Edinburgh Napier University

  Photovoltaic degradation rates play a vital role in visualizing and analyzing the performance of the PV modules over the long run. A site survey is conducted to calculate PV degradation rates. The results have shown that for the first three years since the initial installation, the degradation rates have remained in line with the manufacturer values (i.e., less than 0.6%), while the next two years the degradation rates have almost increased by 40%. This is due to discoloration of the encapsulant causing the reduction of the short circuit current (Isc). Mathematically, modeling such visual loss factors has not considered so far. The visual loss factor equation is developed and incorporated in the output current equation of the PV module. Further, the I-V curves are simulated and compared with the measured I-V curves. The results have shown an acceptable error percentage of around 0.3%.