Researchers have revealed a way to recycle old solar panels into new, more efficient ones using PERC technology, reducing waste and dependence on intensive mining for new materials, thus benefiting the environment and providing a reliable, cost-effective service. By recycling and reusing solar panels, we conserve resources, extend their life, and increase their energy efficiency, refusing to let them degrade and contribute to environmental waste.

What challenges do photovoltaic panels present, what did the researchers show, and how could this help green technology move forward?

What challenges do photovoltaic solar panels present?

Photovoltaic solar panels are one of the most convenient to manufacture and install of all the renewable energies currently available. While their production process may be energy-intensive, and the use of rare-earth materials can make them expensive, their ability to generate electricity simply by being in the presence of sunlight allows them to be installed almost anywhere. Once set up, such panels can have a service life of at least 20 years, and with no moving parts, not much can go wrong with them.

However, the low efficiency of solar panels (generally being less than 20%) means that they require large amounts of land to gather enough energy. This problem is exacerbated when used on residential properties where roof space is a premium. Thus, the energy output of any solar installation is extremely sensitive to small changes in the efficiency of the panels used.

Every 5 years, solar panels can expect to lose between 1% to 2% of their efficiency, and panels manufactured in the previous decade would have life expectancies of around 20 years. This means that after 20 years of service, the panel's output may only be 80% of what it used to be, and this is a significant drop when considering that energy demand continues to rise and the space used by the panels is limited. Thus, thanks to technological improvements, ageing panels are commonly replaced with newer ones with longer lifespans.

But this discarding of solar panels creates an environmental challenge; solar panels are energy-intensive to recycle, and their use of toxic compounds can be dangerous for the environment. The need to melt glass and silicon requires enormous amounts of energy, and this will undoubtedly be sourced from fossil fuels such as coal and gas. Panels discarded in landfills will leach compounds such as lead, arsenic, and cadmium that contaminate underground water supplies.

Simply trying to reuse silicon to make new integrated circuits and panels is also problematic due to the need for ultra-pure silicon. This means that silicon extracted from panels must be carefully refined, which is also energy-intensive.

Researchers develop solar panels from old recycled panels

Recently, researchers from Fraunhofer Center for Silicon Photovoltaics and the Fraunhofer Institute for Solar Energy Systems announced their development of an industry-scale solar recycling method to take old, degraded panels and use them in modern PERC solar cells. Passivated Emitter and Rear Contact solar cells (PERC) are a modern solar panel technology that utilises N-type semiconductors and improved back-reflecting technologies to ensure that incoming light is more likely to come into contact with silicon atoms. Simply put, PERC solar panels are more expensive than standard panels but are more efficient as a result (around 5% points more).

When recycling solar panels, the glass and metal contacts are relatively easy to recycle, so the researchers turned their focus to silicon. To reclaim the silicon, the researchers started by grinding panel fragments to sub-millimetre pieces that were then filtered based on type (glass, plastic etc.). The second stage involved using wet chemical etching to remove silver contacts, anti-reflective layers, and emitter layers.

The third recycling stage turns the remaining clean silicon powered into silicon ingots using standard processes that are then used to create wafers. However, the most crucial step was then recrystallising the silicon without the need for adding pure silicon to the mixture (this is generally needed to crystalise old material). The resulting recrystallised silicon, which was 100% recycled, was then used to create new PERC solar cells whose efficiency was 19.7%.

While this efficiency is lower than typical PERC cells at 22.2%, this figure is still greater than the panels used to create the PERC cells, and this process was done with no new materials.

At Reiling GmbH, the process of separating and collecting solar cell fragments (left) creates valuable by-products. The purified silicon is used to make wafers (middle) from 100% recycled silicon. These wafers are then transformed into high-efficiency PERC solar cells with a 19.7% efficiency rate (right). Image credit: © Fraunhofer ISE.

Why is solar panel recycling so important?

Solar panels installed 20 years ago are finally coming to the end of their lives. Considering that the main objective of solar panels is to provide a clean energy source, needing to consume large amounts of energy to mine, manufacture, and install new panels every 20 years, which is an energy-intensive process, would defeat the purpose of their use. Furthermore, discarded panels leaking harmful compounds into the environment arguably make solar panels worse than some fossil fuels considering that not only is CO2 produced during its manufacture but then pollutes the environment afterwards.

As such, it is essential that solar panels can be cheaply recycled, whereby the energy needed to recycle panels is renewably sourced. It is also vital that the recycling process does not affect the local environment. Otherwise, solar panel waste becomes a similar challenge to that presented by nuclear waste. The researchers have demonstrated a promising future for solar panel recycling whereby old panels can be turned into new ones without the need for mass mining of glass, metal, and silicon.