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Solar FAQs — Photovoltaics — Applications

Q: Where are photovoltaic (PV) systems being used?

A: PV (solar electric) systems are generating clean electric power all over the world, both here and abroad. Today, we can see PV systems at work on urban skyscrapers like 4 Times Square in New York City and in the small rural villages of Brazil. PV systems are especially well suited for places where an electrical grid cannot be accessed easily or where access is too expensive.

In many remote areas, PV is the least-cost option for meeting energy needs. However, PV is proving to be a reliable source of power in an ever-growing number of applications, even where there is easy access to power lines. Cost-effective examples of lighting powered by PV include small garden lights, street lights, lighting for recreational areas, highway signs, warning signs and signals, and lighting for businesses and homes. We can find examples of these applications in both the developed and developing world.

PV is ideal (and often used) for water pumping, because water can be pumped into a storage tank during daylight hours and then distributed by gravity whenever it is needed. These systems commonly pump water for livestock watering tanks in remote areas. In some parts of the developing world, entire village water supplies are powered by PV. Other uses include remote monitoring, refrigeration, and energy for small commercial ventures. Virtually any power need can be met with PV.

Other Resources: To learn more about applications of PV and other solar technologies in the world, please visit our Solar America Tour Also, see PV in Use for other useful applications of PV.

To learn more about energy saving tips and renewable energy technologies, please visit U.S. Department of Energy's Energy Saver's Web site.

Q: Can I use photovoltaics (PV) to power my home?

A: PV can be used to power your entire home's electrical systems, including lights, cooling systems, and appliances. PV systems today can be blended easily into both traditional and nontraditional homes. The most common practice is to mount modules onto a south-facing roof or wall. For an additional aesthetic appeal, some modules resemble traditional roof shingles or can be built right into glass skylights and walls. This building-integrated PV provides a dual-use building material, reduces PV system costs by using the building as the mounting or support structure, and reduces utility bills with on-site power production.

Other Resources: To learn more about energy saving tips and renewable energy technologies, please visit U. S. Department of Energy's Energy Saver's Web site

To learn more about financial incentives in your area, please visit the Database of State Incentives for Renewable Energy (DSIRE) and contact your State's Energy Office. One caveat: any time you work with a contractor, it is wise to check references.

To find a solar energy system designer or installer in your area, please visit our solar yellow pages for a list of sources of solar professionals.

Q: Can I use photovoltaics (PV) to power my business?

A: PV systems can be blended into virtually every conceivable structure for commercial buildings. You will find PV being used outdoors for security lighting as well as in structures that serve as covers for parking lots and bus shelters, generating power at the same time. Indoors, PV systems are used to offset and operate all kinds of electrical systems, including lights, cooling systems, and appliances.

Today's modules can be built into glass skylights and walls. Some resemble traditional roof shingles. Architects can use building-integrated PV to design buildings that are environmentally responsive, aesthetically pleasing, and produce their own power. Building-integrated PV provides a dual-use building material, reduces PV system costs by using the building as the mounting or support structure, and reduces utility bills through on-site power production.

Other Resources: To learn more about energy saving tips and renewable energy technologies, please visit U. S. Department of Energy's Energy Saver's Web site

To learn more about energy saving tips and renewable energy technologies, please visit U. S. Department of Energy's Energy Saver's Web site

To learn more about financial incentives in your area, please visit the Database of State Incentives for Renewable Energy (DSIRE) and contact your State's Energy Office. One caveat: any time you work with a contractor, it is wise to check references.

Q: Can I design and install a photovoltaic (PV) system myself?

A: Maybe! However, unless you are very handy or experienced in home wiring, we suggest using experienced professionals to design and install anything more than the simplest application, for the following reasons:

You might void the manufacturer's warranties.
You might not have a functional system after spending your hard-earned money on the system.
Electricity can be dangerous; you might get hurt.
You might damage your home or appliances during installation.

The goal of a stand-alone system designer is to assure customer satisfaction by providing a well-designed, durable system with a 20-year life expectancy (or more). This depends on sound design, specification and procurement of quality components, good engineering and installation practices, and a consistent preventive maintenance program.

System sizing is perhaps the easiest part of achieving a durable PV power system. To determine the correct system size, you must first analyze your electricity loads.

In addition to sizing the system correctly, a thorough knowledge of the availability, performance, and cost of components is the key to good system design. Price/performance trade-offs should be made and reevaluated throughout the design process. When you start your design, obtain as much information as you can about the components you might use. After studying all the issues, you can do an initial sizing of the PV system and get some ideas about specifying system components.

Other Resources: To find a solar energy system designer or installer in your area, please visit our solar yellow pages for a list of sources of solar professionals.

Q: When will I be able to buy a solar electric or PV-powered car?

A: Because most automobiles are very heavy and aren't very efficient, it would be very difficult to power one with solar cells. But if a car were built specifically for PV, it could provide suitable transportation. As we've seen in many student-built vehicles for competitions, solar cars are very light and efficient and have enough battery storage to travel for miles on a cloudy day or at night. Solar cars can travel the speed limit on normal highways, but only as long as the sun is shining or until their batteries run down.

A more realistic car would be another kind of electric vehicle, one that many companies are working on right now. These cars could be charged by solar panels during the day, for example, while people are at work. They could also be plugged in at home for charging when the sun is not shining. To see an example of this, please visit "grid-connected PV" in the PV in Use pages.

The benefits of solar cars are obvious: they don't pollute, and free sunlight is their fuel. The drawbacks are that, using today's technology, a solar car has to be very lightweight for the panels to provide enough energy to power the car at road speeds, and it has to have enough battery storage to travel long distances without sunlight (e.g., at night and on overcast days).

As part of continued research and development, many organizations are improving the systems used in solar cars to make them more efficient and cost effective and thus more widely used (the systems, anyway). Wider use of solar electric cars (or other electrics) probably depends on the availability of inexpensive, lightweight, compact energy storage methods. Car companies are making great strides in this area with the new gas/electric hybrids, and future progress is likely to be rapid.

Other Resources: For more information about research and development activities related to solar vehicles, please visit these Web sites:

The American Solar Challenge (ASC) is a competition to design, build, and race solar-powered cars in a cross-country event.

Office of Transportation Technologies Web site.

DOE's Alternative Fuels Data Center site on solar vehicles.

World Solar Challenge, an international solar car/vehicle race.

Energy Efficiency and Renewable Energy Network briefing on solar powered vehicles. October 2000.

Q: When will solar electric systems replace coal and nuclear power plants?

A: Right now, our nuclear and fossil-fuel-based energy is quite inexpensive compared with the cost of solar energy. Oil and coal prices are low in most places, so solar energy still can't compete on a first-cost basis in many regions of the world, such as the United States. As this situation changes, we'll begin to see many more solar energy systems being built in areas that now use fossil fuels and nuclear energy for electricity generation.

Another driver in the deployment of solar systems is public demand for clean energy. Fossil-based energy pollutes the environment, and nuclear energy creates hazardous waste. If we stop to consider the environmental and health costs of fossil-fuel and nuclear energy, then solar energy already makes sense today.

However, in developing countries where there is little or no supply system for conventional energy, solar energy is being used more and more. It can be much less expensive than many other options, and the environmental benefits associated with this cleaner form of energy are significant. In developing countries, the key barriers to wider use are the need for financing and for electric distribution networks.

Other Resources: To learn more about solar energy technologies, please visit our solar energy information portal. See also, the Florida Solar Energy Center Website for a wide array of information about solar and PV systems.

To learn more about the business direction of the U.S. Photovoltaics Industry, please see the PV industry's Technology Roadmap, updated January 2003. (PDF 674 KB)
Download Acrobat Reader.

Q: How much space would be needed for photovoltaic systems to meet the entire electrical needs of the United States?

A: If PV were a primary energy source, what would the world look like? Would PV collectors cover every square inch of available land? Contrary to some popular notions, the landscape of a world relying on PV would be almost indistinguishable from the landscape we know today. The impact of PV on the landscape would be low, for three reasons. First, PV systems have siting advantages over other technologies; for example, PV can be put on roofs and can even be an integral part of a building, such as a skylight. Second, even ground-mounted PV collectors are efficient from the perspective of land use. Third, adequate sunlight is ubiquitous and often abundant, and present in predictable amounts almost everywhere. As we move away from fossil-fuel energy, PV will become important because of its land-use advantages:

PV's low-impact siting for flat-plate systems. In the United States, cities and residences cover about 140 million acres of land. We could supply every kilowatt-hour of our nation's current energy requirements simply by applying PV to 7% of this area—on roofs, on parking lots, along highway walls, on the sides of buildings, and in other dual-use scenarios. We wouldn't have to appropriate a single acre of new land to make PV our primary energy source!

PV's efficient ratio of produced energy to land use. Even if it isn't installed on rooftops, flat-plate PV technology is the most land-efficient means to produce renewable energy.

PV has a competitive conversion efficiency, a high capacity factor, and can be "packed" densely in a given area. We still wouldn't have a land use issue, even if we didn't use roofs for PV. We would need only 10 million acres of land — only four-tenths of one percent of the area of the United States — to supply all of our nation's energy using PV. Is that a lot of land? Not for something as important as producing electricity, and not in comparison to some of the other ways we use land.

Other Resources: 

Q: Are photovoltaic (PV) systems used in government buildings?

A: With its 500,000 buildings, the federal sector represents about one-half of one percent of the entire U.S. building inventory, but this is still considerable. Each year, U.S. taxpayers spend more than $3 billion to heat, cool, light, and power those buildings.

During the past 20 years, this energy bill has been reduced by investing in energy efficiency and using renewable energy (including solar) systems in new and existing federal buildings. The federal government is committed to installing solar electric and solar thermal energy systems on 20,000 federal buildings by 2010. In fact, the government exceeded its preliminary commitment of installing 2,000 systems on federal buildings by the year 2000.

Other Resources: To learn more about the federal government's commitment to renewable and energy efficiency, please visit the Federal Energy Management Program (FEMP) Web site.

Q: How do I know if I have enough sunlight for PV?

A: A photovoltaic (PV) system needs unobstructed access to the sun's rays for most or all of the day. Climate is not really a concern, because PV systems are relatively unaffected by severe weather. In fact, some PV modules actually work better in colder weather. Most PV modules are angled to catch the sun's rays, so any snow that collects on them usually melts quickly. There is thus enough sunlight to make solar energy systems useful and effective nearly everywhere in the United States.

Even hail won't harm most PV systems. Most homes have adequate roof space for a PV system, but you will have to size your system first to discover how much space is required. If you don't have adequate roof space, look at other options such as integrating the system into a wall or putting the system in the backyard. You could also use the system to cover a porch or patio in the backyard or mount the system on the roof or wall of a garage. Remember: an energy-efficient building requires a smaller PV system.

Other Resources: To learn more about energy saving tips and renewable energy technologies, please visit U. S. Department of Energy's Energy Saver's Web site.

To obtain information about solar resources in your area, see Solar Radiation for Energy: A Primer and Sources of Data.

To view some helpful decision-making tools, please visit DOE's Building Energy Tools Directory.

To learn more about the basics of PV, please see Sandia National Laboratories (SNL) PV Web site. To request a copy of Stand-Alone Photovoltaic Systems: A Handbook, a very popular handbook that presents recommended design practices for stand-alone PV systems.

See also the Consumer's Guide to Buying a Solar Electric System. September 1999, NREL (PDF 68 KB).
Download Acrobat Reader.

Q: How big a solar energy system do I need?

A: The size of solar system you need depends on several factors—such as how much electricity or hot water or space heat you use, how much sunshine is available where you are, the size of your roof, and how much you're willing to invest. You can contact a system designer/installer like those listed in our PV Directory or other solar industry directories to determine what type of system would suit your needs.

You can also check out DOE's Building Energy Tools Directory for energy analysis tools such as PV-DesignPro (photovoltaic design, tracking systems, solar, electrical design) or RETScreen (pre-feasibility analysis, heating, renewable energy). PC-Solar 2.0 provides passive solar calculations (solar shading, external shading, internal shading, solar incidence).

Other Resources: To learn more about energy saving tips and renewable energy technologies, please visit U. S. Department of Energy's Energy Saver's Web site

To view some helpful decision-making tools, please visit DOE's Building Energy Tools Directory at

To find a solar energy system designer or installer in your area, please visit our solar yellow pages for a list of sources of solar professionals.

To learn more about energy saving tips and renewable energy technologies, please visit U. S. Department of Energy's Energy Saver's Web site

To learn more about financial incentives in your area, please visit the Database of State Incentives for Renewable Energy (DSIRE) and contact your State's Energy Office. One caveat: any time you work with a contractor, it is wise to check references.

To learn more about the basics of PV, please see Sandia National Laboratories (SNL) PV Web site. To request a copy of Stand-Alone Photovoltaic Systems: A Handbook, a very popular handbook that presents recommended design practices for stand-alone PV systems.

Consumer's Guide to Buying a Solar Electric System. September 1999. (PDF 704 KB).
Download Acrobat Reader.

Florida Solar Energy Center — Simplified sizing procedures for solar domestic hot water systems.

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Washington, DC 20585
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