In the present study, a review is conducted on the state-of-the-art research on the potential of nano-fluids in parabolic trough collectors (PTCs) in solar thermal systems. PTCs are one of the most used collectors in applications such as desalination, drying processes, heating and cooling loops, and power generation plant. Despite the plausible thermal performance of the PTCs the thermal efficiency of such systems is low. Hence, much effort has been performed to promote the energy and exergy efficiency of PTCs. PTCs typically work with working fluid and usually to get the better performance nano-fluids are used. Various parameters affect on the efficiency of PTCs. Beside the fluid flow rate, other parameters including volume fraction, type of the base fluid, type of the nanomaterial, size, and morphology affected on the performance of the system. Hence, in the present work, an attempt has been made to deep review of the latest studies conducted on the effect of the mentioned parameters of nano-fluid on the thermal performance of PTCs. Moreover the effect of using PCM and nano-PCM on the thermal performance of the solar systems were reviewed.
