Although shingles cells have been around for some time, Tongwei has been a significant adopter of the technology as a manufacturer with significant scale. If shingling can overcome some hurdles, it could prove to be a welcome solution as unshaded locations for PV become difficult in the mature solar market.
There are new 400 W-plus shingled solar modules on the market, which serve the demand for high-power, more durable, stylish all-black products. The Chinese cell giant Tongwei is responsible for the new modules – its Terra series was released in 2022. The power classes of the Terra series are 400 W to 430 W and efficiencies vary from 20.1 to 21.7%.
Tongwei is notable as a Chinese supplier of shingles, which involves cutting solar cells into strips that are then bonded together with an electrically conductive adhesive (ECA) that overlaps slightly along the edge of the long cell.
Yan Li, director of Tongwei’s shingled module department, says shingled products offer “advantages in power, efficiency and reliability” and technical advantages “due to high-density packaging and flexible interconnection.”
“However, we believe that the different aesthetic appearance of the high-performance Terra shingle modules will target some markets and increase our share and brand influence in the residential construction segment,” says Li. Along with stylish aesthetics and power, shingles also offers durability, Li claims, due to its “low hot-spot risk, micro-crack resistance and exceptional mechanical load performance.”
Tongwei, which has 70 GW of annual cell capacity – and plans to reach 130 GW to 150 GW by 2026 – says it owns 6 GW of Terra lines, while module capacity has reached 14 GW, including semi-broken sets.
While the introduction of Tongwei shingles represents a major technological advance on a scale, the commercialization of shingles has been years in the making. Silicon Valley-based Solaria Corporation, founded in 2000, began selling shielded PowerXT modules in 2016. Solaria claims to own “over 250 issued and pending patents in the field,” many of which are believed to be related to shingles.
The California-based company has been fiercely protective of what it considers intellectual property (IP). In June 2022, it settled a patent infringement lawsuit filed in 2020 against Chinese-Canadian manufacturer Canadian Solar for allegedly infringing shingles technology.
Solaria wants to merge with installer Complete Solar and bring the resulting Complete Solaria business as a vertically integrated company similar to SunPower. A complete Solaria would manufacture the roughly 400W PowerXT modules in a “low capital investment” model, with production being carried out by manufacturers in Thailand, Cambodia, Vietnam and India.
Tongwei says that he started the R&D module in 2016 and considered it important to establish an intellectual property rights system. “Since the beginning of the shingle product project, Tongwei has already started the layout at the patent end,” says Li. “After seven years, Tongwei has formed an independent road map of shingled technology.”
George Touloupas, director of technology and quality at quality assurance firm Clean Energy Associates (CEA), points to Tongwei’s statements that the company has “its own way of interconnecting,” without IP concerns. Touloupas adds, “The technology manager for singled modules is previously from SunEdison and is bringing his shingling experience from that company to Tongwei.”
Looking under the hood, Touloupas notices that the interconnect methods used by Tongwei appear to have additional advantages. “Tongwei is also researching a different connection technology where the shingle cells follow a jagged pattern that is even more resistant to hot spots and has less loss due to shading.”
Researchers at Germany’s Fraunhofer ISE published test results of such a shingled module cell layout in the journal Progress in Photovoltaics in 2021. The researchers call the technique a “matrix layout,” in which cut cell pieces are placed in an offset pattern. , “half cell length” – half-cut shingle cells are placed at the edges, creating a standard rectangular module shape.
“By moving solar cells from one row to another by half the length of the cell, an additional parallel connection is created for the solar cells within each row,” the researchers wrote.
The Fraunhofer ISE team tested matrix tile modules in various shading scenarios, including shading diagonally across the module, and found that the matrix design resulted in significantly increased energy yield. The electric current could bypass the shaded areas more efficiently thanks to the shifted cell layout. The layout also reduced the risk of hotspot mechanisms arising from partial shading.
As ideal, unshaded locations for solar power become increasingly scarce, the Fraunhofer researchers concluded that the matrix layout becomes increasingly valuable. “The huge potential for solar energy production faces a huge number of irregular shading conditions, making shading tolerance a very important consideration,” the researchers wrote.
The advancement of shingling technology and its adoption in manufacturing on a larger scale suggests that the technology may be entering a new era of development. However, the competition with other technologies continues to be fierce.
“Four or five years ago, slab modules had about (a) a 10% efficiency advantage over standard – at the time – full-cell quad-rail modules; this is no longer the case,” says CEA’s Touloupas. “We know how to use half-cut cells, multi-rail, cladding or tiling; that 10% module area efficiency has evaporated.”
As Tongwei and other proponents of shingling argue, there are many benefits beyond efficiency. Using ECA instead of lead-based busbars is one such benefit – it adds environmental aspects to shingles, in addition to durability, shading tolerance and aesthetics. As with some other powerful technologies, the silver content in ECA needs to be further reduced to make it sustainable for use in larger quantities (see box).
Low silver ECA
ECA has a relatively high silver content – researchers have found up to 70-80% silver in commercial products as recently as 2019. However, this may change with silver-coated conductive particles and optimized particle shapes. “We probably started reducing the silver consumption of our adhesives maybe 10 years ago,” says Rich Wells, chief technology officer of Ohio-based Nagase Chemtex America, a Japanese manufacturer with more than 15 years of experience supplying solar companies. . “Recently, I would say there have been some very nice breakthroughs in the last five years.” Wells says progress has been made in reducing the silver content of ECA for solar energy through two key developments. The first is to replace pure silver particles with silver-coated alternatives. The copper at the core of the particles, Wells says, “is one of many options.” Nagase Chemtex worked with researchers at the Netherlands Energy Research Center to develop silver-coated particles for ECA. The Ohio business researchers are also trying to optimize the shapes of the particles. Longer, flatter particles provide equivalent conductivity with less conductive metal. “The percolation models for building a conductive network through the system show that you can create this conductive network with less (metal) loading if you have a higher aspect ratio,” says Wells. Mark Francis, Sales and Marketing Manager at Nagase Chemtex, has a long history in the semiconductor industry. He says that when he joined the company primarily to develop its solar energy business, he was surprised to hear that solar power manufacturers use lead solder to connect cells together. “We see an effort to reduce both the cellular network and interconnections,” says Francis. “I wonder when they’re going to turn around and say we don’t want to do cell interconnects with lead anymore?”
Tongwei reports that it is working to optimize both the ECA’s bond strength and its conductivity – which it calls the non-silver and silver systems, respectively. “We are committed to bringing our efficient and environmentally friendly Tongwei Terra series to more households,” the company states.