A Review on the R&D of heat pipe integrated photovoltaic/thermal systems

To overcome the possible seasonal freezing problem and thus advance the PV/T technologies and enhance their energy performance, heat pipes were brought into use. Heat pipe is a kind of passive heat transportation device that, making use of evaporation and condensation of the working fluid on different sides, can effectively remove heat away from the PV back surface and transfer it to the working fluid to create a highly efficient, safe and passive way of PV cooling and thus enable an improved overall solar efficiency. Therefore, this paper aims to present a review on the solar PV/T systems utilized heat pipe (HP-PV/Ts), identify the typical features and critical barriers of the existing HP-PV/T technologies, and thus develop the potential solutions for tackling these identified challenges. Firstly, the development of PV/Ts and related integrated systems are concisely introduced. Then the principle, structures, practical applications, and research progress of existing HP/LHP applicable to solar PV/T systems are outlined and analyzed. Finally, the challenges and disadvantages for the existing HP-PV/Ts including (1) high cost, (2) replying on the gravity of the working fluid owing to relatively smaller wick capillary effect; and (3) liquid film ‘dry-out’ occurring in the upper part of the evaporator leading to significantly reduced heat transport capacity are instructed, as well as the future development direction are clarified, which provides a reference for the further research and application of Loop Heat Pipe integrated Photovoltaic/Thermal Systems.