- Parabolic trough
A parabolic trough is a type of
solar thermal energy collector. It is constructed as a longparabolic mirror (usually coated silver or polished aluminum) with aDewar tube running its length at thefocal point .Sunlight is reflected by the mirror and concentrated on theDewar tube . The trough is usually aligned on a north-south axis, and rotated to track the sun as it moves across the sky each day. Alternatively the trough can be aligned on an east-west axis, this reduces the overall efficiency of the collector but only requires the trough to be aligned with the change inseason s, avoiding the need for tracking motors.Heat transfer fluid (usually oil) runs through the tube to absorb the concentrated sunlight. Theheat transfer fluid is then used to heat steam in a standard turbine generator. The process is economical and, for heating the pipe, thermal efficiency ranges from 60-80%.The overall efficiency from collector to grid, i.e. (Electrical Output Power)/(Total Impinging Solar Power) is about 15%, similar to PV(Photovoltaic Cells) and less than Stirling dish concentrators. [ Patel99 Ch.9 ]Current commercial plants utilizing parabolic troughs are hybrids;
fossil fuel s are used during night hours, but the amount of fossil fuel used is limited to a maximum 27% of electricity production, allowing the plant to qualify as a renewable energy source. Because they are hybrids and include cooling stations, condensers, accumulators and other things besides the actual solar collectors, the power generated per square meter of space ranges enormously.Energy storage
As this renewable source of energy is inconstant by nature, methods for energy storage have been studied, for instance the single-tank (thermocline) storage technology for large-scalesolar thermal power plants. The thermocline tank approach uses a mixture of silica sand andquartzite rock to displace a significant portion of the volume in the tank. Then it is filledwith the heat transfer fluid, typically a molten nitrate salt.
Existing plants
The largest operational solar power system at present is one of the SEGS plants and is located at Kramer Junction in
California , USA, with five fields of 33 MW generation capacity each. [Cite web | title = Kramer Junction SEGS III, IV, V, VI,VII. | publisher =Solel | url = http://www.solel.com/products/pgeneration/ls2/kramerjunction/]The 64 MW
Nevada Solar One also uses this technology. In the new Spanish plant,Andasol 1 solar power station , the 'Eurotrough'-collector is used. This plant is scheduled to go online in summer 2008 [Cite web | title = The Construction of the Andasol Power Plants | publisher = Solar Millennium AG | url = http://www.solarmillennium.de/Technologie/Referenzprojekte/Andasol/Die_Andasol_Kraftwerke_entstehen_,lang2,109,155.html] and has a nominal output of 49.9 MW.Popular Culture
A parabolic trough solar plant appears in the movie
Gattaca .Notes and References
Bibliography
External links
* [http://maps.google.com/maps?f=q&hl=en&q=kramer+junction,+ca&layer=&ie=UTF8&om=1&z=14&ll=35.012986,-117.554998&spn=0.030157,0.086517&t=k&iwloc=addr Kramer Junction Solar Power Plants] - satellite image, Google Map.
* [http://www.renewableenergyaccess.com/rea/news/story?id=48660 Picture Perfect Parabolic Solar Collector Systems]
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