Thermal Solar Power Gets Hot

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An alternative to the parabolic trough is the "power tower" design, in which a field of mirrors focuses sunlight on a central tower containing a heat transfer medium used to produce steam. This design is able to achieve much higher temperatures than the parabolic trough, though the latter converts thermal energy to electricity more efficiently, and storage is less expensive. The first commercial power tower, a 10Mw facility near Seville, Spain, was built by Abengoa and began operating in 2007.

In the U.S., BrightSource Energy, whose backers include Google (GOOG), BP (BP), Chevron (CHV), Statoil Hydro (STO), and Morgan Stanley (MS), signed a series of agreements to sell the output of a set of power towers it plans to build in the Mojave Desert. The first unit will have 100Mw of capacity and is expected to start operating in 2011. Pasadena (Calif.)-based eSolar, which also counts Google as an investor, signed an agreement in June 2008 to sell power from a 248Mw tower system it will build in southern California.

Bouncing Off a Dish

A third design type is known as the dish system. Dish generators, which look like large satellite TV dishes, concentrate the sun's rays on a focal point in front of the dish in the same way that a satellite dish reflects a TV signal to a receiver. Mounted at the focal point is either a Stirling Engine, which converts heat to mechanical energy, which then turns a turbine, or, less often, a photovoltaic panel. Stirling Engine Systems, a Phoenix outfit majority owned by Irish renewable energy developer NTR, has signed agreements to sell power from two sites in southern California with a combined capacity of 800Mw.

Other companies involved in concentrated solar power include Xcel Energy (XEL) in Minneapolis, which is seeking to build a concentrated solar plant in such states as Colorado, where state law requires the company to have 100Mw of solar generating capacity by 2020. HS Rocketdyne, a subsidiary of United Technologies (UTX), makes a molten-salt system that's used for thermal storage in concentrated solar plants.

In November 2007, the U.S. Energy Dept. announced grants worth $7.2 million to develop concentrating solar technology. Winners of grants included Pittsburgh's PPG Industries (PPG) to develop low-cost, high-performance mirrors; Alcoa (AA) to develop an aluminum reflector and supporting structure; United Technologies' Hamilton Sundstrand unit to develop molten-salt storage for power tower designs; and 3M (MMM) to develop a surface coating for parabolic troughs. In April 2008, the Energy Dept. announced another $60 million in funding available for concentrated solar projects.

Scully is a reporter for Standard & Poor's Editorial Operations .