PV (photovoltaic) Basics
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1. hour battery is about 1200 watts The same battery capacity in cold cranking amps is only about 34 watts Other Components That Should Be Considered With a relatively large PV array installed you can also sell excess power back to the utility that they must buy from you The trick is to sell it back to them when you want to sell it and not when they want to buy it For instance with a grid tied array you sell excess power to the utility during off peak hours The utility uses this excess capacity to do only one thing pump water That s right they pump water to either a reservoir or water tower when the electricity is cheap and then use the potential energy of the water to run a turbine to offset the more expensive peak times You can actually do the same thing especially if you already have the property with an elevation change a pond or both If you also have a fast moving stream there are other options as well to supplement your off grid power system Below is a simple hydroelectric generator that is available for between 850 to about 2K depending upon options This one can generate about 2500 watt hours Bigger models are available if your needs are larger A fast moving stream can be used with the following type of generator if this resource is available at your location You can also supplement with wind not a viable option for this location Lastly consider the following type of human powered generator for use whe2. that the battery combiner can be replaced with a simple three or four way battery switch If you use a battery switch instead of the combiner you should ensure that each battery bank 1s identical in size amp hours and battery type The battery combiner allows you the flexibility of using different size battery banks depending upon the DC source and can allow you to save money by allowing you to optimize the battery bank to each source as opposed to having three identical battery banks sized to the largest DC source requirements hydro2 disconnect hydrol cha controller DC load center PY charge controller Charge disco nect P Battery charger battery bank 1 PV Note that connections on the other side of the DC load center are the same as in the single battery bank setup A Note About Inverters The inverters illustrated above are just two of the many types and sizes of inverters available Usually the higher the power rating the more expensive and heavy the inverter is Also note that pure sine wave inverters are larger heavier more expensive and less efficient than their modified sine wave counterparts of equivalent power rating but operate inductive type loads motors or any appliance that contains a transformer much more efficiently than a modified sine wave inverter Also note that modified sine wave inverters can actually damage some types of sensitive equipment especially medical equipment My inve
3. PV photovoltaic Basics There are generally two types of PV systems The first and easiest though the least flexible is a grid tie system where the power generated by the solar panel panels runs an inverter which is tied directly to the power grid on the home or customer side of the power meter These types of systems are generally less expensive per watt of installed power than a stand alone type of system A big minus is that the inverter is controlled by the utility company and during a power outage you probably won t be able to utilize the energy A less known but equally distracting thing about these types of systems is that the utility generally buys your excess during off peak periods and then sells you back the power during peak times can cost 2 to 10 times more than off peak On the other hand a big plus is that the required expenditure can be considerably less than a comparable stand alone system with batteries The maintenance is also less as batteries don t need to be replaced Two configurations are illustrated below The first one simply uses grid tie panels with the inverters mounted directly to the panels The second one is a little more flexible in that you can use standard panels and add additional panels when you need or want to LOAD LOAD CENTER UTILITY KWH METER UTILITY CEHTER METER AC LOADS AC LOADS ONE METER REQD BY UTILITY 2ND METER REO D BY UTILITY H TE SYSTEM
4. S SHOULD BE DESIGHED TS COMPLY WITH HEC ARTICLE 690 LOAD UTILITY CENTER EWH METER AC DC TO AC INVERTER LOADS SOLAR PY UTILITY INTERACTIVE MODULES a BLOCKING JUNCTION BoxwsuRGE MOPE SHOWH WITH 2HD METER amp DISCONNECT ARRESTER IF REQ D THAT MAY BE REQ D BY YOUR UTILITY S OTHERWISE TIE DIRECTLY TO LOAD CEHTER seep OVERCURREHT REQ DFORROOF po MOUNTED SYSTEMS piceouyects HOTE SYSTEMS SHOULD BE DESIGNED TO COMPLY WITH HEC ARTICLE 690 For stand alone types of systems you will need several basic components which are outlined below 1 PV panel varying wattages available from a few watts to several hundred watts per panel 2 A DC load center for hooking up your batteries charge controller and PV panels Note that AC is not handled by your DC load center Expect to pay between 100 and 500 for this component The Trace DC load center pictured below is about 260 with a 250 amp DC breaker installed A charge controller is used to regulate the output of your PV array and also keep the batteries from being over charged Depending upon the model it can also divert the load to another application such as pumping water when the batteries are fully charged and there is excess capacity The model pictured below costs about 130 and can safely handle 60 amps 12VDC and 24VDC on a continuous basis X 2 poi xantrex IEEE T E A ATTERY FULL oe fF BALE F a en 7 886 a oe ie v oo aas w
5. V array However increasing the battery array size and PV array output can enable your system to run from the battery for more extended periods such as when you need to perform routine maintenance on your generator during an extended power outage Lastly the battery voltage and amp hour ratings as depicted in the diagram are just an example and probably will not meet the requirements of your particular home The second system depicted below relies mainly on several DC type sources to provide AC A utility connection is present but a generator can be hooked up for true off grid applications Again the battery specifications depicted are for example only and aren t representative of what your particular requirements will be From utility ren switch 2 os 7 I3 oar ty I A 24 T erin 4 Me Hh T iS Utility disconnect hydrol disconnect hydrol charge hydro2 charge controller controller DC load center nm r ee E lt eo a lt ESD modified SW inverter disconnect SW inverter disconnect 2 5KW modified sine wave inverter Battery charger battery 12VDC 100 A hr Note here that each DC source now has it s own DC charge controller The above illustration allows the use of only one DC source at a time A more flexible DC hookup arrangement is shown below Here each DC source has not only its own DC charge controller but also its own battery or battery bank Note also
6. d to heat water or run incandescent type lights The last hookup pretty much covers all bases including selling of excess capacity back to the utility OTHER WTIEGRATED UTILITY chs DC SOURCES prt papery AC ENGINE METER CENTER SOLAR PY SOLAR HYDRO oj GENERATOR SET el 2 MODULES ENGINE CHARGER E acm ETC DIVERSION TRUE SINE idk AE INVERTER E UT INTERACT SHOW WITH 2HD METER amp DISCONHECT THAT MAY JUHCTION yy DIVERSION BE REO D BY YOUR UTILITY BOX Vii SURGE LOAD USED ARRESTER BAHK OF Wi OTHER OVERCURREMT SUB PAHEL FOR CHARGE STORAGE SOURCES PROTECTION LOADS piace CONTROLLER BATTERIES ae DISCOHHECTS ESSENTIAL LOADS IF REG D GROUND FAULT SYSTEM HOTE SYSTEMS SHOULD BE DESIGHED TO REQ D FOR ROOF MOUNTED SYSTEMS COMPLY WITH HEC ARTICLE 690 Safety It s always a good idea to include a disconnect DC or AC for each generating component of your system The disconnect should be as physically close to the generating component as practical If the disconnect will be located outdoors then ensure that the enclosure is rated for exposure to the weather Some typical AC and DC disconnects are shown below Also note that if your PV panels will be mounted above the ground roof mounted for instance then a ground fault circuit and lightning protection circuit will also need to be installed Systems A couple of systems are illustrated below Note that these represe
7. g charging but can under extreme conditions and this must be accounted for when choosing a mounting location The glass mat types are generally the most expensive but can be classified as a dry cell type of battery Even when the case is cracked or damaged the electrolyte will not spill They can also have an extended number of charge discharge cycles when compared to the flooded lead acid battery I will add a note here about battery capacities Generally you may see some of the following battery ratings and each is a little different e 20 hour rate This is the amp hour capacity of the battery if it is discharged to 80 of the full charge terminal voltage over a 20 hour period For a 100 amp hour battery the most you can discharge per hour is 5 amp hours or about 60 watts If you discharge at a higher rate the actual capacity of the battery is diminished If you discharged at 100 amp hours for instance the battery will only last about 30 minutes e 25 amp hour reserve This is the battery capacity in minutes that the battery can sustain a 25 amp hour load until the battery reaches 80 of the full charge terminal voltage battery considered dead at 80 terminal voltage or 9 6 VDC for a 12 volt battery e Cold cranking amps This is the maximum amperage the battery can sustain over a 25 second period with an ending terminal voltage of 7 volts Interestingly enough when you consider the total battery capacity the 20 hour rating for a 100 amp
8. h types of inverters 5 An optional but useful component is a bus transfer switch The one shown below has three inputs utility generator inverter and will automatically switch to between the three depending upon which are available The model shown below costs about 230 6 Last but not least is the battery or batteries Generally flooded lead acid deep cycle type batteries are the cheapest ones and offer the most amp hours per dollar Remember that these generally have a limited number of charge discharge cycles and will need to be replaced regularly Don t for instance just put in enough capacity to handle one day s worth of usage as the batteries will most likely last less than a year under these circumstances Instead plan for a few days to a week s worth of capacity Not only will you be prepared for extended cloudy weather but you will only need to change out the batteries every four to six years Of course a down side of these types of batteries is that they produce explosive hydrogen gas during charging and the space where the batteries reside must be vented with a non explosive type of ventilator For larger installations a hydrogen monitor is also probably a good idea be prepared to spend about 500 and up for a hydrogen monitor More expensive amps dollar types of batteries include SLA sealed lead acid and glass mat types of batteries The sealed lead acid batteries normally don t vent the hydrogen gas durin
9. n all else fails This generator coupled with highly efficient lighting and refrigeration can keep you going with nothing else is available Here are some ways of hooking up a PV system The first one is the simplest but illustrates all the key components DC TO AC INVERTER AC LOADS SOLAR PY MODULES bragt a UC LOADS oF sone VERO REE BOX Wi SURGE CONTROLLER ARRESTER IF REQ D BAHE OF CENTERS OVERCURREHT STORAGE GROUND FAULT SYSTEM PROTECTION BATTERIES REG O FOR ROOF HOTE SYSTEMS SHOULD BE DESIGHED TO MOUNTED SYSTEMS COMPLY WITH HEC ARTICLE 690 Note that this system doesn t allow for selling your excess capacity back to your local utility The next setup allows you to charge run your electrical needs from a generator during an extended cloudy period DC TO AC O AC ENGINE S GEHERATOR SET INVERTER Vii CHARGER AC LOADS SOLAR PY MODULES wA A DC LOADS n a Bien Rae BOX W SURGE COHTROLLER ARRESTER IF REQ D BANK OF CENTERS OVERCURRENT STORAGE GROUND FAULT SYSTEM PROTECTIOH BATTERIES REQ D FOR ROOF HOTE SYSTEMS SHOULD BE DESIGHED TO MOUNTED SYSTEMS COMPLY WITH HEC ARTICLE 690 Here the generator is simply hooked to an inverter with charging capability These types of inverters generally have AC pass thru as well so that the generator 1s hooked to the AC load center via the inverter This hookup scheme has limited flexibility The next diagram illustrates a m
10. ng outlets can be split in the box and another set of wires run to the essential load center These loads will then run continuously during a power outage from either the inverter or the generator Also note that most modern inverters can run continuously as their idle power consumption is only a few watts This allows the system to operate as a large UPS until you either start the generator manually or you generator controller starts the generator automatically Note also the UPS and line conditioner illustrated above These are optional components that are in place if you choose to not have your inverters running continuously which will decrease the lifetime of the inverter Here the UPS supplies the essential loads until you can start the inverter and or generator The line conditioner also provides spike and surge protection as well as brownout protection without having to start the generator or inverter for all your AC sources since a compressor can generate a spike even when you aren t connected to the utility grid Also note that only one DC charge controller is used for your PV system and another DC source a manual pedal type generator is shown in the example Battery capacity can also be small especially if the main power source during a power outage will be a generator Here the battery capacity should be large enough to supply your essential loads for five to ten minutes and also large enough to store about two days of output from your P
11. nt only two of countless hookup possibilities with the components discussed thus far Note also that wind generation wasn t discussed as our area isn t conducive to any appreciable power generation from wind Note also that although the hydroelectric generators shown are hooked up to provide DC the same can be ordered to directly produce AC Each system also has a hookup to your local utility but isn t depicted to enable selling excess generation capacity back to the utility grid For off grid type applications the utility disconnect and associated wiring may be omitted The first system relies mainly on AC type generation devices to provide the bulk of the service while allowing DC to provide limited AC during brief power outages and to allow the gasoline or diesel generator to start and warm up prior to supplying the AC loads From utility 3 way tron sfer switch 2 ES s 2 fant ES fil Ws CF CYTE H X lt lir Genset wis ty disconnect disconnect mg Line conditioner modified SE inverter disconnect SW inverter disconnect harge di sconnect TN er 2 5KW modified sine wave inverter Battery charger z battery 12VDbC 255 A hr Note that the load center is separate from the main AC load center for your home This load center should be wired to run only your essential electrical needs These can generally be added by an experienced electrician without the need to go into the walls Existi
12. ore flexible hookup for your generator It can also be used for hooking up other alternative energy sources such as wind or hydroelectric Note that here the AC or DC alternative sources are run thru the charge controller which allows for more alternatives in the choice of your inverter Dc WD DC TO AC R HYDRO GEHERATOR INVERTER AC LOADS SOLAR PY MODULES DC LOADS ye aca E E BOX YW SURGE CONTROLLER ARRESTER IF REQ D BAHE OF CENTERS OVERCURREHT STORAGE GROUHD FAULT SYSTER PROTECTION BATTERIES REQ D FOR ROOF H TE SYSTEMS SHOULD BE DESIGHED TO MOUNTED SYSTEMS COMPLY WITH HEC ARTICLE 690 You can also buy prepackaged control centers which have the inverter charge controller and load centers assembled into one box A hookup for a typical control box is shown below C a OTHER DC SOURCES AC WIHD Ps ita e SOLAR HYDRO GEHERA TOR RM De DIVERSION i E CHARGE FOR HY WIND LOAD aki R GEHERATOR SOLAR PY MODULES RECTIFIER Pe i OC LOADS OR INVERTER JUHCTION Seep BOXW SURGE ar REQ D ARRESTER GROUHD FAULT ca SYSTEM DC CIRCUIT i BANK OF Ty REO D FOR ROOF BREAKERS CONTROL STORAGE MOUNTED SYSTEMS ee BATTERIES Here a DC diversion load is used Diversion loads are important especially when using a hydroelectric or wind generator The diversion load protects these types of generators from over spinning when the load is too small These loads are generally resistive and can be use
13. re hooked up to a Xantrex battery combiner and a Xantrex system monitor I also have a small PV panel with a Xantrex C 12 charge controller that can be used to charge the batteries in addition to the Xantrex battery charger Although everything is kind of spread out in a spare room I plan on mounting all the components and batteries on a cart which I can then role to where it s needed I also plan to add one of your 3 way automatic bus transfer switches to the system in the near future The basic system is pictured below AC Load Center __ WH modified SE for larger loads inverter 3 disconnect LLELLMLLLL 2 5KW modified Line conditioner SW inverter Sine wave inverter w foutlets for disconnect sensitive equip 1KW sine wave inverter Charge di scomnect al a l Battery charger ome Ee
14. rter system is perhaps a little different than most both in terms of complexity and purpose I have one of the Aims IKW sine wave inverters and your no frills 2 5K W inverter as well The 2 5K W inverter is hooked up on the DC side to a 250 amp DC breaker while the 1K W inverter is hooked up to a 100 amp DC breaker The large inverter has an AC disconnect along with a small 30 amp load center I re wired the inverter to bypass the installed outlets and installed a SR 30 30 amp receptacle as this allows the full output to be utilized by a single large load or several smaller loads A mating plug runs from the disconnect For the IKW sine wave inverter I also have an AC disconnect which is hooked up using the installed outlet on the front panel The loads plug into a Tripplite line conditioner which gives the inverted output boost buck capability The system is designed to allow the use of most appliances except heating AC in the event of a power outage The 2500 watt inverter is used for luxury items such as the microwave and toaster oven It s nice to be able to use these things when the lights go out for everyone else and still have lights too The 1KW sine wave inverter is used to run a TV and is used in conjunction with a UPS which keeps a light and the TV going until I can start the inverter and transfer the load with a manual transfer switch The DC side of things is a little more involved as well I have three of the Optima 34M batteries which a
15. u ws 800 ort eppen BATTERY EMPTY oe fh GD a a aa kech 086068668008 T bs a i m A an i 1 S80 000606 manama Ti Su amp ee ee i me a 2 ff Sin oS o o ag F J ars am oe ee er eS Phi e ki isna ir i An inverter is the component used to convert the DC from the PV array and batteries into usable AC power to run your household appliances There are generally two types The least expensive is what is called a modified sine wave This type of inverter is OK for running lights some types of motors and resistive type loads electric frying pan toaster Other appliances such as microwave ovens and anything that uses a transformer may not operate correctly or may even be damaged by this type of dirty power ZA ann RHA AAA 4 DF F 3 AR The second type of inverter is true sine wave inverter These are generally much more expensive than the corresponding modified sine wave inverter of equal power ratings The above 2500 watt modified sine wave inverter will run anywhere from 180 internet to about 400 locally Fry s The same 400 will only get you about 1000 watts of pure sine wave power but the pure sine wave inverter will run any load that runs from your local utility Motors will also operate more efficiently less noise and less heat from a sine wave inverter A 1000 watt model is shown below and lists for about 360 A good general purpose off grid system can and should have bot
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