Edinburgh Napier University

  For a photovoltaic (PV) system, it is widely assumed that the peaks of a partially shaded P-V curve are located at the multiples of 0.8V oc , where V oc is the open-circuit voltage of the PV module. However, this assumption - known as the of 0.8V oc model for partial shading - is not necessarily true. If the same model is used to design the maximum power point tracker (MPPT), it is very likely that the algorithm will scan the wrong region of the P-V curve and, hence, an incorrect global peak detection. This paper attempts to prove the inadequacy of the 0.8V oc model when the number of modules in the string increases. Further, the work suggests a simple relationship to predict the correct position of the peaks. It is found that for a string of 20 modules (V oc of 400 V), the maximum deviation between the actual and computed peak is less than 3 V, while for the 0.8V oc model, the deviation reaches up to 50 V. In addition, using the proposed method, the MPPT efficiency can be improved by approximately 2%.