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Recycling

Solar cells must be designed to be sustainable

The heavy metal lead and strong polymer are used in solar cells, but green technologies should be designed for recycling, researcher in innovation from the University of Southern Denmark point out. Organic solar cells are a good example of a completely new generation of green technology.

By Birgitte Dalgaard, , 2/25/2021

Solar cell farms are popping up everywhere. Among other things, five different solar farms ensure that Google's new data centre near Fredericia becomes CO2-neutral.

Energinet is aware of new, possible solar cell projects that have a total capacity of up to 16 gigawatts. In comparison, Denmark’s wind turbine farms’ capacity is currently approximately 6 gigawatts.

Recycling of solar cells

The solar cells sold today are typically based on mono- and polycrystalline silicon. When recycling solar panels, it is important to know what materials they contain:

  • Glass: 78 per cent
  • EVA polymer lamination: 10 per cent
  • Polyester: 7 per cent
  • Silicon: 4 per cent
  • Silver: 0.4 per cent
  • Copper: 0.3 per cent

(The figures are approximate figures as a percentage of the total weight, source: solcelle.dk)

The lead content is estimated to be 20 mg/W.
(Source: Institute of Photovoltaics, University of Stuttgart)

But what happens to the huge amount of solar panels when they no longer work efficiently and need to be scrapped? The International Renewable Energy Agency estimates that by 2050 there will be 78 million tonnes of solar waste in the world.

– 85 per cent of the material used for solar cells can be recycled today, says researcher in sustainable design and innovation, Lykke Margot Ricard from the Department of Technology and Innovation at the University of Southern Denmark:

– But if we can find a way to dissolve the insistently strong polymer lamination between the glass and solar cells, then it could be possible to recycle more silicon and glass, in whole and separate fractions.

– The strong polymer is used to ensure that the solar panels can withstand all kinds of weather, but it also makes it impossible to split the parts apart in the recycling process. Therefore, today the panels are crushed into smaller pieces of mixed materials leading to low-value recycling option, explains Lykke Margot Ricard:

– If heavy metals such as lead and cadmium are also avoided, then my estimation is that 95-98 per cent of the materials could be recycled.

Toxic lead in solar cells

Lead is a toxic heavy metal that accumulates in nature and in humans. That is why the EU has banned lead in all electronic products with one exception, namely, solar cells.

According to the magazine PV Magazine, which is a leading international solar cell magazine, a typical 60-cell crystalline silicon solar module produced today, contains up to 12 grams of lead (the article is from October 2019).

– I cannot say with certainty how many manufacturers use lead today, but the EU should consider whether it is still necessary to exempt solar cells from the general legislation that applies to electronic. I am convinced that it is completely unnecessary to use lead in solar cells - at least in the solderings.

I am convinced that it is completely unnecessary to use lead in solar cells

Lykke Margot Ricard, Associate Professor

For example, has the electronics and car industry recently shown us that it is possible to make these without lead in the car batteries, says Lykke Margot Ricard and adds:

– To have this exception with the lead today for solar cells does not exactly drive innovation and the development of new solutions.

And the article in PV Magazine backs her up; There are several alternatives that completely replace lead, but the problem is that manufacturers are not motivated to replace lead with more expensive solutions, as long as it is legal to use lead.

Lykke Margot Ricard points out that the exception in EU legislation comes from a time when solar energy had to compete with fossil fuels in terms of price, efficiency, and not least, renewable energy, which has been crucial to attracting investors.

Focus on recycling

But now we are in a different situation. We are no longer satisfied with the fact that technologies such as wind turbines and solar cells give us green energy. We are also aware that when the technologies are scrapped, the materials must be included in circular material flows.

– We see a paradigm shift. Silicon solar cells are designed to be durable, but when we talk about a circular economy and focus on nature's resources, we see a need to make sustainable designs.

– Then it may well be that the solar cells do not last as long - but this is offset by the fact that their materials can be used in new products.

For organic solar cells, sustainability is a ground-rule that is repeated throughout the development process

Morten Madsen, Professor

Lykke Margot Ricard points the attention to her colleague, Professor Morten Madsen. He leads the research group OPV Group, which is at the forefront of developing organic solar cells. The researchers hope that in the long run, organic solar cells will replace silicon solar cells, partly because they are sustainable.

– For organic solar cells, sustainability is a ground-rule that is repeated throughout the development process, emphasises Professor Morten Madsen from the Mads Clausen Institute:

– We completely avoid heavy metals and toxic materials. At the same time, our material consumption is much smaller and when we develop modules, we can use bioplastics or other recyclable materials in the substrates on which the solar cells lie.

– With a long-term plan, we even have a vision of using only biodegradable material, Morten Madsen adds and says that his colleague Vida Engmann has received five million kroner from the Carlsberg Foundation to research biodegradable materials.

A completely different sustainability league

Because organic solar cells absorb light much better, they are 1000 times thinner than silicon solar cells. In addition to less material consumption, it also provides aesthetic benefits. The organic solar cells are flexible and can be freely designed with regards to colour and shape. It makes it possible to design and integrate them into buildings - and even into windows without them being visible.

Morten Madsen does not doubt that the organic solar cells are in a completely different sustainability league than the silicon solar cells, which are market leaders today and research, backs him up.

According to a research article from DTU, organic solar cells have the lowest energy payback time, i.e. the time the solar cells have to produce the same amount of energy that was used for their production. And of all green energy technologies, organic solar cells are the technology with the lowest CO2 emissions per kilowatt-hour.

– For example, manufacturing silicon solar cells requires heating to over 1000 degrees. For the production of organic solar cells, the highest temperature is only around 100 degrees, Morten Madsen points out.

Design for recycling

When you look at this from a design perspective as Lykke Margot Ricard does, she sees a movement towards designing for durability, and we must increasingly consider making sustainable designs.

– Because solar and wind energy are so essential for us to achieve climate goals, we expect that the technologies are also sustainable. Of course, they are also relative to fossil technologies, but we must constantly be critical and ask ourselves if we can do it a little better:

– It does not necessarily make sense to use polymer lamination and heavy metals to achieve 25-30 years of durability in products where the technology develops so fast, emphasises Lykke Margot Ricard.

Because solar and wind energy are so essential for us to achieve climate goals, we expect that the technologies are also sustainable

Lykke Margot Ricard, Associate Professor

Both in terms of longevity and efficiency, organic solar cells are developing at an extraordinary pace, and there is already a commercial market in the making.

CLEAN

Industry, universities and public institutions collaborate in CLEAN - Denmark's Environmental Technology Cluster Clean to identify and disseminate knowledge of new trends and opportunities in environmental technology. Associate Professor Lykke Margot Ricard and Professor Morten Madsen are members of the Clean Innovation Board, where they focus on circular and environmental considerations within design, manufacturing, processing, use and recycling and recycling of materials.

– We work with several manufacturers who today sell organic solar cells, and even though the durability is less than for silicon solar cells, the difference becomes smaller and smaller. Fortunately, organic solar cells have many other parameters they can compete on, so it is also about new thinking about what solar cells can offer in terms of design, integration and sustainability, Morten Madsen emphasises.

Lykke Margot Ricard completely agrees:

– Silicon solar cells are designed to be durable, but when we talk about green conversion, climate and nature's resources, we must make sustainable designs; avoid toxic materials, use fewer materials and make sure we can separate the materials afterwards so that they can be recycled.

– Then it may well be that the solar cells do not last as long, but we must be willing to pay a little more for the most sustainable solution.

(Photo: Colourbox)

Nanoparticles must bring photosynthesis into the future solar cells

  • Associate Professor Vida Engmann from OPV Group will in the Artplast project develop solar cells from bio-based semiconductor materials. Semiconductor components today are typically based on silicon.
  • Preparation of ArtPlast (Artificial chloroPlast = artificial chloroplast) is supported by grants from the Carlsberg Foundation and the Danish Free Research Foundation.
  • “This is a synthetic platform for bioinspired organic nanoparticles that use photosynthetic processes in the same way as nature. These nanoparticles will not only be able to deliver processes that can promote new solar energy generation as well as storage technologies, but they will also be able to do this in the same way as in nature,” says Vida Engmann.
Meet the researcher

Lykke Margot Ricard is an associate professor of innovation at the Department of Technology and Innovation and programme leader in the master's program, MSc in Engineering in Product Development and Innovation.

Contact

Meet the researcher

Morten Madsen is a professor, MSO and research leader at SDU NanoSYD, Mads Clausen Institute.

Contact

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Editing was completed: 25.02.2021