Designing an absorber for solar photovoltaic thermal systems: a heat pipe approach and comparative evaluation

Abstract

Renewable energy power generation is extensively promoting for the global objective of mitigating greenhouse gas emissions. Solar energy leads all renewables due to its ubiquitous nature which can be harvested by solar thermal and solar photovoltaic devices. Solar PV is used widely because of its flexibility in working with both direct and diffuse radiation. However, PV systems experience efficiency loss for every degree rise of solar cell temperature above room temperature. Solar photovoltaic-thermal (PVT) collectors are proposed for co-generation of electrical and thermal energy by utilizing excess heat generated in the PV layer. The low heat transfer rate, energy-intensive nature, and freezing of working fluid in colder regions are some problems that persist in water- and air-based PV/Ts, leading us to consider alternatives. Thus, the present study addresses the current opportunities by utilizing heat pipes as PV/T absorbers. Heat pipe PVT is a passive system which operates in phase transition facilitating a tremendous amount of heat transfer enhancement. To enhance the efficiency of PV/T systems, the integration of advanced technologies, like heat pipe thermal absorbers, becomes imperative. Incorporating cutting-edge solutions, such as heat pipe thermal absorbers, is essential to optimize the performance of PV/T systems. Hence, the current study provides insight into heat pipe design through a case study on the application of heat pipes as thermal absorbers for photovoltaic systems. The existing absorbers with fluid flow configurations like Raster, Spiral or Rectangular spiral, etc. used in PV/T are considered as reference. Copper as tube material and water as working fluid are found to be compatible with each other for the proposed heat pipe. The maximum heat input of 0.55kW is computed by the inadequacy of the mentioned existing PVTs to extract the maximum available heat from the PV surface. Additionally, an analytical approach used to define the optimum size of the system and calculation of minimum requirement of tubes. The optimized design of copper heat pipes was found to be ½ inch in diameter and at least ten heat pipes were required to transfer a computed heat flux of 466kW/m 2 per pipe to outperform the existing PV/Ts.