results of these tests the inverter may require some idle time after bein
25. up almost half of the budget The second most expensive part of the project were the batteries which are a crucial part of the project The rest of the parts were much more cost efficient because the executive decision to build them from scratch From then on vast amount of research was done and documentation for the research section began Collecting part numbers conducting research on the location of the project and designing sections of the project took up the majority time of the Fall semester Throughout the Fall semester which started in August and ends in December most of the focus was spent on research In order to have a successful project it was established biweekly that every member of the Senior Design group needed to provide an update on work currently being worked on and a complete evolution and process of their work This enabled the group to be on the same page and work with the same pace Between September and November the primary focus was to conduct thorough and well documented research The 11 majority of the research was done between October and November as depicted in the table below Table 3 Research Milestone Research 2 n g 2 o o 2 O o Y O c a 2 D 2 O o E D Oo E G 5 oO Bl o 1 o O gt ou N m O The design phase overlapped with the research section The design phase also overlapped with the parts acquisition portions of
26. waste a considerable amount of energy that is painfully collected from the solar panels Lithium ion batteries have a unique characteristic Their ions move from the negative electrode to the positive electrode during discharge and go back to the negative electrode when charging As one of the most popular secondary batteries for portable electronics lithium ion batteries have one of the best energy densities no memory effect and only a slow loss of charge when not in use 22 Size wise they are much lighter than other secondary batteries and come with a wide variety of shapes and sizes However one disadvantage of Lithium ion batteries disqualifies them to be a part of the power generation system high cost Lithium ion batteries are more expensive than any other secondary battery type Due to limited budget lithium ion batteries are not an option for the Pomolong Township project Lead acid batteries on the contrast have the lowest cost and highest price to power ratio among the four secondary battery types They are the oldest 37 secondary battery technology and they are the most widely available in the world Performance speaking lead acid batteries have low internal resistance and can deliver very high currents They are also tolerant to abuse and overcharging In short lead acid batteries are currently the best option due to cost availability and functionality Thus for G7 SAP the research focus is on the lead acid
27. 0 inch Besides being attractive it is dimensionally stable and easy to work with To prevent maintenance issues from occurring we made sure that the battery container was well ventilated and had a snug fit on the frame This is about the depth of three rows of L16s or two rows of larger industrial type cells The length of the box was around 50 inches If space is factored in between each battery for ventilation this translates into a box length of about 60 inches Two or three sheets of 60 inch plywood is enough for most battery enclosures with little of the waste if the panels had been cut from conventional 4 by 8 foot plywood Even if a box can be less than 48 inches long a larger enclosure may be justified A small system that uses golf cart batteries may someday be upgraded to L16s or industrial 2 V cells A golf cart battery is about 10 1 2 inches long an L16 is about 12 1 4 inches So upsizing the box initially to fit future battery possibilities may save money in the long run To plan a successful battery box layout we drew out the batteries on paper and made cardboard templates We left room around battery cases for ventilation to hide rope handles to maneuver a distilled water jug and to get fingers and tools into the box for service We left 5 inches above the battery tops for cables and interconnects Plan the placement and lengths of your interconnects so that all fill caps are readily accessible and battery cables do not lay over t
28. 1 3 Batteries For our project the batteries are reguired to store and smooth out the electricity from the renewable source The five factors that will be considered while choosing the batteries are 1 Cost 2 performance 3 safety 4 size and 5 availability The main purpose of this section is to give a general review of different kinds o batteries and to highlight features 35 to battery LED indications control signals communication Table 9 Factors for Choosing Battery Cost At most 125 can be allotted to one battery Performance The batteries are expected to be able to store the maximum of energy coming from the power source Safety The batteries have to be safe for the people and the environment as well Size Small or regular size batteries are preferred to facilitate transportation Availability The batteries should be easy to find in South Africa 3 1 3 1 Primary and Secondary Batteries Batteries are categorized into two major types primary and secondary Primary batteries are disposable because they irreversibly within limits of practicality transform chemical energy to electrical energy 18 Secondary batteries on the other hand are rechargeable in that they can have their chemical reactions reversed by supplying electrical energy to the cell restoring their original composition 18 Primary batteries have higher energy densities than secondary batteries and are usually utilized when r
29. 1 5kQ tuf g R13 p 1 1 5kQ PMA jz R14 JEZ o gt AAN cs He 1 5kQ a we 555 TIMER RATED iuf T U2 R15 E AAA di 1 5KQ T uzzer ji aa oe 10kQ 100 4700 1ko a E I ra R3 R7 Q s 50 pad 3 Keys MMA IE i Q 1kQ 4702 f Fan LED3 LED2 ene 100 EN z4 1kQ A A lt Figure 34 Signal Generation Figure 35 PCB Design 86 4 5 Monitoring System The monitoring system are sets of systems that are being implemented to observe the status the entire power generation system Some components are instruments that give readouts from the sensors while others give readouts based on calculations of other sensors 4 5 1 Charge Controller Monitoring System The charge control monitoring system is simply the sensors that give information to the charge controller The sensors will also have their reading displayed in small analog displays This will allow any user to know what state in the charging process the charge controller is in The charge controller also has lights that will tell the user if it is charging or not 4 5 2 Inverter Monitoring System There are high end commercial inverter which have a digital monitoring display as well as LED lights in the front panel These monitoring parts are to indicate to the user power status of inverter on off voltage input power output overload warning low input voltage and high input voltage A power inverter is a sensitive piece of equipment and it i
30. 17 Solar Panel Current Sense Circuit c23 0 01uF VERA 2nd order low pass filter C49 GNDPWR PV current sense circuit 12 pel Y GNDPWR The current sensor is also constructed differently on for the PV side of the converter than the battery side Accuracy is far more important when measuring PV current since this parameter is needed for calculating the maximum power point Therefore a simple op amp as was used in the battery current sensor is not sufficient Instead a Texas Instruments INA194AIDBVT current shunt monitor is used U14 in diagram to provide accurate measurement The IC operates with a gain of 50 Op amp U4D forms a low pass filter to remove noise from the signal 4 2 4 MPT612 Microcontroller This subsection consists of the main logic and control portion of the charge controller where the MPT612 controller IC is located The IC handles the sensor inputs temperature inputs UART and JTAG communication as well as outputting PWM gate drive signals to operate the DC DC converter and digital outputs for sending charge information to a logging or monitoring interface 67 Figure 18 JTAG UART Connector and GPIO Connector 3 3V 0 JTAG UART The connector J6 on the left is the JTAG UART connector This connects to the serial communications module for reprogramming the MPT612 It takes a 3 3v power signal and 11 communication lines for RS232 The connector J15 on the right
31. 5 and the second stage has a gain of 10 Finally Op amp U6C is a low pass filter to remove noise from the signal 4 2 3 PV Voltage and Current Sensors The PV sense module is similar to the battery sense module in the context that it is also composed of two separate circuits one for PV voltage sensing and the other for PV current sensing Again these modules take an analog signal from the DC DC converter and using op amps output an enhanced signal for the microcontroller Figure 16 Solar Panel Voltage Sense Circuit cis 0 01uF 35 2nd order low pass filter DPV volt sense boost PV_voltage_refD OK 2H C20 C22 0 01uF 0 01uF mm GNDPWR GNOPWR SA ssa GNDPWR 121E beed La C19 c21 AX T gt PV_volt_sense_buck r Ae OuF 0 1uF c68 GNDPWR 0 01uF s GNDPWR mn GNOPWR R35 R66 am GNDPWR 66 PV voltage sense circuit The PV voltage sensor is somewhat different in design than the battery voltage sensor because two separate sense circuits are used buck mode and boost mode voltage sense The signal enters on the left from a resistor divider in the secondary side of the DC DC converter Op amps U4A and U4B and their associated components operate the boost mode voltage sensor with a gain of 1 1 Op amp U4C operates the buck mode voltage sensor with a gain of 2 The RLC network to the right of the voltage sensors is a passive filter for the 3 3V A analog voltage rail Figure
32. AVX AVX Nichicon Panasonic Corp AVX AVX AVX AVX AVX AVX Kemet Kemet Kemet AVX AVX AVX AVX AVX Fairchild Semiconductor STMicroelectron ics NXP Semiconductors Fairchild Semiconductor NXP Semiconductors NXP Semiconductors NXP Semiconductors 0 06 0 06 0 06 0 17 0 17 0 06 0 06 0 22 0 06 0 18 0 84 0 06 0 06 0 06 0 06 0 06 0 06 0 15 0 45 0 45 0 10 0 06 0 06 0 06 0 79 0 46 1 52 1 44 0 46 0 30 0 05 D11 D12 D13 D16 D17 D18 D19 DC1 DR1 DR2 DR3 DR4 F1 F2 F1 F2 J6 J15 J141 J142 J143 J144 L1 L2 L3 PMEG601 OCEJ ES1B BYV42E LED YEL 24V 0 5W 0 1uF 10k 5 10k 5 10k 5 10k 5 50A FUSE 50A FUSE FUSE HOLDER FUSE HOLDER JTAG UA RT GPIO_CO N 282856 2 282856 2 282856 2 282856 2 85uH 20A 121E_bea d 121E_bea diode 1 SOD323 W DO214 TO220 LED 3MM LED 3MM LED 3MM diode 1 SOD123 SM0805 SMO0805 SM0805 SM0805 SM0805 6 3x32mm 6 3x32mm keystone FH 5X20 keystone FH 5X20 con headers jp HDR 100 2X10 con headers jp SIP 100 10 mors 2p mors_2p mors 2p mors_2p 617 22 SM0603 SM0603 PMEG6010CEJ ES1B BYV42E 150 HLMP 1719 HLMP 1790 HLMP K150 BZT52H C24 08055C104MAT2A RK73B2ATTD103J RK73B2ATTD103J RK73B2ATTD103J RK73B2ATTD103J BK AGC 50 BK AGC 50 751 0056 751 0056 SSW 110 01 T D TSW
33. Advantages and Disadvantages of GEL BatterieS o 40 Table 12 Advantages and Disadvantages of AGM Batteries cee 41 Table 13 Advantages and Disadvantages of Flooded Batteries 42 Table 14 Types of Deep Cycle Batterie ee ee ee ee 44 Table 15 Different Inverter Types a A 45 Table 16 Inverter Applications RR Ee ee ee ee AR EE ee ee ee ee 46 Table 17 Types of Control for AC Driven Loads ee ee ee ee ee ee ee ee ee 48 Table 18 Rotary Converter 21 RR EE ee AR EE ee ee ee ee 49 Table 19 Commercial Power Inverters Comparison 22 52 Table 20 Solar Cell Type and Power Efficiency 21 ee ee ee ee ee 60 Table 21 Solar Panel Characteristics ee ee ee ee no 62 Table 22 Electrical Data STC AS AO 62 Table 23 Electrical Data NOCT onto 62 Table 24 Approximate Vertical Mounting Angle for Solar Panels in Harrismith South Africa PERE Ee EI RE ee seta Ge Ge de EG 63 Table 25 Common Battery Specifications ee ee ee ee ee 76 Table 26 Charge Controller Bill of Materials ee ee ee ee ee ee ee ee ee 96 Table 27 Voltage vs State of Charge iss see ee ee ee ee RR ee ee ee ee eke 110 Table 28 Battery Charge Time ee ee ee ee ee ee 111 Table 29 Battery Discharge Time ee ee RR ee ee ee ee ee ed EE ee ee ee 111 Table 30 VONAGE SENSOR Ee ed es ie es ie ee ee N Ee Ee de 115 lablea1 Current SONAS ii AE AAA ta 115 Table 32 Temperature SenSOr oooocccccncccnccnnccoonc
34. Current Sensor Step Procedure 1 Implement the shunt resistor monitor in the a circuit design 2 The current value is going be verified in both the Microcontroller and the Voltmeter 115 Results Standard R Large R value R Small value Vout lt 5 volts min Circuit simulation should reflect previous expected results Vou Was equal at the designated points Results reflected the simulation results Results Shunt resistor was in series with voltage source Current was the same on both devices Table 32 Temperature Sensor Step Procedure 1 Temperature sensor is connected to the Microcontroller 2 Sensor is tested in room temperature and compared with a thermometer 3 Extra heat is applied to both thermometer and temperature sensor Table 33 Solar Radiation Sensor Step Procedure 1 The Sensor is connected to the Microcontroller board 2 Ambient light will be increased and decreased 3 Sensor will be placed in direct sunlight and in shade 4 The algorithm to translate the reading to lumens will be implemented 116 Results A value was outputted by the sensor Both temperature results were close to equal Increase in Temperature reading in the thermometer matched the sensor s readings Results Data was received from the output of the Microcontroller Noticeable changes in the raw data were observed Similar results as the previous test were obtained Direct s
35. E N N EE AE EEATT 55 3 2 Relevant Technologies we wa ei AR Ge DR ees 59 4 0 Project Hardware and Software Design ee ee ee ee ke ee ee ee ee ee ee ee ee ee ee ee ee 61 4 solarPaiiels is SA AE Che EE GE EDE DR ER N EG ee EG N ee 61 4 1 1 Solar Panel Specifications iii RR AR RA AR RR ee RR ee ee ee ee ee ee ee ee ee ee ee ee ee ee 61 4 2 2 Solar Panel Mount EES Ee Ee bee ER cata 62 4 2 Charge Controller ass EER RE i 64 4 2 2 Battery Voltage and Current Sensors 0 00 00 2 ee ee ee ee ke Re ee ee ee ee ee 65 4 2 3 PV Voltage and Current Sensor iese ee ee ee ee ee Re ee ee ee ee ee 66 425 DCDC Gorivertelr ss N N Gee reeks EE AE ED RD OE EE es 69 O ee ee ee EER EE Re Ge RU nee PE 72 4 3 7 JIAGIUART Add on BOSA eiii 73 4 5 EARLS VSS sd nn ch cds ens td a GN Ge way Ge RE Ee Ge Ed GO pd Be Ge ge N DE E 76 4 dAlnVerlef E AE OE EG EA ae oe ie AR ee GE Se Ee eed ai 81 4 5 Monitoring Oyster to tic 87 46 Erodsing is e 89 we EE EE ER EE EO ER o 91 48 Design Su el ES SE RR OE AD ED Ee OE GO EE eg eg 93 5 0 Project Prototype CONSTITUCION wis ss ed A Ge Re ke Ge di 95 Sal Paris ACQUISTON is be ee sie AA AAA A 95 5 2 Materiale oe se a at O 96 5 3 POB Vender and Assembly soil 104 00 Project Prototype Testi a tad 106 6 11 Solar Panel Testi in 106 6 2 Bate Mesta iii EN GE GE A IE ER De 110 Bo ie AE dae EE RE EE EK ET is 112 0 4 Sens r TOS Da RE sta GE EE EG EG EG EI Ge ee ube 115 6 5 Wiring Testing and Precautions
36. Group 7 South Africa Power G7 SAP Power Generation BY Steven Bularca Genesh Chen Shue Armel Nidjeu Aldo Puente Prepared For EEL4915 Senior Design University of Central Florida College of Engineering and Computer Science April 29 2013 Table of Contents 1 0 Executive SIM AS AAA 1 2 0 Proje tDESGrDUSHE MM ASE a EDE OE T 2 2 1 Project Motivation and Goals ESE AA 2 PAPA O E EEA EG AE EG E EES ES 5 2 2 1 Safety A A EE 5 2 2 2A A MG ME e ee DE N EG a SG Ee IE ie ee EG a dctad 5 2 2 ASCO Use EE dede A A De ee ee ee ee ee Re ee Ee 5 22 4 Charge Controller ie ll ER ie 5 2 2 0 Batteries Dm a RE Rea ER DE Re De DR Se RR GR De Ge ge ed 6 2 2 6 II aii GE Ee SE SG be ee ee a VR N ee eb Po id 6 2 2 rSolar Panels E N aN AAA AAA 6 ENCON OE EP EE a 6 2 2 9 AA AS ET ON NE OE 7 2 3 Project Requirements and Specification ooccccccccccccccccccccccccnccnnnnnnnninininos 8 2 4 Black DAG UW is ss oe cde re dai 9 2 5 Vinielitie iS Sd ed ed 10 2 6 Milestone DISCUSSION ii ed ed De AAA 11 2 7 Budget and Finance DISCUSSION ada SR SR uaa oe Rede dn Ee 17 3 0 Research Related To Project Definition 0 cee RR RR AR RR RA RR Re Re ee ee ee ee ee ee ee ee ee 19 3 1 Existing Similar Projects and Products ee ee ee ee ee ee ee 19 Dy Licl solar Panels ERENS ER REELS RR GE EERS EES GES ER DOE OR ED Ge Wa bu Ge ees eN 19 O o EER BR RR N EE Ee RR isk DR ie ee 31 Ar ALLS IS SA TAE 35 8 14 Inverlefs ii E AT 44 A TO 54 A OE E
37. Hidalgo and S Kobosko Photovoltaic MPPT Charge Controller 2011 Online Available http eecs ucf edu seniordesign fa201 1sp2012 g10 Accessed 26 November 2012 J M Doucet D Eggleston and J S Shaw PWM Pure Sine Wave Power Inverter 25 April 2007 Online Available http Awww wpi edu Pubs E project Available E project 042507 092653 Accessed November 26 2012 MrSolar com amp Online Solar LLC Photovoltaic Effect 2012 Online Available http Awww mrsolar com content photovoltaic_effect php ULO7zoeaXdM Accessed 26 November 2012 A Upadhyaya V Yelundur and R Ajeet High Efficiency Mono Crystalline Solar Cells With Simple Manufacturable Technology University Center of Excellence for Photovoltaics Conference Papers pp 4 8 September 2006 R W Birkmire and E Eser POLYCRYSTALLINE THIN FILM SOLAR CELLS Present Status and Future Potential no 27 pp 625 53 1997 Repins M Contreras M Romero Y Yan W Metzger J Li S Johnston B Egaas C DeHart J Scharf B E McCandless and R Noufi CHARACTERIZATION OF 19 9 EFFICIENT CIGS ABSORBERS in 33rd IEEE Photovoltaic Specialists Conference San Diego California 2008 10 X Wu R G Dhere D S Albin T A Gessert C DeHart J C Keane A Duda T J Coutts S Asher D H Levi H R Moutinho Y Yan T Moriarty S Johnston K Emery and P Sheldon High Efficiency CTO ZTO CdS CdTe Polycrystalline Thin Film Solar Cell
38. I Centre Yearly sum of global irradiation incident on optimally inclined surface Yearly sum of solar electricity generated by 1 kWp system with optimally inclined modules and performance ratio 0 75 East London Global irradiation KVVh m 00 2000 2200 2400 2600 300 km 1350 1500 1650 1800 1950 Solar electricity kWh kWp E 30E PVGIS European Communities 2001 2006 http re jrc ec europa eu pvgis HelioClim 1 Ecole des Mines de Paris ARMINES 2001 2006 http Avww helioclim org 30 Since insolation affects performance it is important to find out how to mitigate low insolence and to find out how to increase insolence Although the Pomolong Township is relatively sunny they do not have a high level of irradiance There are a few methods that can be made to increase solar panel performance to make up for the low levels of solar radiation There are direct methods and indirect methods Direct methods are like solar tracking which involves having sensors on solar panels and motors that point the solar panel in the direction of the highest intensity of sunlight Solar tracking optimizes the amount of sunlight that makes contact with the solar panel by making sure that the panel is always facing the sun Another direct method to increases solar radiation is by using light concentration Light concentration is when mirrors or lenses are used to intensify the sunlight on the solar panel Indirect meth
39. MCS3264RO10FER MCR10EZHF4701 MCS3264ROOSFER MCS3264RO10FER ERJ 6GEYJ330V RK73B2ATTD103J RK73B2ATTD203J MCR10EZPF1002 MCR10EZPF1002 MCR10EZHF6812 MCR10EZPF1002 MCR10EZHF1001 RK73B2ATTD103J MCR10EZHF6812 MCR10EZHF6812 MCR10EZHJ000 RK73B2ATTD103J RK73B2ATTD203J MCR10EZPF1002 MCR10EZHF5101 MCR10EZPF1002 MCR10EZHF6812 100 Semiconductors ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor Ohmite ROHM Semiconductor Ohmite Ohmite Panasonic Corp KOA Speer KOA Speer ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor KOA Speer ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor KOA Speer KOA Speer ROHM Semiconductor ROHM Semiconductor ROHM Semiconductor ROHM 0 17 0 17 0 10 0 05 0 05 0 40 0 05 0 40 0 40 0 07 0 08 0 08 0 05 0 05 0 10 0 05 0 05 0 08 0 10 0 10 0 05 0 08 0 08 0 05 0 05 0 05 0 10 R39 R40 R41 R42 R43 R44 R45 R46 R48 R53 R54 R55 R56 R57 R58 R59 R60 R64 R65 R66 R67 R72 R75 R76 R77 R78 5 1k 1 1k 1 01 68 1k 1 68 1k 1 2 74k 1 10k 1 10k 1 2 74k 1 10k 5 100k 1 10k 1 4 7k 5 1k 5 2 2k 5 18k 1 100k 1 10k 1 4 7k 5 10k 1 10k 5 47k 5 2 2k 5 1k 5 100k 1 10k 1 SM0805 SM0805
40. Power Supply RUS ae lt gt Y E u9 m eya ver collectar SW_rollector 1 a I La ok sers SWemitter 2 lt lt A paa pS dr E Ve rimingicap 3 Sov w 7 csi Se a B Joop soe input o L 2 C53 MC33063A 330pF SV CMAX R96 7 t a zog RE dy Y O Buck power eeable 0 33uF turet A urent ref a D Powerdown wakeu ea a ST VM ego san suana e Rito R105 A MOUNTING_HOLE MT BA entre BO 121 BEAD 124 BEAD I ass EELE 6 15 16 bel C61 Ma GNOPWR d pd EE ae j 4 7nF GHOPWR 72 The circuit can be divided into three regions At the top everything to the left of MOSFET M1 is the standby circuit containing 3 3 volts This circuit is always on as long as the battery is connected Everything to the right of M1 is the active 3 3v rail and 1 8v rail Everything on the bottom is related to controlling the gate pin of MOSFET M1 for entering and exiting standby mode Switching regulator U9 takes the battery voltage as the input and outputs a regulated 3 3V supply The low dropout regulator U10 takes the 3 3v input and outputs a regulated 1 8 volts These rails are only on when M1 is on The standby control circuit is composed of three op amps operating as comparators U11A is the battery voltage comparator If the battery voltage rises above a specified level this comparator triggers the system to enter standby mode to stop charging
41. Similarly if the PV voltage dips too low or the load is too high op amps U11D and U11C will respectively send the power supply into standby mode and stop the charging process The outputs of the comparators are ORed together at the multi input OR gate U12 When the MPT612 is in standby mode and needs to be woken up again a signal is sent from the output of the PV voltage comparator to the chip The Powerdown_wakeup signal is used as an interrupt signal to wake up the MPT612 when the PV voltage rises back up to a nominal level for charging provided that all of the other parameters battery voltage load current are also nominal Finally at the very bottom of the diagram the ground connections are shown The digital ground and analog ground planes are tied together via inductors L5 and L6 The low side of the battery current reference taps into here The mounting hole is grounded and tied to earth ground The battery current reference taps into here as well 4 3 7 JTAG UART Add on Board The JTAG UART add on board is described by NXP as an optional circuit which is used to program the charge controller board For testing it can also be used to monitor its performance 73 Figure 22 JTAG UART Add on Board 16 las 15 i2 cno pla Y 21 en ve La dit MAX3OBCUE a File jtag uart board sch L Sheet __ Title noname sch Size A4 T D Date 6 dec 2012 The top
42. Square wave inverters are much simpler because they simply vary by three different voltage levels Some electronic devices will work with square wave input Unfortunately most electronic devices are only sensitive to the signal produced by an AC wave These electronic devices typically receive or transmit signals themselves examples include TVs 50 and projectors The trouble occurs in the form of distortion in the video image To clean up a square wave as stated before a variety and a vast amount of electronic components such as filters inductors and capacitors are needed Commercially all kinds of inverters are sold Usually the square wave inverters are really cheap and the pure sine wave ones are very expensive For the purpose of the project the option to design and build an inverter that produces a pure sine wave was chosen The last part of an inverter s characteristic that should be taken into account is what needs to be powered with the output of the inverter This is not really a characteristic of the inverter itself per se but is a major consideration when designing an inverter For the purpose of the project the inverter should not have to output more than 700W of power at any given point in time This means that the maximum power coming out of the inverter should exceed the combined power consumption of the electronic devices being used Another way to look at it is that the total load should not be greater than ZOOW 3 1 4 5
43. The main purpose of the project is to design a robust solar energy power generator To do this fully functioning solar panels a charge controller batteries and an inverter are needed The proof of the final project was a working standalone photovoltaic power system The following is the preliminary Budget which includes the parts that were obtained in order to create an off grid photovoltaic power system Table 8 Budget Part Vendor Quantity Price 250 Watt Solar Panel 72 Mono Crystalline Cells Helios 2 700 00 33 Volt 7T2300 2 T105 RE 6V 225 Ah Flooded Battery Trojan 3 400 00 Charge Controller based on MPT612 N A 1 300 00 Designing Pure Sine Wave Inverter N A 1 300 00 Designing Chassis and Weatherproofing N A 1 100 00 Designing Miscellaneous Electronic Components and N A N A 195 00 Wires Total 1995 00 As explained before the project can be broken down into four main sections It is divided into solar panels the charge controller batteries and the inverter Two 250W 33 V solar panels were obtained and set up in parallel to deliver a constant voltage level of 12V to the system For the second section of the project the charge controller and other minor electronics will be discussed in detail Before ordering the printed circuit board there was a period of testing and building of the completed circuit on a solder less plug in breadboard Once the circuit on the breadboard was tested to perform all of its required it wa
44. VX Nichicon Nichicon Nichicon AVX Nichicon AVX AVX AVX AVX AVX AVX AVX Kemet AVX AVX AVX AVX AVX AVX AVX AVX AVX AVX cost 0 22 0 22 1 95 1 59 1 95 1 59 0 06 0 20 0 20 0 20 0 10 0 15 0 10 0 06 0 10 0 10 0 06 0 10 0 10 0 45 0 10 0 10 0 10 0 06 0 10 0 79 0 79 0 10 0 06 0 06 C39 C40 C41 C42 C43 C49 C50 C51 C52 C53 C54 C55 C56 C57 C58 C59 C60 C61 C62 C65 C68 C69 C70 C71 C73 D2 D5 D7 D8 D9 D10 0 1uF 0 1uF 0 1uF 22pF 22pF 0 1uF 0 1uF 330pF 2 2UF 47uF 25V STPS40L 45CG BYV42E ES1B BYV44 12V 0 5W SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 C1V8 C1V8 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM1206 SM1206 SM1206 SM0805 SM0805 SM0805 SM0805 SM0805 DO214 DPAK2 TO220 DO214 TO220 diode 1 SOD123 MMBD414 SOT23 8 08055C104MAT2A 08055C104MAT2A 08055C104MAT2A 08055A220KAT2P 08055A220KAT2P 08055C104MAT2A 08055C104MAT2A 08055C331KAT2A 08055C104MAT2A UVZ1E470MDD EEUFM1A681L 08055C104MAT2A 08055C104MAT2A 08055C104MAT2A 08055C104MAT2A 08055C104MAT2A 08055C104MAT2A C1206C472KDRACT U C1206C475K5PACT U C1206C475K5PACT U 08055C103MAT2A 08055C104MAT2A 08055C104MAT2A 08055C104MAT2A 08055C334MAT2A ES1B STPS40L45CG BYV42E 150 ES1B BYV44 500 BZT52H C12 MMBD4148 97 AVX AVX AVX AVX AVX AVX AVX
45. a battery bank is series parallel wiring The series parallel wiring is a best way of combining batteries to get the desired 77 voltage and storage capacities to match the rest of the components in the system Series wiring means to connect the positive terminal of one battery to the negative terminal of the next battery By doing so it multiply the voltage of the individual battery by the number of batteries interconnected until it reaches the desired voltage Figure 24 Series Wiring Permission Pending Series Connection Voltages Add Capacity is A mg 20Ah A 12 24V 20 Ah 20Ah Y ras gt eS Wire Parallel wiring multiplies the capacity in amp hours of the battery while the voltages stay the same In parallel we wire the positive terminal of one battery or string to the positive terminal of the other battery or string Figure 25 Parallel Wiring Permission Pending Parallel Connection Voltage ls Constant Capacities Add Para el Connection TT i y T aN uy 12V 2V Mm a 20 Ah Series parallel wiring is the combination of the series and parallel wiring It is the technique of wiring used commonly for wiring battery banks in renewable energy systems 78 Figure 26 Series Parallel Example Permission Pending Series Parallel Connections Example Series Parallel Connections Example 1 Eara I A 12V 12V 20 Ah Nire i 24V di 12V EE VA a CES 20 Ah To promote equ
46. a conclusion was made to work on a renewable energy source for the township of Pomolong in South Africa During the first few weeks research of the project began At first a dual powered system with wind power and solar power was the focus of the research However after research of the location of the township of Pomolong it was concluded that there was not enough wind for a wind powered generator to be beneficial The wind was very minimal and it would take a big wind turbine with blades approximately15 feet long to make the power generation of the reguired scale viable Thus it was decided that concentration solely on solar power would be the best option The benefits of solar power are plenty The only real downside is that during low sunlight and night time it generates little to no power This was an unavoidable problem that had to be endured Research on solar powered systems began in earnest From the research the system was simplified into manageable parts All the parts that were needed to build a complete system were studied in full After a week or so of research it was decided that the main parts of the project would involve solar panels wiring a charge controller an inverter and batteries From then on pricing data was collected in order to form a proposal Keeping costs low was a major factor when drafting the initial proposal From what was seen the most expensive part of the project was going to be the solar panels which took
47. a general idea on what design plans will be implemented The four major parts to this project are the Solar panels the Charge Controller the Battery Bank and the Inverter The Solar Panel is the portion of the project that generates the power It is being implemented because of the two forms of renewable energy it was the most practical for the limited budget at hand The kind of solar panel was chosen based on price availability durability and efficiency Solar panels are the most expensive part of the project so a lot of research was done in comparing the prices to see what panels were the most price competitive while retaining a high efficiency The result of the research showed that grade A Mono crystalline silicon photovoltaic panels were the most efficient cost effective solar panels that could be obtained For approximately 1 000 00 US dollars two 700W panels could be bought costing a little over a dollar per watt Batteries are the second most expensive part of the project and like solar panels a lot of time was used to determine if more expensive batteries were worth the slight increase in efficiency and safety Although safety is at the top of the design consideration having a working design that could be used by the villagers was almost as important It was found through research that the best batteries were Lithium ion batteries because of their efficiency and ideal characteristics It was found that among Lead Acid Batteries
48. abbreviated in the label by AH An amp hour is one amp for one hour The generally accepted AH rating time for period of batteries used in solar power is the 20 hour rate even though the 6 hour rate and 100 hour rate can also be used The amp hours should be specified at a particular rate because some vendors have chosen to rate their batteries at the 100 hour rate which makes them look a lot better than they really are For instance see table below 38 Table 10 Sample Battery Specs Battery type 100hourrate 20 hourrate 8hourrate _ Trojan T 105 250 AH 225 AH n a Us battery 2200 n a 225 AH 181 AH Concorde pvx 6220 255 AH 221 AH 183 AH Surrette s 460 L 16 429 AH 344 AH 282 AH Trojan L 16 400 AH 360 AH n a Surrette cs 25 ps 974 AH 779 AH 639 AH The internal resistance of a battery affects its performance The higher the internal resistance the higher the losses of energy will be while charging or discharging the battery In other words the batteries with a lower AH will discharge very fast while the one with the higher AH will discharge really slowly That is why batteries with high amp hour are served as an optimal choice for the Pomolong Township project Decisions have been made that the batteries rated at 20 hour rate are chosen for the design of power generation system 3 1 3 4 Types of Deep Cycle Batteries There are three types of deep cycle lead acid batteries flooded gel and absorbed glass mat AGM The comparison among th
49. actical and durable measure for use in South Africa where replacing specialized parts are difficult and protecting fragile parts are not possible Further research on the different kinds of panels their costs and their levels of efficiency were required in order to select the best solar panels to use for this project Panel placement and panel temperature were also important in increasing the efficiency at which solar panels capture solar energy 3 1 1 2 Types of Photovoltaic Cells This section is going to describe the different kinds of photovoltaic cells available and what makes them different The amount of different kinds of PV cells is 20 daunting which makes organizing them into groups the first thing that should be done in this section Solar cells can be generally be grouped by generation of their technology Silicon is first generation technology and Thin film is second generation technology Silicon can be further subdivided into being either Mono crystalline or Poly crystalline Thin film is further subdivided into Gallium arsenide amorphous silicon Cadmium telluride and Cadmium indium selenide A third generation technology is also emerging in the form of Polymer solar panels This new technology is an extension of Thin film technology and is currently being heavily researched because of a potential decrease in production cost but the technology is still under development In order to discuss the strengths and weakn
50. age sunlight hours of Johannesburg is 8 67 hours per day and the average sunlight hours of Durban is 6 58 hours giving the Township approximately an average of 7 63 hours of sunlight per day which makes it a great location to utilize the sun as an energy source With that said it is important to know how much energy from the sun will actually be supplied to Pomolong To do this a little bit of knowledge of irradiance and how it affects solar panels is needed Why do solar panels perform better in the middle of the day versus morning or evening lt was discussed earlier that solar panels actually decrease in efficiency as the temperature goes up so it is known that the increase in 29 performance is not due to an increase in temperature In actuality the intensity of solar radiation or irradiance is the main reason which explains why solar panels perform better in the middle of the day versus in the morning or in the evening Solar radiation is the electromagnetic radiation emitted from the sun Insolation is the amount of solar radiation received on a particular surface area over a period of time measured in power per surface area To put it in perspective the amount of insolation from the Sun on Earth s surface averages at 1368 W m2 The figure below shows the irradiation levels of South Africa Figure 5 Irradiation Levels of South Africa Optimum inclination of PV modules to maximize yearly energy yield So uth Afri ca 4 Ed a Joint D
51. al charging and discharging within a battery bank it is important to limit the number of parallel connections There is one two and three series string that are usually used to connect batteries However the one series string is best for equal charging and discharging of the battery bank But some designers prefer the two series string for redundancy in case one of the battery or cell fails there will still be one functional series string at the correct voltage to rely on until the failed battery can be replaced The three series strings are considered marginally acceptable but more parallel connection introduces too many paths for the electron to choose from when entering or leaving the battery strings Some cells can be chronically undercharged due to minute variations in cells and inter interconnection resistance which will decrease the life of the battery bank In sum a good designer uses batteries with higher amp hour capacities and limits the number of parallel connections lt can be tempting to design a battery bank with plans to add capacity in the future but this is not a good practice because of the batteries sensitivity to unequal charging and discharging whiting the bank The batteries should all be the same make and model and ideally manufactured in the same company You should always size for the future from the beginning because adding new batteries even with the same make and model to a battery bank that is more than a year old i
52. ary electrical switch in certain types of electrical motors or generators After a few years a synchronous converter was introduced which does what a rectifier does today To put it simply it converted AC power to DC power This brought both the motor and generator into one section with motor slip rings in one end and the commutator at the other Now given the right control equipment an eletromechanical rectifier can run backwards to convert DC to AC thus making an inverter 19 Next transistors that are common today were not available back in the 1950 s Back then they only worked with low voltage and current However with the introduction of silicon controlled rectifiers the production of inverters commonly known today began Rectifiers do not turn off when the gate control signal is off they only turn off when the current being passed is below the minimum holding current Different kinds of rectifiers have different minimum holding current levels So for rectifiers connected to an AC power source rectifiers turn off every time the source voltage reverses However for rectifiers connected to DC power the current would have to be forced to be below the minimum holding current in order to shut off the rectifier So we see that an AC source is a more natural way to work with the rectifier than a DC source 19 Rectifiers are often classified by the number of current pulses that come from the DC source to the output AC There are one pul
53. ating in buck mode Q3 is open and Q4 is closed Filter capacitors C4 and C7 are placed across the output to smoothen the signal Bulk capacitors C3 and C5 are used to temporarily store energy while the main switching transistor Q1 is in the off state Q1 is responsible for the pulse effect which excites the inductor It 70 is driven by a high side gate driver circuit U3 at the bottom of the figure U3 is an International Rectifier IRS21171 single channel high side gate driver It takes in the Buck_PWM signal from the microcontroller and outputs it to the gate of Q1 The DC DC converter also includes protection circuitry to reduce the risk of battery or PV panel damage Diode D13 on the left protects the system if the PV panels are connected backwards Similarly diode D5 and fuse F1 on the right protects the system if the battery bank is connected backwards MOSFET Q2 controls the load If the load cutoff signal is sent high from the MPT612 Q2 will turn off and disconnect the load from the battery Fuse F2 protects the load from short circuit damage The sense resistors used in the PV and battery sensor modules are found in the primary and secondary sides of the converter They are a low ohmic type 0 01 ohms R6 is used to measure PV current R8 is for measuring battery current and R10 measures load current Resistor divider R4 and R7 measures battery bank voltage and divider R3 and R5 measure PV panel voltage The switching frequency of the
54. aximum power point tracking MPPT to maximize efficiency Photovoltaic systems have many inherent losses so it is essential for the maximum power to be extracted The intent was to create an extremely efficient charge controller that is able to monitor the power generated by the photovoltaic array and deliver the maximum amount to the battery bank during varying atmospheric conditions This combined with a modified sine wave inverter ensures that the community center is able to use every little bit of power generated In order to achieve the desired functionality several major components were integrated into the final system First compact power generation devices were researched and implemented such that they produced practical amounts of energy and were easy to use requiring no specialized knowledge A power storage subsystem was also designed and implemented to provide an efficient means of transferring the power generated into a stored and ready to use form available for use This includes a charging system utilizing maximum power point tracking as well as the most efficient battery given the typical anticipated usage patterns of the project An inverter was also designed and implemented that converted the stored energy into the familiar AC and DC sources that the end consumer would prefer A monitoring system was also planned to be designed and implemented which allows the user to have a convenient way to know how much power they are generatin
55. batteries 3 1 3 3 Cycles in Lead acid Batteries Lead acid batteries are divided into three categories starting deep cycle and marine Starting lead acid batteries are designed for starting automotive engines Obviously their most significant specialty is the ability to output a high current with almost no delay In order to achieve this ability starting lead acid batteries have many thin plates designed to maximize surface area which allows for maximum current output However they are also vulnerable to deep discharge and repeated deep discharges will result in capacity loss and ultimately premature failure Deep cycle lead acid batteries on the other hand have thicker plates Although they do not output as high current as starting batteries do they can endure frequent discharging and recharging without degradation Marine batteries have thicker plates than starting batteries but thinner plates than deep cycle batteries They are designed to serve as a compromise between the two lead acid batteries above and therefore have a current output and life time lying between starting batteries and deep cycle batteries Since the goal of the Pomolong Township project is to construct a power generation system high endurance in frequent discharging and recharging are more important than high current output Therefore deep cycle lead acid batteries are chosen for the design Batteries are also rated in amp hours which are usually
56. batteries are what were implemented for the project because deep cycle batteries are made to be complete drained and completely recharged They are made to cycle between being completely full and almost empty charge positions many times However the AH amperes per hour needs to match the system as best as possible with minimal deviations or there may be safety problems with the system The ultimate goal was to find the right number of batteries to include in our system because too many batteries will never be fully charged and too few batteries will be completely charged too quickly 2 2 6 Inverter The inverter is a part of the system that is critical to the project The inverter takes the power from the charged batteries in the form of a DC input The inverter then outputs AC which can be used by instruments such as laptops TVs and cell phone chargers In order to get the most stable flow of current from the batteries a modified sine wave inverter was designed If the AC is not in a sine wave then some instruments plugged into the system may not function properly such as printers chargers and laptops 2 2 1 Solar Panels Solar panels are the part of the system which captures solar energy and converts it into usable power Simply put if the solar panels stop working then the rest of the system will be useless because there will be no input energy No expense will be spared on the solar panels The best quality solar panel made with grad
57. ce anything else can damage the inverter Make sure to connect the 24V DC power source correctly positive to the red terminal and black to the negative terminal If not connected right the inverter will be damaged Do not connect the inverter to any appliance that uses over 700W of power to operate It will not operate due to surge power requirements Do not use this inverter with medical equipment Do not use this inverter while in motion In the event of anything irregular with the system IMMEDIATELY turn the inverter off and disconnect any appliances from the inverter The group plans on having the above warning label contents in a warning label on the surface of the inverter where it is clear to see and read by the users The following is a sample of how the warning label will look like Note that the above guidelines are not on the label however they will be in the finished product 113 Figure 40 Warning Label Sample Permission Pending PLEASE READ THE FOLLOWING MESSAGES Next we address surge power for the appliances being used with the inverter The surge power also called peak power or load is the initial power input an appliance needs to start Once started the appliance needs less power to operate In the case of this inverter the surge power is 600W Any appliance with a higher surge power will not start or operate with this inverter This operating power of an appliance is called continuous load in terms of pow
58. cept there are batteries so power is stored This method further minimizes the power that the residence being supplied obtains from the grid Off grid systems are completely not connected to the areas power grid They are completely standalone residences with no connection to the power grid These systems almost always use batteries for power storage Backup solar systems are used when there is a power outage in a grid supplied area When this occurs the backup system activates and provides power for the residence with power stored in the systems battery bank In the case of the South Africa Project the township of Pomolong is completely off the grid therefore the system will be an off grid system with batteries 60 4 0 Project Hardware and Software Design The purpose of this section is to describe the design process and selection process for the design of the South Africa power generation system This section will discuss specifics regarding the main components of the project including the solar panels the batteries the charge controller and the inverter The specifics that will be discussed will be the parts and models that will be used in the design as well as the physical properties assembly and integration 4 1 Solar Panels Although there are many options for solar panel technologies it is quite clear that the most reasonable choice for this project is the Mono crystalline silicon photovoltaic panel Poly crystalline silicon panel
59. control this The Arduino PPT uses an iterative approach known as the Hill Climbing algorithm The Hill Climbing algorithm works by first increasing the conversion ratio of the DC DC converter and measuring the wattage output by the panels If the output is greater than the last measurement then increase the conversion ratio again and measure again Otherwise if the output is less than the last measurement then decrease the conversion ratio and loop again This implementation loops through the algorithm at about 1Hz 32 While it is slightly more complex than the 555 timer based controller and does provide the desired MPPT behavior as well as support for monitoring and logging the Arduino PPT solar charger was not chosen for use in this project because there is still little to no circuit protection and the use of an Arduino was considered to be a cop out in the context of a computer engineering senior design project A micro controller based IC approach is preferred which makes it easier to provide digital real time charge information and data logging as well as current and voltage monitoring for circuit protection All of these features can be implemented with only a moderate increase in circuit complexity Several integrated circuits exist with embedded micro controllers which are specifically made for use in solar charging applications Three of the chips considered were the Texas Instruments BQ24650 Synchronous Switch Mode Battery Charge
60. cussed in detail are Gallium Arsenide Thin film panels which are also known as GaAs panels GaAs panels are very similar in properties to CdTe panels in respect to the fact that the materials to make the compound are rare and dangerous and the fact that GaAs panels maintain their performance in higher temperatures GaAs panels are made up of a mixture of Gallium which is a rare metal and Arsenic which is a poisonous metalloid The reasons that GaAs panels are so special are their efficiency Their efficiency ranges from 20 to 25 with a peak of 30 11 According to the National Renewable Energy Laboratory the high efficiency was a result of GaAs having an almost ideal bang gap Using these panels reqires a tradeoff and for most people the prices for Gallium Arsenide Thin film panels are far too high for the benefit of the impressive increase in efficiency 3 1 1 3 Factors that Affect Performance When it comes to the overall performance of solar panels the ideal conditions of a lab are not present in the real world and the efficiency of any given panel could be affected by an array of possibilities Factors that could change performance are important because solar panels are the largest investment in the project and performance is one of the major considerations when implementing a photovoltaic in a design To best understand the factors that affect performance this section will look at the physical properties of solar panels as well as d
61. d The width of the switching frequency in the oscillator is changed which controls the AC voltage at the output As we can see this process involved feedback from the output part of the inverter to the PWM controller section thus making the pulse width changes The pulse width change of the switching pulse will cancel whatever changes occur in the output voltage Therefore the inverter output will stay constant regardless of different loads 83 In order to construct a pure sine wave inverter it is simpler to split the project into parts Thus the following illustrates a simple block diagram of a PWM inverter which is split into parts for easier understanding and constructing Figure 31 Block Diagram for PWM Inverter Permission Pending PNM controller Driver Output circuit circuit circuit Output socket Battery charger Battery Block diagram of a basic PWM inverter wars circuitstoday com First we start with the AC IN which is the AC voltage coming from the solar panels which is managed by the charge controller Thus the batteries are charged and output DC voltage Next is the PWM controller circuit which is where the regulation of the output voltage takes place Additionally the oscillator circuit which is where the switching freguency is generated is here For the oscillator circuit a Bubba Oscillator circuit is used to create a PWM signal using analog devices The sine wave to be created is to operate at a f
62. d to weather elements Thin film cells even work when they are damaged but at a lesser rate This is a major advantage over silicon panels because if a single cell of a silicon panel is damaged the entire thing ceases to work entirely To add on even more advantages Thin film cells are much lighter than their silicon counterparts This makes them easier to mount and work with for residential use Another important feature that Thin film solar panels exhibit that must be noted is that they do not have a significant decrease in performance when exposed to high temperatures or when in there is shade due to their material properties With all of this in mind it is generally easier to design solar panel systems with Thin film technology because of their advantages in weight durability and usability in generally adverse weather conditions At this point it may seem pointless to use first generation technology over the send generation Thin film but Thin film photovoltaics also have disadvantage The largest quantifiable disadvantages that Thin film cells have are their low efficiency at converting light to electrical current The efficiency of Thin film technology is generally around 7 8 This is significantly less efficient than Poly crystalline silicon and about a third of the efficiency of Mono crystalline silicon Additionally Thin film solar 22 panels are fairly new compared to their predecessors so how they endure the test of time has
63. deas for projects and what needs to be worked on 2 Group Selection Pick team members for the group 3 Project Selection Arrive to a final decision on the project to be constructed 4 Identify Parts Start selecting parts to be implemented for the project 5 Initiate Proposal Using the information from the previous week begin documentation for parts proposal 6 Research Project Begin researching every aspect of the project including hardware components assembly circuitry and location of final residence 7 Research Project Same as above 8 Begin Begin writing documentation of the project Documentation 9 12 Continue Start writing schematics for the project and Documentation studying individual components and continue writing documentation 13 Review Review the documentation and make final touches Documentation Draft 14 Turn in Turn in the documentation for Senior Design Documentation 15 Order Parts Start ordering parts for the project 10 2 6 Milestone Discussion During the first weeks of the semester brainstorming began for various project ideas Several ideas went by Some were very far fetched while others were very practical However it was decided that the best idea would be to wait and listen to some of the projects presented by the sponsors Dr Wang s presentation for supplying power to people in need was really attention grabbing because it was challenging but at the same time humanitarian Once all the presentations were over
64. dica 14 October 2008 Online Available cleantech com Accessed 12 December 2012 23 J H Hahn Modified Sine Wave Inverter Enhanced Power Electronics Technology pp 20 22 August 2006 24 E L Owen Origins of the Inverter IEEE Industry Applications vol 2 no 1 p 64 66 1996 25 Allen Bradley Pulse Width Modulated PWM Online Available http Awww ab com support abdrives documentation techpapers PWMDrives01 pdf Accessed 5 December 2012 26 N Hawkins Rotary Converter Single Phase to DC in Hawkins Electrical Guide Volume 5 Theo Audel amp Co 1917 p 1459 126 27 Amazon com Amazon com Amazon com 5 December 2012 Online Available www amazon com Accessed 6 December 2012 28 Agilent Semiconductors Practical Temperature Measurements 2012 Online Available http cp literature agilent com litweb pdf 5965 7822E pdf Accessed 6 December 2012 29 T Bui T Bui C Davis and S Holman Portable Solar Tracker 2010 Online Available http eecs ucf edu seniordesign sp2010su2010 g01 FINAL 20PAPER pdf Accessed 29 November 2012 30 Qwiki MAXIMUM POWER POINT TRACKING Qwiki 2006 Online Available http www qwiki com q Maximum_power_point_tracking Accessed 29 November 2012 31 R Janssen Introduction to polymer solar cells Eindhoven Netherlands 2005 32 Helios USA LLC 7T2 Series Milwaukee WI 2012 33 Greenstream Publishi
65. dosumentation Thank you for your help in these issues Tf your enquiry relates to a current recent o i ante ESEE E ee oes 121 To allanOpositiveenergysolar com CC Subject permission to use an illustration Tahoma vi0ov B I U He Y A Allan Sindelar Hi Allan I am an electrical engineering student at the University of Central Florida I would like to know if i can use your illustration on how to connect a battery bank for my senior design project the illustration is on the link below www homepower com issue gallery This figure shows the connection of the battery bank Thanks for your time ARMEL NIDJEU Undergraduate Electrical Engineer Student College of Electrical Engineering and Computer Science University of Central Florida email narmel knights ucf edu phone 407 288 5555 Mas Genesh T Chen Shue Email ge548518 knights ucf edu Telephone 3863831194 Comment Hi Deltran lam an engineering student from the University of Central Florida For our senior design project we are designing a solar power based power generation system for an impoverished African village In designing our battery bank we wanted to describe typical features of different battery configurations and wanted to use an image in one of your datasheets The image can be found on http oatterytender com includes languages english resources Connecting_Bat teries_and_Charger
66. e A Mono crystalline silicon solar cells were obtained The difference between Mono crystalline and Poly crystalline cells is important because Mono crystalline cells are cut into thin wafers from a singular continuous crystal that is only used for this purpose Poly crystalline cells are made by melting the silicon material and pouring it into a mold 2 This means that Mono crystalline cells are more efficient because they have fewer impurities 2 2 8 Enclosure A robust weatherproof and safe enclosure to keep all of the entire system secure is a crucial part of the project A gutted computer chassis was used to encase the inverter and the charge controller The solar panels will be mounted to the community center but will be designed to be detachable in order to be more convenient for storage Batteries will be covered in a wooden container with vents to prevent harmful gas accumulation The equipment was designed to be easy to access for maintenance or any other reason 2 2 9 Wires Finally the highest quality wiring possible was used Wiring can be dangerous and if the incorrect wire gauge is used for anything other than its intended purpose the results would be disastrous and potentially fatal This is critical because a hot wire can cause a fire and or damage the system For the batteries low gauge wire were used and a medium to high gauge wire were used for the electronic components As far as wire material copper wiring were us
67. e resetting Maximum load current is fused and rated at 20A Warning the voltage at the load terminals is dangerous and potentially life threatening Do not connect any load with exposed wiring or around children or animals without proper supervision 7 2 Operation Once the PV panels battery bank and loads are connected the system can be turned on via the power switch The power switch is responsible for giving battery power to the charge controller Once the switch has been closed the load should begin receiving power If there is sufficient solar energy available the status LEDs should also light up Without sufficient solar energy PV voltage gt 11V 118 the controller will remain in standby mode with all LEDs off The load will still work in this state The status LED indicators are as follows i Green ON Battery is charging ii Green blinking Battery is fully charged iii Yellow blinking Battery is low iv Red ON Battery is low and or load is too high cut off v All LEDs OFF System is in standby 1 3 Monitoring and Logging The charge controller can be monitored via a serial connection to a PC laptop Using hyperterminal or any similar serial connection application the output can be viewed by creating a connection on COM1 with the following parameters i Baud rate 57600 bps ii Data bits 8 iii Stop bits 1 iv Parity None Once the connection is opened real time data will begin scrolling on screen
68. e being efficient when used Mono crystalline cells are expensive to produce because the Czochralski process results in excessive waste of silicon As a result of this waste the production cost is high so the price per panel stays high However you can maximize the amount of watts per square foot of panel used since these panels are so efficient This is an important design feature if limited space is an issue Another one of the disadvantages of Mono crystalline solar panels are that they are very fragile and care must be given during the shipping and installation processes Although the cost to produce these panes have increased most online solar panel retailers have recently dropped the prices for these panels due to decrease in demand making their prices competitive with the prices of the Poly crystalline panels With higher efficiency and similar cost to its competitors Mono crystalline photovoltaic cells are ideal for the South Africa project 21 The second kind of solar cell that was commonly used are Poly crystalline silicon cells In the present market Poly crystalline solar cells are the most popular for home installations They are popular because they are cheaper to produce than Mono crystalline panels To make these cells molten silicon is cast and cooled in a rectangular shape The rectangular block is made up of tiny silicon crystals that look like broken glass This block is then sliced into thin sheets Compared to Mono crys
69. e system pointless Sensors give data on the status of the system and without them vital information about the system would not be known This would be a problem because without knowing vital information of the system identifying when the system is malfunctioning would be almost impossible 3 1 6 1 Voltage Current Sensors Part of the design for the project will be to be monitor the amount of voltage and current that is being outputted by the solar panel This information will be sent to the microcontroller and displayed on the monitoring system The voltage of the solar panel can range from around 0 to 33 volts This voltage range must match the maximum input voltage range of the microprocessor chip which is between zero and five volts To measure the voltage coming from the panels a sensor is not needed but a voltage sensing circuit will be implemented By connecting a voltage divider in parallel with the solar panel the maximum output from the solar panel can be dropped to match the maximum voltage of the microprocessor The following equation R2 Vout Volg 1 2 Equation 1 55 Where Vou is the maximum voltage of the microprocessor and Vi is the maximum voltage of the solar panel the values of R and R can be found A Zener diode can be connected in parallel with the microcontroller which would help regulate the voltage such that it does not exceed the microcontrollers threshold voltage level A spike in voltage can damag
70. e the microcontroller A voltage spike due to overcurrent may be caused by lightning strikes electrostatic discharge or solar panels operating above the maximum voltage range Most microcontrollers work in a range from OV to 5V This is why a Zener diodes are chosen to regulate the incoming voltage into the microcontroller to be no more than 5 V The data which will be sent from the voltage divider circuit will be sent to the microcontroller Before this is done Operational Amplifier will be used The use of Op Amps will be important to the design because they help ensure that the data being sent to the microcontroller will be accurate by decreasing the noise When traveling long distances in cable voltage signals tend to develop noise This unnecessary noise can affect the data being outputted This can lead to misleading results which is why the use of Op Amps in this circuit are very important There are many kinds of Operational Amplifiers but Unity Gain Op Amps have characteristics which fit the design requirements for this project and is a favorable design consideration This type of Op Amp is useful because the overall gain of the circuit will be in unity It is important to minimize external influences to the output The reason for this is that added gain to the output will generate incorrect values and extra circuitry would be needed to step the voltage down before the signal can be received by the microcontroller A current sensor will b
71. e three battery types above in their advantages and disadvantages are listed below 39 Table 11 Advantages and Disadvantages of GEL Batteries Advantage Disadvantage Totally Maintenance Free Higher Initial Cost Air Transportable Heavier Weight Spill Proof Leak Proof Water Cannot Be Replaced If Continually Overcharged No Corrosion Typically Cannot Be Used To Replace Flooded Or AGM Types Without Adjusting Or Replacing The Applications Existing Chargers Superior Deep Cycle Life Automatic Temperature Sensing Voltage Regulated Chargers Must Be Used And Charge Voltage Must Be Limited 14 2 To 14 5 Volts Maximum At 25 C 77 F Installs Upright Or On Side Very Low To No Gassing Emission Compatible With Sensitive Electronic Equipment Superior Shelf Life No Recharge Current Limitation At 13 8 Volts Rugged And Vibration Resistant Very Safe At Sea With No Chlorine Gas In Bilge Operates In Wet Environments Even Under 30 Feet Of Water Will Not Freeze To 20 F 30 C 40 Table 12 Advantages and Disadvantages of AGM Batteries Advantage Disadvantage Totally Maintenance Free Shorter Cycle Life Than Gel In Very Deep Cycle Applications Air Transportable Automatic Temperature Sensing Voltage Regulated Chargers Must Be Used Spill Proof Leak Proof Water Cannot Be Replaced If Continually Overcharged No Corrosion Charge Voltage Must Be Limited 14 4 To 14 7 Volts Maximum At 25 C 77 F Installs Upright Or O
72. e utilized to monitor the DC current which is being outputted from the solar panels Sensitivity for the panels is more important than for the batteries so more precise measuring methods are used for the panel side For the batteries an Op amp based system will be used and for the PV panel side a current shunt monitor will be used There are several different technologies which can serve the purpose of a current sensor The ones available are surface mount Hall effect sensors Hall effect current clamp sensors the Hall effect open loop current sensor the Hall Effect current sensor and the Inductive current sensor For DC currents measurements are made using the Hall Effect while for AC currents measurements are made using Inductive technology 3 1 6 2 Temperature Sensors Temperature is a very important consideration This is because temperature affects the efficiency in both the batteries and the solar panels To circumvent this methods have been made to keep these components at idea temperature The problem is that you can t moderate temperature without knowledge of the temperature The logical conclusion is that it would be beneficial to know the 56 temperature To gain knowledge of the temperature the addition of a temperature sensor is needed To implement a temperature sensor the sensor will need to have direct physical contact with the components that need it most Namely the batteries and the solar panels The optimal sen
73. eady exist and comparisons in options available that will affect the overall design of the project 3 1 Existing Similar Projects and Products This project is not the first time that an MPPT charge controller has been used to control the charge levels coming from photovoltaic panels going into a battery bank In fact this general idea was derived from the numerous other projects that experimented with this concept Although the ideas and technology used for this project are not completely unique the condition in which this project is being applied for has the potential to make the greatest societal impact Previous senior design projects conducted by students at the University of Central Florida in the summer of 2009 3 provided insight into a solar project that fulfilled the requirements of a UCF senior design Another UCF project designed in the fall of 2011 4 made further advancement by using an MPPT charge controller in their design This documentation provided a large amount of insight into the processes and features needed to design a stand alone charge controller The third most influential project was the Pure Sine Inverter project designed a senior design group from the Worcester Polytechnic Institute in the A B C term of 2006 5 which showed all the advantages of a pure sine inverter as well as providing a good basis for a model design This project has been influenced by the ideas above but the incorporation and application of
74. echarging is not demanded However the solar system in the Pomolong Township project requires recharging so secondary batteries type will be the focus of battery research There are a plethora of chemistries to choose from within primary and secondary batteries The most prevailing chemistries used in batteries are lithium lead and nickel Batteries are also rated according to the following attributes capacity in ampere hours AH voltage specific energy and power C rate and cold cranking amps CCA More details concerning such attributes will be addressed in the following sections 3 1 3 2 Chemistries in Secondary Batteries The most common chemistries used in secondary batteries are nickel cadmium Ni Cd nickel metal hydride NiMh lithium ion and lead acid 36 Ni Cd batteries utilize nickel oxide hydroxide and metallic cadmium as electrodes They have many advantages when compared with other rechargeable batteries Ni Cd batteries are able to tolerate deep discharge for long periods they also have a higher number of charge discharge cycles Size wise they are smaller and lighter than comparable lead acid batteries due to their much higher energy density However the disadvantages of Ni Cd batteries are not negligible Performance speaking there is a significant negative correlation between the internal resistance and the cell temperature which can result in considerable charging problems Besides Ni Cd batteries also suffe
75. ed because it is the preferred choice for any electrical application and has proven itself through time 2 3 Project Requirements and Specification The main requirements for the solar energy power generator are to provide the township of Pomolong with about 500 Watts of power an hour for about 4 hours every evening Thus the solar panels will charge the batteries with power during the day and at night the power will be used The output is 220V power as opposed to 120V that is used in the United States Even though newer electronics and laptop adapters are able to work from 120 220 V this will guarantee that all electronics in South Africa be able to work with the system Safety is a major concern so the highest measures were implemented Batteries were ventilated and the highest quality wires were used throughout the system All electronics were kept in metal enclosures to protect them from adverse weather a temperature changes Last but not least fuses and other electrical safety designs were incorporated into the design to prevent electrical fires due to overcurrent The complete system incorporates solar panels a charge controller batteries and an inverter Each has important requirements in order for the system to work together and for the objectives to be achieved The following table summarizes the requirements and specifications for our project Table 1 Specifications Spec Specification 1 Ability to capture about 6 hour of
76. eir low cost and favorability for the Climate in Pomolong Township The specific flooded battery chosen for the project is the Trojan T 105 Battery shown below Two will be used for the device This battery is manufactured by Concorde and will be bought from www wholesalesolar com for 139 The battery is rated for nominal 12V and 225Ah capacity at a 20h 0 042C charge rate The battery can deliver about 40 CCA and can be deep cycled 1000 times if never discharged lower than 50 capacity For the project when the battery bank reaches 50 depth of discharge DOD no power will be delivered to the load This battery has the dimensions 7 71 x 5 18 x 8 05 cubic inches and weighs 30 lbs This battery is also extremely resilient to shock and vibration forces In addition the Trojan T 105 can withstand very hot temperatures which would ruin AGM and GEL lead acid battery The battery also features small self discharge of 1 to 3 per month This battery is a great battery for solar energy purposes for it provides a high capacity long deep cycle lifetime and efficient energy storage The comparison among three types of deep cycle batteries are summarized below according to the six factors 1 Cost 2 performance 3 safety 4 size 5 availability and 6 maintenance 43 Table 14 Types of Deep Cycle Batteries Flooded Cost UB GC2 6V 225 AH is 139 Performance 88 charge discharge efficiency Safety Hazardous Size 6V 12V 24V
77. er requirements Most appliances will not mention how much power it needs to start and operate So the user has to determine these two values If it is looks for values in Watts W in a stick or label of the appliance or its charger or user s manual If not then we can calculate from Amperes A by multiplying the Amperes 120V which equals the continuous load in Watts W For most appliances one can multiply the continuous load in Watts W by two to find the surge power requirements also in Watts W Note that this is just an approximations and some appliances including refrigerators have a much higher surge power requirement 114 6 4 Sensor Testing A testing plan shown in the following tables has been made in order to make sure that all of the sensors that are going to be incorporated work the way they are supposed to work This also helped to eliminate the possibility of any factory defects existing before they were implemented into the final design The following tables contain each sensor to be tested with the test plan that was put in place for each sensor followed by the results Table 30 Voltage Sensor Step Procedure 1 Devise a voltage divider configuration 2 Calculate appropriate resistor values based on the Solar panel and microcontroller specs 3 Simulate Voltage Divider using a circuit simulation software 4 Build a voltage follower connected to a low pass filter 5 Construct circuit and test it Table 31
78. er on off and a 3 digit monitor display Next for the circuitry we will first assemble it in a breadboard and make sure the circuitry outputs the desired output The reason for this is that to achieve a pure sine wave a lot of tweaking will need to be done along with an oscilloscope until the final circuitry is achieved Then with a schematic on hand the pcb board will be ordered with the components integrated At this point the enclosure and the board will be connected This includes the power switch connection the monitor display and anything else that is attached with the enclosure The inverter will take in 24V DC and output 210V AC in a pure sine wave form the conclusion of this design summary will end on a solemn note The best and most expensive parts were unfeasible to use and implement in the design due to budget constraints With the tools that were available robust design in a MPPT charge controller as well as a Perfect Sine inverter are implemented to give the people of Pomolong the best that could be given It was fully wished and desired to use the most expensive parts but as they were not available what can be given is something that will work as well or better 94 5 0 Project Prototype Construction The purpose of this section of the documentation is to highlight how construction of a working prototype can be accomplished This includes a plan on acquiring parts listing the bill of materials and developing a plan to ha
79. er small devices like iPods cell phones and other such things The following is a picture of how a battery bank wired in series in the figure is typically attached to a power inverter Figure 11 Battery Bank Connected to Power Inverter es Positive Terminal MM Negative Terminal Inverter Back Panel 3 1 5 Encasing Good battery enclosure design and construction will protect the people of the Pomolong township from potential battery mishaps and can enhance the effectiveness of the battery bank as well Battery enclosures serve four main functions 54 1 Provide physical protection to the batteries from tools falls dust debris etc 2 Isolate and safely vent hydrogen gas to the outdoors 3 Maintain a consistent temperature among the cells 4 Meet the requirements of the National Electrical Code Articles 480 and 690 Section 690 71 The Batteries store electrical energy using a chemical reaction and can cause acid burn electrical burns or be an explosive hazard These dangers can be prevented if they are properly handled or contained When it comes to housing the batteries the goal should be to provide a clean dry ventilated semi conditioned space that prevents unqualified people from coming into contact with the battery bank 3 1 6 Sensors Sensors are a very important part of this project Without sensors the charge controller would not be able determine voltage levels of the battery making an entir
80. ere tilted so that they were facing the sun perpendicularly The recorded current was then measured against the specifications on the back of the panel to test for actual output Efficiency of the system was determined after testing was complete These two tests can be performed before purchasing a Solar Panel so that the system is confirmed to work as rated or better but we could not do it since we purchased our panels online To find how much power is being produced this simple eguation for DC power was applied Equation 6 DC Watts Voltage X Current The power is measured in Watts W the voltage is measured in Volts V and current is measured in Amperes I The power generated in full sunlight depends upon the resistance of the electrical load connected to it Ohm s law states that V x R meaning that a simple method of measuring power output of a solar panel is to connect different values of resistors of to the panel and measure the voltage The measurements were used to plot the power output and a performance graph for the individual panel The manufacturer of the photovoltaic cell panel usually has this chart already prepared results from individual testing can check the actual against the theoretical The only way to test if a solar panel is charging correctly is to test it with a battery The photovoltaic cells will be producing DC voltage and current so there is no problem in applying it directly to the battery using
81. esign information equations and parameters for a prototype development board In other words this charge controller was chosen because it is the goldilocks of all of the controllers researched The MPT612 has an embedded RISC processor with patented MPPT algorithm included It also supports over voltage and over current protection thermal protection has programmable libraries for different charge profiles alarm conditions and vast documentation and flexibility for use in any environment and with any size panel and battery bank 34 Figure 6 MPPT Charge Controller Reference System Block Diagram 17 Permission Pending MPPT charge controller BUCK BOOST CONVERTER BUCK ON battery current and voltage sense PV voltage sense ANALOG SIGNAL LOAD CONTROL CONDITIONING CIRCUIT _PV current sense AND MONITOR to DC load BAT voltage sense CIRCUIT BAT current sense temperature sense MOSFET GATE hai MPT612 IC DRIVER CIRCUIT POWER SUPPLY O RESET AND Ed ALCAN serial The core of the charge controller is the buck boost DC DC converter which transfers energy from the PV panels to the battery in short pulses via a switching MOSFET which is controlled by the MPT612 The duty cycle of the MOSFET is varied by the MPT612 based on the demands of the MPPT algorithm The other elements of the charge controller include the voltage and current sensors a power supply and clock generator gate driver and serial UART communications 3
82. ess of each of the major kinds of photovoltaic cells each of the cells will be reviewed in detail chronologically The first solar cells that were commonly used are Mono crystalline silicon cells Although they are no longer commonly used this first generation technology is the oldest and most tested photovoltaic As its name suggests Mono crystalline solar cells are made from the same silicon crystal ensuring that minimal impurities irregularities and imperfections are maintained To produce this kind of silicon the Czochralski process is used To do this a crystal silicon seed is dipped into molten silicon and withdrawn slowly At the end of this process when the molten silicon crystallizes around the seed a two meter long cylindrical single crystal ingot is produced The ingots are then doped in proportions based on intended future use and cut into wafers The silicon wafers can then be used for semiconductor devices or for photovoltaics The main advantage to this type of production is that when the impurities are minimized the photovoltaic cell is more efficient Efficiency is a based on percentage of how much current is produced given the amount of light that is absorbed Mono crystalline cells can achieve efficiency of about 17 7 Due to their high efficiency these panels are expected to have an above average life expectancy and are usually rated to last for around twenty five years with some actually lasting fifty years Despit
83. f a passive cooling method would be attaching a heat sink or cooling fins to dissipate heat from the panels The problem with most cooling methods available right now is that the efficiency gained by utilizing them does not offset the cost to implement them The last inefficiency associated with solar panels that will be discussed is their ability to absorb light Most solar panels cannot use the entire light spectrum to convert light into current Light energy is lost in several ways Some energy is lost from photons being reflected To mitigate this loss an antireflection coating is used on almost all solar panels Some energy is lost because the photons of light do not get absorbed because they do not have the right wavelength to match the semiconductor band gap As a result more than half of the light spectrum available becomes useless to the solar panels To help fix this issue band gap engineering has been developed as one of the leading methods used to increase light absorption efficiencies Electrical design engineers maximize power by maximizing photo current or photo voltage individually Photo current is maximized when the amount of photons of light from the solar radiation spectrum captured are maximized To perform this method a small energy band gap is selected so that photons with low energy can excite electrons in the energy conduction band The downside to using a small energy band gap is that it lowers the photo voltage and phot
84. g how much energy is stored and other diagnostic information All of this was done while still employing all of the best electrical safety principles given that this system is intended for to be used by villagers with minimal technical education 2 0 Project Descriptions The project descriptions section of this paper is intended to describe both tangible and intangible parts of the project such as reasons for undertaking this project how long it will take specific objectives and brief descriptions of different components of the project as a whole 2 1 Project Motivation and Goals There is great need of electricity in the small South African community of the Pomolong Township which is occupied by the less fortunate people of South Africa due to the aftereffects of apartheid They are cut off from the rest of the world because they do not have electricity that will enable them to use electronic devices such computers cell phones and TVs Due to the extreme poverty in the community they cannot afford the cost of power utilizing the power grid from the local utility company Even if they could afford the cost of power the township is not close to the power grid When added together the combination of these factors have put the people of the Pomolong Township in a difficult situation To solve this problem a device that utilizes renewable energy to generate power for this village was planned and designed This device will allow the village
85. g run at its max AC load According to commercial inverter s user manuals and information considers the electrical components of the inverter the surrounding air temperature should be between 20 C and 40 C To help dissipate the temperatures from the inverter the group plans to make the enclosure of the inverter of metal as well with small slits to provide ventilation 33 Next we address the warning caution labels The group plans to have a label on the inverter that addresses all the safety procedures that are involved when using the inverter These also include the appliances which our solar panel powered energy source can be used safely These warning label contents include but are not limited to the following e Danger of shock or electrocution Please treat the inverter outlets the same as you would treat a standard power outlet 112 Do not use the inverter near flammable materials or any location that can contain flammable gases Note that when disconnecting or connecting a device from to the inverter a brief spark may occur Do connect any appliance to the inverter that are wet or damaged Do not let minors handle the inverter Do not allow any liquids to contact the inverter Do not leave the inverter in direct sunlight Do not cover the inverter Keep the inverter in a clear area that has good air circulation Do not input anything different than a 24V DC power source The inverter is made to work with 24V DC power sour
86. gram and implementation All diagrams were created using the KiCad EDA Software Suite Circuits are based on Application Note AN10936 from NXP Semiconductors which is a reference design manual for the MPT612 MPPT microcontroller used in the charge controller 4 2 1 High level overview The high level overview is KiCad s root sheet in its hierarchical sheet layout It shows all of the modules in the system and the digital signals that interconnect them These modules can be built separately and joined with ribbon cable as it is easier to debug and prototype or they can all be built on a single board to optimize cost on the final product Figure 13 Charge Controller Root Sheet Sheet DC DC converter A _ BAT_overvoltage lt Buck PWM Buck mode enable Load cutoff Load current ref AD oad current ref BE BAT current ref AF PV_voltage_ref y er es q A BAT current ref BI t 4 PV_current_refA BAT hace pate e t BAT ee IPV current ref B voltage_refL TT Sheet BAT voltage and current IS BAT c it ref A Fite dc_dc_converter sch gt BAT_current_ os DBAT current ref B 4 Hp BAT voltage ref Sheet PV voltage and current sense PV voltage ref KIBAT_overvoltage PV current ref Ad KIBAT current charge PV current ref Bd H KIBAT volt sense File HAT volt curre
87. he cell tops The inside of the box was carefully caulked and treated with a penetrating sealer to resist minor spills or corrosive vapors For best results a liner of 40 mil EPDM 89 rubber or pond liner available at many nurseries or home improvement stores was placed in the bottom and about 6 8 inches up the sides folding instead of cutting for the corners This liner protects the wood and forms a leak proof layer See the Figure below Figure 37 Enclosure Design 90 4 7 Wiring To keep the performance of the project in creating a power source out of solar energy it is important to have good wiring throughout the system Wire failure can not only lead to system failure but also to more dangerous cases such as a fire Therefore top of the line wiring with good insulation was used throughout the system Throughout the system the most important part as far as wiring is concerned is at the battery and inverter level To maintain good performance of the inverter and efficient power flow the group plans to use 4 AWG copper cable with at least a 90 C insulation rating These type of cables are designed to withstand up to 135 A of current These are very thick wires that provide low resistance and transfer energy in a safely manner The following is a picture of the power cables that will be used for the battery and inverter part of the system 32 Figure 38 Power Cables Permission Pending Next we take a look at the specif
88. hotovoltaic cells are the main reason why they perform better than Poly crystalline cells In Poly crystalline photovoltaic cells the impurity concentration and the structure abnormality associated with multiple crystals of silicon increases the electron hole recombination rate If the electron hole recombination rate is increased then the efficiency of the panel decreases 26 The next factor that was taken accounted for was temperature Temperature is another negative factor that affects solar panel performance Crystalline silicon panels suffer the most when their cell temperature rises When the temperature of the semiconductor rises the conductivity also rises If there is an increase in conductivity the electric field of the p n junction decreases If the electric field decreases then the voltage across the photovoltaic cell decreases Less voltage across the solar cell results in a smaller power output and lower efficiency 15 New research is being done using non silicon semiconductor materials on thin film panels to circumvent the restriction that occurs as a result of a reduction of panel sensitivity due to temperature The ideal weather conditions that will put solar panels at their peak performance are cold and sunny days Those kinds of days are not typical in most places in the world Understanding this the project took the temperature effects on the selected solar panel with great consideration Every Solar panel has a temperat
89. ications for the power cables used e 4 AWG cable with at least 90 C insulation rating e Should be as short as possible in order to reduce the voltage drop between the batteries and inverter e The ends of the power cables should be a metal terminal which allow secure connection to the battery and terminal Additionally the connection will be covered with rubber 91 e Red power cables will be reserved for positive terminals e Black power cables will be reserved for negative terminals For the terminals they were soldered to metal terminals To do this the ends of the power cables were stripped then solder will be heated and poured into the terminals and then the wire will be inserted to ensure a strong solder As stated above once connected they will be covered with rubber covers to prevent contact Note it was important to correctly wire up the polarities of the inverter with the batteries if this is failed the inverter colld fail and could possibly get damaged 92 4 8 Design Summary The purpose of this section is to give a general overview on what is planned to be designed for this project The South Africa project to help generate power to the community center for the impoverished African village of the Pomolong Township is divided into four distinct parts All the research and design of each of the parts have been explained in detail What remains in this section is just a cursory overview for the purpose of getting
90. icient because the resources are scarce and utilizing every bit of energy gives the townspeople more time to enjoy the electricity The more time the villagers have socializing and utilizing the facilities the greater the impact the project will have With all of these considerations inefficiency is not an option 2 2 3 Ease of Use Keeping in mind the technology aptitude of the users ease of use became an unavoidable objective Overall design will cater to being simplistic portable and color coded to prevent and reduce user error A monitoring system on an LCD screen connected to the charge controller and indicating all conditions of the project such as current levels voltage levels and temperature will be included 2 2 4 Charge Controller One of the objectives is to successfully capture as much sunlight energy as possible This is done through a MPPT charge controller system The reason behind this controller is to vary the electrical operating point of the modules so that the modules produce the maximum power possible regardless of the climate conditions This is very critical for the system because this eliminates the need to manually alter the current and voltage coming from solar panels To do this the MPPT charge controller changes the incoming current and voltage and matches it to the batteries voltage and current resulting with the maximum power 2 2 5 Batteries Batteries are also important to the project design Deep cycle
91. igital outputs which connect to green and yellow LEDs to indicate charge status Pins 46 13 14 29 and 30 are for power control serial communication and ground Finishing the right side of the diagram pins 22 all the way down to 38 are all for sensor input PWM output GPIO and buck boost control Pin 39 is for temperature input from the NTC which measures the ambient temperature All of the pins along the bottom row are grounds Pins from 20 to 11 form the oscillator and clock generator circuit while pin 6 forms the reset circuit Lastly pins 27 up to 8 are for UART JTAG communication Architecturally the MPT612 features an ARM 32 bit processor and 32kB on chip flash memory and 8kB static RAM Pins that are not connected to a specific peripheral function are controlled by GPIO registers They can be dynamically configured as inputs or outputs The MPT612 also contains one 10 bit Analog to Digital Converter ADC capable of performing more than 400 000 samples per second The chip also has two UARTs two I12C bus controllers and two serial VO controllers 4 2 5 DC DC Converter The DC DC converter is the muscle behind the charge controller It is responsible for taking energy from the PV panels and via PWM pulsing it through the inductor which allows the energy to be converted to a different voltage and current in a theoretically lossless manner The converter is using a buck boost topology and can operate in buck boost mode or buck onl
92. is the General Purpose Input Output GPIO connector which can be used for custom input and output signals Figure 19 MPT612 E II 121E bead LS WOOT 121E bead a LAR 2 o 5 La DITTO a hal o FLAG PURFIAL yy a an 2 El ae D 1uF zn ml O tuF 0 1uF AA Se a po G P1019 2 bitch mode erabie 3 e 2 P1020 OES ss 3 P1021 a SAS s gt gt pioi 44 EINTS sw 2 ayes gt E 159 TMS pio17 1 47 P1027 i ads U AR is TCK piots 48 EY P1018 j da WT 4 265 3 0 T PI013 i ex 28 RTCK PIO15 n DEBUGSEL 27 JTAGSEL P1016 48 TER aPaverdewn wakeup 9 R67 z PIOO TXDO 13 Ey e POL 000 g PI08 Pie 10 RST 6 RST _ U15 30 pais DRY MA E ha MPT612FBD48 PIO9 ME di a P104 22 oBrckponerrnable Ey T PIO5 LE D Load cutott Te xt PIO6 H lt 2 7 PWMOUTO 28 D Buch PWM gt _18 pio2 48 _ roxy pro3p21 F PWOLTSENSEBUCK W22 py vele sense turt x2 PYVOLTSENSEBOOST 3 Pisattcsemiechoost PVCURRENTSENSE 4 ap currentsense L2 VODIRTO PIOLO 3 N p geld RIXC2 8 moio Ss Mas a P1025 8 To G a P1026 os 2 31 43 pp Pa Sa 68 Starting from the top left of the MPT612 and moving clockwise first there are the power supply rails two 3 3V rails and one 1 8V rail Pins 1 2 3 44 47 and 48 are for GPIO power input and buck boost control Pins 41 and 45 are d
93. iscuss the conditions that could alter those properties making the photovoltaic less than ideal To describe the physical properties of solar panels a brief overview of the photovoltaic effect is necessary in order to explain factors that can change the physical property of a solar panel Simply put the photovoltaic effect is the physical phenomenon that allows a photovoltaic cell to convert solar energy into usable electricity The photovoltaic cell is usually constructed of some light absorbing semiconductor material like silicon All semiconductors are associated with a specific energy band gap 12 The energy band gap is the potential difference between the lowest energy level on the energy conduction band and the highest energy level on the energy valence band The conduction energy band is the range of energy that allows an electron to become free from an atom The energy valence band is the range of energy where the electrons on an atom are not free When electrons are in the energy valence band they are considered to be in steady state lf given input energy the electrons can become excited If given enough energy they will jump to the energy conduction band and will be considered to be in an excited state The electrons in the energy current band are responsible for the direct current that is produced by the solar cells In the case of solar cells the input energy will be solar energy in the form of packets of photons containing differen
94. isition and also included component level testing Once a part was acquired the component testing consisted of individual parts testing to confirm that it works and provides reasonable information This was especially important with sensor implementation to make sure they were scaled correctly and provided meaningful data The circuit design was first prototyped on a solder less breadboard As previously stated the development of the packaging did not commence until the main modules were finalized 14 Table 6 Prototype Milestone Prototype Solar Batteries Microcontroller Inverter Charge Controller 13 JAN 20 JAN 7 FEB 14 FEB 23 FEB 9 MAR 18 MAR 26 MAR The final stage of the project consisted of testing The testing plan and methods covered component level module level and system level testing The table below shows that testing should commence in March overlapping with the final stages of prototyping The testing and documentation encompassed all of April up until the last week in which the final presentation took place 15 Table 7 Testing Milestone wia SAS a1nuzg SIEMDIEH HModsuei Huibeyoeg ainpsd01g J9JeS Bulbseyy s n yeg Testing leued 1elos 16 MAR 19 MAR 22 MAR 29 MAR S APR 16 APR 20 APR 26 APR 16 2 1 Budget and Finance Discussion
95. l is its price Helios offers this panel in packages of 2 for 850 00 The specs of the panel are in the tables below 61 Table 21 Solar Panel Characteristics Dimension 1 984 mm x 984 mm 78 11 x 38 74 Area 1 95 m2 20 99 Sa Ft Thickness 40 mm 1 58 Weight 26 kg 57 2 lbs Table 22 Electrical Data STC Rated Power PMPP W 305 MPP Voltage V 36 70 MPP Current A 8 30 Open Circuit Voltage V 45 08 Short Circuit Current A 8 87 Table 23 Electrical Data NOCT Rated Power PMPP W 229 MPP Voltage V 33 85 MPP Current A 6 75 Open Circuit Voltage V 41 60 Short Circuit Current A 7 20 4 2 2 Solar Panel Mounting When mounting the solar panels all measures to ensure safety should be made It is also important to note that any damage incurred towards the glass of the solar panel is irreparable The location of mounting the solar panel is important To choose a good location the highest elevation with the least amount of possible shade is the best 62 choice In the Southern Hemispher the sun is due north at noon The following table gives the optimal angle of inclination for the solar panels to maximize sunlight throughout the year Table 24 Approximate Vertical Mounting Angle for Solar Panels in Harrismith South Africa 28 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 45 O Ol e ad i 1090 ol 53 HAS ke 63 4 2 Charge Controller This section details the charge controller circuit dia
96. left is the JTAG connector This is used for flashing new software to the MPT612 IC The button on pin 12 is for enabling JTAG The connector J7 on the right is what interfaces to the charge controller It is a 20 pin header The circuit on the bottom is the serial interface U13 is the MAX3221 RS232 level connector IC In windows using the HyperTerminal one can connect to the charge controller over the serial interface to monitor charge performance First connect the JTAG UART board to the charge controller Then connect the D SUB connector on the JTAG UART board to a serial COM port on the PC Open HyperTerminal or TeraTerm and set baud rate to 38400 Connect the external load on the charge controller Connect the 12V battery to the charge controller as well as the PV panels Press any key in the console to display a menu for open loop efficiency testing The functionality is executed once the menu key is pressed The LED status indicators will show the current system function Green fully on means the battery is charging When the green LED is blinking the battery is fully charged Yellow means battery is low Red means battery is low cut off or overload cut off If none of the LEDs are on the system is in standby Before running the test measure the PV voltage PV current battery voltage and battery current using a multimeter Once sufficient PV power is available the output of 74 the application program is displayed on the PC terminal
97. ll tracks at very close tolerances for surface mount components such as the LOFP48 may prove to be somewhat difficult Etching a double sided board may also be more difficult than it seems Shorts and opens may exist and not be discovered until later requiring a partial or full rework of the whole board Hackvana is a PCB and electronic components vendor based out of Shenzhen China Hackvana nirvana for hackers has supplied nearly 4 000 PCBs in just the last year alone Since they are based in China shipping time may be longer however manufacturing costs are greatly reduced Hackvana is able to manufacture professional high quality circuit boards of any shape and size Different color options are also available as well as silk screen text Lastly there is 4PCB 4PCB is an American based circuit board manufacturer located in Aurora Colorado Tempe Arizona and Maple Grove Minneapolis 4PCB is going to be the vendor of last resort for this project considering the higher costs associated They may also be considered if a PCB needs to be made and delivered ASAP since they are in the USA Being that 4PCB is a much larger and more established company than Hackvana they are clearly reputable and reliable Ultimately the available funds and time will determine who wins the bid for circuit board vendor 105 6 0 Project Prototype Testing The purpose of this section of the project report is to give a detailed explanation on how testing of each
98. measure the full DC current e Turn the photovoltaic cell away from sunlight e Disconnect multimeter e Connect the Solar Panel directly to the Battery using appropriate gauged wiring e Connect the multimeter 108 Set multimeter to DC Amperes to measure the amount of DC current flowing into the battery Rotate the photovoltaic cells away from the sun Record highest amount of current drawn Turn the photovoltaic cells away from the sun Disconnect the battery 109 6 2 Battery Testing When testing a flooded battery it is very important to visually inspect it for obvious problems Check to see if there is anything loose or broken Verify also that the terminal clams are not corroded dirty or wet Get a digital voltmeter with 0 5 or better accuracy to test the state of the battery The table below helped tp estimate the state of the battery Table 27 Voltage vs State of Charge Digital Voltmeter Approximate State Of Charge 12 65 100 12 45 75 12 24 50 12 06 25 11 89 0 After that we tested a battery charge time and discharge time in order to gauge the time of charge needed for the battery to be fully charged or discharged The time of battery charge mainly depends on solar panels output power which in turn depends on the irradiance level The battery discharge time determine the maximum charge supplied to the inverter See the tables below 110 Table 28 Battery Charge Time Steps Procedure 1 Connect the battery
99. mponent being powered It takes two steps for an inverter to change low voltage DC to high voltage AC First low voltage DC power is converted to high voltage DC source Next the high voltage DC source is converted to an AC waveform using pulse width modulation A different way to build an inverter is to take the low voltage DC power convert it to low voltage AC power Next use a transformer to raise the voltage to our desired of 220 240V AC for South Africa It was decided that the first method to produce the inverter was more applicable to our project design and it should be implemented to our project 29 As stated before the group is looking to make a pure sine wave inverter as oppose to modified sine wave inverter Modified sine waves are closer to square waves than curvy sine waves it passes the high voltage DC for a period of time so that the average power and rms voltage are closer to a pure sine wave These modified sine wave inverters are generally cheaper than pure sine wave inverters however the group has decided to build a pure sine wave inverter A pure sine wave inverter is the best output for AC voltage it is the same as a households power outlet Some electronic devices will only run on pure sine wave AC voltage and even go so far as to get damaged These devices include laptops printers and TVs Electronic noise is also at its lowest when using pure sine wave AC voltage The following is picture displays modified and pure si
100. mponents and their respective tracks on the circuit board were revised to support higher currents about 50A maximum in order to sustain at least 500W of solar energy without fault The other active components such as quad op amps current shunt monitor and switching voltage regulator were cataloged from ON Semiconductor Texas Instruments and International Rectifier These 104 components were also changed because the design moved to a through hole topology The system is estimated to cost around 300 USD including the cost of the circuit boards The most expensive component found during selection was the inductor coming in at over 25 of the total cost at 26 49 This is likely due to the cost of materials associated with winding copper wire to create the inductor Second to the inductor was the MPT612 chip itself Though not nearly as expensive it comes in at 7 98 Three different options were considered during research for fabrication of the printed circuit board Home fabrication Hackvana PCBs and 4PCB Home fabrication of the PCB is most desirable as it shows a high level of skill in the general prototyping and design field It is also cost effective as a homemade circuit board can be fabricated for a fraction of the cost compared to sending it out to a vendor The drawbacks for homemade circuit boards are that they are not as professional looking absent expensive machinery such as a CNC or drill press Furthermore etching sma
101. n Side Compatible With Sensitive Electronic Equipment Very Low To No Gassing Emission Excellent For Starting And Stationary Applications Work Well Under Extreme Cold Conditions Superior Shelf Life Fast Recharge Ability Rugged And Vibration Resistant Very Safe At Sea With No Chlorine Gas In Bilge Due To Sulfuric Acid And Salt Water Mixing Operates In Wet Environments Even Under Water Typically No Need To Replace Or Adjust The Applications Existing Chargers When Replacing The Batteries 41 Table 13 Advantages and Disadvantages of Flooded Batteries Advantage Disadvantage Lowest Initial Cost Spill Able Good For Higher Current Applications Operates Upright Only Water Can Be Added Shorter Shelf Life Excellent For Starting Applications Fewer Shipping Options More Tolerant Of Improper Recharge Cannot Be Installed Near Sensitive Voltages Electronic Equipment Certain Designs Are Good For Deep Watering Will Be Required Cycle Applications Replacements Readily Available Requires Maintenance And Safety Practices Work Well Even Under Extreme Hot Conditions Now that the advantages and the disadvantages of the deep cycle lead acid batteries are listed a choice among flooded gel electrolyte and absorbed glass mat AGM needs to be made Flooded batteries are the most inexpensive deep cycled batteries and work well under extremely hot conditions Performance speaking they have a low amount of discharge rate due to
102. ne waves 81 Figure 28 Modified Pure Sine Wave Permission Pending Voltage Sinewave Modified squarewave Squarewa ve As we can see a modified sine wave is closer to a sine wave then a square wave This modified square wave is easy to produce because it simply is 3 different constant values at different points in time The differences between AC Alternating Current and DC Direct Current is that DC is a constant voltage through a circuit which results in a constant current Batteries and digital circuitry use DC power because of logic purposes 1 and 0 since voltage will be constant high or low for either logic AC oscillates between two voltage values at a frequency In addition transmission power loss is proportional to current squared however DC is unable of being transformed for long distance transmission while AC is capable Inverters come in all shape and sizes from lower power functions such as powering a clock to being part of a backup system for a building A DC AC power inverter which is the type our group will be using The following is a picture of what a small power inverter typically looks like Figure 29 Commercial Power Inverter Permission Pending 82 Usually these type of power inverters are used today for many tasks like powering appliances in a car such as cell phones radios and televisions as we can see they come in handy when performing outdoor activities such as camping hiki
103. ng Solar Angle Calculator The Solar Electricity Handbook 2012 Online Available http solarelectricityhandbook com solar angle calculator html Accessed 6 December 2012 34 ABS Alaska DC to AC Power Inverters ABS Alaska 15 January 2008 Online Available http www absak com library dc ac home power inverters Accessed 6 December 2012 35 MIT Pulse width modulation MIT October 2000 Online Available http fab cba mit edu classes MIT 961 04 topics pwm pdf Accessed 6 December 2012 36 M Barr Introduction to Pulse Width Modulation PWM Embedded Systems Programming pp 103 104 September 2001 37 Amazon com Amazon com Amazon com Online Available http www amazon com Cobra CPI A4000BC 4 AWG Heavy Duty Inverter dp B001550DVU Accessed 6 December 2012 38 Power Bright ML900 24 Bright Manufacturing LLC 2010 127 Appendix C List of Figures Figure 1 Project Block Diaries LI AAA By ei ssw on eg 9 Figure 2 Silicon Solar Cell Structure and Mechanism 14 ee ee 26 Figure Sl VE ure 1G J eit Ai 27 Figure 4 Geographic Location of Pomolong Township in Relation to Harrismith 29 Figure 5 Irradiation Levels of South Africa ee RR RR RR RR RR RR Re ee ee 30 Figure 6 MPPT Charge Controller Reference System Block Diagram 17 35 Figure 7 Simple Diagram of PWM GeneratoF ee ee ee ee RR ee ee ee ee ee ee 47 Figure 8 Output of PWM Generator 6 ie ee ee
104. ng or fishing Pulse width modulation is a technigue used often to power AC devices that have a DC power source In this technique there is a variation of duty cycle in the signal which provides a DC voltage across the load which is in a pattern that appears to be AC signal for the load To create this pattern electronic analog components and a digital microcontroller are used 30 Analog PWM requires both a modulating and a carrier signal that inputs into a comparator which outputs a signal based on the difference between the input signals 31 The modulating signal is sinusoidal and operates at the desired output frequency and the carrier signal is a triangular wave which runs at a much higher frequency When the voltage of the carrier signal is higher than the modulating signal the output is at one state When the opposite happens then the output is in its second state The process is shown in the following figure with carrier signal in red and the modulating signal in blue and output signal in green Figure 30 Pulse Width Modulation Permission Pending al FU Finally the output source is connected to the load through transistors or similar electronic components which work corresponding to whether the output signal is high or low PWM inverters also keep the desired output regardless of the load In other inverters the output changes with changes in the load To do this a PWM inverter changes the output voltage according to the load connecte
105. ng and the other stationary contact Therefore the contact of the spring is continuously moving back and forth between stationary contacts creating a switch This form of electromechanical inverter switch is called a vibrator or buzzer Of course nowadays this method has been replaced by transistors and other semiconductor based electronics 19 46 In more advance designing there are many different circuit designs and control strategies Depending on how the inverter is to be used the different inverter designs differ So to begin with we specify the kind of waveform we want by filtering using capacitors and or inductors For example low pass filters are applied to allow the important parts of the waveform but not allowing distortion to go through the signal If one wants to keep a constant frequency in the signal a resonant filter can be used the opposite can be done as well as long as the maximum frequency supported by the filter is higher than the waveforms frequency could ever be Now feedback is required around each semiconductor switch because a path is needed for loads that contain inductance So when the switch is turned off there exists a path for the peak inductive load current The feedback can be implemented through rectifiers or anti parallel diodes Now to create the AC signal output from the Pulse Width Modulation PWM technique is used As mentioned before to create the signal a switch that turns on and off fast is used T
106. nnnonnnnnnnononononnncnonanonnnnnnanennnnonos 116 Table 33 Solar Radiation SenSor ooooconoonnnnccnocononocooonancnnonnnnnnnnnnonananarnnnnnos 116 129 Appendix E List of Eguations EUA OR N OE EE OO EE EE EA RA 55 EU La A A AD e ER 71 Eg ation Ds RAS A EAN AAA EG SG Ee Dk Ge Et 71 EQUINA Ar A AAA AAA AAA AAA AA As 71 EUA AS cia 71 ENGER Dr AA AAA AA A ad aaa 107 130
107. nt sense sch PV current senselt PV volt sense buck D PV volt sense boost Fite PV volt current sense sch Sheet pwr supply Ul gt BAT_volage_ref HH t DPV voltage ref Load current ref A Load current ref B D Buck power enable Sheet mpt612 digital circuit schematic gt PV_current_sense BAT_current_charge lt JBAT_current_ref_B DPV volt sense buck BAT volt sense HH JLoad current sense JPV volt sense boost oad current sense TTT IPowerdown_wakeup Powerdown_wakeup lt File pwrsupply sch Buck_PWME FTP Buck mode enable D P Buck power enableD Load cutoffD mpto1Z sch 64 sense The charge controller is composed of five main modules DC DC converter power supply microcontroller PV voltage current sensors battery voltage current sensors and an optional serial UART module Each of these modules is described in greater detail in the subsections below 4 2 2 Battery Voltage and Current Sensors This module consists of two separate circuits a voltage sensor and a current sensor for the battery bank Both of these sensors take in an analog input signal from the DC DC converter and output an amplified signal for input to the microcontroller The operational amplifiers are used for both circuit protection and amplification purposes Figure 14 Battery Voltage Sense Circuit 5 a e S S 2nd order low pass filter R36 BAT_voltage_refC c29 0 04uF R38
108. o expand on that all the electric components of the inverter are turned on and off to generate proper RMS voltage levels Today a microcontroller is used to control this switching as oppose to using a magnetic field tied to a spring that was historically used The following is a picture of PWM generator Figure 7 Simple Diagram of PWM Generator Permission Pending PWM Generator Triangle MAA Generator ae PWM Modulation Generator So a triangle wave generator and a modulation sine wave generator go into an Op amp to produce PWM from the diagram above The triangle generator is called the carrier signal and it controls the frequency of the switching The modulation generator produces the signal that determines the width of each pulse hence the RMS voltage level of the signal Next the output of the PWM Generator will be seen Figure 8 Output of PWM Generator 6 Permission Pending 47 Output of PWM Generator Now in the figure above the carrier signal can be seen with the modulation signal on top of it The bottom signal is the actual PWM signal If observed closely it can be seen that the bottom signal is constructed by the modulation signal setting the width of the pulses in the PWM signal all of this happens while the carrier controls if those pulses are on or off Due to the microcontroller mechanism the inverters that use the PWM scheme have varying levels of control There are four basic types of control f
109. o four categories These categories are input voltage surge power the wave output of the inverter and load that needs the power in the form of a sine wave The first is to take note of the input voltage of the inverter It is important to match the power source voltage to the operating voltage of the inverter If the voltages do not match it could be hazardous This is because the inverter is in danger of catching on fire due to overvoltage Next is the peak or surge power The surge power is the initial power to first start up an electronic device For example when turning on a television or a washing machine the lights may begin to dim This event is an example of a surge power to the television or washing machine affecting the lights When a high power consumption machine turns on the effect of surge power is more evident It is important to note the surge power rating of an inverter to tell if it will deliver enough initial power for a device Third the wave output of the inverter is a very important characteristic There are two distinct kinds of output waves The output wave could be a sine wave or a square wave The output coming from a standard power outlet is a pure sine wave With that said it is obvious that having an inverter output a sine wave is the most desirable wave output However due to requiring more electronic components and having a more complicated design pure sine wave inverters cost more than square wave inverters
110. ods to increase solar panel performance include using a Maximum Power Point Tracking system also known as MPPT This system maximizes delivery of electricity by managing the charge of a battery bank in relation to the solar panels MPPT systems are charge controllers that use an MPPT chip to optimize the output voltage of the photovoltaic panels to match the voltage levels of the batteries To do this the MPPT charge controller constantly maintains the power of the solar panel as it monitors the voltage level of the batteries As the voltage level of the battery increases the charge controller decreases the amount of photovoltaic panel output voltage while increasing the photovoltaic output current This setup ensures that the photovoltaic s power level remains relatively constant without causing possible problems with the batteries 3 1 2 Charge Controllers A charge controller circuit was required in between the PV panels and the battery bank to perform crucial protection functions as well as implementing the maximum power point tracking MPPT algorithm in order to extract as much energy as possible out of the PV panels Several approaches exist varying from a purely analog topology to using micro controllers Arduino and specialized integrated circuits 3 1 2 1 555 Timer One of the simplest charge controllers considered during research was based on the ubiquitous 555 timer This controller used the 555 timer IC to compare the battery
111. of the project components as well as the project as a whole will be conducted 6 1 Solar Panel Testing Testing solar panels are not an easy task and setting up the appropriate testing environment was the first order of business when it comes to testing solar panels The first thing that needed to be set up was to have a sturdy apparatus constructed for the solar panel to sit on The elevation around 6 feet at 30 degrees The power system was tested on the ground for safety reasons although the final design is meant for the panels to be mounted on a roof Before testing the panels proper safety precautions were made The safety procedure included the following e Checking if wires are grounded e Making sure rubber grips are used e Using Multimeters that are capable of handling the current and voltage load from the solar panel All of the Rating specifications are often found on the back of any solar panel As part of the safety measures all labeling will be read before testing To get an accurate read the testing occurred in a full sun time of the day which was easy to do in April in Florida This means that the sun needed to be fully exposed This was conducted during the middle of the day The first test that was conducted was a Voltage test To do this you need to get the voltage of an open circuit In order to test voltage a multimeter s leads needs to be attached at the positive terminal and the negative terminal This is whe
112. ons with higher energies become dissipated as heat instead of being converted into electricity Photo voltage is maximized when the electrical design engineers choose a higher energy band gap The problem with this method is that photons from lower energy levels than the energy band gap will not be captured or absorbed This will result in a lower photo current which will reduce the total output current The two competing energy band gap methods are balanced by choosing optimal band gaps near the middle of the energy spectrum for solar radiation High quality silicon wafers with a band gap of 1 1 eV and GaAs with a band gap of about 1 4 eV are readily available and have nearly the optimal band gap for solar energy conversion in a conventional single junction solar cell 12 28 3 1 1 4 Climate Conditions of the Pomolong Township The Pomolong Township is located at 28 14 39 82 S 29 6 46 02 E which is 265 kilometers southeast of Johannesburg South Africa and 304 kilometers northwest of Durban South Africa The closest developed town to Pomolong is Harrismith which is 7 6 kilometers south so there isn t a lot of climate data for the exact area of the township such as precise numbers regarding hours of available sunlight to the township Figure 4 Geographic Location of Pomolong Township in Relation to Harrismith Reproduced under Google provision Imagery 2012 TerraMetrics Map data 2012 AfriGIS Pty Ltd Google The aver
113. or AC drives They are shown in the following table 20 Table 17 Types of Control for AC Driven Loads Type of Control Description V Hz Basic control method which provides variable frequencies thus providing control over speed and power Sensorless Improves control of speed and starting power Vector Flux Vector Gives more precise control of speed and power control with dynamic response Field Oriented Provides the best overall control over AC motors giving DC performance 3 1 4 3 History of Inverter Inverters have been used since the late 1800s However in their inception they were not called inverters These inverters were actually motor generators or similar machines which would convert DC to AC power It was not until the 1950s where the that the modern day inverter was invented The following is a figure of a rotary converter machine which was used as a rectifier in the 1800s 19 48 Table 18 Rotary Converter 21 Public Domain Image Copyright expired DIRECT CURRENT uy a WA tes amp Z N je e S a gt IS wi 10 gt is A j A y Electromechanical inverters were originally not made to convert DC power to AC power They were actually intended to perform the opposite function They used induction from synchronous AC motors directly connected to a generator Inside the generator a commutator would reverse its connections at the right moments to produce DC power A commutator is a rot
114. ource of entertainment as well Movies will be shown during the evenings where township people can relax after a long day Imagining a day without energy is hard to picture for most first world citizens where energy is almost always present but for the Pomolong Township and many other places on Earth this is not something that is readily available or even expected According to United States Central Intelligence Agency about 30 of the population of South Africa is 0 15 years of age In addition the life expectancy is about 49 years of age 1 which is attributed to many reasons such as food shortage clean water and lack of medical supplies However one of the major motivating reasons why this project was chosen was to fulfill the lack of education which was seen as the underlying factor for such substandard living conditions Simple things such as knowing why one should wash their hands as to more complex things such as how to make a homemade water filtration system can be learned from the internet An internet connection can help in other things that are overlooked such as employment According to the United States Central Intelligence Agency about 24 9 of South Africa s population is unemployed This number is very high and through an internet connection employment search can be easier The amount of internet users in South Africa is ranked 54th in the world which is considerably low considering its population size 1 but a consistent po
115. r from a memory effect which causes them to gradually lose their maximum energy capacity if they are repeatedly recharged after being only partially discharged because the batteries appear to remember the smaller capacity 19 Other than unsatisfactory performance Ni Cd batteries are more expensive than lead acid batteries due to the higher cost of nickel and cadmium Furthermore the fact that Ni Cd batteries contain between 6 and 18 cadmium which is a toxic heavy metal makes them an environmental hazard Ni MH batteries are very similar to Ni Cd batteries in that they both use nickel oxide hydroxide as positive electrodes however Ni MH batteries use a hydrogen absorbing alloy instead of cadmium Therefore they have many advantages of Ni Cd batteries without endangering the environment or any higher forms of life Besides they are comparable to lithium ion batteries in providing specific energy and power with a significant lower cost to produce One of the most particular advantages of Ni MH batteries is their performance for high current drain applications where over the duration of single charge use they outperform primary batteries 20 However one disadvantage of Ni MH batteries makes it unsuitable for the Pomolong Township project the high rate of self discharge Research shows that Ni MH batteries lose up to 20 of their charge on the first day and up to 4 per day of storage after that 21 which would
116. r system 7 1 Setup Connecting the photovoltaic PV panels The photovoltaic panels are polarized and must be connected properly The charge controller has terminal studs labeled PV and Battery The PV panels must be connected at the studs labeled PV The positive lead of the PV panel array must connect to the stud labeled and the negative lead connects to the stud adjacent to it PV inputs are rated for a maximum of 20A Warning failure to connect the PV panels with the proper polarity may result in damage to the charge controller Connecting the batteries The battery bank is also polarized and likewise must be connected properly The charge controller has two terminal studs underneath the PV terminals The positive lead of the battery bank must connect to the stud labeled and the negative lead connects to the stud adjacent to it Maximum battery current is fused and rated at 20A Warning failure to connect the PV panels with the proper polarity may result in damage to the charge controller Connecting the loads Loads can be connected via the wall outlet located on the charge controller next to the PV and battery terminals The load will be powered by a 115 120V 60Hz modified sine wave Any load up to 500 watts will function normally If there is a surge in current or the load is too high an alarm will sound and the load will be cut off from the power source In this event the power switch will requir
117. re a warning needs to be made because photovoltaic panels are live when exposed to sunlight and it would result in serious injury if improper contact was made with the potential difference Live voltage will be flowing through the terminals of the output When this happens arc flashes sparking or shocking could happen The next step in measuring the voltage is to double check that the multimeter is set to DC Voltage at the 200 V marking and on voltage The rated open circuit voltage is on the back of the panel and the voltmeter should read approximately the same value as the rated open circuit voltage 106 The next measurement that will be tested will be the short circuit current The rating for the short circuit current should also be on the panel and that is the value that will be compared To test the closed circuit current the photovoltaic panel must be completely covered A solution to this problem is to turn the panel away from the sun to that it is not absorbing direct photons This is another safety precaution that will be put in effect to prevent sparking when hooking the photovoltaic cell to the Multimeter As stated before Photovoltaics in daylight are live When checking the current the leads from the Multimeter must be pushed firmly into the input and output of the panel and set to DC Amperes on the 10 Amperes range Once connected the panel will be turned to face the sun again Once directly facing the sun the solar panel w
118. requency of 60 Hz which is the standard frequency for AC voltage from a power outlet A Bubba Oscillator produces a stable sine wave signal with little to no distortion which is perfect for this project The following is a schematic for a Bubba Oscillator as we can see a quad op amp will be used for this part of the inverter 84 Figure 32 Bubba Oscillator Diagram Permission Pending R2 Most of the time a single PWM integrated circuit takes care of this task Examples of the PWM IC are the KA3525 or TL494CN shown below Figure 33 Tl TL494CN Permission Pending Next the driver circuit adjusts the signal according to the switching frequency To do this transistors or driving integrated circuits are used for the driver circuit The driver circuit is similar to an amplifier Last the output circuit handles the load it consists of a step up transformer for stepping up the battery voltage to the new voltage in its first stage To do this MOSFET devices are primarily used for the step up transformer The final output voltage is then available in the second stage of the step up transformer We decided to design a modified sine wave inverter We originally planned to design and build a pure sine wave inverter but due to difficulty we designed a modified sine wave inverter with the schematic for the signal generation and the PCB ordered from Hackvana seen below 85 R12 AM 1 a
119. res such as full bridges and ADCs compared to a simple 555 timer The NXP Semiconductor MPT612 Maximum power point tracking IC was selected for its flexibility power and high level of documentation It has plenty of protection features which prevent catastrophic failure in the event that the panels or battery are connected backwards It has load cutoff if the load gets too high or the battery voltage goes too low The MPT612 can automatically switch between buck boost and buck only mode depending on the relative voltages of the PV panel and battery and uses operational amplifiers and current shunt monitors to accurately and precisely monitor the voltage and current of both the PV panels and the battery Accurate measurement of the PV current is vital for the microcontroller s ability to latch onto the maximum power point To summarize the inverter design many ideas have been gathered from previous inverter technology To begin with the enclosure will be metal with air vents on the sides of the inverter to help with cooling if possible fins will also be incorporated During testing we will measure temperatures while in different levels of operation If it is required then fans will be incorporated to the enclosure on the back panel of the inverter The enclosure will also have a warning label on the top part of the inverter On the front panel of the inverter there will be two power outlets a power switch 3 LEDS input mode output mode Pow
120. rmistors are temperature sensitive resistors made up of semiconductor material They have a resistivity that is specially designed to sense temperature Thermistors have special characteristics due to the properties used to make them They also come in 2 types Thermistors that have a Negative temperature coefficient have a resistance that decreases as the temperature increases Thermistors that have a Positive temperature coefficient have a resistance that increases as the temperature increases 23 Thermistors are cheap user friendly and adaptable They are comparable in sensitivity with thermocouples The biggest drawback to using them are that they have a relatively long equation that becomes more complex as the temperature increases that could give the microprocessor possible errors This problem makes them impractical for use in applications that need to measure higher temperatures 3 1 6 3 Solar Radiation Sensors In order for determine irradiation levels it is necessary to figure out a way to sense light from the sun The common term for solar sensors are photodiodes Photodiodes are P N junction diodes that are designed to harness the photoelectric effect The photodiode is a versatile solid state device that has 57 many applications Photodiodes are used as light detectors power sources and light emitters Photodiodes have many uses and a use for them has been described previously because Solar cells are another kind of photodiode
121. roduce electricity This method of generating energy from solar power is a strong competitor for large scale power but uses many unigue parts that are hard to replace This kind of device is not as scalable as photovoltaics making it less practical for use in the South Africa Project The second way to obtain solar energy is by using photovoltaics With photovoltaics photons are absorbed by a photovoltaic cell which contains a semiconducting material such as silicon The energy from the photon is then transferred to an electron in an atom of the photovoltaic cell The energized electron is then able to escape its bond with the atom and generates an electric current 6 Photovoltaic cells also known as solar cells are primarily made of crystalline silicon When the cells are interconnected they form a solar panel that produces a direct current Aluminum is used to build the panels in order to increase their durability The cells are then placed behind tempered glass which keeps the cells safe durable and protected against adverse weather conditions A clear resin is used to insulate the back of the solar cells and also keep them in place against the top panel glass It is clear that solar panels are made to be robust and sturdy and that many manufacturing designs have been made with the understanding that the panels will spend the duration of their use out in the elements This project used solar panels because it was concluded to be a more pr
122. rs output an AC signal composed of many DC voltage levels inputs to create an even closer wave to a sine wave The efficiency for powering AC loads is higher than a modified sine wave but not as efficient as a pure sine wave Pure Sine These inverters are the best in their field They produce a Wave nearly perfect sine wave with less than 3 distortion which is the same as a supplied power company s AC signal This comes at a higher cost due to its complex design All AC loads will work with these inverters The table above are the main types of inverters It is worth mentioning that there are other less used and or known type of inverters such as resonant grid tied synchronous stand alone solar solar micro air conditioner and CCFL inverters 3 1 4 1 Inverter Applications Inverters can be used in many applications as stated before Their main purpose is to convert a DC power source to an AC power source This can then be used to power AC loads However with this in mind there are other applications in which inverters can be used which are summarized in the following table 45 Table 16 Inverter Applications Purpose Description Uninterruptible An uninterruptible power supply is a type of backup system Power Supply which supplies AC power when the main power source is not available Induction A low frequency AC power is converter to higher frequency Heating AC power which heats an electrical conducting object typically a
123. rs to have a source of energy that is be self sustainable Now that the problem and the solution are known research was done to conclude which source of renewable energy should be chosen to be harnessed for this Senior Design project Some of the sources that were considered were wind hydro solar and mechanical kinetic energy After research of the area it was observed that there is not much wind flow in the area and that mechanical kinetic is not the best choice for the Pomolong Township The use of hydro was not feasible since the project will be located in the Pomolong Township community center meaning that the project cannot be located near a river or other major water system Also there are droughts and South Africa has a sub tropical climate system With all other sources invalidated utilizing solar energy as a renewable energy source was the only realistic choice In the present time an internet connection is critical to the accumulation of knowledge and through a projector people will be able to learn by watching educational videos presentations and documentaries Being able to connect to the internet will give the villagers the opportunity to gain knowledge which in turn will give them the tools and the power to improve their standards of living They will be able to have tutorials guides eBooks etc at the tips of their fingers Not only will the energy source project help in educational ways but it will give the township a s
124. rters above are square wave power inverters Pure sine wave power inverters cost about four times as much as these inverters Next the controls for most Power Bright power inverters will be looked at Figure 9 General Power Bright Inverter Permission Pending A Two standard North American AC outlets each rated at 15 Amps B Overload LED Indicator If continuous power draw of appliance s exceeds the inverters continuous power this light will turn ORANGE RED and the inverter will automatically shut down When this occurs turn off the inverter and determine the cause of the overload before turning the inverter and the appliance back on C ON OFF Switch Turns the inverter circuits ON and OFF As seen the Power Bright power inverters are pretty simple and easy to use There is a switch to turn the inverter on and off and two North American power outlets Also take note of the fins of the enclosure to keep the power inverter cool and the LED indicator if the appliance power consumption being powered exceeds the output power of the inverter Next the controls of a general Cobra power inverter will be looked at 53 Figure 10 Cobra Power Inverter Patent Pending Protection amp Power Indicators USB Outlet E On Ott AC Outlets O i Power Switch For the most part the Power Bright power inverters and the Cobra power inverters are pretty much the same However most of the Cobra power inverters have a USB outlet to pow
125. s in NCPV Program Review Meeting Lakewood Colorado 2001 11 National Renewable Energy Laboratory Gallium Arsenide as a Photovoltaic 125 Material 4 January 2002 Online Available http www azom com article aspx ArticlelD 1166 Accessed 30 November 2012 12 B Burnet The Basic Physics and Design of III V Multijunction Solar NREL Denver Colorado 2002 13 X Wang G I Koleilat J Tang H Liu I J Kramer R Debnath L Brzozowski D A R Barkhouse L Levina S Hoogland and E G Sargent Tandem colloidal quantum dot solar cells employing a graded recombination layer Nature Photonics vol 5 p 480 484 2011 14 Cyferz Silicon Solar cell structure and mechanism Wikipedia 2007 15 solarpower2day Solar cell efficiency solarpower2day 2009 Online Available http www solarpower2day net solar cells efficiency Accessed 1 December 2012 16 Squirmymcphee l V Curve Wikipedia 2008 17 NXP B V AN10936 Photovoltaic MPPT battery charge controller using the MPT612 IC reference board 2011 18 Fink Batteries and Fuel Cells in Batteries and Fuel Cells p Ch 11 19 D Linden and T B Reddy Handbook of Batteries 3rd Edition New York McGraw Hill 2002 pp 28 18 20 R Lewallen 1 5 Volt vs 1 2 Volt Batteries 2007 21 Duracell Ni MH Batteries Technical Bulletin 2011 22 M S Ballon Electrovaya Tata Motors to make electric In
126. s Texas Instruments ON Semiconductor Texas Instruments Texas Instruments NXP Semiconductors Texas Instruments NXP Semiconductors ECS 0 05 0 14 0 05 0 05 0 05 0 08 0 08 0 05 0 08 0 07 0 05 0 08 0 11 3 15 1 19 1 19 1 19 0 79 0 63 1 19 0 32 2 14 7 98 1 09 99 71 5 3 PCB Vender and Assembly The PCB layout for the charge controller is shown below The board in its current state features 209 components mostly of surface mount packaging The final design was mainly done on perf boards divided into modules as outlined in the schematics Building the system in a modularized fashion allowed for more effective testing and debugging Also moving to a purely through hole component selection was desired for easier assembly and prototyping Figure 39 PCB Os Tajo AN Pe i ooo0oo0o00000 As outlined in the bill of materials many of the parts were available at Mouser electronics Components which were not found in the Mouser catalog were either found in DigiKey s catalog or Future Electronics All of the electrolytic capacitors were chosen from Nichicon All of the ceramic capacitors are AVX branded surface mount 0805 components Some of them are size 1206 and Kemet branded Nearly all of the resistors are size 0805 and from ROHM Semiconductor or KOA Speer The current sense resistors are size 1225 Most of the diodes and transistors are NXP Semiconductor branded These co
127. s found to not be very cost effective to order a PCB for the charge controller so it was built using perf boards The third component is composed of the batteries which did not require allot of design They were be wired up to the system in order to create a fully working photovoltaic power system which has the ability to store and distribute power The fourth component the inverter was also fully designed Like the charge controller the circuit was first designed and tested on a solder less breadboard Once the required tasks were checked to be fully working then the final circuit board was ordered 17 To fund the South Africa project sponsorship and funding by Progress Energy which give grants according to energy sustainability projects was heavily relied upon Since the project involves a renewable and self sustainable energy source it falls in accordance to their Senior Design project funding requirements Groups wanting to claim this sponsorship along with the funding had to submit proposals which included the above budget table along with project objectives specifications a block diagram the project s impact on renewable energy and sustainability and the timeline of project completion 18 3 0 Research Related To Project Definition The research related to the project definition section of this paper is intended to show all the research done on all of the parts of the project The research done will show what was discovered to alr
128. s inviting problems the system This is because the old batteries will already have higher internal resistances We decided to use CSB HRL12280WFR 12V Deep Cycle Flooded 75Ah batteries as seen below 79 Figure 27 CSB HRL12280WFR 80 4 4 Inverter The last part of the project or the final stage of the system is the inverter The inverter is a very important part of the project because it is through this device that the user will have the opportunity to access the power stored in the batteries that was originally obtained from the solar panel and managed by the charge controller The main function of the inverter in layman terms is to take the DC voltage stored in the batteries and transform it into AC voltage that can be used by the township of Pomolong to power their electronics A good inverter will have different socket shapes for EU and NA to cover all electronic appliances out there such as cell phones projectors and laptops Another feature the inverter should have is that it should be able to deliver a good amount of power evenly to its sockets that way it can power more than one device at a time instead of only one at a time Additionally it is crucial for the inverter to have a simple to use interface with little to no knowledge in electrical components to operate safely Lastly the inverter should be power efficient which means a pure sine wave output which uses the maximum amount of AC voltage available for the electronic co
129. s less efficient and are not competitively cheaper than Mono crystalline panels The small savings in initial cost does not compensate for the savings in energy cost through the lifetime of the panel use Thin film modules were taken out for their lack of availability questionable reliability and inferior efficiency This project will not be using Polymer technology because the technology has not been developed enough for a solid conclusion on whether it would be more beneficial to incorporate Polymer solar panels than to use tried and tested older technology Other than the lack of resources and the fact that the technology is not fully developed the entire purpose of this technology is to decrease production costs on a large scale to make widespread use of solar power feasible The problem with this is that the resulting effect is that the cost dose not scale down well when used on a smaller scale like the South Africa project So after all of this consideration Grade A Solar Panels will be used Grade A is another alias for Mono crystalline silicon photovoltaic panels and is a common term used in the industry 4 1 1 Solar Panel Specifications The main company considered in the solar panel market was Helios The panel that has been chosen for use in this project is the Helios 7T2 305W Solar Panel Mono Cell It has the second highest power output panel in the 7T2 mono crystalline series 22 Another advantage in choosing this specific pane
130. s the groups wish to have a similar monitoring system to the one in some commercial inverters to make it easier for users to deal with the inverter The following is a picture commercial inverter s monitoring display Figure 36 Example of Inverter Monitoring Display Permission Pending Voltage Input amp Power Output Indicators Power MEDE ETWU 87 The group made a similar monitoring system to the one displayed above There will are three LEDS of different color they indicate power input mode and output mode The power LED simply indicates whether the inverter is on or off The input mode LED will let the user know that the number display is giving values of inverter input in Volts In our case the input are the batteries which we want to keep around 12 V So if the battery output is less than 10V or higher than 15V the inverter flashes the LED to warn the user and powers down The output mode LED lets the user know that the number display is giving values of inverter output in Watts So depending on the devices that are connected to the outlets of the inverter the output Watts change However note that the inverter is rated up to 400W which means that it cannot exceed this limit If it does the LED will flash indicating inverter overload and shutdown In case of shutdown the user should address the issue which caused the shutdown and then simply turn off and back on the inverter 88 4 6 Encasing The enclosure design
131. s were connected to other devices 4 AWG wire were used to do the connection of the batteries Finally it was important to identify the polarity of the power cables and its terminals red is for positive and black for negative This was really important because if a device is connected with the wrong polarity the internals of the device can blow up and become damaged Thus we connected the power cables from the batteries to the inverter using 8 AWG cables A spark may occur which was fine because the batteries contain power thus giving a chance of spark It was important to be far away from any flammable materials or liquids when doing the connections As an extra precaution there will be a fuse between the batteries and inverter to prevent overload of the inverter The fuse has an ampere rating of 30 which will cover all operations up to 600W which is less than the surge power of the inverter So if any wiring short occurs the fuse will burn out before the inverter To conclude after all the wires were connected it was important to trace all the wiring and make sure they were all secure and safe A regular check can be beneficial due to the fact that over time wire connections can become loose Also it is important to stress that all devices must be powered off when performing connections to prevent any damage to the system 117 7 0 User Manual The Purpose of this section is to give the user detailed instructions on how to operate the powe
132. s_in_Series_and_Parallel pdf Please let me know ifwe can use the image for strictly academic and information purposes in our research dosumentation Thank you for your help in these issues Genesh Chen Shue 122 Email info rvworldstore co nz Tel 03 541 0994 Postal Address PO Box 3068 Richmond Nelson 7050 New Zealand Name Email Genesh T Chen Shue ge548518 knights ucf edu Telephone 3863831194 Comment Hi RV World lam an engineering student from the University of Central Florida For our senior design project we are designing a solar power based power generation system for an impoverished African village In designing our inverter we wanted to describe typical features of a modified sine wave and wanted to use an image in one of your blogs The image can be found on http www tvworldstore co nz blog inverters Please let me know if we can use the image for strictly academic and information purposes Where did you hear about us ls EIE Internet search engine eg Google Content Permission Request y Genesh T Chen Shue ge548518 knights ucf edu Hi Howstuffworks am an engineering student from the University of Central Florida For our senior design project we are designing a solar power based power generation We would like to use an image hosted by you in our research documentation found http electronics howstuffworks com gadgets automotive dc ac power inverter htm
133. se two pulse three pulse and six pulse circuit rectifiers To calculate the pulse the phase of the rectifier and its wave output needs to be checked There are half wave and full wave rectifiers Half wave rectifiers have a one pulse and full wave rectifiers have two pulses To get the number of pulses in a circuit the phase number must be multiplied by the 49 number of pulses in the rectifier Depending on the phase of the rectifier and the desired output a higher voltage or current can be obtained by connecting rectifiers in series or parallel Although inverters can work backwards as rectifiers inverters are also classified by pulses The higher the pulse number in a rectifier system the less the harmonic content in an AC input while outputting reduced distortion to the DC output voltage In the inverter mode a higher pulse number gives lower distortion to the AC output waveform 19 In order to create an inverter a DC source is needed This means that circuits that would force a rectifier to shut off would have to be implemented in the inverter design This is not a problem High quality transistors that can be turned off by control signals can solve this problem A separate controlling circuit is not needed to force a shut off In all inverter designs today transistors are the way to go 3 1 4 4 Characteristics of an Inverter Important characteristics of an inverter to pay attention to when purchasing or constructing one fall int
134. solar energy by our 500 W solar panel system Solar panels will be two 250 W solar panel each which will be mounted on the roof of the community center of township 2 Must be able to power up to 500 W electronics for a period of 4 hours daily 3 Must be robust weatherproof safe long lasting and easy to maintain 4 There must be a gauge to measure battery charge 5 Inverter must support input of 12V and output 120V 6 Batteries must last at least 4 years They will be placed in parallel making a 12V unit Each battery will be 12V 7 Charge controller must implement MPPT for the solar energy capture 2 4 Block Diagram Solar Panels Step Down Sorat Gene Converter Standby Circuit Charge Controller MCU Charge Controller Inyerten Solar Panels H Bridge Filter Pantery Gate Driver Sensors Inverter MCU Gate Driver Power Line Control Line Figure 1 Project Block Diagram 2 5 Timeline By the final week of Senior Design the 120 page research paper will be completed As the following table displays the majority of the research and part selections will be completed by the end of the first semester The second semester would be dedicated to hardware assembly and testing The project will be completed in its entirety and the final project will be operational and will output usable power Table 2 Senior Design 1 Project Milestones Week Action Description 1 Choose Project Think about different i
135. sor would be reliable inexpensive and easy to replace To choose one research has been done on a few sensors that might be used in the design of he South Africa Project The first method that can be used to measure temperature is with the thermocouple This temperature sensor is a junction of two different metals When the temperature is different between them there will be a potential difference between the two metals One of the two metals is treated as a reference temperature The other metal is at the location where the temperature is to be measured Thermocouples are cheap tough and reliable over a wide temperature range One thing to remember when using thermocouples is that it each of the metals are connected to copper wires to integrate them in a circuit or into instrumentation This connection will create two extra junctions These two junctions will have a voltage difference that is temperature dependent With this in mind it is important to make sure that the junction connections are at some standard temperature If they are not then errors in the readings may happen The problem with thermocouples is that it is sometimes difficult to keep the circuit in a condition where the standard temperature can be kept This is especially true if the circuit was in direct contact with solar panels that were getting direct sunlight for an extended period of time The second method that can be used to measure temperature is with a thermistor The
136. still not been seen Hopefully Thin films prove to be as good as the lab models suggest Although a general review on Thin film technology has been made there are different kinds of Thin film technology and discussing the physical properties that make them unique will prove beneficial in deciding the optimal technology that should be used for the South Africa project The first Thin film that will be discussed specifically will be amorphous silicon Thin film mainly because of their widespread use and popularity Amorphous silicon Thin films were among the first thin films and were originally popular for use in small electronic devices that needed a small amount of power like pocket calculators These are inefficient and are not practical for larger scale power generation The reason that this particular photovoltaic was mentioned was because of its historical significance to the advancement of Thin film technology and because of its impact on most Thin film panels researched today There are three major kinds of Thin film photovoltaic cells that are currently popular in the market and they will be discussed in full The first Thin film that will be discussed in detail will be the Copper Indium Gallium Selenide panel also known as CIGS These panels are made in the general method made to make Thin films where the compound is layered on glass but their fabrication process is vacuum based The advantages of Copper Indium Gallium Selenide are that
137. struments SM72442 The SM72442 Programmable MPPT controller also by Texas Instruments was a close second in the charge controller decision process Part of the SolarMagic 33 group of components the SM72442 features an integrated 8 channel 12 bit A D converter used to sense input and output voltages and currents for protection and monitoring as well as a four PWM gate drive signals for a 4 switch buck boost converter Along with the SM72295 Photovoltaic Full Bridge Driver this controller can operate with efficiencies up to 99 5 The MPPT performance of the SM72442 is very fast MPPT is achieved by varying the PWM duty cycle of the switching transistors to maximize energy transfer and convergence to the MPP is achieved typically within 0 01 This enables the controller to maintain MPP behavior even under the most erratic and fast changing conditions This chip does have the required MPPT behavior like the BQ24650 and also provides programmability It was not chosen in favor of the MPT612 because of increased complexity using four PWM signals a full bridge driver and using it would have required the entire controller be redesigned using the SolarMagic family of components 3 1 2 5 NXP Semiconductor MPT612 Thus the MPT612 from NXP was selected as the charge controller of choice It not only includes all of the features of the BQ24650 is simpler than the SM72442 but an application note from NXP Semiconductor also provides detailed d
138. t In In c 20 Ah Lbs Group24 12 10 00 7 00 9 00 70 85 50 Group 27 12 12 00 7 00 9 00 85 105 60 Group31 12 13 00 7 00 9 50 95 125 70 4D 12 20 75 8 75 10 00 180 215 130 8D 12 20 75 11 00 10 00 225 260 160 Gc2 6 10 50 7 00 11 00 180 225 70 L 16 6 11 50 7 00 16 75 325 415 120 4 3 2 Climate and Temperature Always take into consideration the climate factor when trying to decide which battery will be suitable for the renewable energy source application Most battery specifications are based on the ideal battery temperature of 77 degrees Fahrenheit That is the attainable temperature for conditioned spaces If the batteries are out in the cold some adjustments will be necessary Flooded and sealed batteries behave a little differently under various temperature ranges so be sure to check manufacturers specifications 76 Sizing correction Factors Temp F Flooded AGM Gel 77 1 00 1 00 1 00 50 1 19 1 06 1 11 32 1 39 1 20 1 25 14 1 70 1 35 1 42 For a system requiring 1000 Ah of capacity using flooded batteries in sterling VA with common 40 F winter temperatures by extrapolation of the above table we will get a correction factor of 1 29 Therefore 1 000 Ah x 1 29 1 290 Ah battery bank size for winter temperatures Below freezing temperatures the electrolyte becomes very weak in discharged flooded batteries The electrolyte can freeze solid which will ruin the battery and the case can crack from the expanded ice Internal connec
139. t levels of energy corresponding to the different wavelengths in the light spectrum When the input energy matches the energy of the band gap in the material the photons with energy levels equal to the energy band gap are absorbed by the semiconductor the photons with energy greater 24 than the energy band gap are The photons with higher energy levels than the energy band gap are dissipated in the form of heat and the photons with lower energy levels than the energy band gap are not absorbed at all With this in mind when designing a solar cell choosing a semiconductor material with an energy bang gap as close to the center of the solar radiation spectrum would yield optimal results The full solar radiation spectrum ranges from infrared to ultraviolet Unfortunately there is no semiconductor found to date that responds to the full solar radiation spectrum There have been solar cells recently invented that can respond to the entire spectrum 13 but they are unavailable for widespread commercial use Another way that a solar cell can be viewed would be to compare it to a diode Photovoltaic cells can be compared to a diode because of the p type and n type semiconductor materials used to fabricate them are similar in application to the p n junction in a diode Like diodes there are two metal contacts attached to each side of this p n junction When the electron hole pair is formed across the p n junction a forward voltage is created between
140. talline cells the process to make Poly crystalline cells is much cheaper and faster This means it is more profitable but there is a tradeoff to this reduction of cost Poly crystalline cells are typically less efficient than their Mono crystalline counterpart having an efficiency to convert photons to electrons of approximately 10 8 This reduction in efficiency is due to a decrease in the grade of silicon as well as an increase in the amount of imperfections The imperfections cause energy to be lost at fusion points between two adjacent crystals This loss in energy causes a decrease in efficiency The third kind of solar cell that will be discussed is part of the second generation technology of Thin film cells Before going into detail about the various kinds of Thin film photovoltaics a brief summary of Thin film technology is necessary Thin film solar panels are made by placing thin layers of semiconductor material onto glass or other similar material The reason they are called Thin film is because of the amount of semiconductor material used giving the appearance of a thin film in the form of a flexible semiconductor laminate The flexible laminate makes the panels bendable This makes the Thin film cells easier to mount on uneven surfaces and also makes them durable during extreme weather conditions Being weather resistant is a major reason why Thin film technology is increasing in popularity because panels need to be continuously expose
141. the absorption of light the separation of charge carriers of opposite type and the separate extraction of those carriers to an external circuit 21 So what is happening is that the photons are absorbed electrons are knocked out of the photons and separated creating a potential difference then the electricity is captured and send through the output The following is a chart which shows the semiconductor material of the solar cell power conversion efficiency and technology As clearly seen Crystalline cells are the most efficient making them the most favorable choices for consideration in design Table 20 Solar Cell Type and Power Efficiency 21 Semiconductor Material Power Conversion Efficiency Technology Mono crystalline silicon 20 24 Crystalline Poly crystalline silicon 13 18 Thick and Thin film Gallium arsenide 20 29 Crystalline Amorphous silicon 8 13 Thin film Cadmium telluride 10 17 Thin film Cadmium indium selenide 10 19 Thin film Solar panel systems have different ways of being set up as well Solar panel systems are either grid tied grid tied with batteries off grid or simply used as backup Grid tied system are tied to the power grid that a residence gets its power from They do not involve any batteries The solar panels simply output whatever power they get to the residence they are supplying This results in minimizing the power obtained from the grid A grid tied system with batteries is the same as the former ex
142. the appropriately gauged wire A multimeter were then connected through short circuit to find how much current is flowing through to the battery This test also reveals the internal resistance of the battery Once this was completed using the same equations as 107 before an accurate assessment of how well the solar panels are actually charging the battery was made and actual power estimates were produced The single most important factor when performing these tests was to perform them in the middle of a clear shining sun This is because only direct sunlight will give correct readings as to what the peak performance of the panels truly are Above all when working with high voltages and current safety must be the highest priority Utmost caution must be used in connecting the solar panel to anything while in direct sunlight Under sunlight the photovoltaic cell is producing DC voltage and current and can cause sparking r arc flashes when connecting Solar Panel Testing Checklist e Set multimeter to DC Voltage e tests performed in the clear sunny sky e Turn panel away from sun e Perform Open Circuit Voltage test with multimeter e Rotate the photovoltaic cell both away from the sun e Turn the panel away from the sun e Disconnect multimeter e Set multimeter to DC Amperes e Perform short circuit current test with multimeter e Turn the photovoltaic panel towards the sun e Rotate the photovoltaic cells perpendicular to the sun to
143. the project The design began once each section was researched and the parts that need to be purchased were identified As indicated in the chart below the design stage will take place in the final weeks of Senior Design and will continue through the first month of Senior Design II During the Christmas break the parts will still be investigated as the design progresses Initial design concepts were presented in the Senior Design documentation 12 Table 4 Design Milestone Design Solar Panels Inverter Charge Controller Microcontroller MPPT Batteries Over winter break as certain aspects of the design were finalized some parts were ordered for early prototyping in the Spring semester Parts acquisition increased significantly following the break and continued until April The goal was to have ordered all of the necessary parts for the project by mid February The parts necessary for the packaging of the final circuit board and electronics were acduired later as shown in table below once the design was been tested and the final board was fabricated 13 Table 5 Acquisition Milestone Acquisition Solar Panels Micro Controller Batteries Sensors Circuit Board 20 JAN 23 JAN 28 JAN 4 FEB The table below shows the schedule for prototyping This phase began immediately following parts acqu
144. the systems enclosure is weatherproof and durable enough to last a long time In conclusion there is strong motivation to make an efficient and reliable energy source for the people of Pomolong Township Giving them power and the benefits that come along with it are desirable If successful other areas in South Africa can benefit from this project and the idea of renewable solar energy can be expanded There are many areas around the world which have no power but can harness a natural resource for their power needs This project can be used as a base that others can model in order to help provide power to other impoverished areas of the world 2 2 Objectives There are several objectives that need to be addressed for the completion of the project The following are objectives and explanations 2 2 1 Safety The absolute most important objective is safety because ensuring that the system is safe protects lives and mitigates damages There are many precautions to make when it involves electricity because even though electricity is beneficial and the entire point of this project it will mean nothing if the device is not safe To ensure safety precautions such as fuses and safety designs will be implemented If the project were not safe then the villagers that are being helped would be worse off than if nothing had been done at all 2 2 2 Efficiency A major objective of this project is for the power generating system to be extremely eff
145. their low internal resistance they can keep the charge even after being placed in the storage for months without usage Their low internal resistance also enables them to handle shock and vibration very well Flooded batteries are very reliable and work well with all types of design Their life expectancy is between 5 and 15 years depending on the battery For maintenance purpose flooded batteries are required to be watered and ventilated in order to expel the gas that they produce Gel electrolyte batteries are almost twice the price of the flooded battery However they are maintenance free and do not need watering They also do not have the risk of leakage because they are sealed Gel batteries works well under the extremely cold condition Their life expectancy is 5 to 10 years depending on the manufacturers Gel batteries use a recombination reaction to prevent the escape of hydrogen and oxygen gas that is normally lost in a flooded lead acid battery Gel batteries can also be operated at any position However they have 42 a short lifespan in hot climates because the water in the electrolyte evaporates the water cannot be replaced since it is sealed The AGM batteries cost about the same price as the gel batteries They are also maintenance free The AGM batteries are sealed and have a low internal resistance They have almost the same property as the Gel battery For the Pomolong Township Project flooded batteries will be chosen for th
146. tions may be damaged For these extreme climate conditions sealed batteries are a better choice because their electrolyte solution has a much lower freezing point On the other hand the flooded batteries are more adapted for the hot climate 4 3 3 Location and Safety Make sure to have adequate and appropriate space to put the battery bank Batteries need to be near the inverter They should be within 10ft of the inverter Batteries need to be protected from unauthorized access They need to be properly enclosed and vented to keep corrosive and flammable gasses outside of occupied spaces High temperatures will shorten a battery s life especially for sealed batteries so keep them out of direct sun and provide air circulation if needed Good access is critical for inspection cleaning replacement and watering especially for flooded batteries Therefore it will be hard to maintain them if they are hard to get to That is why it is very important to choose a good and safe cite for the battery bank For remote systems take into consideration the ease of transporting and installing the batteries In sum the proper temperature ventilation and spill containment are important for a safe and long lasting battery bank 4 3 4 Installation of the Batteries Just having good batteries with high amp hours are not a guaranty that they will not fail This is why it is very important to connect them properly The standard technique for installation of
147. ttery bank the charge controller and the Inverter A budget for the project was proposed and mentioned earlier in this paper but this section goes into detail on the specification and price of each part that will be purchased Table 26 Charge Controller Bill of Materials ref C1 C2 C3 C4 C5 C7 C13 C14 C15 C16 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C30 C31 C32 C34 C35 C36 C37 C38 value 4 7nF 4 7nF 1000uF 680uF 1000uF 680uF 0 1uF 10uF 10uF 10uF 0 01uF 10uF 0 01uF 0 1uF 0 01uF 0 01uF 0 1uF 0 01uF 0 01uF 4 7uF 0 01uF 0 01uF 0 01uF 0 1uF 0 01uF 0 33uF 0 33uF 0 01uF 0 1uF 0 1uF footprint SMO805 SMO805 C2V10 C2V10 C2V10 C2V10 SM0805 C1V8 C1V8 C1V8 SM0805 C1V8 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM1206 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 SM0805 part number C0805C472K2RACT U C0805C472K2RACT U UHD1H102MHD UHD1V681MHD UHD1H102MHD UHD1V681MHD 08055C104MAT2A UVZ1E100MDD UVZ1J100MDD UVZ1J100MDD 08055C103MAT2A UVZ1C100MDD 08055C103MAT2A 08055C104MAT2A 08055C103MAT2A 08055C103MAT2A 08055C104MAT2A 08055C103MAT2A 08055C103MAT2A C1206C475K5PACT U 08055C103MAT2A 08055C103MAT2A 08055C103MAT2A 08055C104MAT2A 08055C103MAT2A 08055C334MAT2A 08055C334MAT2A 08055C103MAT2A 08055C104MAT2A 08055C104MAT2A 96 vendor Kemet Kemet Nichicon Nichicon Nichicon Nichicon A
148. und that even though the design sounded good it would not be beneficial in the system The reason that it would not be beneficial is because the mechanical parts can wear out and stop functioning over time Also the gain of solar energy from the tracking is not worth the energy consumed to have the system run On the other hand maximum power point tracking is a valuable technique that will be integrated to the project s charge controller The benefits of MPPT will enable the charge controller to get the most of the solar panels while charging the batteries To do this the MPPT technique changes the voltage of the panels to keep at its maximum potential For example to charge a 12V battery approximately 13 5V would be needed to charge However most solar panels work at a higher voltage of about 20V and the Amps current stay the same Since power is equal to current multiplied by voltage it is the purpose of the MPPT system to sample the output of the cells and apply the proper resistance load to obtain maximum power for any given environmental conditions 20 In the figure below the yellow rectangle gives the output power The top right is the maximum power point which is the target desired Figure 12 MPPT Graph 26 Isc Prax Irradiated Photovoltaic cells refer to the cells in material that generate energy from the transformation of electricity from sunlight Photovoltaic cells have three 59 attributes The attributes are
149. unlight 100 000 lux Cloudy sky 5 000 10 000 lux Moonlight Less than 0 25 lux 6 5 Wiring Testing and Precautions When connecting the wiring between the different parts of the system we first powered off all parts including the charge controller and inverter We made sure the power cable was not connected to the inverter as well The first step began by connecting the solar panels to the charge controller The length and elevation of the wire was very important Minimizing these factors allowed a decrease in the voltage drop Now since the solar panels will be mounted on the roof of the Pomolong community center and the charge controller will be placed inside the center it was estimated to be about 20 feet of wire distance between the two Also it was taken into account that the solar panels run at 8 5 A at maximum capture Multiplying this by two to factor in two panels was 17 A Finally the solar panel connection were 48V These specifications required a 10 AWG wire for the this connection Next we connected the charge controller to the batteries The same size wires were used because these wires did not carry any more current than the solar panel to the charge controller connection Next the connection between the batteries were addressed Since we are using two batteries in parallel the connection was very simple and straightforward The positive of one battery was connected to the positive of another battery The other terminal
150. ure coefficient and an l V curve that describes its l V characteristics The temperature coefficient is the rate of power reduction for every degree above the operating temperature The standard operating temperature is 25 degrees Celsius The I V curve that describes the photovoltaic s l V characteristics shows the relationship of current and voltage for different degrees of temperature The area under the I V curve is an approximation of the maximum power that the photovoltaic would produce if operating at both open circuit voltage and closed circuit current From the figure below it is shown that total photovoltaic cell power diminishes as the temperature of the panel increases Figure 3 l V Curve 16 Reproduced with Permission under the CCLA 3 0 4 0 Current A SH sa WN NS o a o a o on o o 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 Voltage V 27 As seen previously and in the figure above solar panel temperature must be as close to an operational temperature of 25 degrees Celsius in order to optimize efficiency Right now research is underway to on developing cooling methods that will maintain low temperatures in solar cells There are currently two major ways to cool the cells The two major ways in maintaining a lower solar panel temperature are active cooling methods and passive cooling methods An example of an active cooling method would be pumping a coolant or a refrigerant through the backside of the solar panels An example o
151. urposes in our research documentation Thanks Genesh Chen Shue SUBMIT CLEAR Subject request to use picture in a datasheet for senior c Description Hi NXP am am Electrical Engineering student at the University of Central Florida For our senior design project we are designing a solar power based power generation system for an impoverished African village In designing our charge control system we are using the MPT612 and wanted to use an image from the datasheet in explaining our reason for using it The datasheet is found at http www nxp com documents data_sheet MPT612 pdf Please let me know if we can use the image for strictly academic and information purposes in our research documentation Than you for any help regarding this issue Genesh Chen Shue 120 Email ge548518 knights ucf edu Zip Postal Code Country Questions Comments Hi Powerbright lam an engineering student from the University of Central Florida For our senior design project we are designing a solar power based power generation system for an impoverished African village In designing our inverter we wanted to describe typical features of an inverter and wanted to use an image in one of your datasheets The image can be found on http Avww powerbright com pdfi ML900 24 MANUAL _english_french_02 pdf Please let me know if we can use the image for strictly academic and information purposes in our research
152. ve the PCB ready for final project 5 1 Parts Acquisition Our project was entirely sponsored by Progress Energy The group turned in a proposal with a budget of 1995 estimated for all the parts required for the project and the budget was approved We had to order parts and give the receipts to a coordinator who later reimbursed the money in the form of a check The group could not be reimbursed for any parts purchased online and shipped to their residence so anything purchased from the internet had to be addressed to UCF Before the acquisition of any part all group members had to approve the purchase The reason behind this is if any other group member may know where to get it cheaper if they already have that part or a replaceable part or if they already acquired the part The last thing the group wanted to do was to waste money and if there is anything that we already had that could be used then so be it Additionally there was an inventory of all parts used in the project indicating how it was obtained how it was used and how much it cost If for any reason we did not get the Progress Energy sponsorship or the group did not get the full amount asked in the proposal the cost of parts would be be split between group members 95 5 2 Bill of Materials The following is the component list and price that is reguired for construction of the South Africa Project This project is roughly divided into the photovoltaic panels the ba
153. voltage to a predefined level which was determined by a potentiometer When the threshold was reached a transistor would switch on a relay which in turn diverted the PV energy to a dummy load One of the implementations which were looked at that utilized this chip also included switches for manual operation of the controller One switch was for diverting the load to the dump resistors and 31 another switch for diverting it to the battery Additionally monitoring LEDs were included one for indicating the controller is in dump mode another for indicating the controller is in charging mode Some of the advantages of the 555 timer based charge controller are cost availability and simplicity The 555 timer is one of the most mass produced and most popular integrated circuits in history Thus it is extremely cheap One of these can be purchased for just a few cents just about anywhere on Earth The simple design and high component availability would make this charge controller extremely reliable easy to build maintain and repair Not much electronics knowledge would be required to understand and repair this charge controller While the 555 timer itself is very highly available and would have made the charge controller cheap and easy to repair the same cannot be said for the rest of the solar generator system The PV panels are costly components and the pure sine wave inverter is a complex circuit Thus trying to optimize only one part of the
154. wer source is needed before consistent internet can even be considered Our energy project is to be placed in the townships community center which will be able to host most of the township The project is designed to be weatherproof and robust even though the project will probably be under a roof After reviewing the energy requirements a goal of about 500W an hour at operation time was made The township will be in need of the equipment for about 4 hours in the evenings This means that during the day the solar panels will be gathering energy and at night the Pomolong Township will consume the stored energy Given the location of the village it was estimated that about 6 hours of sunlight a day will be available and two 250W solar panels were designed and are planned to be used The goal is to store approximately 3000W a day This should be more than enough to power the instruments of the people of Pomolong Township The ability to monitor the charge of the batteries to check if the charge of the batteries is low will also be planned The battery life depends on complete depletion of batteries so knowing the levels of charge are necessary at all times Another goal is to make the system portable ergonomic and as compact as possible Since there will probably be no access to sunlight from inside the community center ensuring that the project is easy to move in and out of the community center is a major design consideration As stated before
155. window Sample application output is shown below Figure 23 Charge Controller Application 10 00 OV UN fe Ls BE aas j ke ED 13 SHAAATATARAT AT TAT eee TERRE RR TERE RR TEER RR TREER MPT612 Sample Charge controller Application v1 0 SATA Tee tee arrest ere AAA SWCONV_BOOST Waiting for minimum power to be present Scanning gt full Prtrb MPP LATCHED Vmpp mV 16101 Prtrb MPP LATCHED Vmpp m 15992 Prirb MPP LATCHED Vmpp mV 15956 SWCONV_BUCK Prtrb MPP LATCHED VmpplmV 16177 Prtrb MPP LATCHED Vmpp mV 16439 Prtrb MPP LATCHED Vmpp mV 16613 75 4 3 Batteries This section describes the design and implementation of the Battery Bank 4 3 1 Size Codes and Common Names Although each manufacturer has their own model numbering system standard sizes exist for commercial batteries Battery Council International BCI is a trade organization that sets some battery standards including sizing codes Some batteries have acquired their names from their intended use For instance GC2S were named from being used as golf cart batteries Batteries with the same code or name will have approximately the same dimensions but their capacities may differ significantly This is especially true between flooded and sealed units The table below show some of the more common size seen Table 25 Common Battery Specifications Size Volts V Length In Width Height Capacity Weigh
156. with the specific application of using the current from the photoelectric as a power source With that brief explanation of what a photodiode is and its general application this section can now go into detail about another application for photodiodes Other than being used for generating power photodiodes are used to sense light intensity The more intense the sunlight the higher the current This information is useful in research in solar tracking to optimize the direction in which the solar panels are angled towards the sun to maximize light exposure This information can also be used to help determine what areas get the most sun 58 3 2 Relevant Technologies With the objectives and requirements of this project decided upon it was necessary to spend some time researching other models and projects that implemented similar technologies to this project Fortunately there is a lot information about solar power generators available There has been many different designs involving solar energy in UCF s senior design Some have been more successful than others and other groups past experiences to make the design of the South Africa Project better An example of this is Solar Tracking This technology was considered to be incorporating into the system Solar Tracking involves the movement of the solar panels mechanically by feedback from sensors 19 The sensors detect where the sun is shining brightest and moves the panels accordingly It was fo
157. y mode In buck only mode the PV voltage must always be higher than the battery voltage In buck boost mode both the PV voltage and battery voltage can be variable values with the system switching between buck and boost based on the relative voltages The power electronics circuit is shown below 69 Figure 20 DC DC Converter Ma ami P tage to Y ges gt ea ok d 14 T dies tu R vpe 5 c y Pa n s STE eee od vE A 23 an we amp 7 uf C7 02 r 5 4 e a Eb ii i gt eee PSNNBR2 BOYS Lo a a hd ED N Rserse qe PSNNIRJ KYL LAG N m gt 9 BAT voltage reto y Wi BA current ref AG H 0 tuF i a de a BAT current ref 3 OQ m pad surent et RO ER Lond_current_ret_AG Y hagr PMV65XR PMV65XP c59 s H y R424 wE j al L Buri mode snable 4 PBSSid 601 2121 N M5 M6 ER b d gt yas ad TT PESSALGOT om i bl y 275 o tut e 7 Y nad cut o ik SA hH 23 akr 09 EE a made enable G70 aa ot ri mn gt GOPWE 7 o Sas sa CuOPwR z A mn GNDEWR R31 2 E u3 R24 IRS21171 Buck PWMD rs A IN HO cr vs R32 4 Jen wo BAT_overvoltegeD A 35 a Nc x The main components in the DC DC converter are MOSFETs Q1 Q2 Q3 and Q4 rectifier diode D2 and inductor L1 When the converter is operating in boost mode MOSFET Q3 is closed and MOSFET Q4 is open Similarly when oper

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