May 1, 2009 Made up of more than 1200 mirrored heliostats surrounding a huge 54 story high tower, the world's largest solar power tower plant is now on line near Seville in Spain. Developed by Spanish engineering company Abengoa, the PS20 plant generates 20 megawatts (MW) of electricity, enough to supply 10,000 homes. Concentrating solar thermal technology has been used in desert areas in Spain and the southwest U.S. for decades and is seeing a resurgence as utilities seek to reduce reliance on fossil fuels.

A solar thermal plant generates electricity in much the same way a conventional coal fired or nuclear power plant does, only the heat source is different. In fact up to 80% of the world's electricity is generated using the Rankine cycle to heat water into high pressure steam that drives a turbine, which in turn connects to an electrical generator. In a tower concentrator system the heat is provided by a field of heliostats, or mirrors, that focus sunlight onto a receiver held near the top of a tower.

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At the PS20 plant each heliostat is 1291 ft2 (120 m 2), which gives the entire heliostat field a massive area of 155,000 m 2. Each heliostat tracks the sun throughout the day on two axes and concentrates the radiation onto a receiver located on the upper part of the 531 ft (162 m) tower. The receiver converts 92% of received sunlight into steam which is piped down to a turbine driven generator at the base of the tower.

The same site also has the world's second largest and first commercial power tower plant (PS20 is the second), PS10 which has been operational since 2007. PS10 features 624 mirrors pointed at a 377 ft (115 m) tower and generates 10 MW. The structures are part of an envisioned complex slated to produce 300 megawatts by 2013. When complete, the Solucar solar thermal power station will cover 800 hectares and deliver electricity to 240,000 homes. The PS20 plant brings Spain’s total solar capacity up to 3,000 MWs, making it a close second to the world’s leading solar producer Germany (with a capacity of close to 4,000 megawatts). Spain is the third largest producer of Wind Power in the world, behind the US and Germany, with 16,740 megawatts wind capacity installed at the end of 2008.

Paul Evans

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