Heterojunction Technology in Solar Panels

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Written by Giannis Taousanidis, electrical engineer at Wattcrop

HJT (heterojunction) panels, also known as HIT (heterojunction with intrinsic thin layer) panels, are the new generation of solar panels. They are known for their high efficiency and improved performance under different weather conditions, making them an attractive option for residential and commercial solar installations. But what sets them apart from traditional solar panels and why are they becoming increasingly popular?

The technology behind HJT panels is based on the use of a heterojunction, which is created by layering a thin film of amorphous silicon on top of a substrate of crystalline silicon. This combination allows for the absorption of a wider range of light wavelengths, leading to higher energy conversion efficiency. HJT panels have efficiency rates of over 23% (Longi claimed in November 2022 an efficiency rate of 26.81% achieved in their labs), compared to around 20% of older panels and around 22% of PERC panels. While not significantly more efficient, HJT panels have other advantages such as better performance in low light conditions and high temperatures, which can lead to higher energy yield over the course of a year.

HJT technology was first developed by the Japanese company Sanyo, and later adopted by other major solar panel manufacturers such as Canadian Solar and JinkoSolar. Not only are they more efficient, but HJT panels also have a smaller environmental footprint compared to traditional solar panels as they require less silicon and other materials to produce.

Another major advantage of HJT solar panels is that they tend to have lower degradation rates compared to traditional c-Si solar panels. This is achieved because of the intrinsic thin layer that is used in the manufacturing process. This thin layer protects the solar cells from environmental factors such as high temperatures and UV light, which can cause traditional c-Si solar panels to degrade more quickly. Therefore, HJT panels can maintain a higher level of performance over a longer period, leading to a longer lifespan and higher energy yield.

In terms of utility-scale projects, HJT solar panels are not yet widely used due to the higher cost today, but they are expected to be increasingly adopted in the near future. Utility-scale solar power plants require a large amount of solar panels to generate significant amounts of electricity. The increased efficiency and lower degradation rates of HJT panels make them a more attractive option for these projects as they can generate more electricity per panel and maintain a higher level of performance over the years compared to traditional solar panels. Additionally, utility-scale projects are more likely to benefit from economies of scale, which could further reduce the cost of HJT panels.

Although the cost for producing and therefore purchasing HJT solar panels is now higher, the keystone when assessing energy projects is, as we know, the Levelised Cost of Energy (LCoE)*. For HJT solar panels, the LCOE is generally lower than traditional solar panels, due to the increased efficiency and lower degradation rates. A 2020 study from the National Renewable Energy Laboratory (NREL) showed that HJT panels had an average LCOE of $0.06 per kWh, compared to $0.09 per kWh for traditional c-Si panels.

In conclusion, HJT panels are probably the next big thing when it comes to solar panels, due to their higher efficiency and mainly improved performance under different weather conditions. They have a smaller environmental footprint and a relatively low LCOE compared to traditional solar panels, which makes them financially attractive for solar power generation. While HJT solar panels are currently used primarily in residential and commercial solar installations, they are expected to be increasingly used.