Photovoltaics: Basic Principles and Components

1 If you are thinking of generating yourown electricity, you should consider aphotovoltaic (PV) system a way to gen-erate electricity by using energy from thesun. These systems have several advan-tages: they are cost-effective alternatives inareas where extending a utility power lineis very expensive; they have no movingparts and require little maintenance; andthey produce electricity without pollutingthe publication will introduce you to thebasic design Principles and Components ofPV systems. It will also help you discussthese systems knowledgeably with anequipment supplier or system this publication is not intended tocover everything about designing andinstalling a PV system, a list of additionalPV resources is provided at the end. Introduction to PV TechnologySingle PV cells(also known as solarcells ) are connected electrically to formPV modules,which are the building blocksof PV systems.

2 The module is the smallestPV unit that can be used to generate sub-stantial amounts of PV power. Althoughindividual PV cells produce only smallamounts of electricity, PV modules aremanufactured with varying electrical out-puts ranging from a few watts to morethan 100 watts of direct current (DC) elec-tricity. The modules can be connected intoPV arraysfor powering a wide variety ofelectrical primary types of PV technologiesavailable commercially are crystalline sili-con and thin film. In crystalline-silicontechnologies, individual PV cells are cutfrom large single crystals or from ingots ofcrystalline silicon. In thin-film PV technologies, thePV material is depositedon glass or thin metalthat mechanically sup-ports the cell or modulesare produced in sheetsthat are sized for speci-fied electrical addition to PV mod-ules, the componentsneeded to complete a PVsystem may include abattery charge controller,batteries, an inverter orpower control unit (foralternating-currentloads), safety disconnectsand fuses, a groundingcircuit, and wiring.

3 (SeeBalance-of-System Equip-mentsection.)Photovoltaics: Basic DesignPrinciples and Components CLEARINGHOUSEENERGYEFFICIENCY ANDRENEWABLEENERGY TOFENERGYDEPARTMENUENITEDSTATSOFAERICAMT his stand-alone PV system consists of four modules, each with 36 cells. It provides power for lights, radios, televisions, and otherloads at remote homes in New Mexico. This document was produced for the Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national document was produced by the Information Services Program, under the DOE Office of Energy Efficiency and Renewable Energy. The Energy Efficiencyand Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based oninformation known to EREC and NREL at the time of printing.

4 No recommendation or endorsement of any product or service is implied if mentioned by with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer wasteDOE/GO-10097-377FS 231 March 1997 Jim Yost / PIX01809PV System ApplicationsMany people are familiar with PV-pow-ered calculators and watches, the mostcommon small-scale applications of , there are numerous large-scale,cost-effective PV applications, including: Water pumpingfor small-scale remoteirrigation, stock watering, residentialuses, remote villages, and marine sumppumps; Lightingfor residential needs, bill-boards, security, highway signs, streetsand parking lots, pathways, recreationalvehicles, remote villages and schools,and marine navigational buoys; Communicationsby remote relay sta-tions, emergency radios, orbiting satel-lites, and cellular telephones; Refrigerationfor medical and recre-ational uses; Corrosion protectionfor pipelines anddocks, petroleum and water wells, andunderground tanks; Utility gridsthat produce utility- orcommercial-scale electricity; and Household appliancessuch as ventila-tion fans, swamp coolers, televisions,blenders, stereos, and other decreasing cost of PV systems and theincreasing number of manufacturers anddealers for PV equipment have con-tributed to widespread use of the technol-ogy.

5 In PV s early days, do-it-yourselfershad to search for companies that manufac-tured PV modules and often had to adaptor reconfigure Components from othernon-PV systems. Today, dealers offerready-to-use systems and state-of-the-artequipment designed specifically for PVsystems. Many dealers have computersoftware that helps to design systems andspecify appropriate Components . As PVmarkets expand, dealers are gaininggreater experience with PV applications,making it cheaper and easier to purchasePV Do I Select a PV Dealer?Choosing a PV professional will be one ofyour most important decisions. If youchoose a competent dealer, you won tneed to know all the details of designing,purchasing, and installing your PV sys-tem. Instead, you can rely on the dealer sexpertise to design and install a systemthat meets your needs. However, just likebuying a car or a television, you musthave confidence in the dealer s productsand services and be an informed con-sumer.

6 With the growth of the PV indus-try, the number of regional dealers,mail-order businesses, and local distribu-tors has expanded rapidly. Many tele-phone directories contain listings for PVdealers under the Solar credentials are one indicationof a PV dealer s knowledge and qualifica-tions. Ask dealers what PV-related coursesthey have taken, certifications they haveearned, and licenses they have consideration is the dealer sexperience in the field. How long has thecompany been in business? The local Bet-ter Business Bureau can advise youwhether any customers have registeredcomplaints about the dealer. You shouldalso ask the dealer how many systems likeyours he or she has designed andinstalled. Ask to see installations, and talkwith owners of systems similar to the oneyou want to purchase. Athird consideration in selecting a systeminstaller is the variety and quality of prod-ucts offered for each component of thesystem.

7 Because PV systems are oftendesigned for a specific site, one company sproducts may not be appropriate for allapplications. Competent dealers will stockcomponents manufactured by severalcompanies. Avariety of product optionswill help ensure that the most appropriatecomponents are available for your a dealer recommends a product, askwhat the recommendation is based on,whether there are consumer or indepen-dent testing facility reports you can read,and whether the products are listed withUnderwriters Laboratories (UL).Fourth, consider the service agreementsand performance guarantees the dealerprovides and the warranties given by theproduct manufacturers. No system ismaintenance-free, nor will all componentsfunction flawlessly forever. When prob-lems emerge with your system, what ser-vices will the dealer provide? What2 Hundreds of cost-effective applicationsfor PV systems havebeen do the manufacturers provide?

8 What costs should you expect to pay, andwhich costs will be assumed by the dealerand/or the manufacturer?Finally, you should compare prices fromdifferent dealers. Because distributionchannels and dealer networks haveexpanded dramatically, the opportunity to shop around is much greater today. Ifpossible, approach more than one dealerabout a draft design and cost estimate foryour Are PV Systems Appropriate?People select PV systems for a variety ofreasons. Some common reasons for select-ing a PV system include: Cost When the cost is high for extend-ing the utility power line or usinganother electricity-generating system in aremote location, a PV system is often themost cost-effective source of electricity. Reliability PV modules have no mov-ing parts and require little maintenance compared to other electricity-generatingsystems. Modularity PV systems can beexpanded to meet increased powerrequirements by adding more modulesto an existing system.

9 Environment PV systems generateelectricity without polluting the envi-ronment and without creating noise. Ability to combine systems PV sys-tems can be combined with other typesof electric generators (wind, hydro, anddiesel, for example) to charge batteriesand provide power on systems are not cost-effective for allapplications. The following discussiongives some general guidelines to considerwhen deciding whether a PV system isappropriate for your , if your site is already connected to autility grid, or within one-quarter mile ofthe grid, a PV system will probably not becost-effective. Each utility companyspreads the cost of its power plants andfuel costs among all its customers. Mostutilities can provide electricity to con-sumers for about 6 cents to 14 cents perkilowatt-hour. When you install a PV sys-tem, you are essentially installing your ownmini-utility system.

10 You pay all the costs ofgenerating the electricity you the sun s energy is free, the PVequipment is not free. The electricity gener-atedby PV systems at current module andbalance-of-system prices can cost 20 centsto 40 cents per kilowatt-hour, dependingon the installation cost and intensity andduration of the sunlight at the site. Second, small PV systems are not practicalfor powering space-heating systems,water heaters, air conditioners, electricstoves, or electric clothes dryers. Theseloads require a large amount of energy tooperate, which will increase the size andcost of your PV system. Therefore, selectthe most energy-efficient loads example, if your PV system willpower lights, look for the most energy-efficient light bulbs. If your system willpump water for toilets and showers, lookfor the most water-conserving the United States,PV systems musthave unobstructedsouthern s Path in the SkyJune 21 December 21 WestSouthEastNorthPV modulesThe sun s noontime height above the horizon changes seasonally.