Analysis of hotspots in half cell modules undetected by current test standards

Today, hotspots are a major source of failure for photovoltaic modules in the field. Modules based on half-cut solar cells are an attractive pathway to reduce cell-to-module losses and are projected to have a 40% market share by 2028. However, the current standard for module testing IEC 61215-2 can leave critical hotspots undetected in such a module configuration. In this paper, the hotspot effect of half-cell modules using parallel connected cell substrings is studied in comparison with conventional full-cell modules. Significant hotspots are induced in both half- and full-cell modules, when suffering current mismatch, in this case induced by partial shading. When shaded by the same area, the hotspot temperature of the cell in a half-cell module is 19 °C lower than the full-cell module in this experimental work. Critically, multiple unshaded weak cells are found to dissipate heat when the parallel-connected substring is shaded. In an experimental situation with a total shading ratio of only 4%, we measure hotspots of over 90 °C - a situation that can occur in the field due to uncontrolled plant growth and bird droppings.