New Fraunhofer Solar Cell Stringer Uses Adhesives For 2% Boost

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An R&D team at Fraunhofer ISE has unveiled a new solar cell stringing machine that can boost cell performance 2% by using electrically conductive adhesives to fix solar cells to a foil substrate in a shingled pattern. The process reduces the number of manufacturing steps that soldering a connective ribbon would require, and imparts more efficient cell performance in several incremental ways.

The new assembly process involves an ethylene-vinyl acetate (EVA) foil substrate already formed to created minimally shingled rows of cells. Fraunhofer has applied for a patent for the process, terming it SlimLine. “The power output of shingle modules is increased by significantly enhancing the active cell area within the module, decreasing shading and soiling losses, reducing interconnection losses,” the lab says.

Adhering solar cells in shingle formation boosts performance. Credit Fraunhofer ISE

The cell stringer machine from Maschinen und Anlagen GmbH applies the electrically conductive adhesive, or ECA, using a screen-printing technique and connects the cells with high precision. “The aesthetics and the high power density will push the shingle technology forward, especially in the automotive industry and for building-integrated applications. European module manufacturers inquire increasingly about application-oriented developments and technology assessments for shingle solar cells,” commented Achim Kraft, the head of Interconnection Technologies at Fraunhofer ISE, in a statement.

While shingled solar cells have been under study for 50 years, this is the first time they are being assembled in a cost-competitive way, Fraunhofer suggests. “Through shingling, the gaps between the cells disappear, maximizing the possible module area used for electricity production and giving the module a homogeneous, aesthetic appearance,” the lab says.

“The higher efficiency of shingle, as compared to conventional, modules is due to the larger active area of the module, and also due to the avoidance of shadow losses caused by conventional surface-mounted cell interconnectors,” the lab says. The resistance losses are also reduced because of the lower current densities in the cell stripes, the lab states.

One cell variation that Fraunhofer is using the adhering process for is bifacial panels, which absorb light both front and back. “To manufacture bifacial shingle solar modules with a high power output, the p-type Silicon shingled Passivated Edge, Emitter and Rear (pSPEER) cell,” was employed.

The pSPEER cells are based on the Passivated Emitter and Rear Cell (PERC) design approach and include a passivated edge, the lab explains. The module design features a combination of series and parallel connections for each cell to significantly reduce losses when parts of the module surface are shaded or soiled, it adds.

A September 2018 paper on shingled cells by a Fraunhofer team lead by researcher Andrew Mondon notes that “manufacturing methods such as SlimLine may decrease total module fabrication costs by allowing very narrow cell overlap. Shingled module concepts offer main advantages in cases where highest power density and good partial shading response is beneficial, where the latter is satisfied best by the matrix layout.” The paper was presented at the 35th European PV Solar Energy Conference in Brussels.

Work is not complete on the new SlimLine adhesive stringing process. Currently the Fraunhofer team is working on optimizing the amount of adhesive used, on the cell design, and on new areas of application.

Support for the Fraunhofer shingle cell work has been supported by the German Federal Ministry for Economic Affairs and Energy, within the broader PV-BAT400 solar project.

SunPower also is manufacturing solar cells with shingled orientation. The company is assembling its 19% efficient Performance Series solar panel (P19 or P-Series) for commercial customers in its new Hillsboro, Oregon, factory, leveraging US-made automated stringing equipment.

SunPower’s P19 solar panel architecture “leverages a unique cell interconnect technology developed by a U.S.-based company called Cogenra Solar and funded in part by the U.S. Department of Energy (DOE) SunShot Initiative,” the company said in a statement. SunPower acquired Cogenra in 2015 and introduced P-Series solar panels that year.

Now made in several geographies, P-Series panels are “currently the most deployed shingled cell solar panels in the world and are highly reliable,” SunPower said. “For the second year running, DNV GL – a global independent energy expert and certification body – has named the P-Series solar panel a top performer in all five DNV GL tests that measured reliability through thermal cycling, damp heat, humidity-freeze, dynamic mechanical load and potential induced degradation,” the company added.

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