The effect of Joule heating to thermal performance of hybrid PVT collector during electricity generation

Abstract

The aim of this paper is to discuss the performance of a hybrid photovoltaic and thermal (PVT) collector by focusing on the utilization of Joule heating as additional heat for improving thermal efficiency, when both thermal and electrical energies are generated (PVT-mode), by comparing with when only the thermal energy is generated (T-mode). During the maximum power point and the peak irradiation, the temperature differential in PV material was increased due to the rise in current flow. The Joule heating or internal heating also increased proportional to the square of electric current. The conducted heat also increases through the PV surface to the thermal absorber in the PVT collector. For that reason, the experiment was performed using higher irradiation with a bigger PVT collector at four different inlet water temperatures, i.e., 12, 15, 20, and 25 °C. The water flow rate was 6.7 × 10−5 m3/s (≈4 L/minute). The irradiation data was collected for an hour from 12:00 to 13:00 to keep a steady-state thermal performance and also to minimize the hysteresis effect. In the present PVT collector's system and configuration, the result showed that even a moderate wind speed below 1 m/s results in a non-negligible loss of the thermal efficiency. The thermal efficiency of PVT collector in PVT-mode is higher than T-mode at the lower range of first order thermal efficiency gradient, when the inlet water temperature is close to the ambient air temperature, or when the total irradiation is high. The behavior of the thermal efficiency of PVT-mode also seems to be appreciably influenced by other factors, such as the internal heating during the operation. During the higher irradiation periods, the Joule heating effect has the potential to improve the thermal efficiency of PVT-mode up to 13%. The internal heating in PV cell apparently affects both the effective absorption and heat loss coefficient. The practical relevance of Joule heating in a real-life PVT system is for low temperature applications, such as swimming pool heating, low temperature source heat pumps, and floor heating.