A three-year field experiment comparing the performance and reliability of passivated emitter and rear cell (PERC), tunnel oxide passivated contact (TOPCon), and silicon heterojunction (SHJ) modules in desert climates found that HJT modules exhibited the highest degradation, while TOPCon modules showed the lowest degradation.

Scientists from Qatar’s Hamad Bin Khalifa University (HBKU) have conducted a comprehensive three-year field experiment, comparing the performance and reliability of PERC, TOPCon, and HJT solar modules in desert climates. They assessed the panels indoors and outdoors to evaluate degradation over time, performance ratios, and specific energy yield across seasons.

“While PERC serves as the industry benchmark, TOPCon and HJT technologies whose field performance and reliability remain inadequately studied are rapidly being adopted,” researcher Maulid Kivambe told pv magazine. “The desert climate, characterized by high irradiance, elevated temperatures, intense UV radiation, heavy soiling, and high humidity, provides an ideal environment to gain critical insights into their real-world energy yield, degradation mechanism, and material-level reliability.”

The experiment included eight sets of modules: one HJT monofacial panel, one HJT bifacial, two TOPCon bifacial, and four PERC bifacial from undisclosed tier-1 manufacturers. The modules were installed in 6-module strings, each connected to an inverter operated at maximum power point tracking (MPPT).

The testing field was located in Doha, with a near-latitude tilt of 22 degrees, facing south, and with about 1.1 meters of ground clearance. The modules were tested in the field and after one year and three years in a lab.

“HJT modules, despite their high initial efficiency and favorable temperature coefficients, exhibited a degradation rate of up to 8.73% over a three-year period,” Kivambe said. “It must be noted that the manufacturer’s datasheet linear maximum power degradation was 0.25% per year, and the guarantee of power after 25 years was 92%.”

Overall, HJT modules have shown the highest degradation in power, with an 8.73% loss for SHJ-M1 and a 6.50% loss for SHJ-M5. Multicrystalline PERC and cast-mono PERC modules exhibited higher first-year degradation compared to monocrystalline PERC and TOPCon modules. TOPCon-M2 modules degraded by 0.14%, the lowest degradation of all modules.

“The study revealed significant variability in the reliability of TOPCon modules. One model demonstrated substantial degradation, while another exhibited the lowest degradation among all tested modules,” said Kivambe. “This suggests that the reliability of TOPCon modules in desert climates may be highly dependent on specific design choices, materials, and manufacturing processes.”

Bifacial HJT and TOPCon modules demonstrated superior and consistent performance compared to PERC when measuring specific energy yield (SEY), especially during the summer months. In winter, however, the energy yield gap between PERC and the more advanced technologies narrowed.

“A particular PERC model showed energy yield and performance ratios similar to HJT and TOPCon modules across all seasons. This indicates that, with appropriate design and materials, PERC modules can perform competitively, even in desert environments,” added Kivambe.

The team compared the standard performance ratio (PR) to the temperature-corrected PR to analyze the performance loss caused by heat. Their calculation showed the highest heat-related performance loss at 9.89% for TOPCon-M2, while SHJ-M5 had the lowest loss rate at 5%.

“We plan to investigate the back-contact technologies (BC-TOPCon and BC-HJT), as the industry is shifting towards this technology,” said Kivambe. “We also plan to complement our findings with modeling to develop an understanding of the degradation mechanisms and ways in which SHJ and TOPCon PV modules can be optimized for reliability and durability improvement.”

They presented their findings in “Comprehensive assessment of performance and reliability of PERC, TOPCon and SHJ modules in desert climates,” which was recently published in Solar Energy.