Thermal model of a solar hybrid module as the heat source for a CO2 heat pump

In recent years, the possibility of combining photovoltaics (PV) and solar thermal collectors into one solar hybrid module (PVT-module) has been increasingly investigated. PVT-modules produce thermal and electrical energy at the same time. Since the efficiency of a photovoltaic module decreases with increasing temperature, the temperature of the heat transfer media is often limited to about 30 °C and the PVT-module is combined with a heat pump, which increases the temperature on the “warm side”. A common approach is to integrate the PVT-module directly as an evaporator in a heat pump system (PVT-direct). This paper presents a thermal model of a PVT-direct module as the heat source for a R744/CO
₂
heat pump. Due to the combined effect of flow channel patterns, solar radiation, the ambient conditions and possible condensation and frost formation, heat transfer and thermal distribution conditions of the PVT-direct evaporator are inevitably complicated to determine. The proposed thermal model of this hybrid solar module that has CO2 direct evaporation in microchannels will be used to simulate the behavior of the module under different climatic operating conditions. Furthermore, it will quantify all energy inputs and/or losses as well as their influence on the total energy supplied by the PVT-module. This will be used to investigate the overall CO
₂
-PVT heat pump system performance in prospective simulations.