The document discusses solar parabolic collectors, specifically cylindrical parabolic trough collectors. These collectors use curved reflectors to concentrate sunlight onto an absorber tube to produce high temperatures. The absorber tube is coated to absorb solar energy and emit little infrared radiation. Parabolic trough technology is currently the most proven solar thermal electric technology, with nine large commercial plants operating since 1984 to produce steam for electricity generation. The document also discusses parabolic dish collectors which focus sunlight onto a small receiver but require dual-axis tracking.