Concentrating Solar Power (CSP), or Solar Thermal Power (STP), is a technology to convert solar radiation into electricity. Beam radiation from a clear sky is concentrated with highly reflective mirrors onto a focal spot (tower, dish) or focal line (trough, linear-Fresnel). At least the mirrors are required to be tracked with the movement of the sun over the sky.
The highest optical efficiency is reached, when also the receiver moves with the reflectors, staying on the optical axis, and thus reducing losses of astigmatism, shading/blocking, and focal distance. The concentration of the sunlight leads to temperatures of 200-600°C for linear concentrators with concentration factors of typically 10-100, and to temperatures of up to well above 1000°C for the point focusing concentrators with their concentration factors of 100-10 000. A heat transfer fluid transports the thermal energy from the absorber to the thermal engine, in most cases a steam turbine. Other concepts work with gas turbines, Stirling engines, organic Rankine cycles, or thermal use for water desalination or absorption cooling, or combinations thereof.
Typical applications are large scale, due to the advantages in cost effectiveness of large thermal power blocks (steam power plants, combined-cycle power plants). Thermal applications, or combined heat, power, and cooling applications make use of concentrating solar collectors, in particular trough or linear-Fresnel systems.
Since their market introduction in California in 1986 the CSP technology variants have been re-introduced into public awareness by a small group of very engaged pioneers in the first decade of the 21st century. Outcome of their work has been until now technological results, demonstrators and pilot plants in particular in Spain and USA, feed-in tariffs in a growing number of countries, European policy towards renewable electricity and r&d efforts, and in particular a significant number of new solar thermal power plants in Spain and Nevada, spreading out from these spots into neighboring countries.Very advantageous conditions for the technology can be found in the Mediterranean (Southern Europe and North Africa), Arab Countries, South Africa, South-West of USA, and Australia. A number of companies are involved in the related economic activities. Many of them have been active over more than 10 years and are now applying their long-term experience and technological networks. Others are new-comers, joining the promising activities in the field of CSP.