Experimental investigations of fault tolerance due to shading in photovoltaic modules with different interconnected solar cell networks

In a photovoltaic module, solar cells are generally connected in series. The series connection of the constituent cells makes the module most susceptible to power loss due to mismatch in their electrical characteristics. In this paper PV modules of 50 Wp each, have been designed and developed by changing the conventional series architecture of network of 36 cells into series-paralleled 9x4 architecture with different schemes of interconnection of cells. Simple series-parallel (SP), bridge linked (BL) and total cross tied (TCT) are the three schemes of interconnection of cells used in this study along with the standard series (SS) configuration of cell network. Rigorous experimental investigations have been carried out in real operating conditions to find the configuration of cell network that is least susceptible to environmental stresses such as partial shading and temperature. Fifteen diverse cell level partial shading scenarios have been created artificially using sheets of paper of different transmissivity. Comparative performance assessment for these cell networks is done with respect to maximum power point, voltage and current at maximum power point, shading loss, mismatch loss and presence of secondary power peaks on the output characteristics. Additionally, important parameters such as series resistance, shunt resistance, fill factor, temperature coefficient of current, voltage and power have been determined for each cell network at standard test conditions and compared. It is found that the performance of series paralleled 9x4 configuration with TCT/BL cell interconnection excels over conventional series configuration under partial shading conditions producing power enhancement ranging from 63% to 2%. The problem of appearance of secondary power peaks due to bypass diodes in standard series configuration is also circumvented by using series-paralleled 9x4 configuration of cell network.