Solar-thermal power plant putting the desert to use

The sun over Nevada is supplying environmentally friendly electricity, thanks to a solar-thermal power plant that recently went online in the desert there. The facility with an area of one square kilometer focuses sunlight for heating water, with the resulting steam used to drive a 64-megawatt turbine built by Siemens. The power plant currently supplies around 14,000 households with electricity. Similar new power plants are now set to be built worldwide, according to the magazine Pictures of the Future.

Owned and operated by the Spanish energy company Acciona Solar Power, the Nevada Solar One plant contains parabolic mirrors with a total length of 76 kilometers. These mirrors focus and direct solar rays onto a receiving tube containing a special thermal oil that heats the concentrated solar energy to a temperature of approximately 400 degrees Celsius. After this, a heat exchanger uses this energy to heat water, and the resulting vapor is then used to drive the turbine. With its installed capacity of 64 megawatts, the facility can generate around 134 million kilowatt hours of power each year, while at the same time saving about 80,000 tons of carbon dioxide emissions in terms of the global energy mix.

The steam turbine from Siemens Power Generation (PG) had to meet very specialized requirements for use at the solar facility. For one thing, a solar-thermal power plant depends on the sun, and it’s run up and shut down daily when the sun rises and sets. This is why the turbine has two turbine sections — a high-pressure section and a low-pressure section, which also makes more flexible turbine operation possible. Siemens’ success has made it the world market leader in this area, and plans already call for two new solar-thermal facilities to be built in Andalusia in Spain in 2008 and 2009. In the meantime, the further development of solar-thermal technology continues at a fast pace, as the German Aerospace Center is currently developing and testing a direct steam process, and there are now plans to build and put into operation a test solar-thermal facility that uses water instead of oil as a heating medium. Using water rather than oil eliminates the need for the heat exchanger and the toxic thermal oil.