Performance of solar photovoltaic installations: Effect of seasonal variations

Abstract

A 20kWp Solar Photovoltaic (SPV) system was set up on the library roof-top in Indian Institute of Science, Bangalore, India. This roof-top photovoltaic (RTPV) system partly powers the Central Office of IISc. The main objective of setting up this SPV system was to study the performance of solar plants under different seasons and climatic conditions of Bangalore. The system has been producing an average daily yield of approximately 80kWh for the past two years which translates to an annual yield of 28.9MWh. The overall yield of the system up to 14th September 2015 is 70MWh. This work focuses on the evaluation of the performance of SPV systems using the popular grading systems, namely Capacity Utilization Factor (CUF) and Performance Ratio (PR). The CUF of the SPV system is 16.5%, which lies within the range of CUF of well-performing solar plants located in India. Average Performance Ratio (PR) of the SPV system is around 85%, which indicates that the performance of the SPV system is satisfactory. PR of the SPV system is correlated with the behaviour of SPV modules in different seasons, with module temperature (Tmod) as the key factor of comparison. In summer, the SPV modules attain maximum efficiency (ηmax) at Tmod of 45°C, but in winter, it is at 55°C. In summer, for Tmod>45°C, module efficiency (η) reduces by 0.08% per degree rise in temperature. In monsoon, for Tmod>35°C, η reduces by 0.04% per degree rise in temperature. In post-monsoon period, for Tmod>38°C, η reduces by 0.06% per degree rise temperature. However, in winters, the modules attain ηmax at Tmod of 55°C, without much drop in efficiency. This is mainly because of intermittent natural cooling that takes places at the surface of the modules, due to cool breeze and lower ambient temperatures.