Question

For what is a parabolic trough used?

Answer 1

http://en.wikipedia.org/wiki/Parabolic_trough
A parabolic trough is a type of solar thermal energy collector. It is constructed as a long parabolic mirror (usually coated silver or polished aluminum) with a Dewar tube running its length at the focal point. Sunlight is reflected by the mirror and concentrated on the Dewar tube. A vacuum flask (also known as a Dewar flask, Dewar bottle or Thermos) is an insulating storage vessel which keeps its contents hotter or cooler than its surroundings.