Understanding Hotspot Effects in Solar Panels: What They Are, Why They Matter, and How to Prevent Them
As solar systems age and reach the end of their operational life, not all failures are visible to the naked eye. One of the most critical yet often overlooked indicators of panel degradation is the presence of hotspots.
It’s important to know how hotspots impact system performance and potential reuse, and why anyone involved in solar decommissioning, repowering, or recycling should treat them as a diagnostic tool.
What is a hotspot on a solar module?
A hotspot is an area on a solar panel where excessive heat builds up. It’s often due to uneven electricity flow caused by a malfunctioning or shaded cell. Individual solar cells are connected in a series of crystalline silicon solar modules. When one cell stops generating electricity, whether from shade, dirt, damage, or internal degradation, its resistance increases. However, the rest of the cells in the string continue to push current through the inactive cell. This mismatch leads to localized heating, which is released in the form of thermal energy instead of electrical output. Over time, these overheated spots, or hotspots, can cause irreversible damage not just to the affected cell but also to adjacent components and, in severe cases, the entire module.
How do hotspots affect solar panel performance?
The consequences of hotspots extend beyond energy loss. The immediate impact is a drop in power generation, as the affected cells cannot contribute to energy output effectively. Repeated heating and cooling cycles in those areas also introduce mechanical stress to the materials. Over time, this thermal expansion and contraction can lead to physical degradation, such as microcracks, delamination, or even burns on the module surface. Hotspots also place stress on internal components, including connectors and wiring, which may deteriorate from prolonged exposure to elevated temperatures. This not only compromises safety but can also lead to the failure of the bypass diodes that are designed to protect against such issues. If left unchecked, hotspots can shorten the operating life of the entire solar system and erode long-term reliability.
What causes hotspots to form in the first place?
Hotspots can arise from a mix of environmental, mechanical, and electrical issues, and one of the most common causes is partial shading. A tree branch, a patch of dust, or even a single leaf can block sunlight to one or more cells, creating an imbalance in light exposure. Bird droppings or grime accumulation have similar effects. Beyond surface conditions, internal issues like uneven cell aging, where some cells degrade faster due to inconsistent sun exposure, can lead to mismatched current flow and thermal stress.
Manufacturing defects, such as poor solder joints or microcracks that escape initial inspection, may also play a role. In some systems, improper series matching of modules with different output levels results in current mismatches, especially during times of high irradiance. Faulty bypass diodes further increase the likelihood of hotspots as they fail to reroute currents around compromised areas.
Environmental conditions can amplify all of these risks. Excess heat, poor airflow, or extreme cold can create more volatile temperature differences across a module, increasing the strain on shaded or damaged cells. In snowy climates, for instance, partial ice coverage can shade cells unevenly, triggering the same hotspot behavior. Even installation errors, like poor tilt, orientation, or lack of ventilation, can concentrate heat in specific areas, allowing it to accumulate rather than dissipate naturally.
How can you detect a hotspot?
A noticeable drop in system output is often the first clue that something is wrong, though this alone doesn’t confirm a hotspot. Solar technicians often conduct a thermographic inspection to pinpoint the problem. This process uses an infrared camera to scan the surface of the module while it’s in operation. On a sunny day, differences in surface temperature are visible in the thermal image, allowing technicians to locate precisely where overheating is occurring. These inspections are particularly valuable because they don’t require system shutdowns and can be done quickly, making them ideal for preventive maintenance.
Are hotspots dangerous?
Yes, hotspots present both performance and safety concerns. The most immediate issue is thermal damage to the panel, but in extreme cases, the heat buildup can ignite flammable materials near the module. This is particularly dangerous in dry climates or locations with overhanging vegetation. While solar panels are typically equipped with bypass diodes to prevent this, diode failure can render that protection useless. Even when functioning, these diodes reroute current around the damaged cell and often the entire string, which helps avoid a fire but reduces overall system performance. The result is lower energy production and financial losses for system owners.
What can be done to prevent hotspots?
Prevention starts with choosing the right technology. High-performance solar panels, such as Interdigitated Back Contact (IBC) modules, are more resistant to localized heating. Their design allows for better current distribution, even when parts of the module are shaded. Panels with integrated bypass diodes add another layer of protection by redirecting current around underperforming cells. Equipment alone isn’t enough, and proper installation is just as critical. Ensuring the modules are positioned for optimal sun exposure, mounted with sufficient airflow, and spaced to allow heat dissipation can significantly reduce the likelihood of thermal buildup.
System monitoring and maintenance also play a major role. Regular cleaning prevents the accumulation of dust, dirt, or bird droppings, all common triggers for shading-induced hotspots. Operators should also watch for changes in surrounding vegetation, especially over systems expected to run for 20 years or more. Trees grow, foliage shifts, and what starts as an unobstructed system can become partially shaded within a few seasons. Keeping an eye on these developments can help avoid performance loss. More frequent inspections and cleaning schedules may be warranted in regions with high temperatures or heavy pollution.
What if a hotspot is already present?
If the issue is external, such as debris or shading, then removing the obstruction may resolve the problem. However, if a hotspot is caused by a defective cell or failed diode, the affected panel will likely need to be replaced. This requires careful attention to ensure the new module matches the voltage and current ratings of the existing system. Using an incompatible replacement could create further mismatches and cause new problems. In some cases, sourcing a matching module may require reaching out to secondary marketplaces or specialty suppliers, especially for older systems.
Hotspots are often overlooked until they begin to impact system output or cause visible damage. With proper system design, regular maintenance, and the right hardware, they are largely preventable. Addressing hotspot issues early keeps energy generation stable, improves equipment longevity, and reduces the risk of failure or fire. As the solar industry continues to scale, paying attention to technical details like hotspot mitigation will remain a core part of safe, reliable solar deployment.
Resources
https://www.sciencedirect.com/science/article/abs/pii/S0038092X21008938
https://www.sciencedirect.com/science/article/pii/S1364032124007998
https://www.sciencedirect.com/science/article/pii/S2352484722008022
https://docs.nrel.gov/docs/fy14osti/60169.pdf
https://www.sciencedirect.com/science/article/pii/S037971122300139X
https://www.sciencedirect.com/science/article/pii/S2667113125000038