Comparison analyses of three photovoltaic solar-assisted heat pumps based on different concentrators

Abstract

The main problem of concentrated photovoltaics is the high temperature caused by high radiance, which deteriorates the electrical efficiency and service life of photovoltaic cells. Most concentrated photovoltaics are assembled into the photovoltaic/thermal systems and cooled by water. However, if concentrating photovoltaics is combined with an evaporator in a direct-expansion solar-assisted heat pump, the photovoltaic damages (reduced life span and conversion efficiency of photovoltaic cells) caused by the high temperature in concentrators will be much better alleviated. But at present, there is little research on the combination of concentrating photovoltaic and direct-expansion solar-assisted heat pump. To enrich the relevant content and explore the optimal concentrating method combined with heat pumps, three hybrid heat pumps with different concentrating evaporators are proposed and investigated. Results indicate that in the photovoltaic heat pump system based on Fresnel concentrator, photovoltaic heat pump system based on compound parabolic concentrator, and the photovoltaic heat pump system based on 3-D crossed compound parabolic concentrator, the electrical efficiency could achieve 30.31%, 15.37%, and 11.66% under 300 W/m2. The coefficient of performance (considering both electricity and heat) could reach 7.65, 5.67, and 5.45 under 800 W/m2, meanwhile, the 29.87%, 16.25%, and 13.66% exergy efficiency can be obtained under the same irradiation. Therefore, the photovoltaic heat pump system based on Fresnel concentrator has the best capacity, followed by the system based on compound parabolic concentrator and 3-D crossed compound parabolic concentrator. Besides, in the FPV-SAHP system, two concentration ratios are designed and discussed. And the effect of ambient temperature, water temperature, as well as solar irradiance on the systems is also explored.