Phase Change Materials for thermal management of PV modules

Abstract

Whilst research in solar cell materials lead to higher efficiencies every year, new difficulties arise with every breakthrough to get an even higher efficiency. Therefore, every component of a PV system should be examined, as well as how their behaviour under operation affects performance to improve the overall PV yield. In particular the temperature of a module can have a negative impact on the power output. The drop in power output is a consequence of a negative thermal coefficient that results in a decrease of open circuit voltage with increasing temperature. For silicon solar cells, efficiency drops of 0.4-0.65%/°C have been reported in literature. Moreover, daily repetition of temperature cycles can cause mechanical degradation, thereby decreasing the lifetime of PV modules. In this thesis, phase change materials (PCM) have been studied as a method to passively reduce the operating temperature of PV modules. This is based on the ability of materials to stay at a relatively stable temperature during a phase change. By placing a PCM at the back of a PV module, the temperature difference between the module and the melting PCM causes a thermal gradient, resulting in conduction of heat away from the
module. In order to find the optimal properties of a PCM, a thermal model was first developed in COMSOL Multiphysics and benchmarked with field measurements from literature. Simulations for Rotterdam, the Netherlands, revealed that an optimized PCM could increase the yearly electrical yield by 1.23% for a rack-mounted module, or 3.52% for a roof-mounted module. Furthermore, measurements were performed with commercially available PCMs under a Large Area Solar Simulator (LASS). These were able to reduce the average module temperature by 30-36°C, albeit under heavy infrared radiation coming from the simulator.