Experimental study on active cooling for concentrating photovoltaic cells working at high concentration ratios

Concentrated photovoltaic (CPV) attracts a lot of attention recently because it can achieve much higher efficiency than traditional solar cells by concentrating sunray with an in-expensive Fresnel lens or parabolic mirror. However, heat dissipation is a critical challenge for CPV solar cells particularly at a high concentration ratio (CR) since the concentrated solar irradiance also results in a large amount of excessive heat. Experimental studies about CPV working at high CR were documented by a few pieces of literature. In this study, the electrical and thermal behavior of active cooling heat sinks with multi-stage channels for CPV solar cells at both indoor (248× CR) and outdoor (500× and 900× CRs) conditions were comprehensively investigated. The effects of water flow rate, water inlet temperature, season change, and CR on the performance of heat sinks with the different channel numbers and overall size were examined. Convection heat transfer coefficient, electrical, thermal, and cogeneration efficiencies of the heat sinks were evaluated. Results show that the maximum temperature of CPV is significantly reduced as the increase of water flow rate or decreases in the water inlet temperature, meanwhile, the output power is slightly enhanced. The benefits of channel numbers increase are limited, while heat sinks with a cooling area equal to the unpacked cell have higher overall efficiency. Moreover, the convection heat transfer coefficient of the recommended heat sink can reach above 10 kW/(m² K), with the average CPV cell temperature can be maintained at 63.2°C under 500× CR on Summer Solstice, and 71.4°C under 900× CR on Frost's Descent. Highlights: Indoor and outdoor tests of active cooling for CPV cells at high CR were studied. Influences of heat sink designs and operating parameters were analyzed. Convection heat transfer coefficient above 10 kW/(m² K) is reached. CPV cell average temperature of 63.2°C is achieved on Summer Solstice.