Study effect of flow rate on flat-plate water-based photovoltaic-thermal (PVT) system performance by analytical technique

Abstract

This paper assesses the effects of mass flow rate on the performance of a commercial Photovoltaic thermal (PVT) system in the dynamic tropical environment of Ghana. A water-based flat plate PVT and a conventional photovoltaic (PV) were installed side-by-side on a roof top in Kumasi, Ghana. The electrical, thermal and exergy performances of the PVT were studied for mass flow rates from 0.025 kg/s and 0.083 kg/s. For a specific solar irradiance, no significant change on module temperature occurs when flow rate is increased above 0.082 kg/s. The PVT exhibited a steady exergy efficiency of approximately 12.75% at manufacture's recommended mass flow rate of 0.033 kg/s irrespective of the irradiance. This was however lower than the exergy efficiency of the PV (13.0–12.75% for irradiance of 710–790 W/m2) for irradiances below 790 W/m2 and vice versa. Also, although the PVT's energy-saving efficiency is generally above 50%, its thermal efficiency of 38.8–43.1% was below average compared to experimental (non-commercial) PVT systems. This could be attributed to poor thermal contact between the PV layer and the thermal absorber in the studied PVT module. In addition, from our experimental data, an expression between PVT module temperature and water-flow rate was derived and presented.