Solar PV is now the dominant technology for new electricity generation capacity additions. That's a huge achievement, but it brings up the vital question of what will happen to all those panels when they reach the end of their useful life.

In April, GTM reported on what was then unpublished research showing that solar panels can be landfilled without endangering human health. That's good news, but landfills are hardly an ideal way to deal with solar industry waste. The cumulative mass of end-of-life PV modules is expected to hit 8 million metric tons globally by 2030, so improving recycling rates is an increasingly critical issue for the industry.

The main problem with recycling PV materials is that doing so costs more than dumping them in a landfill, says Garvin Heath, senior scientist at the National Renewable Energy Laboratory and co-author of the since-released study by the International Energy Agency’s Technology Collaboration Programme on Photovoltaics Power Systems.

"There’s only one crystalline silicon recycling facility in the world now, and that’s in France,” Heath told GTM.

To help remedy the situation, the recently published IEA paper on crystalline silicon PV recycling outlines five research recommendations for the solar industry.

1. Focus on getting the silicon back

The most expensive components of PV modules are the silicon wafers. They account for around half the cost of the module, and silicon accounts for the bulk of PV waste once the aluminum frames and glass covers are stripped off the module.

High-grade silicon is valuable, capable of fetching $100 per kilogram or more. But you can’t get that price for recycled silicon, for two reasons.

First, the mechanical crunching and smashing involved in recycling old modules add impurities to the silicon. And then there's the fact that the silicon that's used in new modules today is much purer than it was in modules made in the past. Even if you didn’t add any impurities through recycling, the output still wouldn’t be good enough for today’s solar manufacturers.

The first priority for PV recycling, then, is finding ways to improve the purity of the silicon that is recovered — without breaking the bank in the process.

2. Forget about trying to recover intact silicon wafers

If silicon wafers are so valuable, why not just recover the ones in old PV panels and reuse them? This sounds attractive but doesn't work in practice for a number of reasons.

The main one is that few solar cells reach the end of their lives without developing cracks that impair performance. And the situation is getting worse because newer cells tend to be thinner and thus more prone to cracking.

On top of that, changes in cell efficiency, lifetime, silicon purity and form factor all mean that old wafers are unlikely to be of interest to today’s PV manufacturers.

3. Figuring out what recycled silicon really looks like (and how to purify it)

We know that recycled silicon is less pure than what’s used for manufacturing new cells. But we don't really know what the impurities are. That makes it harder to find customers willing to take the recycled silicon.

“To convince an industry that has invested capital in processes built around virgin silicon supply chains to use recovered silicon, impurity profiles for a complete list of potential impurities will be required yet currently is lacking,” says the study.

The modern solar industry has perfected the art of purifying virgin silicon. There’s no reason why the same couldn’t be achieved with recycled silicon — once it's clear what the impurities are. In reality, however, purifying recycled silicon might require different processes from those used today, so an important avenue for future research will be working out what’s needed.

4. Don't forget the other materials

While solar panels mostly consist of glass and aluminum, which can be recovered fairly easily, plus silicon, which rightly deserves the most research effort, they also contain a long list of other materials, such as copper, silver, tin and lead.

Some of these materials, like silver, are worth recovering even when present in very small amounts. Solar panels are said to use up 10 percent of the world’s supply of silver, although the motivation for recycling this is declining because cost reductions are leading to less and less of the metal being used in panels.

With other materials, such as lead, the prime reason for recycling might not be financial but rather environmental or health-and-safety related. For this reason, further research is needed to explore the most cost-effective ways to recover potentially valuable materials and neutralize hazardous ones.

5. Make sure recycling can cater to tomorrow’s industry

Changes in solar panels are already making it difficult to recycle or reuse the products from days gone by. So it will be important to anticipate further changes before investing massively in recycling.

“The infrastructure investments that the waste management industry has been thinking about making need to be cognizant of, if not adaptive to, the changing landscape of this input stream,” said Heath. “The PV industry is not standing still.”

All in all, the recommendations add up to a busy research agenda if the PV sector is to achieve efficient, cost-effective and fully integrated recycling as part of wider efforts to also improve the repair and reuse of existing products.

But this is a task that solar is already taking seriously, said Alex Hobson, vice president of communications at the American Council on Renewable Energy. “Creating a healthier planet by reducing harmful carbon emissions and being good environmental stewards is central to the mission of the renewable sector,” Hobson said in an email.

“There are innovative programs underway and initiatives being explored by companies, industry advocates and governments to sustainably manage waste and end-of-life disposal of renewable parts.”