LAUSR

Recently, a new in situ measurement technique has been developed using miniature digital relative humidity (RH) sensors. The measurement technique proved to be a valuable tool not only for in situ monitoring of water concentration in the photovoltaic (PV) modules exposed to accelerated test conditions in climatic chambers but also for long-term outdoor monitoring under field conditions. In this paper, we present a completely new in situ setup, which is based on a wireless radio-frequency identification (RFID) technology. In our design, up to seven digital humidity sensors can be soldered on a 130 μm thick polyimide foil that also integrates RFID antenna and all required readout electronics. Their ultra-small size and wireless design allows placing them anywhere in the PV module either in front or at the back side of the solar cells. All measurement data can be read by a dedicated RFID reader which also provides the power needed during the measurement and communication cycle. The systems were applied in mini-modules with one full-size crystalline silicon solar cell and exposed to the elevated temperature and humidity conditions (40 °C/85 %RH and 50 °C/70 %RH). The acquired moisture ingress data agree well with the two-dimensional simulations using the realistic dimensions and diffusion coefficient of ethylene-vinyl acetate.