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9 November 2022

LONGi launches HPBC-type module for distributed market

Last week LONGi, launched its new solar module product, Hi-MO 6, which uses Hybrid Passivated Back Contact (HPBC) technology, and is geared towards the distributed solar market segment.

It’s only now with this product announcement, using HPBC, that LONGi’s post-PERC technology route takes shape. Already by now the rest of the industry had largely announced plans to move onto TOPCon and heterojunction, with around 210 GW and 150 GW of manufacturing expansion efforts announced respectively. So those are the two main next steps beyond Mono PERC, whose efficiency has been ratcheted up to levels very close to its theoretical limit of 24.5%.

LONGi is the largest solar manufacturer, with $12.5 billion revenue in 2021, and 50%+ revenue growth so far this year. Even with a stronger position among wafers than downstream (60 GW wafer output, 30 GW module in the first nine months of 2022), it was time for the company to announce its post-PERC cell and module technology route.

LONGi’s R&D budget is one of the largest in the industry, or perhaps the single biggest of all, but its efforts are split between technology routes, not to mention its recent foray into alkaline electrolyzers. Its R&D budget has produced a string of heterojunction cell efficiency records over the past year or two, the latest ratings being 26.5% and 26.1% for n-type and p-type heterojunction. Incidentally the company has also reached 25.21% and 25.19% efficiency for n-type and p-type TOPCon. Yet the company’s largest heterojunction manufacturing effort so far is a 1.2 GW pilot line announced in April, miniscule by the standards of an industry leader.

In contrast it opened a 15 GW HPBC factory in September, and will manufacture some 25 GW next year, according to statements from August. LONGi has a dubious advantage over its rivals for cell efficiency laboratory results in general, and a clear advantage for heterojunction, but for HPBC it stands alone, and still near-alone counting similar technology.

The question then is how transformative this HPBC technology is, which LONGi calls “epoch-making” and describes as the product of “many years” of research. For the metric of cell efficiency, LONGi claims over 25% for its HPBC and 25.3% for its hydrogen-passivated HPBC variant. That is somewhat better than many TOPCon results, but not as high as the various heterojunction records most of which LONGi has produced itself.

HPBC is more advanced than TOPCon, which LONGi has branded merely “transitionary.” HPBC and other variants of Interdigitated Back Contact (IBC) can in theory be combined with heterojunction, and LONGi surely will try that. With LONGi’s announcement TOPCon and heterojunction are no longer a lone duo following on after PERC. According to the crude metric of maximum theoretical efficiency, IBC, the third option, may even be more advanced than heterojunction (29.1% compared to 28.7%), but this also means it is harder to manufacture and may remain too costly to sweep the industry.

IBC cell designs involve moving the cell’s busbars to the rear. Put simply, the result is a product that is more efficient in the face of partial shadow and other low-light conditions, but more challenging to manufacture. Incidentally, the busbars are also not visible to onlookers, which has some aesthetic advantage for BIPV installs. That may be appreciated just fine in Shanghai and Beijing and other Chinese cities, but this product sounds bound for export for the greater part by far to places such as Japan and Europe.

We ought to mention another company, more focused on this type of technology. Aixu Technology’s IBC variant is called All Back Contact (ABC). Launched earlier this year Aixu claims cell efficiency of 25.5% and module efficiency of 23.5%, little different from LONGi – but its actual cell efficiency has been recently claimed at a superior 26.2%. Aixu claims to have eliminated costly silver from its designs, which if straightforwardly true strikes a contrast with both TOPCon and heterojunction, but its costs are still higher than LONGi’s HPBC, with a production process featuring fully fourteen steps.

Aixu shipped up to 9 GW of PERC cells in Q3, and soon opens a 6.5 GW ABC cell factory in Zhuhai, Guangdong province, which will combine with another 2 GW of ABC production capacity.

For mass production module efficiency the Hi-MO 6 product variants range from 21.8% to an impressive 23.2%, up from below 22% for number 5 in the series and below 21.5% for number 4. Li Hua, a senior LONGi researcher, states that HPBC could even surpass heterojunction to reach 26.5% cell efficiency and 24% module efficiency.

Without claiming an advantage on these simple overall efficiency ratings, LONGi states that overall output is nonetheless 10% higher than PERC products based on simulation of real-world conditions for various regions of the world. This average generation advantage is attributed to subtler factors such as reduced efficiency losses from high temperature and strong low-irradiation performance.


Low-irradiation performance is valuable for rooftop and especially BIPV installations due to generally inferior conditions and usually no trackers. But LONGi also advertises its new product as suitable for the distributed sector on the basis of quality assurance. HPBC will allow a simpler approach to back-welding than a conventional Z-shaped ribbon connection design, making the cells physically sturdier and less liable to crack. And IBC or HPBC type designs suffer less degradation from partial shadow.

A related claim is that these Hi-MO products will have “intelligent optimizers” which will react to shadowing, high dust coverage, and other threats to the system to prevent damage to the electronics – with reactions including module-level and also string-level automatic shutdowns. Then there’s claims of aesthetic adaptability – so this is a high-quality product, including for buildings where any repair work after the initial installation would be an unwelcome obstruction.


Another property identifying Hi-MO 6 as a distributed product is more prosaic – it is 182mm-based, not one of the 210mm 600+ Watt mammoths which are too heavy and unwieldy for various types of rooftop installs. Even the most powerful Hi-MO 6 variant weighs the same as previous products – 27.5 kilograms for between 580 Watts and 600 Watts.

LONGi’s release of a distributed solar product fits with China’s 2022 solar policies, which have seen 35.3 GW of distributed solar built in the country in the first three quarters of the year and only 17.3 GW utility-scale. But it’s also matched by a global trend, with distributed-heavy European markets revving back up from a decade of slumber, and even the US’ First Solar working to release a distributed module product for the first time come 2024.

The fall of polysilicon and thus module prices will bring utility-scale solar back for a few years, but the longer-term trend is for ever greater dominance by distributed solar installations, as these benefit disproportionately from further market reforms and structures such as VPPs.