Effect of glass cover and working fluid on the performance of photovoltaic thermal (PVT) system: An experimental study

In this paper, an experimental study of glass cover and working fluid effects on photovoltaic thermal (PVT) system performance is presented. Two similar photovoltaic thermal systems, one with glass cover and one without, are designed and fabricated to perform the experiments. The considered working fluids consist of water, ethylene glycol (EG)/water mixture (50 wt%) and pure ethylene glycol. Outdoor experiments are achieved on selected days in August at the Ferdowsi University of Mashhad, Mashhad, Iran. Energy and exergy analyses are carried out to evaluate electrical and thermal efficiencies of the PVT system. Furthermore, the results for a mixture of EG/water are compared to those using pure deionized water. It is observed that using EG/water mixture (50 wt%) as working fluid not only has a lower freezing point compared to pure ethylene glycol but also has higher overall energy and exergy efficiency compared to those of pure ethylene glycol. Therefore, the EG/water mixture (50 wt%) is recommended as a suitable working fluid for cold climate conditions. The extensive results also show that since the electrical efficiency of the unglazed PVT system is higher than that of the glazed PVT, when electrical energy is the main interest, the unglazed PVT is preferred. However, if a higher overall energy efficiency is required, the glazed PVT system is recommended.