Solar systems and their integration with heat pumps: A review

This paper presents a review of the available literature on solar systems (solar thermal collectors and Photovoltaic-Thermal (PV/T) collectors) and their integration with heat pumps. Most of the research covered in this review show that the dominant source of solar assisted heat pumps (SAHPs) is liquid with a thermal storage; direct expansion or indirect expansion. SAHPs are mostly used for heating purposes. Few studies investigated the possibilities of combining a solar system with an air source heat pump (ASHP). The integration of a PV/T system with a heat pump, which provides both thermal energy and electrical power, existing in most researches is PV-evaporator type, which is the evaporator of the heat pump. It is required to control the mass flow rate of the refrigerant to prevent remaining liquid refrigerant at the outlet of the PV-evaporator due to the fluctuation of solar radiation; consequently, the system works inefficiently. It is possible to overcome this issue by separating the PV/T unit from the heat pump evaporator. There is a lack of investigations of connecting an air-based solar system (especially PV/T system) with an ASHP, including air-based thermal energy storage.