Unglazed PVT collectors as additional heat source in heat pump systems with borehole heat exchanger

An unglazed photovoltaic-thermal (PVT) collector provides a double benefit in a heat pump system compared to a conventional heat pump system with PV and borehole heat exchanger. First, the PV cells in the PVT collector are cooled, leading to lower cell temperatures and a higher PV efficiency. Second, the PVT heat raises the temperature level of the heat pump and the borehole heat exchanger and consequently leads to a higher heat pump system performance. In this context a system was measured with a 39 m2 unglazed PVT collector field. The impact of the solar heat to the heat pump is determined by TRNSYS simulations using energetic weighted temperatures for validation and to quantify the impact of the solar heat. The investigated system revealed a temperature increase of 3 K which equals 9% lower electricity consumption. The yearly additional PV yield was determined to 4% by reference measurement of uncooled conventional PV panels. Additionally, system simulations in TRNSYS are presented.