Concentrating solar thermal systems use optical devices (usually mirrors) and sun-tracking systems to concentrate a large area of sunlight onto a smaller receiving area. The concentrated solar energy is then used as a heat source for a conventional power plant. A wide range of concentrating technologies exists, the main ones being parabolic troughs, solar dishes, linear Fresnel reflectors, and solar power towers. The primary purpose of concentrating solar energy is to produce high temperatures and therefore high thermodynamic efficiencies.