DOE/GO-10097-377 FS 231 ENERGY March 1997 EFFICIENCY Photovoltaics: Basic Design AND RCLEARINGHOUSE ENEWABLE Principles and Components ENERGY If you are thinking of generating your Introduction to PV Technology own electricity, you should consider a photovoltaic (PV) system—a way to gen- Single PV cells (also known as “solar cells”) are connected electrically to form erate electricity by using energy from the PV modules, which are the building blocks sun. These systems have several advan- of PV systems. The module is the smallest tages: they are cost-effective alternatives in PV unit that can be used to generate sub- areas where extending a utility power line stantial amounts of PV power. Although is very expensive; they have no moving individual PV cells produce only small parts and require little maintenance; and amounts of electricity, PV modules are they produce electricity without polluting manufactured with varying electrical out- the environment. puts ranging from a few watts to more than 100 watts of direct current (DC) elec- This publication will introduce you to the tricity. The modules can be connected into basic design principles and components of PV arrays for powering a wide variety of PV systems. It will also help you discuss electrical equipment. these systems knowledgeably with an equipment supplier or system installer. Two primary types of PV technologies Because this publication is not intended to available commercially are crystalline sili- cover everything about designing and con and thin film. In crystalline-silicon installing a PV system, a list of additional technologies, individual PV cells are cut PV resources is provided at the end. from large single crystals or from ingots of crystalline silicon. In thin- film PV technologies, the PV material is deposited on glass or thin metal that mechanically sup- ports the cell or module. Thin-film-based modules are produced in sheets that are sized for speci- fied electrical outputs. In addition to PV mod- ules, the components needed to complete a PV system may include a battery charge controller, batteries, an inverter or power control unit (for alternating-current loads), safety disconnects and fuses, a grounding Jim Yost / PIX01809 Jim Yost circuit, and wiring. (See This stand-alone PV system consists of four modules, each with Balance-of-System Equip- 36 cells. It provides power for lights, radios, televisions, and other ment section.) loads at remote homes in New Mexico. NT O ME F E T N R E A R This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory. P G E Y D The document was produced by the Information Services Program, under the DOE Office of Energy Efficiency and Renewable Energy. The Energy Efficiency U A N and Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based on C I I T R E information known to EREC and NREL at the time of printing. No recommendation or endorsement of any product or service is implied if mentioned by EREC. D E M S A TAT ES OF Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste PV System Applications tem. Instead, you can rely on the dealer’s expertise to design and install a system Many people are familiar with PV-pow- that meets your needs. However, just like ered calculators and watches, the most buying a car or a television, you must common small-scale applications of PV. have confidence in the dealer’s products However, there are numerous large-scale, and services and be an informed con- cost-effective PV applications, including: sumer. With the growth of the PV indus- try, the number of regional dealers, • Water pumping for small-scale remote mail-order businesses, and local distribu- irrigation, stock watering, residential tors has expanded rapidly. Many tele- uses, remote villages, and marine sump phone directories contain listings for PV pumps; dealers under the “Solar” heading. • Lighting for residential needs, bill- boards, security, highway signs, streets Professional credentials are one indication and parking lots, pathways, recreational of a PV dealer’s knowledge and qualifica- vehicles, remote villages and schools, tions. Ask dealers what PV-related courses and marine navigational buoys; they have taken, certifications they have • Communications by remote relay sta- earned, and licenses they have received. tions, emergency radios, orbiting satel- lites, and cellular telephones; A second consideration is the dealer’s • Refrigeration for medical and recre- experience in the field. How long has the ational uses; company been in business? The local Bet- • Corrosion protection for pipelines and ter Business Bureau can advise you docks, petroleum and water wells, and whether any customers have registered underground tanks; complaints about the dealer. You should • Utility grids that produce utility- or also ask the dealer how many systems like commercial-scale electricity; and Hundreds of cost- yours he or she has designed and • Household appliances such as ventila- installed. Ask to see installations, and talk tion fans, swamp coolers, televisions, effective applications with owners of systems similar to the one blenders, stereos, and other appliances. you want to purchase. for PV systems have The decreasing cost of PV systems and the A third consideration in selecting a system increasing number of manufacturers and been developed. installer is the variety and quality of prod- dealers for PV equipment have con- ucts offered for each component of the tributed to widespread use of the technol- system. Because PV systems are often ogy. In PV’s early days, do-it-yourselfers designed for a specific site, one company’s had to search for companies that manufac- products may not be appropriate for all tured PV modules and often had to adapt applications. Competent dealers will stock or reconfigure components from other components manufactured by several non-PV systems. Today, dealers offer companies. A variety of product options ready-to-use systems and state-of-the-art will help ensure that the most appropriate equipment designed specifically for PV components are available for your system. systems. Many dealers have computer When a dealer recommends a product, ask software that helps to design systems and what the recommendation is based on, specify appropriate components. As PV whether there are consumer or indepen- markets expand, dealers are gaining dent testing facility reports you can read, greater experience with PV applications, and whether the products are listed with making it cheaper and easier to purchase Underwriters Laboratories (UL). PV systems. Fourth, consider the service agreements How Do I Select a PV Dealer? and performance guarantees the dealer Choosing a PV professional will be one of provides and the warranties given by the your most important decisions. If you product manufacturers. No system is choose a competent dealer, you won’t maintenance-free, nor will all components need to know all the details of designing, function flawlessly forever. When prob- purchasing, and installing your PV sys- lems emerge with your system, what ser- vices will the dealer provide? What 2 warranties do the manufacturers provide? compared to other electricity-generating What costs should you expect to pay, and systems. which costs will be assumed by the dealer • Modularity—PV systems can be and/or the manufacturer? expanded to meet increased power requirements by adding more modules Finally, you should compare prices from to an existing system. different dealers. Because distribution • Environment—PV systems generate channels and dealer networks have electricity without polluting the envi- expanded dramatically, the opportunity to ronment and without creating noise. “shop around” is much greater today. If • Ability to combine systems—PV sys- possible, approach more than one dealer tems can be combined with other types about a draft design and cost estimate for of electric generators (wind, hydro, and In the United States, your system. diesel, for example) to charge batteries and provide power on demand. PV systems must When Are PV Systems Appropriate? PV systems are not cost-effective for all have unobstructed applications. The following discussion People select PV systems for a variety of gives some general guidelines to consider southern exposure. reasons. Some common reasons for select- when deciding whether a PV system is ing a PV system include: appropriate for your situation. • Cost—When the cost is high for extend- First, if your site is already connected to a ing the utility power line or using utility grid, or within one-quarter mile of another electricity-generating system in a the grid, a PV system will probably not be remote location, a PV system is often the cost-effective. Each utility company most cost-effective source of electricity. spreads the cost of its power plants and • Reliability—PV modules have no mov- fuel costs among all its customers. Most ing parts and require little maintenance utilities can provide electricity to con- sumers for about 6 cents to 14 cents per kilowatt-hour. When you install a PV sys- Sun’s Path in the Sky tem, you are essentially installing your own mini-utility system. You pay all the costs of June 21 generating the electricity you consume. Although the sun’s energy is free, the PV equipment is not free. The electricity gener- ated by PV systems at current module and balance-of-system prices can cost 20 cents to 40 cents per kilowatt-hour, depending on the installation cost and intensity and West North duration of the sunlight at the site. Second, small PV systems are not practical for powering space-heating systems, December 21 water heaters, air conditioners, electric stoves, or electric clothes dryers.