Jan. 10, 2022 

By Hongbin Fang
Director of Product Marketing

The solar industry faces a long list of challenges and opportunities as it moves toward its terawatt future. From dealing with supply chain constraints, a shifting policy landscape, and climate-induced extreme weather on the one side to rapid innovation, accelerating deployment, and fast-growing grid penetration on the other, the solar community indeed lives in interesting times.

PV magazine USA recently convened a virtual roundtable titled “Solar Opportunities in An Age of Extremes,” where I joined other participants to talk about the ripple effects of the shift to large-format modules (500 W-plus) and how those big modules are driving design changes. Large modules have been a compelling topic lately, and we at LONGi have been active participants in the industry discussion (for example, see the recent article I cowrote with my colleague CJ Fu for Solar Power World and my previous blog post).  

Reliability is the Foundation

I made a brief presentation before the panel discussion, noting how reliability is the foundation for achieving a lower levelized cost of energy (LCOE). Our comprehensive, life-cycle management approach to reliability starts with R&D, including module design and material selection, such as the robust glass-glass construction of our larger modules and inherent durability of monocrystalline wafers. The life-cycle continues all the way through the value chain of process optimization, rigorous testing, high-quality manufacturing, field performance testing, and a continuous loop of data analytics to after-sale care focused on ensuring reliable performance.

Some of the main value propositions of large modules are their ability to help bring down balance of systems (BOS), O&M and labor costs while increasing energy yields, which then pushes down the LCOE. But without reliable performance over the lifetime of the system, those benefits can be lost. It’s critical that consistent energy yield be ensured throughout the 30-year-plus lifetime of the system, I explained. There must be enough margin in the module design to survive and perform in extreme weather conditions for decades. 

Not All Large Modules Are Created Equal

As I often say, not all large modules are created equal. Supported by 2 mm + 2 mm glass in the middle, module size cannot go infinitely larger without compromising on reliability. I shared a few examples of certain reliability risks inherent in oversized modules (210 mm, 60-cell or 66-cell format) that are not found in 182-mm, 72-cell large-sized modules. For example, the oversized modules are 1.3 meters wide, which our stress tests have shown can lead to at least 40% more deformation under the same mechanical load. This raises the risk of cell microcracking and glass breakage, leading to compromised reliability. Other issues include the higher current of the oversized modules, which can require redesigned string and related electrical BOS configurations.

As Pedro Magalhães of Arctech Solar noted, large-format modules now make up the vast majority of utility-scale projects. He estimated that approximately 85% of new builds in the U.S. now feature the large modules, with almost all of those he was aware of using the large-sized, 182-mm format versions. He also explained some of the challenges that tracker suppliers like Arctech face in adapting their trackers to these larger-dimension, heavier panels, and the need to address structural stability, electrical BOS, and extreme weather resiliency issues in their equipment.

Ben Damiani of Solar Inventions also talked about how the larger size of the modules results in greater flex and stress on all the layers of the module, including the cells, glass and interconnections. He also noted that just because a module has a certain STC (standard testing condition) rating, it may not necessarily perform at that level once it’s fielded. He foresees cell microcracking issues with the larger modules, leading to more hotspots and impacts on the overall long-term health of the modules—and performance of the overall system.

Future Direction: Boosting Efficiency

As we neared the end of our session, I said that the key moving forward is not to make larger and larger modules for the sake of more power output (and sacrificing reliability), but to focus on cell and module efficiencies to drive down LCOE even more. One clear takeaway from the discussion is that while many customers have an understanding of the possible reliability risks with some large-format modules, we all want more field performance validation of these relatively new products. With that real-world data, we can design and build even more reliable, robust and efficient modules that will help accelerate the deployment of large-scale solar projects in the U.S. and around the world.