Fill factor dependence of bilinear I–V curve translation accuracy

This paper presents an application of the bilinear interpolation/extrapolation I–V curve translation method [1–3] for the calculation of indoor curves of different photovoltaic devices at variable irradiance levels. Special attention was paid to modules exhibiting distorted I–V curves due to degradation provoked by 20 years outdoor exposure. The accuracy of the method was investigated for both interpolated and extrapolated curves at different levels of irradiance and compared to the IEC method. The accuracy of the bilinear curve translation is greater than the IEC method for devices with strongly distorted I–V characteristics (reduced FF) but similar for modules with high FF. Moreover, the bilinear method enables the translation of the I–V curves to irradiances varying by more than 30% from the recorded ones giving accurate results.