Thermal management of PVT collectors

Hybrid photovoltaic-thermal PVT collectors are a promising technology that combines the solar generation of electricity and heat in a single component and thus utilizes solar areas more efficiently. The PhD thesis by Manuel Lämmle from Fraunhofer ISE focusses on the development and modelling of glazed PVT collectors with an optimized overall efficiency. A combination of experimental and numerical methods is applied at both the collector and system level, allowing a multifaceted analysis and optimization of the PVT technology. The application of transparent low-emissivity coatings reduces radiative heat losses and thus improves the thermal efficiency by 60 % at typical operating conditions. The collector performance is evaluated in the system context by means of assessing annual electrical and thermal yields of typical PVT systems. The newly defined characteristic temperature describes the mean operating temperatures of a PVT system and thus enables a consistent comparison of yields. Furthermore, three innovative overheating concepts are specifically designed for PVT collectors, which limit the stagnation temperature to subcritical levels but maintain high energy yields.