This document provides critical insights into the challenges of partial shading in photovoltaic systems and evaluates the latest technical innovations for optimising energy performance under such conditions.
Partial shading, a common issue in urban environments with roof-mounted or façade PV systems, can result in significant energy losses and even pose risks such as hotspots and module damage. The report investigates the comparative performance of various power electronic systems, including conventional string inverters (SINVs) and module-level power electronics (MLPEs), offering detailed analyses and actionable recommendations for system designers and stakeholders.
Key Findings:
- Detailed performance analyses have shown that with partially shaded PV generators, conventional string inverters sometimes even achieve better performance in these applications than the market-dominating optimisers.
- 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 typically overestimated at 2 %. However, as these annual performance differences between optimisers and string inverters are usually less than 3 % in a market dominated by lightly to moderately shaded PV systems, optimiser manufacturers are obliged to provide realistic efficiency data.
- To enable PV planners worldwide to offer their customers the optimal PV design under partial shading conditions, commercial PV software tools need to improve their products both in terms of component efficiency data and in terms of calculating the actual operating points of each optimiser based on each solar cell of the PV module, rather than using simple average unrealistic weighted optimiser efficiency data.
- MLPEs should have the parameter option to switch off the avoidance of hot-spot operating points in order to be able to generate the maximum PV power throughout the year without the risk of a harmful hot-spot effect, as is the case with half-cell modules.
- A wide range of additional research work is being carried out to reduce PV shading effects. They range from new variants of sophisticated power electronics for each solar cell, including the control system, to optimising the mechanical tracking of single-axis large-scale PV power plants on uneven terrain.
- The cost-effectiveness for the end customer of PV partial shading can be characterised not only by the higher investment costs for components and installation, but also by the high costs for tradesmen when replacing defective optimisers. When it comes to comparing the probability of failure rates of optimisers due to the higher ambient temperature on the roof compared to string inverters in the building, the experts still must wait for independent studies of service cases during replacement in the field.
