*6.2.2. Parabolic trough collectors*

PTCs have a parabolic shape and are covered by a bending sheet of reflective material. A metal black tube, covered with a glass tube to reduce heat losses, is placed along the focal line of the receiver. Then, parallel ray's incident on the reflective material and are reflected onto the receiver where a HTF absorbs the solar power [48]. Each collector is connected together in long lines, and a system tracks the Sun´s path throughout the day along a single axis, usually east to west [49]. These technologies have the following advantages: they are feasible commercial options to transform heat, and they are the most advanced of STT because of considerable experience and have several applications [51]. One of their principal disadvantages is the tracking mechanism because it must be reliable and able to follow the Sun with a certain degree of accuracy, returning the collector to its original position at the end of the day, increasing their cost and energy supply [48].
