abstract
Unglazed Photovoltaic Thermal (PVT) collectors provide very high efficiency for heat and electricity generation at low temperatures. Therefore they are particularly suitable to support the heat source of heat pump systems, where low temperature heat is required. In this combination the PVT collector improves efficiency in two ways- of the heat pump by additional low temperature heat and of the photovoltaic module by lower cell temperatures. An increase of 4% of the annual and up to 9% for the daily photovoltaic electricity production and a high collector yield of 450 kWh/(m$^2$ a) was measured at a pilot system between April 2009 and April 2010. As the improvement of the PV and heat pump efficiency depends strongly on the thermal PVT collector performance, efficiency measurements of five different unglazed PVT collectors have been carried out. They showed significant differences, e.g. the conversion factor 0 without electricity production varies from 0.33 to 0.73. Further, a simulation model for unglazed PVT -collectors is presented. It is based on thermal performance parameters of EN 12975 and PV performance data at standard test conditions and it further includes thermal collector capacity and condensation effects.