When old solar modules have had their day, the silver, copper and aluminum in them can be recovered.

But the semiconductor material silicon, of all things, ends up in the trash.

Around 10,000 tons of silicon from old modules are produced in Germany every year.

A proud amount that is likely to reach several hundred thousand tons from 2029, because that is when those systems that were installed in the first major expansion wave between 2009 and 2011 will no longer benefit from the twenty-year EEG subsidy.

Now the Fraunhofer Institutes for Solar Energy Systems (ISE) in Freiburg and for Silicon Photovoltaics (CSP) in Halle an der Saale, together with the recycler Reiling from Harsewinkel near Gütersloh, want to put an end to waste.

They have developed a technique with which the silicon can be recovered in almost pure form - regardless of the manufacturer of the modules, as the project partners point out.

ISE researchers have made new solar cells from the recycled silicon, which, at 19.7 percent, have a lower efficiency than premium cells made from fresh crystalline silicon.

These come to 22.2 percent.

In terms of service life, on the other hand, the two don't sacrifice anything.

In the CSP, the easily recoverable recyclable materials are first separated and the silicon cells are smashed.

The fragments, which are 0.1 to one millimeter in size, end up in a wet-chemical etching bath that removes the electrical contacts and other impurities.

This clears the way for melting down.

The silicon is then processed into so-called ingots.

These are huge blocks from which fine saws cut thin discs, the wafers.

Finally, the ISE engineers can apply photoelectronic layers to the wafers obtained in this way, which convert sunlight into electrical energy.