Discarded solar panels could add up to 80 million metric tons of waste globally by mid-century yet there currently is no common plan for managing the problem or recycling the valuable materials that the modules contain, researchers at the National Renewable Energy Laboratory have found.
NREL said the report, which was published at Nature Energy earlier this month, is the first global assessment of how photovoltaic panels could be managed at the end of their 30-year service life. Researchers found there also is no standard for how to recycle the valuable materials the modules contain or how to handle toxic materials and minimize threats to the environment.
Much of the study was focused on the recovery of crystalline silicon, which is used in more than 90% of all modules. It accounts for about half of the energy and carbon footprint of a solar panel, but only a small amount of its bulk.
Lead author Garvin Heath, a senior scientist at NREL who specializes in sustainability science, said in a news release, “PV is a major part of the energy transition. We must be good stewards of these materials and develop a circular economy for PV modules.”
The article, “Research and development priorities for silicon photovoltaic module recycling to support a circular economy,” was written by a 15-person team. The assessment comes at a time of explosive growth in the capacity of PV panels globally, from 1.4 gigawatts (GW) in 2000 to 512 GW in 2018. Solar modules now produce about 3% of electricity worldwide.
Solar panels are responsible for no direct greenhouse gas emissions, and low lifecycle emissions, and provide both local-cost power and a lot of jobs. “However,” the authors said, “as large-scale global PV deployment continues, the challenge of how to handle large volumes of PV modules at the end of their approximately 30-year lifetimes is emerging.”
By 2030, outdated panels are expected to total 8 million metric tons, which will grow 10-fold by 2050 to exceed 10% of all electronic waste globally.
Stranding valuable materials
Reuse or repair of older modules is one option that researchers examined. They predicted that approach would lower the environmental impact of solar modules while increasing their lifetime electricity production. “These are worthwhile circular economy strategies for the PV industry to investigate,” the report notes, “though numerous business model, economic and regulatory challenges must be addressed.”
Among them are the environmental costs of shipping spent panels to repair or reuse facilities, and the need for manufacturers to establish testing and repair procedures as well as an inventory of spare parts. The high cost of the solar business not directly related to the modules—what the report calls the “balance of system costs”—also is a concern.
No matter how good the industry gets at keeping aging panels functioning, they eventually must be replaced. Researchers found that in Europe a priority has been to make sure that valuable materials in the modules are not lost in landfills. The cumulative potential value of materials that could be recovered from obsolete panels will be an estimated $15 billion by the year 2050. Those materials could be used to make an additional 2 billion new modules with a total capacity of 630 GW.
Regulations to guide module recycling are slowly being developed, but adoption appears spotty. The European Union added a PV category to its Waste Electrical and Electronic Equipment regulations eight years ago, but Washington State is the only U.S. jurisdiction so far to require that panels be recycled. Efforts to address the problems are underway in Korea, Japan, Australia, and India, but the recycling process so far isn’t especially effective.
“Even in the EU, where PV recycling is mandatory, very few recycling facilities designed to handle PV modules exist and information about their recycling efficacy and economics is not publicly available,” the NREL report says. Existing recycling lines are good at retrieving bulk materials, such as the aluminum frame, copper wire, and glass. But silver, copper, silicon, and lead, which make up most of the module’s potential value and potential environmental impact, are not recovered.
To date, there have been plenty of small-scale attempts at separating and salvaging valuable materials from modules, the authors said, adding, “We note that little or no consensus about the commercial viability of these approaches exists.”
In the United States, the Solar Energy Industries Association (SEIA) has six firms that are capable of recycling modules and inverters; five of them will accept crystalline silicon panels and one will recycle its own thin-film panels. The busier recyclers process only about 100 tons of silicon per month. “Owing to the low volumes of modules being sent for recycling,” the report says, “recycling lines dedicated to c-Si PV modules have not been developed in the U.S.”
Some modules are being taken to landfills, while others are being stored until better recycling options become available.
Recommendations for improving the system
The authors propose a research and development agenda with three goals for recycling crystalline silicon: make recycling cheaper than disposal; find a way to use recycled materials in new modules; and make recycling an environmentally better option than throwing old panels out and using virgin materials to make new ones.
The report makes these points and suggestions:
- Because of contamination, the metallurgical grade silicon recovered from panels now is worth about $2 per kilogram, but if the recycling process could be improved so that the silicon was of solar grade, its value would increase to $10 per kilogram or more.
- Less attention should be focused on trying to recover intact silicon wafers. Newer wafers are much thinner than older ones, making intact recovery difficult.
- Convince an industry that has relied on virgin silicon supply to use recovered silicon. To do so, complete impurity profiles will be required so manufacturers know exactly what to expect. That process hasn’t started yet.
- Designing modules so they are easier to take apart or recycled hasn’t caught on, but increasing awareness of the issue and using emerging international standards such as Cradle-to-Cradle certification would help.
Scott Gibson is a contributing writer at Green Building Advisor and Fine Homebuilding magazine.