Solar Thermal

Solar thermal energy is a technology for harnessing solar power for practical applications from solar heating to electrical power generation. Solar thermal collectors, such as solar hot water panels, are commonly used to generate solar hot water for domestic and light industrial applications. Solar thermal energy is used in architecture and building design to control heating and ventilation in both active solar and passive solar designs. This article is devoted primarily to solar thermal electric power plants; that is, solar power plants that generate electricity by converting solar energy to heat, to drive a thermal power plant. These plants include the Solar Energy Generating Systems, Nevada Solar One, and Solar Tres. The article on photovoltaics reviews solar power generation by means of solar electric panels

Concentrated solar power (CSP) plants
Where temperatures below about 95°C are sufficient, as for space heating, flat-plate collectors of the nonconcentrating type are generally used. The fluid-filled pipes can reach temperatures of 150 to 220 degrees Celsius when the fluid is not circulating.

A concentrating collector intercepts the same amount of solar radiation as a flat-plate collector of the same area, but contains a parabolic reflector that focuses the energy onto the surface of an absorber of much smaller area. This concentration of energy heats the absorber to a much higher temperature than that produced in the flat-plate type. Whilst the amount of energy remains the same, the higher temperature enables the system to generate electrical or mechanical energy more efficiently. This is because the maximum theoretical efficiency of any heat engine increases as the temperature of its heat source increases.

Parabolic trough power plants are the most successful and cost-effective CSP system design at present. They use a curved trough which reflects the direct solar radiation onto a hollow tube running along above the trough. The whole trough tilts through the course of the day so that direct radiation remains focused on the hollow tube for as long as the sun shines. A fluid, normally thermal oil, passes through the tube and becomes hot. Full-scale parabolic trough systems consist of many such troughs laid out in parallel over a large area of land. A solar thermal system using this principle is in operation in California in the United States, called the SEGS system.[1] At 350 MW, it is currently not only the largest operational solar thermal energy system, but the largest solar power system of any kind. SEGS uses oil to take the heat away: the oil then passes through a heat exchanger, creating steam which runs a steam turbine. The 64MW Nevada Solar One plant also uses this design. Other parabolic trough systems, which create steam directly in the tubes, are under development; this concept is thought to lead to cheaper overall designs, but the concept is yet to be commercialized