Two-layer ETFE cushions integrated flexible photovoltaics: Prototype development and thermal performance assessment

ETFE (ethylene tetrafluoroethylene) cushion integrated flexible photovoltaics (PV) is an extension of building integrated photovoltaics into membrane structures, which could be near zero-energy, sustainable and environmental-friendly buildings. This paper focused on a two-layer ETFE cushion integrated flexible photovoltaics with experimental study and theoretical analysis. Field experiments on a prototype were carried out to investigate temperature distribution and characteristics. It is found that temperature distribution was the result of solar irradiance, incident angle and surface curvature of ETFE cushion and that solar irradiance had an essential effect on temperature distribution. The theoretical thermal model was developed based on energy balance equation and the corresponding differential equation was solved by the Runge-Kutta method. Maximum temperature difference of 3.3 K between experimental and numerical results demonstrated that this thermal model could predict PV temperature appropriately. Furthermore, a modified equation to determine heat transfer coefficients was proposed and average heat transfer coefficients of PV and ETFE foil were 4.89 W/(m2 K) and 4.39 W/(m2 K). In general, this study could provide basic values and observations for investigating thermal performance of ETFE cushion integrated flexible photovoltaics.