Solar After Sunset

EPRI launched a strategic initiative to guide EPRI research on end-of-life issues for solar and wind generation as well as battery energy storage

By Brent Barker

The year is 2040. The Richardson family trades in their aging rooftop solar photovoltaic (PV) system for a more advanced version that comes with a manufacturer’s guarantee to recycle 95% of the components. The contractor ships the 2025-vintage, crystalline silicon modules to the local outlet of the National Solar Photovoltaic Recycling Network established by federal regulation in 2025. PV recycling is profitable now, enabled by solar modules’ standardized frame-and-sleeve construction along with advanced technology for material recovery and purification.

At the recycling facility, robots place the modules on a conveyor belt where a laser cuts the weather-tight adhesive seal holding the aluminum frames together. The robots carefully open the frames like a book and remove the thin sleeves of crystalline silicon, placing them on another conveyor to a silicon processing station. The frames—which include top and bottom cover glass,junction boxes, and electrical connections—are placed on a third conveyor, where they are washed, flash-dried, packed, and shipped back to the module manufacturer for reuse.

At the silicon processing station, a chemical bath removes specialty metals such as silver and copper. Machines slice and grind the silicon wafers, and thermal and chemical processes purify and recrystallize the silicon. Robots pack the recovered silicon and ship it to the manufacturer for use in new modules.

This scenario underscores a particular reality about solar PV today: Accelerating deployment of PV foreshadows growth of waste. The International Renewable Energy Agency projects that PV module waste volume will rise from negligible levels today to as much as 78 million metric tons in 2050. That’s equivalent to about 12 million dumpsters of waste. Despite this projection, the infrastructure needed for large-scale recycling has not yet reached the drawing board.

The changing structure and composition of modules make cost-effective recycling a moving target. To cut costs, manufacturers are making modules thinner and are using less valuable materials. This reduces the value of materials that can be recovered.

“Developing the infrastructure and technology for collection systems and recycling processes will take years,” said EPRI Principal Technical Leader Cara Libby. “As module designs and compositions change, we need to adapt and develop processes that can recover high-value materials from the latest modules—such as silver, copper, and high-purity silicon. Manufacturers should consider designing modules that are more easily separable into materials and parts.”

“When PV modules are disposed of in landfills, they have the potential to break open and release toxic substances into soil and groundwater,” said EPRI Technical Executive Stephanie Shaw. “A dynamic, cost-effective recycling industry can reduce landfill disposal, address toxicity concerns, promote reuse of critical resources such as silver, and limit mineral extraction.”

The European Union has taken some initial important steps to build a recycling infrastructure. Under the European Waste Electrical and Electronic Equipment directive, producers are responsible for take-back and recycling of modules. More than 40 recyclers around the world, mostly in Europe, claim to process PV modules or subcomponents, such as frames and junction boxes.

In the United States, there are no federal regulations for PV recycling, and most modules are disposed of in landfills and hazardous waste sites. This is driven by economics. An EPRI study indicates that the cost to recycle a module today ranges from $10 to $30 (not including transportation) while the cost to dispose of a module in a local landfill is less than $3.

PV Recycling: State of the Technology

Recent EPRI technology scouting identified novel mechanical, optical, chemical, and thermal recycling processes at various R&D stages. Recovering high-purity silicon, silver, and copper can dramatically increase the salvage value of a module. EPRI found that many delamination and separation processes aim to keep the front glass intact. This increases the salvage value of the glass and potentially improves the recovery of metals and semiconductor material, but may not be practical for thinner module designs or if the glass is already broken.

Promising methods to improve the yield and quality of recovered materials include leaching, filtration, melting, and electrowinning. Another active research area is automating frame removal.

PV Plants: Repower or Decommission?

As electric utilities own more PV plants, they will increasingly need to consider end-of-life options, which include repowering and decommissioning. Numerous factors drive this decision, including a plant’s performance, safety, and the availability of replacement parts and higher efficiency modules. In some cases, plant owners determine that repowering is cost-effective, replace underperforming modules with new ones, and implement associated plant upgrades. A utility may opt for decommissioning based on an assessment of its generation portfolio.

The electric power industry needs decision-support tools that can estimate decommissioning and repowering costs, including end-of-life component recycling. EPRI is considering developing such a tool, which would involve gathering robust data on decommissioning and repowering costs and salvage value.

In 2017, EPRI estimated decommissioning costs for a representative 11-megawatt PV plant at $69 per kilowatt (dc), assuming modules’ disposal in a non-hazardous landfill. Dismantling labor was the biggest cost. Recovering and selling steel and copper reduced total cost by 25%. Further savings may be possible by recovering inverters and other electrical components and by selling modules that can be safely reused. If modules were assumed to be recycled, decommissioning costs ranged from $95 to $153 per kilowatt (dc).

There are many ways to repower older PV plants, with a range of cost-effectiveness. EPRI is modeling and testing various repowering scenarios at the Solar Technology Acceleration Center (SolarTAC) in Aurora, Colorado.

“Repowering could mean swapping out one or more underperforming modules in a string or in multiple strings—or replacing megawatts of capacity in a section of a plant that has been damaged by severe weather,” said Libby. “Our modeling and field testing can inform how to select replacement modules and how to reconfigure arrays to maximize performance. For example, our modeling suggests that grouping new modules in dedicated strings offers better performance than replacing individual modules in strings throughout a plant. This is because new modules typically have higher power ratings.”

A Strategic Recycling Initiative

Solar is not the only rapidly growing technology that raises end-of-life concerns. In 2019, EPRI launched a strategic initiative to guide existing EPRI research on end-of-life issues for solar and wind generation as well as battery energy storage. Activities of the initiative include:

• Developing relationships with diverse stakeholders, including government agencies, researchers, technology developers, and recyclers
• Identifying research gaps and promising reuse and recycling technologies
• Creating roadmaps for long-term research
• Tracking and informing policies and regulations
• Developing summary communications for utilities

Various EPRI programs will continue to evaluate technologies and develop information and tools for utilities.

“Our objective is to get ahead of the end-of-life issues that will be hitting producers of solar PV modules, wind turbine blades, and lithium ion batteries—three rapidly expanding energy technologies,” said EPRI Technical Executive Ken Ladwig. “We want to conduct and gather research that can identify technologies and inform public policy and regulations.”

While these technologies are made of different materials, they are increasingly deployed as integrated systems. Project economics can often be improved by deploying battery storage along with solar and wind. A comprehensive understanding of future recycling needs is therefore essential.

“Our job is to spur technical development for recycling PV, wind, and batteries—which we expect to play a central role in the future energy system,” said Shaw. “We are shining a light on end-of-life concerns that can no longer be ignored in the rush to advance performance. Recycling is a next frontier for these technologies.”