Cooling design and evaluation for photovoltaic cells within constrained space in a CPV/CSP hybrid solar system

Highlights: • A practical cooling solution is proposed for a novel CPV/CSP hybrid solar system. • Both passive and active cooling techniques were systematically investigated. • Comprehensive experimental and numerical studies were conducted for optimal design. • Active cooling is in great need for a high waste heat flux of 21.8 W/cm². • Passive cooling becomes attractive for a waste heat flux less than 13.0 W/cm². - Abstract: A hybrid solar energy system has been designed by combining the advantages of concentrated solar power (CSP) technology and high performance concentrated photovoltaic (CPV) cells which outperforms either single technology. Thermal management is crucial to CPV cells in this hybrid solar system, as concentrated solar radiation onto the PV cells leads to higher heat flux. If the heat is not dissipated effectively, it can cause obvious temperature rise and efficiency reduction in the cell. In addition, the constrained space available for PV cell cooling in such hybrid solar systems presents more challenges. In this study both passive cooling and active cooling techniques were systematically investigated in both numerical and experimental ways. For the passive cooling method, two different designs from off-the-shelf heat pipes with radial fins or annular fins were proposed and studied under various heat rejection requirements. Results shows that heat pipes with radial fins exhibited narrow capability of dumping the heat, while heat pipes with annular fins presented better performances under the same conditions. Numerical optimal designs of annular fin numbers and fin gaps were then carried out and experimentally validated, indicating a capability of dumping moderate waste heat (∼45 W). For active cooling technique, a comprehensive study of designing plate fin heatsinks were conducted corresponding to high Ingress Protection (IP) rated off-the-shelf fans. Results show that with a less than 2 W fan power consumption, this active cooling method can control the average PV cell temperature below our target temperature of 75 °C even under 45 °C ambient. To evaluate the overall performance in a year round life cycle, the enhancement in the annual electricity output of the PV cells was estimated according to the cooling effects subjected to the climate of Tucson, Arizona. Finally, taking into consideration of both the temperature control results and net gain/loss analysis, an active cooling design was chosen for our system to dissipate a maximum waste heat of 84 W (21.8 W/cm²) due to its lower cost, lower CPV temperature, and higher net energy efficiency gain. It is also demonstrated that passive cooling will become more attractive when the heat dissipation requirement is less than 50 W (13.0 W/cm²).