A solar panel manufacturing process that has gotten some traction recently is “shingling.” Not to be confused with “solar shingles” used in building-applied photovoltaics, shingled modules cut solar cells into strips and overlap them inside the framed module. Intercell gaps are removed, and more silicon cells can be crammed into one module, increasing power output and module efficiency.
Shingled modules are likely the rightmost limit of crystalline silicon solar development. Without the introduction of dual-junction processes, like with heterojunction technology, which combines crystalline silicon with amorphous silicon thin-film to produce a high-power hybrid cell, a shingled module is the highest power and efficiency you can get with traditional, undoped crystalline silicon.
Let’s break down the basics of shingling technology.
While “solar shingles” and “solar tiles” are often interchangeable when it comes to building-applied photovoltaics, a module using shingling technology is actually different from one using tiling technology.
Suvi Sharma, founder of shingling pioneer Solaria, described crystalline silicon solar development as moving among four stages: 1) standard solar panels, 2) half-cut designs, 3) paving or tiling technology and 4) shingled modules.
“As you go toward each one, it’s a little bit better, a little bit better efficiency, a little better aesthetics,” Sharma said. “Shingling is the rightmost end of the spectrum, where you get all the benefits, but it’s also more costly and has the most IP. That’s why many companies have gone a different route to avoid the patents.”
For example, JinkoSolar uses a “tiling ribbon” to eliminate intercell gaps and make busbar connections across overlapped half-cut cells. The cells never actually touch each other and are only cut in half; thus the modules are not considered to be shingling.
“Jinko’s Tiling Ribbon (TR) technology is different from shingled modules. There is some overlap of cells that is facilitated by the tiling ribbon,” said Vikash Venkataramana, director of technical service and product management, JinkoSolar. “The ribbon is designed so that it can be positioned between the overlapping cells to eliminate any direct contact between the overlapping cells, removing any concern of mechanical stress. Special encapsulants are also used in the module to reduce mechanical stress.”
LONGi has been experimenting with what it calls “seamless soldering” to eliminate gaps between cells, that appears to behave similarly to Jinko’s tiling ribbon. In Jinko’s case, the flexible round ribbon that connects the half-cut cells is flatter in the overlapping area to allow for the close packing of cells. Jinko’s tiled modules still use nine visible busbars.
“From a manufacturing process, one of the benefits of tiling ribbon technology is its similarities to a conventional half-cell module manufacturing approach,” Venkataramana said. “Both technologies embrace the philosophy of connecting cells through busbars with a ribbon. As Jinko adopts this new technology, we intend to remain flexible to embrace innovation in a rapidly changing technology landscape.”
True shingled modules have no visible busbars and solar cells are cut into five or six strips and connected with an electrically conductive adhesive. Seraphim Solar’s S2 shingled module uses one-sixth-cut cells in vertical strings separated into three sections. SunPower’s P-Series of modules also uses vertically aligned strings of sixth-cut cells, but SunPower’s cell strings run the length of the whole module.
Solaria, on the other hand, positions its fifth-cut cells into horizontal strips. Sharma said that Solaria found the optimal balance between maximizing power and efficiency and keeping a low-cost production was one-fifth cut cells. Solaria’s PowerXT modules for the residential market are 400 W, 20.2% efficient and all-black with minimal cell spacing. SunPower’s P-series of shingled modules are 350 W and 17% efficient and have even fewer spaces than Solaria’s module line. Seraphim’s S2 shingled line runs around 355 W and 19.6% efficient.
There’s no real reason to keep solar cells at their large square size. By cutting cells even just in half, gaps can be eliminated and more silicon can fit on a panel. Shingled-cell strings can reach the entire length of a module without a gap — like in SunPower’s P-series.
“You’re eliminating a lot of the gaps. That’s why you can get more efficiency or higher power from shingling,” Sharma said. “You’re also eliminating busbars from view. Now you have a much higher amount of silicon surface that’s exposed, so you’re collecting more power. Anywhere you would see a busbar means there’s no photons being converted into electrons at that place.”
In comparison, tiling modules still have busbars. Shingled modules use an electrically conductive adhesive in between the top of one cell strip and the bottom of another strip. That’s what binds them electrically and mechanically connects them into their longer strings — tiling modules don’t use this.
Although Solaria has been a leader in shingling technology and has over 250 patents on the design, the company isn’t trying to hoard all the development of the technology.
“Our view is that the solar industry is a big industry. We’re not trying to be all things to all people. We’re not trying to be the largest panel manufacturer in the world,” Sharma said. “So there is a large swath of the market that we don’t serve, so we can license our technology, which we have done to about a half-dozen companies.”
And in the meantime, Solaria has already shifted R&D to what is beyond shingling — tandem-junction modules.
“If you take a step back, solar panels are getting more efficient, more cost-effective, more reliable. The technology is quite awesome now,” Sharma said. “Other energy technologies, especially fossil fuels, are not going to be able to compete. Semiconductors are going to take over energy just like they took over computing and cell phones. It’s just a better technology with many more levers to pull to improve the efficiencies and cost and yields of solar.”