Solar thermoelectric energy is subdivided into medium temperature and high temperature systems. The most highly developed medium temperature systems at present are plants using parabolic trough collectors. High temperature systems use a central tower installation or solar dish/engine systems.
Parabolic trough collector power plants (medium temperature).
These comprise mirror collectors that reflect sunlight onto a tube in the focal line, which contains a fluid which absorbs and transmits the heat. The fluid is heated to a temperature of up to 400ºC, with solar concentration ratios of between 15 and 50. This produces superheated steam which is fed into a conventional turbine, where it produces electricity. A solar tracking system is needed.
Power tower systems (high temperature).
These consist of a field array of heliostats reflecting sunlight onto a heat exchanger situated at the top of a central tower. Temperatures of up to 600ºC may be reached.
Dish/engine systems (high temperature).
These consist of a set of mirrors which form a parabolic disc focused onto a solar receiver in which a fluid is heated. The fluid is heated to up to 750ºC to generate electricity, currently using a turbine driven by either a Stirling or Brayton cycle engine.