LONGi’s Back Contact Modules Outperform TOPCon in Rooftop PV Demo in Qinghai, China

New operational data from a rooftop photovoltaic (PV) demonstration project in Qinghai Province, China, highlights the superior performance of LONGi’s Back Contact (BC) modules over traditional TOPCon technology. The results confirm a 3.16% power generation advantage for BC modules, further reinforcing their value in real-world residential applications.

Located in a residential complex in Xining, Qinghai — at an altitude of 2,327 meters with 2,500 annual sunshine hours and a continental plateau semi-arid climate — the test site is designed with a fixed-tilt angle of 10°. The performance comparison was conducted between LONGi’s HPBC 2.0 Hi-MO 9 BC modules (11.7 kW system, 650 W/module) and conventional TOPCon modules (49.8 kW system, 610 W/module), both with identical module dimensions (2382 x 1134 mm).

Monthly Generation Performance

Normalized data at the string level showed that in April 2025, LONGi’s BC modules generated 288.21 kWh/kW, outperforming TOPCon modules, which delivered 279.95 kWh/kW. This translates to a 2.95% monthly generation advantage in favor of BC technology.

Weather-Specific Analysis

Overcast Day (April 14): BC modules delivered 3.16% more power per kilowatt than TOPCon. Five-minute interval monitoring revealed that BC modules had a better weak-light response, initiating generation earlier and maintaining higher output during low-irradiance morning periods.

Sunny Day (April 12): Under full sunlight, BC modules retained a 2.82% performance edge, again demonstrating earlier morning activation and sustained higher energy output.

Technological Edge

LONGi’s HPBC 2.0 technology is built on proprietary TaiRay silicon wafers and incorporates advanced dual-polar composite passivation. The front grid-line-free design enhances light absorption and energy conversion efficiency, leading to consistent performance advantages across varied conditions compared to TOPCon.

These results underline the growing viability of BC technology for residential rooftop PV applications, especially in high-altitude, variable-light environments. As LONGi continues to refine its HPBC product line, the technology is positioned to lead in both performance and adoption across global solar markets.