Parabolic trough systems are the most commonly used CSP technology. A parabolic trough consists of a linear parabolic mirror that reflects and concentrates the received solar energy onto a tube (receiver) positioned along the focal line. The heat transfer fluid is pumped through the receiver tube and picks up the heat transferred through the receiver tube walls. The parabolic mirror follows the sun by tracking along a single axis. Linear Fresnel reflectors use various thin mirror strips to concentrate sunlight onto tubes containing heat transfer fluid. Higher concentration can be obtained, and the mirrors are cheaper than parabolic mirrors, but a more complex tracking mechanism is needed.