The increasing demand for TOPCon bifacial solar modules has raised concerns among industry professionals about their potential for unsafe installation, particularly on sheet metal roofs.

TOPCon bifacial modules, which are primarily manufactured in glass-to-glass format, are not ideally suited for installation above sheet roofs due to their structural and performance requirements.

These modules are designed to capture sunlight from both sides, offering higher system efficiency.

However, installing them on opaque, unventilated sheet roofs blocks rear-side exposure to light and traps heat. This limits power generation and significantly increases the risk of overheating and, in extreme cases, fire.

Naveen Kumar P, Proprietor of SolarGeNext Energy Solutions, stated, “These modules are meant to perform with adequate rear-side exposure and airflow. The lack of ventilation on sheet roofs leads to heat buildup, which can ignite the modules.”

The risk of fire increases when modules are installed using structures designed for monofacial modules, rather than bifacial systems.

Monofacial modules lack cells on the rear side, allowing them to be mounted on any type of roof without requiring additional considerations. A common mistake is using standard monofacial mounting structures. These structures include purlins, which are horizontal beams that support the weight of the roof. Purlins cast shadows on the back of bifacial modules, significantly reducing energy gain from reflected sunlight.

According to Kumar, bifacial modules must be installed with a minimum clearance of one meter from the surface of reinforced cement concrete roofs, along with white floor painting to reflect light to the rear side. This ensures optimal performance and system efficiency.

Karthik P, Manager (Electrical) at Tata Consulting Engineers, noted, “We always leave a minimum clearance, usually around 200 mm to 300 mm, between the roof and the panels for ventilation. The mounting structure is designed to allow wind to flow through the rows, and we make sure the panels are not directly touching the hot metal sheet.”

There have been instances of bifacial modules being installed on sloped metal sheet roofs using existing structures designed for monofacial panels. “These structures are too short and do not allow rear-side light access. The increased number of cells in bifacial modules intensifies the heat accumulation, sometimes resulting in fire,” said Karthik.

Such incidents highlight the risks associated with using improperly rated balance-of-system (BoS) components. Harshal Akhouri,  co-founder and CEO of Strolar, a manufacturer of solar trackers and mounting structures, had recently explained how the absence of standards for BoS components used in solar projects could potentially harm the structural integrity of solar projects.

Installers often use cables for 500-watt or lower mono modules, which are not sufficient for high-wattage TOPCon modules. This mismatch can lead to overheating of cables and potential system failure. “Initially, we suspected the cable sizing was the issue, but the real problem was rear-side shading and insufficient ventilation,” Kumar said.

Karthik explained that cables are routed neatly, fixed properly, and tested for continuity and insulation before the system is energized. The selection of cables accounts for the rooftop temperature, and care is taken to ensure that connectors are crimped and matched correctly. Once the installation is complete, the team conducts resistance checks, tests for voltage drops, and inspects for any loose connections. Bunching cables too tightly is avoided, as it can lead to heat buildup.

“TOPCon bifacial panels can run at slightly higher currents than standard modules, so poor connections or incorrect cable sizing can lead to overheating,” he added. “On metal rooftops, this is compounded by heat reflection.”

One of the problems arises from the lack of awareness among consumers about the BoS components. They insist on good module and inverter brands but are unaware of other critical components that are essential for a safe setup.

Industry experts emphasize that installers are responsible for ensuring safety, but the growing demand for rooftop installations has led to widespread outsourcing to local electricians who may lack adequate training in solar systems. This has led to an increase in the non-compliant and unsafe installation practices.

Karthik emphasized that with the introduction of newer module technologies like TOPCon, the teams receive updated training. They are trained to handle higher currents, assemble connectors properly, follow the correct torque specifications, and maintain clearances per the module datasheets. The training also includes safe rooftop installation practices.

As rooftop solar installations under the PM Surya Ghar: Muft Bijli Yojana reach 1 million nationwide, concerns have arisen about the lack of quality checks for the components and the absence of standardization. Several new installers with little to no experience have entered the rooftop solar market to capitalize on increasing consumer demand.

To address these concerns, SolarGeNext is now designing new structures for metal sheet roofs that provide sufficient clearance, reduce shading, and prevent overheating. Kumar said, “With these changes, we are seeing only a 2% difference in efficiency between monofacial and bifacial modules, but the safety and system performance are far more reliable.”

Trained personnel and the use of safety harnesses are now standard practice for Kumar’s team at SolarGeNext to prevent site-level hazards. The experience gained from recent incidents has led to greater awareness about the importance of structure design, ventilation, and appropriate BoS components in ensuring bifacial solar systems’ safe and efficient functioning.