Dynamic thermal model for hybrid photovoltaic panels

Photovoltaic technology is a consolidated solution for electricity production in residential, commercial and industrial facilities. Despite that, the solar-to-electrical energy conversion is still low and many efforts are still needed in order to increase the panel efficiency. Since the photovoltaic modules performance decreases when the cell temperature increases, solutions have been investigated to cool down the panel with a refrigerated thermal plate installed on the PV rear surface. In standard applications, the photovoltaic thermal panel (PV/T) systems can produce both thermal and electrical energy and they are typically used for domestic hot water (DHW) production. Moreover, hybrid solar panels must be coupled with a heat pump system at the evaporator side, realizing a photovoltaic solar assisted heat pump (PV-SAHP) plant. Generally, a careful design of these integrated systems must involve accurate control strategy to optimize energy savings during operation. In fact, the behavior of the PV/T panels is heavily influenced by the very quick variation of the external conditions during daytime (mainly due to solar irradiation), affecting the working conditions of the other equipment. Therefore, models able to reproduce the dynamic behavior of the PV/T panels represent a flexible tool for developing innovative and user-adapted system control criteria, in a global system optimization perspective. In this context, the aim of the present paper is to describe a simplified numerical model able to reproduce the short time dynamic behavior of the PV/T panel. The model has been validated using experimental data which have been collected during outdoor tests conducted at the University of Genoa using a prototype realized by retrofitting a commercial PV collector. Several simulations have been performed by comparing the PV/T outlet temperature provided by the numerical model against experimental data.