Experimental study on the operating characteristics of a novel low-concentrating solar photovoltaic/thermal integrated heat pump water heating system

A novel low-concentrating solar photovoltaic/thermal integrated heat pump system (LCPV/T-HP) with both electricity and heat outputs has been developed. A solar photovoltaic/thermal collector with fixed truncated parabolic concentrators reflecting the incident sunlight onto the surface of PV cells also as the evaporator of the heat pump system. Refrigerant, R134a, flows inside the multi-port flat extruded aluminum tubes placed underneath the PV cells, absorbing solar heat and evaporating. Refrigerant's condensing heat is used to heat water in condenser. Experiments on the novel LCPV/T-HP system were carried out in Nanjing, China, and its operating characteristics evaluated using an LCPV system without being cooled as a benchmark. Experimental results showed that the LCPV/T-HP system achieved an averaged COP of 4.8 for heating water from 30 °C to 70 °C on a sunny summer day, with an output electrical efficiency of 17.5%, 1.36 times higher than that of the LCPV system. Furthermore, the experimental results suggested that flux concentrating rate of the fixed parabolic concentrators was 1.6. Finally, the influences of PV cells' operating temperature on the photovoltaic output characteristics were analyzed, and an optimized control method to achieve a higher power output and electrical efficiency was further discussed.