Parabolic-trough collectors involve the most mature solar technology to generate
heat at temperatures up to 400
C for solar thermal electricity-generation or process heat applications. The biggest application of this type of system is the Southern
California power plants, known as Solar Electric Generating Systems (SEGS),
which have a total installed capacity of 354 MWe[13]. Other applications of PTC
collectors are reported by Bakos et al.[14] and Kalogirou[15]. Trough reflectors
with a parabolic shape concentrate the direct solar radiation onto an absorber tube
located in the focal line of the parabola. A single-axis tracking system follows the
sun position over the day. The thermal performance of the absorber is enhanced by
a selective coating with a high absorptivity in the solar spectrum and low emissivity
in the infrared radiation band associated with the operating temperature.