India is witnessing rapid adoption of bifacial modules in rooftop solar installations driven by the decreasing availability of monofacial alternatives and the promise of higher energy yields. Bifacial modules capture sunlight from both sides, offering higher system efficiency. However, many installations fail to consider the structural requirements to optimize bifacial performance.

A common oversight is using conventional monofacial mounting structures, such as those incorporating purlins – horizontal beams that support the roof’s weight. Purlins cast shadows on the rear of bifacial modules, significantly reducing energy gain from reflected sunlight. These shadows diminish system performance and introduce long-term reliability concerns, including the risk of hotspot formation due to uneven power generation. Over time, such inefficiencies can accelerate module degradation and even lead to system failure, undermining the financial viability of the investment.

Harshal Akhouri, Co-founder & CEO of Strolar, a solar mounting structures manufacturer, noted, “Bifacial modules leverage albedo, boosting efficiency up to 11-18%. However, to realize this potential, proper mounting strategies are essential. Structural design plays a critical role. To avoid shading and maximize light capture, mounting systems must prevent interference with module cells within 100 mm of the backsheet. Additionally, bifacial modules are 10-12% heavier, requiring reinforced support structures. This adds complexity to rooftop installations, where clamping methods must adjust for weight distribution.”

Design Refinements Crucial

Akhouri noted that purlins should contact module frames, while rafter-column assemblies must be positioned at the module edges to prevent shading losses. While this increases mounting system costs by 40-45%, the impact on overall cost remains minimal since mounting systems account for less than 6-8% of the total cost of a solar project.

“As bifacial adoption grows, these design refinements are crucial. Well-engineered mounting solutions maximize energy yield and ensure durability,” he said.

Terence Alex, Founder & CEO of Wattsun Energy, explained that bifacial modules perform best when mounted on elevated structures with reflective surfaces underneath. However, installing them on conventional sheet roofs without optimization prevents the rear side from capturing reflected sunlight, reducing efficiency. “Over time, such installations experience higher degradation since they do not utilize the module’s intended bifacial advantage, essentially functioning like a standard monofacial module.”

Structural flaws often arise due to inexperienced engineering, as some installers fail to account for factors such as tilt angles, row spacing, and albedo enhancement. ” Unfortunately, many novice EPC companies overlook the engineering aspects. The right combination of components, such as properly rated inverters and optimized mounting structures, impacts at least 30% of system performance. If the design is incorrect, the energy yield will be compromised, regardless of module quality,” Alex noted.

The problem is exacerbated by an influx of new solar installers entering the industry. “There were a lot of people complaining about new players without technical expertise coming in. Many of them use bifacial modules without proper mounting structures, cables, and other necessary components,” another rooftop installer noted.

Use of Low-Quality Materials

Some installers construct mounting structures using low-quality materials, such as iron pipes available in hardware shops, which they manually cut, weld, and paint. Such makeshift structures lack durability and may compromise system longevity. Similarly, improper cable termination and inverter selection can hinder the additional energy yield that bifacial modules generate.

Alex said studies were conducted using various modules, including polycrystalline, monocrystalline, half-cut, bifacial, and TOPCon technologies. “Considering appropriate inverters are used, we observed that TOPCon modules performed the best, with bifacial modules following closely. However, inverter selection plays a critical role in capturing this additional yield. Older inverters may not efficiently handle higher voltage modules, leading to clipping during peak hours. Newer inverters designed for modules up to 750-800W peak are better suited for optimizing performance.”

Another crucial factor often overlooked is cable specification. “Now, lower wattage modules may need only 4 sq mm cables, but as the module wattage increases, the cable spec needs to be updated. Everyone goes for higher-wattage TOPCon bifacial modules, but no one cares about the cable spec, which must carry the current (which has increased due to the higher-wattage module), according to an installer.

Indian solar module manufacturers have leaned towards TOPCon modules over its other mainstream rival – HJT (Heterojunction).

Installers say bifacial modules should be installed at least one meter above the surface to enhance rear-side light capture and reduce shading risks. Open-racking systems must be used to avoid structural components obstructing the rear surface. Proper tilt angles and row spacing should be carefully designed based on site-specific conditions. The albedo effect can be enhanced using reflective materials like specialized coatings beneath the modules.

“Bifacial modules require different mounting structures, including a tilt and a reflective surface beneath them. While this increases project costs, customers who understand the technology and its benefits are willing to absorb these costs, given the 5-10% additional yield potential. The added cost for necessary modifications, such as reflective paint and elevated structures, is relatively minimal—approximately ₹10,000 (~$114) for a 3-5 kW system,” Alex noted.

The government has been aggressively promoting the PM Surya Ghar: Muft Bijli Yojana, which targets installing rooftop solar systems in 10 million households by 2027. While this has boosted capacity additions in the residential solar segment, the regulatory landscape has been found wanting with regards to newer technologies. Large-scale projects follow standards for mounting structures, but the rooftop solar segment lacks similar enforcement. Distribution companies and the Ministry of New and Renewable Energy’s nodal agencies conduct inspections to verify module wattage and subsidy eligibility but do not evaluate structural integrity or electrical safety.

Harshal Akhouri had recently explained in an interview with Mercom that the absence of standards for mounting structures could affect the structural integrity of rooftops post-solar system installation.

Installers also emphasized the importance of proper maintenance for optimal bifacial module performance. They must carry out regular infrared thermography to detect and address hotspots early, preventing long-term damage. The modules and the reflective surfaces beneath them require regular cleaning, as dirt and debris can significantly reduce efficiency.

The increasing adoption of bifacial modules highlights the need for proper installation techniques. While the additional optimization cost is relatively low, ensuring well-engineered installations is the real challenge. It is time for regulators to prescribe internationally accepted standards for mounting structures and using bifacial modules in rooftop solar installations.