Performance of Partial Shaded PV Generators Operated by Optimized Power Electronics an IEA PVPS T13 Activity

As the potential of PV generation on roofs or façades is to be increasingly utilised in the coming decades, partial shading of PV generators will occur more frequently. Such PV systems suffer from additional power losses, due to nonuniform electrical output within the photovoltaic array depending on the wiring of the individual solar cells and the used power conditioners. This publication discusses some findings of the IEA PVPS Task 13 report published in 2024, which aims to provide an overview of the challenges and state-of-the-art technical solutions for partial shading. Module-Level Power Electronic (MLPE) can potentially improve the performance of such photovoltaic systems relative to conventional String Inverter (SINV). However, most of the promised annual gain in performance using high sophisticated MLPE systems are not realistic for light and moderate shaded systems due to their individual losses. The IEA report contains a compilation of the currently available efficiency measurement results of commercial optimisers at all operating points and thus demonstrates the considerable differences to the data sheet specifications of the MLPE manufacturers. Furthermore, efficiency measurements of micro-inverters are also given, with very good agreement with the manufacturer's specifications but lower efficiencies such as standard SINV. Detailed annual performance analyses have shown that with partially shaded PV generators, conventional SINV achieve in some cases an even better performance than the market dominating MLPEs in these applications. Such meaningful recommendations for high performance systems can only be made if the realistic losses of the optimisers themselves are taken into account, which are often overestimated at typically 2%. However, as these annual performance differences between MLPE and SINV are typically less than 3% for the market dominated light to medium shading PV cases, optimiser manufacturers are obliged to supply realistic efficiencies data. On the other hand, optimiser are more efficient for the smaller market segment of strong shading, and even if very different module orientations occur, with strings that are too short for multi-string inverters. The economics for the end customer with partial PV shading can be dominated not only by the higher investment costs for components and installation but also by the high costs incurred by tradesmen when replacing defective optimisers. As far as comparing the probability of failure rates of optimisers due to the higher ambient temperature on the roof compared to string inverters in the building is concerned, experts still must wait for independent investigations of service cases of replacement in the field. In research, a wide range of additional work is being carried out in relation to the reduction of PV shading effects and some are discussed in the IEA report. They range from new variants of sophisticated power electronics for each solar cell, including control, as well as the optimisation of mechanical tracking of single-axis PV utility scale power plants on uneven terrain.