Solar panels produce a small amount of waste compared to other sources

The world is building a lot of solar panels – they accounted for three-quarters of all new renewable energy in 2023. Solar panels are expected to last under the sun for some 20 to 30 years, after which they’ll need to be handled as waste. Opponents of solar energy frequently focus on this waste issue and present it as evidence that solar energy is unsustainable. Such claims have proliferated on social media and elsewhere for years. Just one example comes from broadcaster Ben Fordham, who recently claimed in his radio show hosted by 2GB Sydney – and later repeated on X – that there’s “nothing green” about solar projects, claiming that 78 million tonnes of solar panels will go to waste by 2050 and that solar panels can’t be economically recycled. Audiences might believe that solar is an inherently wasteful energy source.

A related claim (from both social media users and renewable energy skeptics like Michael Schellenberg) is that solar panel waste is toxic and will leach toxins into the soil if it’s landfilled. Potentially fuelling these claims is official guidance suggesting that solar panels can contain toxic heavy metals. The Florida Department of Environmental Protection’s guidance on disposing of solar panels, for example, says: “Solar panel waste can include heavy metals such as silver, lead, arsenic and cadmium that – at certain levels – may be classified as hazardous waste.” Similar statements can be found on Iowa’s and California’s state government websites, among others. 

So, do aging solar panels really go to waste, is their waste toxic, and does it mean that solar energy isn’t “green”? We’ll investigate these claims below.

The amounts of waste from both daily life and fossil fuels dwarf the amount of waste from solar panels

That 78-million-tonne figure probably originated in a 2016 report from the International Renewable Energy Agency (IRENA) and the International Energy Agency. The report estimated that, if all of the world’s solar panels (also known as photovoltaic modules or PV modules) reached the end of a 30-year lifespan, the world would produce 60 million tonnes of solar panel waste between 2016 and 2050. The total rose to 78 million tonnes in an “early-loss” scenario that accounted for some panels failing before the end of their normal lifespan¹. 

Both figures are in line with other estimates. A 2023 Nature Physics article estimated that between 54 and 160 million tonnes of solar panels will go to waste between 2016 and 2050, depending on how long solar panels stay in use – if they last longer, they’ll generate less waste². Another study estimated that the U.S. alone will generate 9.8 million tonnes of solar panel waste between 2030 and 2060³. 

Not all of this waste will go to landfill – many solar cells might be recycled for raw materials or given second lives. Even so, figures in the millions of tonnes may seem imposing. But we must place them into context: the world produces billions of tonnes of solid waste every year.

The same Nature Physics article estimated that, between 2016 and 2050, the world would produce about 1.9 billion tonnes of discarded electronics, 12.4 billion tonnes of plastic waste, and 70.4 billion tonnes of general municipal waste – all of which are orders of magnitude greater than 54 to 160 million tonnes (Figure 1). 

Heather Mirletz, Researcher at the National Renewable Energy Laboratory and lead author of the Nature Physics article, commented to Science Feedback: “Cumulatively, PV end of life modules are completely dwarfed by these other waste streams, many of which we manage on a monthly or weekly basis.” Indeed, if we take the worst-case estimate of 160 million tonnes at face value, then the entire world will throw away less solar panel waste over 34 years than the over 200 million tonnes of waste that U.S. households alone collectively throw away in a single year.

The same is true even if we focus on just the waste from energy generation, as certain fossil fuels create their own streams of waste. When coal is burned, it leaves behind several different types of ash, which builds up in furnaces and boilers unless power plant operators and other coal-burners dispose of it. Petroleum, too, produces waste in the form of sludge: a mix of heavy hydrocarbons, water, and solid particles that piles up in tanks, refineries, and other equipment that comes in contact with crude oil.

According to the Nature Physics paper, if the world continues burning fossil fuels at current rates, it will generate 249 million tonnes of oily sludge and 45.6 billion tonnes of coal ash between 2016 and 2050 – in other words, more than 250 times as much coal ash as even the highest-end estimate of PV solar panel waste. 

In fact, it’s estimated that the world’s coal power plants create at least 780 million tonnes of coal ash each year⁴. Mirletz commented to Science Feedback:

“As a fun anecdote, in a conversation with a colleague who supports energy generation facilities, including coal, I was asked how much cumulative PV waste I was talking, I told them tens of millions of metric tonnes, and they said ‘oh, we handle that every few weeks for our coal plants; that’s nothing!’”

So, solar panels are predicted to produce no more than a metaphorical drop of waste in a much larger waste bucket (Figure 1). In addition, the numbers suggest that swapping coal plants out for solar panels – thus curtailing the amount of coal ash the world creates – may actually dramatically reduce energy-related waste.

The same is true of aged wind turbine blades, which are often targets of similar waste-related sustainability claims, and which we’ve discussed in another recent review.

Solar panel recycling is limited, but does exist

Evidence does suggest that, today, most of the world’s solar panels aren’t recycled. As of 2018, about 10% of solar cells around the world were recycled. However, saying “no one has managed to recycle solar panels at a scale and at a profit, so for now, they’re headed to landfill” is an oversimplification – that recycling rate is significantly higher in some scenarios.

We should be more specific about the materials we’re discussing. The large majority of solar panels on the market today – between 85% and 97% of those sold around the world in 2023 – are made from crystalline silicon cells. Other cell types are only usually seen in specialized applications, and the 13-fold increase in annual PV cell production between 2013 and 2023 was overwhelmingly driven by crystalline silicon.

In most of the world today, most crystalline silicon panels aren’t recycled. “It costs too much money, and it doesn’t bring enough revenue,” Julien Walzberg, Researcher at the National Renewable Energy Laboratory, told Science Feedback. Recycling makes economic sense if the value of recycled materials offsets the costs of separating those materials. We can recycle the 90% of a crystalline silicon solar panel’s mass that consists of the aluminum frame and protective glass (Figure 2), but these are relatively inexpensive materials; meanwhile, we don’t have the technology to effectively separate out the more valuable silicon and other metals (though there’s a great deal of active research in this area). So it’s usually cheaper for owners of used solar panels to send them to the landfill than to pay for recycling.

Reviewers told Science Feedback that, ironically, another reason solar panel recycling isn’t more widespread may be that comparatively few solar panels have reached the end of their lives in the first place. The vast majority of the world’s solar panels have only been installed within the past decade. Walzberg commented to Science Feedback:

“Of course, we don’t have nearly enough PVs, as we might have in the future. If we actually install, develop, and transition towards a clean-energy electricity grid, we would have so much more. In some ways, recyclers could get benefits from economies of scale, and it might just make it more profitable. Right now, one of the problems is that there’s not enough PVs anyway.”

However, it isn’t accurate to say that no solar panels are recycled. For example, in the European Union, solar panels are classified as electronic waste and subject to regulations that require many panels to be recycled or reused at the end of their lives, regardless of the economics at play. Consequently, as of 2021, more than half of solar panel waste was already recycled or reused in many EU member states.

Additionally, it is common to recycle cadmium telluride solar panels, which comprise nearly all non-silicon solar panels. Cadmium telluride panels are mostly used in settings like large-scale solar farms (meaning that, for example, people installing solar panels on their homes will probably never encounter them). Manufacturers often recycle retired cadmium telluride panels. Reviewers told Science Feedback that cadmium telluride is an expensive material that can be effectively recovered from old panels.

The toxicity of solar panel waste is exaggerated

Researchers have studied solar panels’ potential toxicity, and many studies have found that solar panels are unlikely to leach toxins into their surroundings^6-8. While crystalline silicon panels do contain lead and silver, and while cadmium telluride panels obviously contain cadmium, these heavy metals only appear in minuscule quantities, and solar panels’ designs prevent them from leaching.

To understand why, let’s start by understanding what lead and silver actually do in a crystalline silicon solar panel. As light strikes the silicon, it excites electrons in the silicon atoms. Those electrons will only turn into usable electricity if the silicon is properly fitted into a complete electrical circuit. Lead (Pb) is often combined with tin (Sn) to create solder used to fasten that circuit’s wiring (see “Pb/Sn solder” in Figure 2). Silver (Ag) is often applied to a solar panel’s sun-facing side to complete that circuit from the top (see “Front Metal Grid (Ag)” in Figure 2). 

Due to these extremely minor roles, lead makes up no more than 0.1% of a crystalline silicon panel’s mass, and silver less than 0.01%⁶. “Most of the research we’ve been doing so far shows that they [lead and silver] are present in very small quantities,” Walzberg commented to Science Feedback. 

Scientific analyses have demonstrated that these small quantities are generally too low to cause harm even if they enter the soil, air, or water⁷. The design of most solar panels – which seal their inner components away behind layers of encapsulation and glass (Figure 2) – tends to keep solar panels’ materials from leaching. For example, one test showed that, even after crushing solar panels with six passes of a landfill compactor, their encapsulation remained intact⁶.

Cadmium is not found in standard crystalline silicon solar cells, but it is a component of cadmium telluride cells. Rather than using silicon, these cells turn sunlight into electricity with a layer of the compound cadmium telluride (hence the name) that’s thinner than a human hair. Partly because this layer is so thin, cadmium actually makes up very little of a cadmium telluride panel: at most, about 0.1% by mass⁸. 

Furthermore, although cadmium in isolation certainly is toxic, cadmium telluride is much less so, and it’s a stable compound that doesn’t tend to separate into its components⁸. Scientists, then, consider cadmium telluride panels relatively unlikely to leach their cadmium into the environment, made even less likely by cadmium telluride panels’ higher recycling rates.

Moreover, there is no evidence that either crystalline silicon or cadmium telluride panels contain arsenic, gallium, germanium, hexavalent chromium, or perfluoroalkyl substances (PFAS), even though official resources like U.S. state government websites list these substances as potential solar cell contents². Some of these substances are used in specialized solar cells (for example, gallium arsenide, a compound of gallium and arsenic, is used for solar panels in outer space), but these constitute an insignificant fraction of solar cell waste today. Some researchers have designed solar panels that use PFAS, but these aren’t on the market, and safer alternatives are available anyway. The vast majority of people who handle solar panels will never come into contact with any of these substances.

It’s worth noting that further reducing this already low toxicity is another priority of solar panel research and development. “Many PV module manufacturers are moving toward lead-free modules,” Mirletz commented to Science Feedback.

It is also worth noting that fossil fuel waste – which, as we’ve previously stated, could be cut down by replacing fossil fuels with solar energy – is proven to be toxic. Both coal ash and oily sludge contain heavy metals, including lead, as well as organic pollutants like polycyclic aromatic hydrocarbons (PAHs), which include known carcinogens. Coal ash is prone to leaching these pollutants, and research has linked living near coal ash storage facilities to respiratory illnesses in workers and neurological issues in children⁹.

Conclusion

When opponents of solar energy claim that aging solar panels will turn into millions of tonnes of non-recyclable waste over several decades, their claims are missing important context. While their numbers are in line with (or directly taken from) published estimates of solar panel waste, they’re also very small relative to billions of tonnes of waste produced globally every year. In fact, fossil fuel sources of waste alone dwarf the estimated amount of solar panel waste.

While most solar panels today do go to landfill, it is inaccurate to say or imply that all do.European Union member states mandate that most of their solar panels be recycled, and cadmium telluride solar panels are often recycled even in the U.S. Furthermore, claims that solar panel waste will leach heavy metals into the soil greatly exaggerates both the amount of leaching and the amount of heavy metals in a solar panel in the first place.

References

1. IRENA and IEA-PVPS. (2016) End-of-Life Management: Solar Photovoltaic Panels.
2. Mirletz et al. (2023) Unfounded concerns about photovoltaic module toxicity and waste are slowing decarbonization. Nature Physics.
3. Domínguez and Geyer. (2019) Photovoltaic waste assessment of major photovoltaic installations in the United States of America. Renewable Energy.
4. Tamanna et al. (2023) Coal bottom ash as supplementary material for sustainable construction: A comprehensive review. Construction and Building Materials.
5. Heath et al. (2020) Research and development priorities for silicon photovoltaic module recycling to support a circular economy. Nature Energy.
6. International Energy Agency (IEA) PVPS Task 12. (2019) Human Health Risk Assessment Methods for PV Part 2: Breakage Risks.
7. International Energy Agency (IEA) PVPS Task 12. (2020) Human Health Risk Assessment Methods for PV Part 3: Module Disposal Risks.
8. Maani et al. (2020) Environmental impacts of recycling crystalline silicon (c-SI) and cadmium telluride (CDTE) solar panels. Science of The Total Environment.
9. Chen et al. (2024) A comprehensive review of toxicity of coal fly ash and its leachate in the ecosystem. Ecotoxicology and Environmental Safety..