SOURCE: Scientific American

DATE: December 1, 2019

SNIP: The solar economy continues its dramatic growth, with over a half-terawatt already installed around the world generating clean electricity. But what happens to photovoltaic (PV) modules at the end of their useful life? With lifespans measured in decades, PV-waste disposal may seem to be an issue for the distant future. Yet, the industry ships millions of tons every year, and that number will continue to rise as the industry grows. Total e-waste—including computers, televisions, and mobile phones—is around 45 million metric tons annually.

By comparison, PV-waste in 2050 will be twice that figure. Motivated by concerns about exposure to toxic materials, increased disposal costs and overcapacity at landfills managed by underfunded local governments, researchers are exploring global solar waste management solutions based on concepts like the circular economy.

At the same time, demand for everything from sand to rare and precious metals continues to rise. While supplying only about 1 percent of global electricity, photovoltaics already relies on 40 percent of the global tellurium supply, 15 percent of the silver supply, a large portion of semiconductor quality quartz supply, and smaller but important segments of the indium, zinc, tin, and gallium supplies.

In the U.S., there is no federal e-waste regulation to motivate PV-waste collection and recycling. Federal law only requires special management for PV modules that are characterized as hazardous waste under the Resource Conservation and Recovery Act. Some PV modules are considered hazardous waste because of lead or cadmium, others are not considered hazardous waste at all. Since it is not possible to tell whether a PV module is hazardous from visual inspection, many argue it is simpler to collect all PV modules.

The primary challenge to recycling PV today is finding value in the recovered materials compared to the costs of collection and recovery. The International Renewable Energy Agency reported that recovered materials could exceed $15 billion dollars (U.S.) by 2050. But a cost-effective PV-waste collection and recovery system capable of high-value material recovery remains elusive. Most of the value in PV-waste is in the aluminum frame and the silver in the metallization paste. Getting higher-value PV recycling will require expertise in managing glass. 80–90 percent of a module by weight is made from glass.

Recycled glass can be returned to its highest value form many times over, if free of contamination. The challenge today is that recyclers are not able make to high-quality glass from from PV-waste because of contamination by antimony (added forclarity), and plastics debris from the backsheet and encapsulant. Decision-making about glass materials is an area in need of both innovation in recycling technologies, but also better communications between product designers and waste handlers.

Recycling PV-waste will require innovations in material processing and reverse logistics. Many types of recovery processes have been explored, including recycling all types of PV-waste in bulk, versus specific methods for particular PV technologies. The optimal mechanism to take-back PV is also unclear at this time. How to best collect distributed PV-waste with minimal driving. The best pathways forward have yet to be identified.