Editing Parabolic trough (section)

{{Short description|Technology used in concentrated solar power stations}}
[[File:Parabolic trough at Harper Lake in California.jpg|thumb|upright=1.3|Parabolic trough at a plant near Harper Lake, California]]

A '''parabolic trough collector''' (PTC) is a type of [[solar thermal collector]] that is straight in one dimension and curved as a [[parabola]] in the other two, lined with a polished metal [[mirror]]. The [[sunlight]] which enters the mirror parallel to its plane of symmetry is focused along the [[Parabola#Proof of the reflective property|focal line]], where objects are positioned that are intended to be heated. In a [[Solar cooker#Parabolic troughs|solar cooker]], for example, food is placed at the focal line of a trough, which is cooked when the trough is aimed so the Sun is in its plane of symmetry.

For other purposes, a tube containing a fluid runs the length of the trough at its focal line. The sunlight is concentrated on the tube and the fluid heated to a high temperature by the energy of the sunlight. The hot fluid can be piped to a [[heat engine]] (e.g. ORC or water/steam Rankine cycle), which uses the heat energy to drive machinery, or to generate electricity. This solar energy collector is the most common and best known type of parabolic trough.

When heat transfer fluid is used to heat steam to drive a standard turbine generator, [[thermal efficiency]] ranges from 50 to 80%. The overall efficiency from collector to grid, i.e. (electrical output power)/(total impinging solar power) is about 15%, similar to [[photovoltaic cell]]s but less than [[Stirling engine|Stirling]] [[Solar thermal energy#Dish designs|dish concentrators]]. Large-scale solar thermal power plants need a method for storing the energy, such as a [[thermocline]] tank, which uses a mixture of silica sand and quartzite rock to displace a significant portion of the volume in the tank. It is then filled with the heat transfer fluid, typically a [[Molten salt|molten nitrate salt]].

As of 2014, the [[List of solar thermal power stations|largest solar thermal power systems]] using parabolic trough technology include the 354&nbsp;MW [[Solar Energy Generating Systems|SEGS]] plants in California, the 280&nbsp;MW [[Solana Generating Station]] with [[molten salt heat storage]], the 250&nbsp;MW [[Genesis Solar Energy Project]], the Spanish 200&nbsp;MW Solaben Solar Power Station, and the [[Andasol Solar Power Station|Andasol 1 solar power station]].<ref name="nrel.gov">NREL.gov [http://www.nrel.gov/csp/solarpaces/by_country_detail.cfm/country=US Concentrating Solar Power Projects in the United States], 17 February 2014</ref><ref name="ReferenceA">NREL-gov [http://www.nrel.gov/csp/solarpaces/by_country_detail.cfm/country=ES Concentrating Solar Power Projects in Spain], 17 February 2014</ref>