Development of a new vacuum-based photovoltaic/thermal collector, and its thermal and exergy analyses

Photovoltaic-thermal (PV/T) solar collectors convert solar radiation into electrical power and heat. Part of received solar energy can be lost to the atmosphere from the top surface of the PV/T module, especially in windy regions. Thus, in this study, a new vacuum-based photovoltaic thermal (VPV/T) collector is designed and comparatively analyzed with the conventional PV/T collector. The new design differs from the conventional PV/T design by including a vacuum layer above the silicon wafer. Besides, to enhance the heat dissipation from the silicon wafer in the VPV/T design to the thermal absorber, the thicknesses of ethylene-vinyl acetate and tedlar polyester tedlar layers underneath the silicon wafer are decreased. A comprehensive 3D conjugate thermal model is developed and validated. The comparison is conducted under steady and transient conditions. The effects of Reynolds number (Re), wind speed, glass emissivity, and vacuum pressure are investigated. And finally, exergy analysis results for both designs are compared. The results showed that the new VPV/T collector has accomplished a 26.6% increase in the thermal power without changing the electrical power gain at Re of 50 and solar irradiance of 1000 W m(-2). In addition, the vacuum pressure degradation from 0.01 Pa to 10 Pa slightly decreases the gained thermal power of the new VPV/T collector. A further increase in the vacuum pressure from 10 Pa to 1.013 x 10(5) Pa significantly decreases the gained thermal power with a slight increase in the electrical power. Furthermore, the total predicted VPV/T and the conventional PV/T exergy efficiency are 39.6% and 32%, respectively.