Analysis of solar photovoltaic system operating under partial shading conditions

Abstract

With the introduction of government grant rebates, EU2020 targets and reduced costs have made the PV industry in Malta boom. Although being one of the cleanest and most reliable, a big problem which it faces every day is shade. The larger the PV system the greater the chance of it being affected. A computational model was thus developed in this dissertation to simulate a PV array and then subject it to various partial shading patterns. The aim was to develop this model into a scalable version which could be configured in any array size desired and examine with simulation and experimental results their operation under partial shading conditions with the use of bypass diodes. Bypass diodes are usually found in a solar panels’ junction box, usually three in number, dividing the series connected panel into three separate sections allowing the panel to operate more efficiently under shading conditions. This is achieved when one part of the panel is subject to shade, and thus since a panel emulates a current source, the excess current is allowed to pass through these diodes instead of flowing through the panel and damaging it. The existence of these diodes however leads to introduce multiple peaks in the powervoltage characteristic of the solar panel. A proposed technique was hence introduced to predict these peaks under various shading scenarios. Classical MPPT (Maximum Power Point Tracking) algorithms, like the Perturb and Observe method, are made ineffective by the introduction of these peaks since they are unable to distinguish between local and global power maxima. Another objective for this dissertation was therefore to assess the performance of these classical MPPT algorithms and improve them to accept these multiple peaks. Realistic shading analysis was also examined to verify our data in real life, where a statistical analysis also confirmed how serious shading needs to be taken when installing a PV system.