Solar power converts the sun's energy into a pollution-free source of heat, light and electricity. Thanks to technological leaps in solar panels, solar power has become dramatically less expensive in the last few decades, and is now spreading through the residential suburbs and into businesses, industry and power plants. Thanks to the fact that satellites use solar panels, we already rely on solar power for many of the gadgets we use on a daily basis, from cell phones, pagers, and GPS systems to ATM machines, solar highway signs, microwave transmissions and DirecTV©.

How It Works

The sun's energy can be captured to generate electricity or heat through a system of panels or mirrors.

• Solar, or photovoltaic, cells convert sunlight directly into electricity. Most photovoltaic cells are made primarily of silicon, the material used in computer semiconductor chips, and arranged on rectangular panels. When sunlight hits a cell, the energy knocks electrons free of their atoms, allowing them to flow through the material. The resulting DC (direct current) electricity is then sent to a power inverter for conversion to AC (alternating current).
• Solar thermal collectors use heat-absorbing panels and a series of attached circulation tubes to heat water or buildings.
• Solar concentration systems use mirrors -- usually arranged in a series of long, parabolic troughs, a large round dish, or a circle surrounding a "power tower" -- to focus the sun's reflected rays on a heat-collecting element. The concentrated sunlight heats water or a heat-transferring fluid such as molten salt to generate steam, which is then used conventionally to spin turbines and generate electricity.
• Passive solar design is the creative use of windows, skylights and sunrooms, building site and orientation, and thermal construction materials to heat and light buildings, or to heat water, the natural way.

Where It's Used

Commercial concentrating solar power plants have proven particularly effective in the American Southwest, but solar power can be used wherever the sun shines. Homeowners, farms and businesses across the country are turning to solar to reduce their electric bills and/or heat their water using a solar thermal collector. Many farms and businesses, with their open acreage and/or large buildings, can install enough solar to pay their entire electric bill -- even in northern states.

At the Oak Grove organic farm in Hunterdon County, New Jersey, Ted and Susan Blew grow hundreds of varieties of specialty hot peppers and other vegetables, several grains, and hog-based pork products for restaurants and other buyers in the New York area. Their solar panels take up one corner of a former horse pasture, with cut flowers planted between them to make the land even more profitable. When the panels were first installed, the farm's monthly electric bill plunged instantly from $1,500 to just over $2, and the Blews had a surplus of more than 500 kilowatts going into their first winter with the system.

In Canton, Minnesota, Philip and Mary Rutter built a solar-powered greenhouse without ever connecting it to the grid, as that would have required them to clear trees, dedicate land and lose productive potential. Instead, they spent $5,600 to create a structure that is partially subterranean, superinsulated with south-facing windows and fully powered -- including lights, fans, water pump and retractable insulating shutters -- by six photovoltaic panels and a small wind turbine. The Rutters expect the energy savings to recoup their costs in ten years, and in the meantime they realize tax benefits by financing the energy system within their mortgage and depreciating it as business equipment.

In southern California's Mojave National Preserve, a 10.88-kilowatt photovoltaic hybrid system provides power for the Hole-in-the-Wall Fire Station -- a site load of 50 kilowatt-hours per day, including the garage and a 16-person dormitory. The flexible, amorphous-silicon roofing laminates are backed up by an inverter, an industrial flooded battery bank, and an on-demand propane generator. The system can be remotely monitored and controlled by the manufacturer, SunWize, if problems arise.

In a significant development at the community level, St. George, Utah, in the state's southwestern corner, is building Utah's first utility-scale solar installation, with an innovative financing scheme: every St. George resident will be invited to buy a share in the St. George Solar Farm, and the purchase will qualify for the same solar tax credit that homeowners receive. Serving several hundred homes at first, the system will be expandable if demand justifies a larger capacity. Shares went on sale in late 2008, and construction is under way.

How Much It Costs

The cost of solar energy has fallen sharply over the last 20 years. Still, electricity from a concentrated solar power plant can cost about 10 to 14 cents per kilowatt-hour, compared with about 4 cents per kilowatt-hour from a coal or natural gas power plant. Electricity from small or medium-scale solar photovoltaic arrays (installed on homes or businesses) costs around 25 to 40 cents per kilowatt-hour, but these prices should continue to drop thanks to falling installation costs and the growing number of incentives and tax packages offered by nearly every state government

Photovoltaic Technology Characteristics
Performance
Typical Duty Cycle	Peaking-Intermediate
Net Plant Capacity (MW)	20
Integrated Storage	None
Capacity Factor (%)*	25-30
Economics (2008$)
Total Project Cost ($/kWe)**	$6,500-7,500
Variable O&M, Typical Duty Cycle Peaking ($/MWh)	n/a
Fixed O&M ($/kW)	$35
Levelized Cost of Energy (¢/kWh)	20.1-27.6 cents
Applicable Incentives	30% federal ITC; five-year MACRS***
* Depends on location ** Costs are in 2008 dollars, based on kWe AC rating. *** The Modified Accelerated Cost Recovery System (MACRS) is the current method of accelerated asset depreciation required by the U.S. income tax code. Source: Black and Veatch, Renewable Energy Transmission Initiative, Phase 1A, table 5-7

Advantages

• Sunlight is free and infinitely renewable.
• Unlike conventional fossil fuel and nuclear power, solar power produces no polluting emissions, including those that cause global warming.
• With no moving parts, solar panels are silent, easy to operate and rarely need maintenance.
• Solar power can slash utility bills for both residential and commercial consumers. By installing solar panels on its enormous roof, Hawaii's Mauna Lani Bay Hotel began saving enough on energy bills to pay for the investment in just five years.
• Solar photovoltaics can help utilities avoid brownouts and blackouts. When demand for electricity is high, utilities can use solar panels to generate extra energy rather than fire up expensive and polluting "peak" power plants that otherwise lie dormant.
• Several solar-photovoltaic manufacturers are based here in the United States, employing about 20,000 people in high-earning, high-tech jobs. This domestic industry helps reduce our dependence on foreign oil, coal and natural gas.

What's around the Corner

• One million solar energy systems will be installed on roofs across the United States by 2010; the Department of Energy's Million Solar Roofs program kicked off in 1998 and is already ahead of schedule. These systems could eliminate carbon dioxide emissions equal to those of 850,000 cars.
• Concentrating solar-power plants will be built in the Southwest, providing clean electricity for millions of homes and businesses in the region. According to Sandia National Labs, costs are expected to fall to about 5 cents per kilowatt-hour by 2020, a price competitive with those at new coal- or gas-fired power plants.
• Solar photovoltaics will be cheaper and more efficient thanks to cheaper raw materials, improved production methods and easier installation methods. Financial analysts and industry experts expect the cost of electricity from photovoltaics to fall below retail electricity rates in much of the country between 2013 and 2018.

Renewable Energy Meets Wildland and Wildlife Conservation

Certain sensitive lands -- such as parks, monuments and wildlife conservation areas -- and ecologically sensitive marine areas are not appropriate for energy development. In some of these places, energy development is prohibited or limited by law or policy, and in others it would be highly controversial. NRDC does not endorse locating energy facilities or transmission lines in such areas. Siting decisions must always be made extremely carefully, with impacts mitigated and operations conducted in an environmentally responsible manner.

For more information on the intersection between clean energy development and wildland and wildlife conservation in the American West, including locations of parks, wildlife refuges and other conservation areas, see this Google Earth-based feature.