The performance of photovoltaic modules depends on the temperature of the modules and the surrounding ambient air temperature. The rule of thumb is: “the warmer the module, the lesser the performance”. In fact, modules heat up considerably as a result of solar radiation. This is impaired by a hot roof surface such as a bare waterproofing membrane or a gravel roof. However, if combined with a green roof, solar modules will perform better. Through the cooling effect caused by evaporation at plant level, the ambient air temperature is cooler and photovoltaic cells improve their performance.