A parabolic trough is a type of solar thermal collector that is straight in one dimension and curved as a parabola in the other two, lined with a polished metal mirror. The sunlight which enters the mirror parallel to its plane of symmetry is focused along the focal line, where objects are positioned that are intended to be heated. In a solar cooker, for example, food is placed at the focal line of a trough, which is cooked when the trough is aimed so the Sun is in its plane of symmetry.
Parabolic trough at a plant near Harper Lake, California
Inside an enclosed trough system
Andasol Solar Power Station in Spain.
A 1917 patent drawing for Shuman's parabolic trough solar energy system
A solar thermal collector collects heat by absorbing sunlight. The term "solar collector" commonly refers to a device for solar hot water heating, but may refer to large power generating installations such as solar parabolic troughs and solar towers or non water heating devices such as solar cooker, solar air heaters.
Water heating system deployed on a flat roof. The pipes that carry the heat away can be seen embedded in the absorber, a flat plate painted black. In this example the heat is stored in the tank above the panels.
Evacuated tube collector
An array of evacuated tube collectors on a roof
An array of evacuated flat plate collectors next to compact solar concentrators
