The 11MW PS10 near Seville in Spain.

The solar power tower (also known as 'Central Tower' power plants or 'Heliostat' power plants or power towers) is a type of solar furnace using a tower to receive the focused sunlight. It uses an array of flat, movable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target). The high energy at this point of concentrated sunlight is transferred to a substance that can store the heat for later use. The most recent heat transfer material that has been successfully demonstrated is liquid sodium. Sodium is a metal with a high heat capacity, allowing that energy to be stored and drawn off throughout the evening. That energy can, in turn, be used to boil water for use in steam turbines. Water had originally been used as a heat transfer medium in earlier power tower versions (where the resultant steam was used to power a turbine). This system did not allow for power generation when the sun is not shining.

Examples of Heliostat Power Plants

The 11 megawatt PS10 solar power tower produces electricity from the sun using 624 large movable mirrors called heliostats.

Europe's first commercial concentrating PS10 solar power tower is operating near the sunny southern Spanish city of Seville. The 11 megawatt solar power tower produces electricity with 624 large movable mirrors called heliostats.^[1] The mirrors were delivered by Abengoa, the solar receiver was designed and built by Tecnical-Tecnicas Reunidas, a Spanish Engineering Company; and the Solar Tower was designed and built by ALTAC ^[2], another Spanish Engineering and Construction Company.

Each of the mirrors has a surface measuring 120 square meters (1,292 square feet) that concentrates the Sun's rays to the top of a 115 meter (377 foot) high, 35-story tower where a solar receiver and a steam turbine are located. The turbine drives a generator, producing electricity.^[1] This power is three times more expensive than power from conventional sources, but prices are likely to fall, as they have with wind power, as the technologies develop. ^[3]

PS10 is the first of a set of solar power generation plants to be constructed in the same area that will total more than 300 MW by 2013. Power generation will be accomplished using a variety of technologies. The first two power plants to be brought into operation at Sanlucar la Mayor are the PS10, and Sevilla PV, the largest low concentration system photovoltaic plant in Europe.^[1]

The 10 MWe Solar One and Solar Two heliostat demonstration projects in the Mojave Desert have now been decommissioned. The 15 MW Solar Tres Power Tower in Spain builds on these projects. In Spain the 11 MW PS10 solar power tower was recently completed. In South Africa, a solar power plant is planned with 4000 to 5000 heliostat mirrors, each having an area of 140 m². A site near Upington has been selected.^[1][2]

BrightSource Energy entered into a series of power purchase agreements with Pacific Gas and Electric Company in March 2008 for up to 900MW of electricity, the largest solar power commitment ever made by a utility.^[3] BrightSource is currently developing a number of solar power plants in Southern California, with construction of the first plant planned to start in 2009.

In June 2008, BrightSource Energy dedicated its Solar Energy Development Center (SEDC) in Israel's Negev Desert. The site, located in the Rotem Industrial Park, features more than 1,600 heliostats that track the sun and reflect light onto a 60 meter-high tower. The concentrated energy is then used to heat a boiler atop the tower to 550 degrees Celsius, generating steam that is piped into a turbine, where electricity can be produced.^[4]

Cost

The decommissioned Solar Two near Barstow, CA

The US National Renewable Energy Laboratory NREL has estimated that by 2020 electricity could be produced from power towers for 5.47 ₡/kWh.^[5] Google.org hopes to develop cheap, low maintenance, mass produceable heliostat components to reduce this cost in the near future. ^[6]

See also

• List of solar thermal power stations
• Solar furnace
• Solar thermal energy

References

1. ^ 100 MW Solar Thermal Electric Project in South Africa
2. ^ http://www.sabregen.co.za Eskom Website
3. ^ BrightSource Energy signs whopper solar contract with PG&E. CNET News (2008-03-31). Retrieved on 2008-06-11.
4. ^ BrightSource / Luz II Dedicate Negev Solar Energy Development Center. Cleantech Investing in Israel (2008-06-12). Retrieved on 2008-06-12.
5. ^ Assessment of Parabolic Trough and Power Tower Solar Technology Cost and Performance Forecasts
6. ^ Google's Goal: Renewable Energy Cheaper than Coal November 27, 2007

External links

• National Solar Thermal Test Facility
• Detailed Description of Central Receiver Systems
• Power Station Harnesses Sun's Rays BBC article about solar plant near Seville in Spain
• Description of first commercial Solar Power Tower
• http://pointfocus.com/

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