Making recyclable back-contact solar modules a reality

Circular solar

PARSEC is a Dutch RVO-funded research project that has brought together four key solar players with one common goal: to develop fully recyclable back-contact solar modules - and ultimately pave the way for greater uptake of this high power-density technology.

At DSM we’re playing our part in the quest to Design for Recycling (D4R) through the development of a unique hot-melt encapsulant that enables everything from precious metals to glass and polymers to be re-used when the module reaches its end-of-life.

Solving a ‘sticky’ solar challenge

Today, the majority of polymeric components in solar modules (and the valuable materials captured within) are incinerated at end of life – at great financial and environmental cost. In the EU alone, some 4 000 tons of solar panels are dismantled  every year; and as solar energy gains further traction, that number is only expected to increase. 

The best end-of-life solution to date has been more ‘down cycling’ than recycling, where modules are milled into small pieces and subsequently materials with low purity and value are recovered. One major obstacle to recover high value, high purity materials  concerns the nature of the standard EVA (ethylene vinyl acetate) encapsulant applied on the front and back side of solar cells in order to secure the contents. Based on cross-linking technology (which involves the lamination of the cells and EVA in a vacuum) this causes the encapsulant to become physically inseparable from the module materials themselves, thus making their uncontaminated retrieval virtually impossible.

This is the challenge that DSM and its peers have been attempting to help solve for several years now: first as part of a research program called DEREC (where success was achieved using small prototype modules); and now as part of Project PARSEC – which aims to create a full-size recyclable back-contact solar module.

A next generation module encapsulant

As Research, Technology & Development Manager for DSM’s own Conductive Backsheet program, Frank van Duijnhoven, is also leading the team’s contribution to project PARSEC. “We created two encapsulants – one for the front of the module which joins the glass and cells together; and a slightly different formulation for the back of the module, which attaches cells and backsheet together,” he explains. “The key point is that our encapsulant is a unique adhesive film based on hot-melt technology that enables the individual materials of the module to be separated and retrieved at high purity.”

Like regular PV modules, back-contact modules contain silicon, copper and even silver (within the cells themselves) – all precious materials that could be re-used. They also contain glass, polymers and other materials, all of which can potentially be recycled.

A true innovation collaboration

So, why has PARSEC chosen to focus on back-contact modules?

From a practical standpoint, back contact modules are ideal for recycling because unlike traditional mono-crystalline modules, they feature all the cell interconnection (including almost all precious bussing and wiring) in one layer on the backside in between the encapsulant and the backsheet rather than intertwined with the cells connecting front to backside. This makes it easier to disassemble the individual components…provided the right encapsulant is used.

But ultimately, back-contact technology is a potentially transcendent force in the industry - able achieve the highest power density, thus maximizing every square centimeter of available module space  while minimizing resistive losses. It’s why DSM has been joined in project PARSEC by leading industry names including Mat-tech (developing lead free interconnection materials); Exasun, who manufactured the full-size solar panels; and last – but definitely not least – TNO, one of the early developers and driving forces of back-contact technology.  

“We have worked closely with TNO research institute for some years already – and they were instrumental in the development of our own DSM Conductive backsheet,” says Frank. “As part of this project we will also be working closely with them on the testing and validation of the prototype modules that are produced to ensure they perform long-term.”

Creating the Solar Industry Standard

Ultimately, the new encapsulation must be demonstrated to work seamlessly with the standard lamination process used for all solar modules. Once this is achieved, the PARSEC-developed recycling technology is well placed to become the industry standard, not only in back-contact technology but for all PV modules.

In fact, eventually, PARSEC will result in a set of materials that allow full and high value recycling of solar panels, as well as performance that is at least double that of standard IEC requirements.

Truly, a design for (end of) life.

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