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Solar FAQs — Concentrating Solar Power — Applications

Q: Since the sun doesn't shine 24 hours a day, can we count on solar energy to supply power when we need it?

A: Concentrating solar power (CSP) technologies can include cost-effective thermal storage techniques. These allow a CSP system to set aside the heat energy that accumulates during the day for later conversion to electric power. CSP plants can also be part of a hybrid power system, in which one part runs on fossil fuels. Both options enable CSP plants to generate electricity even when the sun isn't shining — for example, at night or during cloudy weather.

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Q: Since concentrating solar power plants are reliable, why haven't more been built in the last few years?

A: One reason is the relatively low cost of fossil energy in most areas of the United States. The majority of today's power plants run on inexpensive coal. And the current utility environment generally favors new natural gas power plants, which have comparatively low initial costs (first costs). With fossil fuel plants, however, customers (ratepayers) must bear the risk of higher fuel costs in the future.

In contrast, the fuel needed to run a concentrating solar power (CSP) plant is sunlight, which is free. A CSP plant uses its field of mirrors to deliver the thermal energy that's provided by the fossil fuels burned in a conventional (e.g., gas- or coal-powered) plant. So, investing in a CSP plant is the equivalent of buying a lifetime supply of fuel. But the first costs associated with CSP plants can be high. To guarantee that they'll recover their first costs, most CSP plant operators would probably want to have some long-term power purchase agreements lined up, to minimize the financial risk.

Other factors could also play a role in delayed investment in CSP. These include the perceived risks associated with new technologies and a need for tax equity with conventional technologies. Financial and regulatory incentives, advances in CSP technologies, and cost reductions resulting from economies of scale are just some of the things that could help to increase investments in CSP.

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Q: Since Solar Two is no longer operating, are solar power tower plants considered failures?

A: Some of the following documents are available as Adobe Acrobat PDFs. Download Acrobat Reader.

No. Solar Two was an adaptation of the Solar One experiment of the 1980s. The goal was to validate solar power generation using molten salt for thermal energy transport and storage and to show that the technology is viable for dispatchable power. The Solar Two project successfully met all its objectives. And some key U.S. industry participants in the project have begun a commercial solar power tower project in Spain. They are actively seeking U.S. customers for domestic plants.

Other Resources: For general information about CSP, please see the U.S. Department of Energy's Sunlab Web site

For more information about power tower systems, see the following documents:
Technology Characterization: Solar Power Towers (PDF 303KB)

Solar Two Demonstrates Clean Power for the Future (PDF 557KB)

Q: Do concentrating solar power (CSP) plants require a lot of land? How much, exactly?

A: Relatively speaking, no. Consider Hoover Dam, for example. Nevada's Lake Mead, which is home to the dam, covers nearly 250 square miles. In contrast, a CSP system occupying only 10 to 20 square miles could generate as much power annually as Hoover Dam did in one recent year. And if we take into consideration the amount of land required for mining, CSP plants also require less land than coal-fired power plants do.

It's hard to say exactly how much land is required for a CSP plant, however, because this depends on its generating capacity and the particular technology used. For example, a 250-kilowatt plant composed of ten 25-kilowatt dish/engine systems requires less than an acre of land. And a parabolic trough system uses about 5 acres for each megawatt of installed capacity. But in any case, the solar resource needed to generate power using CSP systems is quite plentiful. Imagine being able to generate enough electric power for the entire country by covering about 9 percent of Nevada — a plot of land 100 miles on a side — with parabolic trough systems!

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Q: Where are the best places to build a concentrating solar plant?

A: In the United States, the Southwest is ideal for concentrating solar power plants. The National Renewable Energy Laboratory has developed highly accurate maps of solar resources for the United States and many other regions; these resource maps allow us to assess potential sites with great accuracy.

Other Resources: 

U.S. Department of Energy
1000 Independence Avenue, SW
Washington, DC 20585
www.eere.energy.gov www.energy.gov