A new generation of flexible, light modules is coming to the market. Thanks to back contact technology, which offers its own design flexibility and durability, new products can break into a difficult market segment.
It’s an argument as old as the modern solar industry: Not all roofs or other surfaces are suitable for traditional glass-encased solar modules. As a result, special modules are needed to overcome obstacles. There is a wide range of module sizes and dimensions, lightweight versions for roofs that cannot withstand the load of glass, adhesive installation to avoid penetration of ceiling surfaces and even curved or flexible modules that can follow the contours of the roof.
The logic of this thinking is clear. To achieve the goals of rapid and large-scale decarbonization, it is necessary to install solar energy on as many available surfaces as possible. To some extent, there is recent evidence to suggest that this is understood. One example is balcony solar power, which became common in Europe as EU countries stared at an energy crisis fueled by Russia’s invasion of Ukraine.
About a decade ago, the first solar technology that attempted to meet the need for a flexible and lightweight application was thin film – specifically copper indium gallium selenide (CIGS) solar. Manufacturers such as Global Solar and MiaSolé are aiming to introduce flexible modules that could offer relatively good conversion efficiency – 10.6% and 14.3% – in a flexible form.
However, both companies struggled to compete and were effectively shut down after being acquired in 2013 by Hanergy – a company whose shares were suspended from trading on the Hong Kong Stock Exchange for three years before the company pulled the stake and went private. .
The next generation of flex
What a difference a decade makes. At the Solarex trade fair in Istanbul, Chinese metal winding (MWT) manufacturer Sunport Power presented its S-Flex module – a light, flexible product with an efficiency of 21.8% and a power of 365 W to 385 WW
“Flexible modules are very new in Turkey, so the reaction is very good,” says Katrina Xu, Sunport’s marketing director, as show attendees stopped by the company’s booth to explore S-Flex. “In March, we were at Solar Solutions and there was a lot of interest, because the housing market in Europe is growing well. In Germany, these modules are often used in balcony applications.”
This year, Sunport enters the international scene after more than two years of isolation due to China’s strict Covid-19 restrictions. “It was difficult for us to go outside of China,” says Xu. “For a new product, we have to talk directly with customers. And in the last three years, we couldn’t do that.”
The MWT technology used in the S-Flex is a back contact cell where laser drilled holes or through holes are formed through the disc, allowing the front metallization to wrap through the hole to the back side. The cell itself in this case is a PERC device (passived emitter rear contact). The cells are encapsulated in a light but durable polymer material – in company parlance “2D encapsulation” – resulting in a 5.7 kg module that can withstand a bending radius of up to 0.3 meters.
As a back contact technology, MWT eschews traditional busbar cell connection and instead uses copper front metallization and a conductive backplate. “This makes the technique particularly suitable for flexible encapsulation,” says Xu. “If you make a strip for a solar cell, when the module is bent, there is tension at the welding point, which easily causes microcracks. And the railless design reduces the shading area of the module to increase the conversion efficiency of the module. We only have a self-made copper conductive backing plate. So we have no welding voltage. And if you bend it, we don’t have any problems like with the power rail module.
Connecting MWT to flexible encapsulation seems to be a neat trick. Suntech pioneer Zhengrong Shi thinks so, noting that “because the tab is on the same surface, you don’t have to consider bending.” As of 2018, Shi has been marketing “glassless” lightweight modules under the Sunman Energy brand.
That the two companies are charting a similar course isn’t entirely surprising, as Sunport CEO Fengming Zhang is a former chief scientist at Suntech, and both Zhang and Shi are alumni of the University of New South Wales. Shi says Sunman delivered 200MW of light crystalline silica modules in 2022 and expects that to “at least double” this year.
When it comes to shipments, Sunport has bigger goals. The company aims to sell 300 MW to 1 GW of S-Flex this year. “The main market is Europe, but we are also looking at Brazil, Japan and Australia,” says Sunport’s Xu.
The advantages of rear contact
Conductive backing plates provide additional benefits. Material supplier Endurans supplies leading backplanes primarily to European and North American module manufacturers. Materials business director Lawrence Theunissen compares it to a printed circuit board in the way it conducts electrons “according to the layout of the cells in the module.” In addition to the flexible modules themselves, this functionality provides “flexibility” for module manufacturers, he says.
“Another way to look at flexibility—and this is another big advantage of using conductive backplanes—is the use of flexibility to set up the electrical pattern,” he explains. “Usually traditional modules have a couple of strings inside the module – a matrix layout – so it’s not too complicated.”
In contrast, Theunissen says, module manufacturers can propose cell configurations for Enduranes and the backplane material can be designed accordingly. This can be particularly useful in new solar applications, such as vehicle-integrated photovoltaics. Endurans worked with startup Lightyear on the aborted development of the Lightyear 0 solar vehicle.
Although the Lightyear team failed in their attempt to bring a high-end electric vehicle to market, “they made really good progress, especially on the solar side,” notes Theunissen. The modules developed by Lightyear were curved to fit the aerodynamics and aesthetics of the vehicle. In an attempt to pack as much active solar area as possible into a limited space, Theunissen says, “the cells are not aligned in a matrix arrangement, but in a non-linear fashion that seamlessly follows the shape of the car.”
Lightyear used interdigitated back contact (IBC) cells in their design instead of MWT, but both are served by conductive back plates. The material has a higher cost profile, as Endurans admits, but this is offset by the creation of added value, the company claims.
“For module manufacturers, we have clear evidence that the business model can be even more attractive than with standard modules,” says Theunissen. “It has a higher cost, but the pricing can be higher in the end market.” The Endurance executive adds that efforts are continuing to reduce material costs, including replacing copper in the backplate with aluminum.
Despite the promise of opening up a wider range of surfaces for PV through new module formats and back-contact technology, the space remains a niche market. “The reason solar is so successful is that it’s a standardized product that has a pretty good lifespan when it’s installed well,” says Jenny Chase, Swiss solar insight manager at BloombergNEF, a business intelligence firm. “This will be the biggest contribution to curbing climate change.”
Chase admits, however, that vehicle-integrated solar power can offer “psychological benefits, especially if it’s lightweight.” Knowing that the sun is charging while I shop can give me peace of mind.”
Of the applications that can be addressed with flexible, lightweight solar, he suggests that balcony solar might be “the best of them because it has some use.” The ease of installation also provides value to the industry, he said. “There is a bottleneck in installation work in Europe.”
A plus for Sunport is that S-Flex can be installed on roofs using sheet metal without drilling holes in the roof. “This product is very suitable for factories with metal roofs,” says marketing director Xu. “If you use our flexible module, you can directly use the glue and attach it. You don’t have to drill holes in the ceiling that can let water in.”
There are also savings in balance of system (BOS) and labor, Xu says, offsetting the higher panel price—a function of the higher material costs of the modules themselves. “If you see the total BOS costs – including installation systems – with traditional modules and the human resources required for installation, the costs are comparable. We only use glue, so the VSP is smaller.”
There is no doubt that rear contact technology in various forms is on the roadmap of many module manufacturers – including large producers. Sunport itself planned to release its next-generation technology at the SNEC trade show in Shanghai last month.
“It’s another back-touch technology,” says Xu. “The technology is familiar to us because it is rear contact. The surface has no holes, no strips, so the aesthetics are very good.”