solar thermal systems focus sunlight onto a tube or surface
to heat a fluid to high temperature (200 to 500 ºC),
the heat energy stored in the fluid is converted into electricity
using conventional steam turbine or heat engine generators.
Linear concentrators focus sunlight onto linear absorbers
such as tubes using parabolic mirrors or linear Fresnel lenses;
field concentrators focus sunlight onto absorbing surfaces
using dishes or heliostats. One advantage of thermal systems
is that solar energy can be stored as heat for several hours
facilitating the generation of electricity overnight when
sunlight is not available. Concentrator solar thermal systems
also offer a 10:1 energy payback ratio.