A PVT collector concept with variable film insulation and low-emissivity coating

Hybrid photovoltaic-thermal (PVT) collectors co-generate solar electricity and heat in a single component with an optimum utilization of space. Spectrally selective but transparent low-emissivity (low-e) coatings are a proven method to reduce thermal losses. However, overheating and stagnation are critical issues for these collectors due to material degradation, thermal stress, and low electrical efficiency. This paper presents a PVT collector concept with variable film insulation as overheating protection. An inflatable glass-film cushion regulates thermal losses. Performance and stagnation tests were carried out with a prototype. During normal operation the collector achieves a high thermal efficiency. In periods of standstill, the deflated cushion has a high heat dissipation rate by deactivating the low-e coating. Stagnation temperatures are thus limited to 95 &C. To conclude, the PVT collector combines the advantages of glazed and unglazed PVT collectors which are a high thermal efficiency and low stagnation temperatures.