Highly accelerated stress method for measuring water vapor transmission rate of PV backsheet

In this study, we investigate the water vapor transmission rate (WVTR) with highly accelerated stress test (HAST) for the backsheets of the photovoltaic module. According to the Fick's equation, the WVTR can be fitted by the water concentration of EVA with time dependence. In order to receive the trend of the relative humidity in the photovoltaic module, the flexible printed circuit with high accuracy humidity sensors were embedded in two ethylene-vinyl-acetate (EVA) stacks and laminated with glass and backsheet. Compare to result of the commercial method, this way can reach high accuracy in 3 cycles. However, we get the WVTR of backsheets using dry process in the open air space, but the inhomogeneous temperature and humidity cause the lower WVTR.