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Published June 25, 2008 09:22 AM

Utility-Scale Solar Thermal Growing Fast

Concentrating solar power (CSP) plants produce electricity at a utility scale by using mirrors or lenses to concentrate sunlight. New technology has made CSP the fastest growing utility-scale, renewable energy source in the U.S. after wind power, with utility companies such as California’s Pacific Gas and Electric and Arizona Public Service planning to add over 4,000 megawatts (MW) of new CSP over the next ten years.

Although the power of concentrated sunlight has been recognized since ancient times, modern-era, utility-scale CSP sprang from the sands of California’s Mojave Desert in the late 1980s when Israel’s Luz Industries (now Luz II) built nine CSP plants that, combined, still generate 354 MW. The CSP industry in the U.S. has been virtually dormant since then, but it is now seeing a resurgence thanks to an increase in demand for clean energy and a decrease in costs.

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In 2001, the price of CSP-produced electricity averaged 35 cents per kilowatt-hour (kWh). According to John O’Donnell, executive vice president of the solar technology developer Ausra, two CSP giants have recently demonstrated dramatically reduced prices: Acciona’s brand-new Nevada Solar One plant (see EBN Vol. 16, No. 8) is producing electricity at 17 cents/kWh. Abengoa Solar, a Spanish company, has produced CSP electricity for as low as 14 cents/kWh (APS chose this company to build Solana, a 280-MW plant outside of Phoenix). While new gas-fired plants produce electricity at about 11 cents/kWh—a rate that is expected to increase with rising fuel costs—the U.S. Department of Energy expects the cost of CSP to drop below 8 cents/kWh in the next few years and potentially below 5 cents/kWh by 2015.

There are several common CSP technologies. Parabolic-trough systems use curved mirrors to focus sunlight on a fluid-filled pipe at their centers. Dish-engine systems use large, mirrored dishes to transfer heat to a fluid-filled engine. Power-tower systems use a field of mirrors to concentrate sunlight onto a fluid-filled receiver located in a taller, central tower. And a newer system from Ausra, the compact linear Fresnel reflector, uses standard, flat glass mirrors that tilt towards the sun to focus the sunlight on a water-filled pipe that runs just above the collectors. The heated fluid in these systems expands to spin a turbine, or produces steam, to produce electricity.

All of these systems can store energy as heat, which is much less expensive than storing energy as electricity. So while CSP providers are gearing up to compete with nonrenewable energy sources in cost, the dispatchability of the CSP technology—the ability of a power plant to cost-effectively come online when power is needed—gives it an advantage over other renewable energy sources, such as wind power, which can store electricity but not heat. CSP’s dispatchability is a primary reason why, in a peer-reviewed study performed by Ausra, researchers determined that CSP plants occupying a combined area of less than 10,000 square miles (26,000 km2) could supply all the electric power needs of the U.S.

But it’s not all downhill from here. “New transmission lines will have to be added,” says Charles Ricker, senior vice president of business development for BrightSource, Luz’s U.S. partner, explaining how the industry would move all of that CSP-produced electricity from the “superior” solar areas, such as Nevada and Arizona, to the rest of the country. “That's really the most limiting factor for how fast these [CSP plants] can be built,” he noted. Another key factor in the industry’s development is the 30% federal investment tax credit for solar power, which the industry has petitioned to see extended through 2016, but which are currently in question.

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