I'm working on cooling photovoltaic panels using phase-change materials. I wanted to see what kind of phase-change material is usually used to cool solar panels and increase their efficiency?
The paper titillated Phase-change materials to improve solar panel's performance found in the link may of help to you: Article Phase-change materials to improve solar panel's performance
The main criterion for the selection of a suitable PCM for cooling photovoltaic panels is its phase transition temperature (melting point), which should be close to the normal PV operating temperature of 25 °C. In addition, other important parameters including high values of thermal conductivity, latent heat, and stability in the cycling heat process are taken into account in order to reach an appropriate decision.