Three-year field test proves reliability of TOPCon and HJT solar modules in desert regions

Researchers from Qatar's Hamad Bin Khalifa University (HBKU) conducted a comprehensive three-year field experiment comparing the performance and reliability of PERC, TOPCon and HJT solar modules in a desert climate. The panels were evaluated both indoors and outdoors to assess degradation over time, performance ratios and specific energy yield in different seasons.

While PERC serves as the industry standard, TOPCon and HJT technologies, whose performance and reliability in the field have not yet been sufficiently explored, are rapidly gaining ground. The desert climate, characterised by high solar radiation, high temperatures, intense UV radiation, heavy pollution and high humidity, provides an ideal environment for gaining important insights into their actual energy yield, degradation mechanism and reliability at the material level.

The experiment involved eight sets of modules: one monofacial HJT panel, one bifacial HJT panel, two bifacial TOPCon panels and four bifacial PERC panels from undisclosed Tier 1 manufacturers. The modules were installed in strings of 6 modules, each connected to an inverter operating in maximum power point tracking (MPPT) mode.

The test field was located in Doha, with a tilt angle of nearly 22 degrees, south-facing and with a height above ground of approximately 1.1 metres. The modules were tested in the field and after one year and three years in the laboratory.

Despite their high initial efficiency and favourable temperature coefficients, the HJT modules showed degradation of up to 8.73% over three years.

According to the manufacturer's data, the linear maximum power decline was 0.25% per year and the power guarantee after 25 years was 92%.

Overall, HJT modules showed the highest power decline of 8.73%. Multicrystalline PERC and cast mono PERC modules showed higher degradation in the first year compared to monocrystalline PERC and TOPCon modules. TOPCon modules degraded by 0.14%, which is the lowest degradation of all modules.

The study revealed significant variability in the reliability of TOPCon modules. One model showed significant degradation, while another showed the lowest degradation of all modules tested. This suggests that the reliability of TOPCon modules in desert climates may be highly dependent on specific design solutions, materials and manufacturing processes.

Both HJT and TOPCon bifacial modules demonstrated excellent and consistent performance compared to PERC in terms of specific energy yield (SEY), especially in the summer months. However, in winter, the difference in energy yield between PERC and more advanced technologies narrowed.

A specific PERC model showed similar energy yield and performance ratios to HJT and TOPCon modules in all seasons. This suggests that with the right design and materials, PERC modules can achieve competitive performance even in desert environments.

The team compared the standard performance ratio (PR) with the temperature-corrected PR to analyse the power loss caused by heat. Their calculations showed that the highest heat-related power loss was 9.89% for TOPCon, while HJT had the lowest loss at 5%.

The researchers plan to investigate rear-contact panels in the same way, as the industry is moving towards this technology. They also want to supplement their findings with modelling to better understand the degradation mechanisms and ways in which HJT and TOPCon photovoltaic modules can be optimised in terms of reliability and increased lifetime.