Cold-weather field test shows LONGi BC modules outperform TOPCon by up to 7%

In late January 2025, Kunming, normally known for its mild, spring-like climate, experienced a rare period of persistent rain and snow, with daytime temperatures falling to just 4 °C. These unusual conditions created an ideal opportunity to evaluate how different solar module technologies respond to low temperature, low light, and unstable weather. Data collected over six months from a controlled rooftop test shows that LONGi’s second-generation back-contact (BC) modules consistently outperformed conventional TOPCon modules and delivered even greater gains during the extreme cold snap.

Rooftop system compares BC and TOPCon modules directly

The rooftop system, with a total capacity of 169 kWp, includes a dedicated field test area for side-by-side module evaluation. In this test zone, 20 HPBC (Hybrid Passivated Back Contact) 2.0 modules were installed alongside 20 TOPCon modules. Both sets used a 5-degree fixed tilt, mounted 1.5 meters above the surface to simulate typical low-latitude ground-mounted conditions. The system was set up so that most of the solar power generated was used on-site, and any extra electricity was fed into the local grid, making the results reflect typical real-world usage.

Six months of testing confirm that BC modules consistently outperform TOPCon

From November 2024 to May 2025, spanning Kunming’s autumn, winter, and spring, the BC modules in the field test area showed a clear advantage. Per unit of surface area, they generated 7.32 percent more electricity than the TOPCon modules. When measured by output per installed kilowatt, the BC modules maintained a 3.71 percent advantage throughout the period.

These gains mean more energy from the same installation footprint and higher returns from each installed watt, even in a location where weather conditions shift rapidly from sun to rain or snow.

Extreme cold increases performance advantage of BC modules

The January 2025 cold wave provided an even tougher test. Between 15 and 31 January, during the most severe weather, the BC modules delivered an average gain of 5.7 percent over the TOPCon modules, which is nearly two percentage points higher than their six-month average advantage. This demonstrates that the BC technology’s low-light and low-temperature performance not only holds steady under stress but can increase when conditions are at their most challenging.

Kunming field data confirms white paper’s conclusion: BC delivers higher yield and resilience

The results from Kunming confirm that LONGi’s HPBC 2.0 modules offer strong, stable output across a wide range of conditions. For developers, investors, and end users, the message is clear: choosing technology that excels in both everyday operation and extreme weather is the best way to protect energy yield and ensure consistent returns over the lifetime of a solar project.

The test findings also reinforce the conclusions of LONGi’s Back Contact Solar Technology Development White Paper, launched at Intersolar 2025. Both the controlled field data and the broader industry analysis point in the same direction: back contact delivers measurable advantages over TOPCon in efficiency, durability, and system economics. With front-side shading eliminated, BC modules achieve higher conversion efficiencies, and the white paper documents lab-to-production gains above 25 percent module efficiency with a clear roadmap toward 26 percent. In parallel, BC’s lower operating temperatures and reduced degradation rates improve long-term stability and slow the loss of output over decades of operation. For project developers and investors, these technical strengths translate into bankable benefits: higher energy yield per square meter, up to 4-7 percent BOS (balance-of-system) savings from reduced area and mounting needs, and stronger risk protection under extreme conditions. Taken together, the Kunming results offer localized proof of what the white paper establishes at industry scale: BC is not an incremental step but the superior pathway for mainstream PV.

Read the full white paper on BC here or use our summary.