Photovoltaic (PV) panels currently generate about 3 percent of the world's electricity, with much of that capacity having been installed over the past two to three decades. By the year 2030, some of those panels will reach end-of-life (EOL) status, leaving roughly 8 million metric tons of material to be dealt with. Scientists estimate that by 2050, that number will increase tenfold. At that point, spent PV materials will account for 10 percent of all electronic waste. (I hate to break it to you, folks, but no technology is entirely benign. Sustainability is about using technology that causes the least amount of damage. In that regard, solar and wind are still cleaner than fossil fuels.)
The good news is that nearly 80 percent of a solar panel's weight consists of aluminum and glass, both of which are easily recyclable. The bad news is that separating the glass is complicated, and the remaining 20 percent of the materials can be difficult to recover.
Not wanting to push the problem off to future generations, scientists at the National Renewable Energy Laboratory (NREL) completed an assessment of PV recycling around the world, with an eye toward identifying the most promising solutions. Here's a brief synopsis of their report, "Research and development priorities for silicon photovoltaic module recycling supporting a circular economy," which was published in the journal Nature Energy.
Non-Landfill End-of-Life Options
Solar panels typically come with 20- to 30-year warranties, but they actually produce electricity for much longer than that—just less efficiently. After 30 years, a panel may produce just 70 to 80 percent of its nominal rating, which isn't terrible but certainly not acceptable at the utility-scale. When panels on a large PV farm dip to that level and are replaced, they can be refurbished and resold for applications where efficiency isn't a high priority. Unfortunately, the PV industry suffers from the same affliction as the electronics industry: new equipment is better and less expensive, so it rarely makes economic sense to downcycle products, as the cost of transporting, refurbishing and testing exceeds the price of purchasing new. On the other hand, used-but-functional panels could be donated to a non-profit organization that is looking to offset some of its utility expenses. While that may delay the problem for a few decades, at some point the panels will cease to function. Sooner or later, we'll need to deal with the waste.
Given that downcycling isn't a closed-loop solution, the next option is recycling. With government support, as well as mandates, PV recycling is well-established in Europe and Japan. The US lags in this effort, with no federal incentives or requirements for PV recycling. At the state level, only Washington has mandated PV panel recycling, with the manufacturers responsible for financing the collection and recycling system. On the voluntary side, the Solar Energy Industries Association's (SEIA’s) National PV Recycling Program has kept more than 3,600 metric tons (8 million pounds) of PV-related waste out of the landfills since the program began in 2016.
Over the next three decades, the world will accumulate roughly $15 billion worth of recoverable materials from EOL solar panels—enough to make 2 billion new modules that total more than 600 GW of generating capacity. That looks good on paper, but PV panel recycling is energy-intensive and often involves toxic chemicals.
Recycling a solar panel can be broken down into three basic steps:
- Remove the frame and junction box (a mechanical process)
- Separate the glass from the silicon wafer (a thermal, mechanical or chemical process)
- Separate and purify the silicon and various metals (a chemical and electrical process)
Existing PV recycling centers can perform the first two steps, but the third poses problems. Although metals such as tin, lead, silver and copper can be recycled with existing methods, any silicon recycled is turned into metallurgical-grade silicon, which, at 98 percent purity, isn't suitable for electronics or new solar panels. NREL recommends research into methods to purify silicon from used PV wafers to close the loop on silicon recycling, but the report acknowledges the complications involved in such a process. The semiconductor industry has plenty of experience purifying virgin silicon but reclaimed silicon has different impurities, such as the doping materials and compounds that leach into the silicon throughout its working life. Scientists agree that there are no physical barriers to recycling PV cells into PV-grade silicon, but the economics may not work out. Given the abundance of virgin silicon and the existing infrastructure for turning it into semiconductor material, it may mean accepting that silicon from recycled solar panels will only be used in metal alloys, at least in the short term.
Design for Sustainability
One reason that PV panels are so difficult to recycle is that engineers have focused on efficiency and durability, the latter of which is pretty much the opposite of "easy to disassemble." In order to be competitive, PV systems are designed to obtain the lowest possible Levelized Cost of Electricity (LCOE), but other industries are now taking into account the complete life cycle of a product, cradle-to-grave, including its environmental impacts and recyclability. It's time that the green-energy industry does the same.
NREL's report addresses this as well, although rather lightly. "For recycling services offered directly by PV module manufacturers, recyclability impacts can be considered as part of the change-management process in PV module design and manufacturing." It also suggests that manufacturers try to meet certain industry standards, such as Cradle-to-Cradle certification and the NSF/ANSI Sustainability Leadership Standard for Photovoltaic Modules and Photovoltaic Inverters, which make it easier for purchasers to identify modules designed for recyclability. Recognizing that industries don't always do the right thing unless coerced, NREL also alludes to the European ecodesign directive.
Additional Research on PV Recycling
NREL isn't the only institution that's studying PV recycling. If you're interested in more, check out these reports:
A techno-economic review of silicon photovoltaic module recycling
End-of-life photovoltaic modules: A systematic quantitative literature review
An overview of solar photovoltaic panels’ end-of-life material recycling
In a future article, I'll discuss recycling lithium-ion batteries.
We bring you the latest news about renewable energy, electric vehicles, net-zero buildings, energy harvesting and more. Subscribe to engineering.com's "Electronics Design News" section to stay in the loop!