Abstract
One of the common failures in photovoltaic modules is the degradation of the ethylene-vinyl acetate (EVA) encapsulant due to prolonged ultraviolet exposure and other environmental stress factors, such as temperature and humidity. Experimental studies have shown that significant reduction in the optical transmission due to EVA degradation leads to loss in the available power by more than 50%. In this article, a novel approach to predict the early degradation of EVA encapsulant is proposed by correlating EVA degradation with short-circuit current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SC</sub> ). An electrical circuit simulator, simulation program with integrated circuit emphasis (SPICE), is used to evaluate the short-circuit current obtained under varying optical transmission caused by EVA discoloration. The simulation follows three steps: simulation of the transmitted solar spectrum; simulation of the spectral short-circuit current density; and simulation of the current-voltage (I-V) curve to obtain short-circuit current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SC</sub> ), maximum power output (P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ), open-circuit voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> ) and fill factor. Results show that the reduction in short-circuit current due to EVA degradation differs from the reductions expected due to a spectrally-uniform reduction of intensity of the solar irradiance. Both types of variation are linear, however, the slope due to EVA degradation is larger than the slope obtained for normal intensity variations in the solar irradiance. This model, when applied in conjunction with solar irradiance measurements, can predict early onset of EVA encapsulant failure, thereby enabling preventative measures to be taken.
Highlights
T HE SOLAR spectrum consists of light having wavelengths of varying intensity
The solar spectrum is typically divided into three wavelength regions: ultraviolet (UV); visible; and infrared; some of which can be absorbed by crystalline silicon solar cells and converted into electrical energy
The results show that the differences in the slope of measured short-circuit current density can be used as an indicator of early onset of degradation of the ethylene-vinyl acetate (EVA)
Summary
T HE SOLAR spectrum consists of light having wavelengths of varying intensity. The solar spectrum is typically divided into three wavelength regions: ultraviolet (UV); visible; and infrared; some of which can be absorbed by crystalline silicon solar cells and converted into electrical energy. Several different materials have been used as encapsulants for photovoltaic (PV) modules including thermoplastic polyurethane and polydimethylsiloxane [3]–[5] The latter is superior to other encapsulants when it comes to immunity against environmental stress and UV radiation. The results show that the differences in the slope of measured short-circuit current density can be used as an indicator of early onset of degradation of the EVA.
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