The danger of partial shading in photovoltaic systems.

With the growing adoption of photovoltaic systems in Brazil and worldwide, new challenges are also emerging. One risk, often invisible, has become increasingly frequent: fires caused by failures in solar systems.

Although solar panels are widely considered an environmentally friendly and economical solution, some hidden flaws can have serious consequences.

In August 2025, a devastating fire at a supermarket in Nova Monte Verde (MT) raised concerns about the safety of photovoltaic systems.

It is suspected that the fire was caused by a failure in the solar energy system installed on the roof of the establishment.

This was not the first incident in Brazil. In January 2024, a similar fire struck an industrial building on the edge of the BR-101 highway in Araquari, Santa Catarina, also related to a solar system. Since the beginning of 2024, more than 50 incidents of this type have been recorded globally.

One of the most serious cases occurred in the United Kingdom, where a fire in February destroyed almost an entire commercial photovoltaic installation, resulting in losses exceeding R$480 million.

These incidents not only generate financial losses, but also jeopardize the safety of workers, residents, and maintenance teams.

With the increasing installation of solar systems in homes and businesses, the need for measures to ensure the safety of solar systems has never been more urgent.

Safety in photovoltaic installations: what are the main mistakes made?

But what is behind these fires? Although the cause seems to be directly linked to a system failure, an often-overlooked factor has proven to be the culprit.

This factor is related to partial shadingThis occurs when one or more cells of the solar panel become partially covered by objects such as leaves, tree branches, dust, bird droppings, or even shadows from other roof elements, such as chimneys.

In many cases, these aspects seem harmless, but they can trigger a series of problems, the most serious being a hot spot.

When a cell is shaded, it still attempts to generate electricity, but its production capacity decreases. The surrounding cells, however, continue to function normally and force the electric current to pass through the shaded cell.

This generates heat, and over time, the local temperature can exceed 100°C. This excessive heat increase can damage the panel material, causing bubbles in the backsheet, and in more severe cases, triggering a... fire.

In photovoltaic systems installed on rooftops, the risk is even greater due to the irregularity of shading. The combination of different shade sources can create an unpredictable situation, making the panels more susceptible to thermal failures.

BC technology

Given this scenario, the solar industry has been striving to find solutions that increase the safety of photovoltaic systems. One of these solutions comes from BC (Back Contact) technology, used by LONGi, which has shown promise in preventing the risk of fires caused by hot spots.

Unlike conventional technologies such as PERC and TOPCon, BC modules have electrodes located on the back of the solar cell, creating a more compact and efficient structure. This design offers two crucial advantages in terms of safety.

The first is the integrated bypass: the BC cell design allows the electric current to automatically bypass shaded areas. This means that when a cell is partially covered, the current bypasses the shaded area, preventing excessive heat buildup and the formation of hot spots.

The second advantage is lower conductivity in shaded areas: under partial shading conditions, BC modules limit reverse current, which reduces the conversion of energy into heat. This keeps the panel temperature under control and prevents overheating of the cells.

BC versus TOPCon

Comparative tests between BC and TOPCon modules demonstrated the advantages of BC technology in terms of thermal safety. Under shading conditions, BC modules maintained temperatures 60 to 80°C lower than TOPCon modules.

Furthermore, the hot spots in the BC modules never exceeded 110°C, which represents a significant improvement over conventional modules, which can experience much higher temperatures.

Modules can exhibit 50% to 70% less power loss under shading and offer greater durability. They are less susceptible to yellowing, backsheet bubbles, and thermal stress, in addition to reducing fire risks, reducing thermal stress, and extending the system's lifespan.

Real-life example on rooftops.

Consider a common scenario on rooftops: in the late afternoon, a strip of tree shadow falls on one of the module's edges. In TOPCon or PERC modules, the shaded cell immediately becomes a "stress point," its temperature rises drastically, and the performance of the entire string drops.

If the temperature rises above 180 °C, a dry leaf falling in that area can serve as a source of ignition.

In contrast, BC modules instantly activate their internal bypass and low-conductivity mechanisms. The shaded area remains at a controlled temperature, and the entire string continues to operate without problems.

For owners of rooftop systems, this not only improves energy efficiency but also significantly reduces long-term safety risks.

In complex distributed scenarios, when selecting modules, it is important to pay attention to the electroluminescence (EL) performance of the modules. TOPConPoor EL performance can significantly increase the risk of hotspots.

In contrast, BC modules, due to their unique cellular structure design, can effectively reduce the risks of hot spots and ensure the overall reliability of the module.

The new path for the solar industry: efficiency + safety.

With the rapid expansion of solar energy in homes, schools, factories, and building rooftops, safety performance has become as important as efficiency.

Competition in the sector is changing, shifting from prioritizing only the highest conversion efficiency to seeking a balance between high efficiency and high security.

Thanks to its structural advantages, BC technology offers more proactive and intrinsic protection, allowing modules to operate more reliably in complex shading and high-temperature conditions.

This trend reflects the direction of the sector: only with greater safety at the cell level will solar systems be able to remain stable and reliable for more than 20 years.

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