Solar power tower

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 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. [ [http://www.solarpaces.org/News/Projects/South_Africa.htm 100 MW Solar Thermal Electric Project in South Africa] ] [http://www.sabregen.co.za Eskom Website]

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. [citeweb | url=http://news.cnet.com/8301-11128_3-9907089-54.html | title=BrightSource Energy signs whopper solar contract with PG&E | accessdate=2008-06-11 | date=2008-03-31 | publisher= CNET News] 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. [citeweb | url=http://cleantech-israel.blogspot.com/2008/06/brightsource-luz-ii-dedicate-negev.html | title=BrightSource / Luz II Dedicate Negev Solar Energy Development Center | accessdate=2008-06-12 | date=2008-06-12 | publisher= Cleantech Investing in Israel]

Cost

The US National Renewable Energy Laboratory NREL has estimated that by 2020 electricity could be produced from power towers for 5.47 ₡/kWh. [ [http://www.nrel.gov/solar/parabolic_trough.html Assessment of Parabolic Trough and Power Tower Solar Technology Cost and Performance Forecasts] ] Google.org hopes to develop cheap, low maintenance, mass produceable heliostat components to reduce this cost in the near future. [ [http://www.google.com/intl/en/press/pressrel/20071127_green.html Google's Goal: Renewable Energy Cheaper than Coal November 27, 2007] ]

See also

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

References

External links

* [http://www.sandia.gov/Renewable_Energy/solarthermal/nsttf.html National Solar Thermal Test Facility]
* [http://www.powerfromthesun.net/Chapter10/Chapter10new.htm Detailed Description of Central Receiver Systems]
* [http://news.bbc.co.uk/2/hi/science/nature/6616651.stm Power Station Harnesses Sun's Rays] BBC article about solar plant near Seville in Spain
* [http://www.abengoasolar.com/sites/solar/en/nproyectos_ps10.jsp Description of first commercial Solar Power Tower]
* http://pointfocus.com/