POWER TOWER

Power towers use 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 working fluid for conversion to electrical energy in a heat engine, or in some instances, stored for nighttime usage, in order to provide a more continuous output.Parabolic troughsParabolic troughA long row of parabolic mirrors concentrates sunlight on a tube filled with a heat transfer fluid (usually oil). As with the power tower, this heated oil is used to power a conventional steam turbine, or stored for nighttime use. The largest operating solar power plant, as of 2007, is one of the SEGS parabolic trough systems in the Mojave Desert in California, USA (see Solar power plants in the Mojave Desert).Concentrating collector with steam engineSolar energy converted to heat in a concentrating collector can be used to boil water into steam (as is done in nuclear and coal power plants) to drive a steam engine or steam turbine. The concentrating collector can be a trough collector, parabolic collector, or power tower.
A parabolic solar collector concentrating the sun's rays on the heating element of a Stirling engine. The entire unit acts as a solar tracker.Solar energy converted to heat in a concentrating (dish or trough parabolic) collector can be used to drive a Stirling engine, a type of heat engine which uses a sealed working gas (i.e. a closed cycle) and does not require a water supply.Until recently, a solar Stirling system held the record for converting solar energy into electricity (30% at 1,000 watts per square meter). Such concentrating systems produce little or no power in overcast conditions and incorporate a solar tracker to point the device directly at the sun. That record has been broken by a so-called concentrator solar cell produced by Boeing-Spectrolab which claims a conversion efficiency of 40.7 percent.