Shading of modules is a common occurrence in practical application scenarios, and no PV power station can completely avoid it. Examples include fixed shading from buildings, equipment, cables, trees and other objects around the power station, as well as local shading caused by dust, bird droppings, fallen leaf cover, snow accumulation and so on.
Shading on modules triggers a chain reaction, with the impact being further amplified, which in turn leads to irreversible losses. A module is composed of several solar cells connected in series, and modules in a power station are also connected in series in groups. This series connection between cells and modules means that a shaded solar cell will affect the performance of the entire module and string, resulting in the "barrel effect". The output of a module or string is limited by its poorest-performing solar cell, leading to a sharp drop in the power generation of the entire module string and thus impacting the overall power station performance.
Laboratory tests conducted by TÜV Rheinland show that shading covering approximately 50% of a half-cell leads to a module power loss of around 10%. In contrast, China General Certification Center (CGC) has carried out outdoor empirical research on the impact of shading on PV string, which found that when three modules are shaded outdoors, the power output of the entire string drops by more than 30%—a change that truly sets off a chain reaction with a single small trigger.
If shading is a visible hazard, hot-spots are the hidden and upgraded damage it triggers. This risk becomes even more insidious and destructive in power stations where modules are densely arranged. When a local area of a PV module is shaded, the shaded spot acts like a large resistor (a fast heating element), generating an enormous amount of heat that directly causes a hot-spot. A normal module surface has a temperature of 40~60°C, while the temperature of hot-spot can surge to 100~200°C—essentially turning a solar module into a solar cooker. In tests conducted by TÜV Rheinland, hot-spot temperature can reached as high as 169°C.
Local hot-spots show no obvious visual changes and can only be fully exposed under an infrared camera. This often leads to the issue being overlooked manually, resulting in a missed optimal remediation window. Furthermore, maintenance personnel are at risk of thermal burns and other safety incidents if they do not exercise due caution during operation and maintenance.
Prolonged high temperatures accelerate material aging, causing yellowing, delamination and other defects. In extreme cases, excessive heat can even melt the EVA film, fuse solder joints, ignite the backsheet or damage the glass—leading to permanent power degradation or even complete burnout of the module. Worse still, it may ignite accumulated dust and dry grass, triggering large-scale fires and incurring huge economic losses. For distributed PV power stations, such fires may even spread to ignite roof structures, resulting in massive property damage and potential threats to personal safety.
Ignoring hot-spots risk is tantamount to planting long-term hidden dangers for the safety and revenue of PV power stations. For instance, a total of 8,213 abnormal hot-spot points were detected during an in-depth inspection of a 20MW power station, each posing a significant safety hazard to the facility. Research on numerous power stations conducted by Solar Bankability shows that approximately 41% of module failure cases stem from shading-induced hot-spots. The hot-spot effect caused by shading has become a core bottleneck restricting the safe operation of photovoltaic power stations and the improvement of their power generation efficiency.
In summary, shading and hot-spots pose a dual threat to the power generation revenue and safe operation of PV power stations, and the two are interrelated with superimposed hazards. In terms of the impact of shading, it is prevalent in all types of power station scenarios. Whether it is fixed shading or local coverage, it amplifies hazards through the "barrel effect" and becomes a core obstacle to lowering the overall power generation efficiency of power stations. In terms of the impact of hot-spots, as a hidden upgraded hazard caused by shading, they are highly concealed and destructive. They not only cause the local temperature of modules to soar to 100-200°C, leading to permanent power degradation and accelerated aging of modules, but also may trigger safety accidents such as fires, bringing irreversible economic losses to power stations.
To address shading and hot-spots, in addition to timely operation and maintenance, power station owners should select modules with excellent protective performance in the module selection stage to cut off hidden dangers from the source and lay a solid foundation for the long-term, efficient and safe operation of power stations.