Solar Photovoltaic Module Design Has Wide-Ranging Impacts On Our Clean-Energy Future

In order for the United States to meet its 2050 decarbonization goals, it must install up to 20 times more solar photovoltaic (PV) modules than are installed today. In order to achieve this goal, the United States must increase its PV production and installations rapidly, but there are more solutions than simply installing more of the same. NREL researchers are suggesting that a need for longer-living PV modules could reduce the number of materials and manufacturing required.

The NREL research team conducted the first quantitative analyses of how PV module lifetimes and recycling rates can affect the flows of PV materials through 2050 in a 100%-decarbonized U.S. grid. In a new journal article, the researchers covered several what-if” scenarios related to Circular Economy Priorities for Photovoltaics in the Energy Transition.

“PV is a no-brainer for sustainability as a source of clean energy, but there are still concerns about waste, material impacts, and energy justice, especially considering how fast PV manufacturing must grow to meet decarbonization goals,” said Silvana Ovaitt, an NREL PV sustainability researcher and an author of the article. “With this work, we hope to put these challenges into perspective and quantify potential solutions.”

“When considering a sustainable PV supply chain, there is a tendency to jump straight to recycling as the solution, when there are a lot of other circular economy levers to try first, like lifetime extension,” said Heather Mirletz, the article’s lead author and a Ph.D. student at the Colorado School of Mines. “Our PV sustainability team gets a lot of questions about repowering existing PV installations and PV recycling. Ultimately, we want to advise how to design and deploy PV in the most sustainable way possible, so we first need to understand the material flows in the context of the energy transition.”

To study the flow of PV module material through 2050, the researchers used PV deployment projections from the U.S. Department of Energy’s Solar Futures Study and the “PV in the Circular Economy” tool.

In the above graph, the mass of PV modules that are expected to be installed (dotted line) and the mass of end-of-life modules (dashed line) are shown for a baseline scenario in which PV modules with a 35-year lifetime are deployed.

The researchers considered 336 scenarios in their study. Out of the 336 scenarios, two scenarios represented the upper and lower bounds of possible approaches to a circular economy of PV modules. The two scenarios were for modules with an extended 50-year lifetime and shorter-lived, 15-year modules with a high rate of closed-loop recycling (meaning materials are reused in new modules). The two scenarios were compared to a baseline scenario that assumed a 35-year module lifetime and a low recycling rate that is reflective of current technology. Since 15-year modules are unlikely to be produced and 50-year modules are not yet available, the two scenarios simply act as extreme points of comparison.

With longer module lifetimes, the amount of new material needed could be reduced by 3% over the baseline scenario since it would reduce the need for additional solar deployment to achieve the same goals in the United States. The short-lived modules would need a closed-loop recycling rate of 95% or higher to avoid requiring larger quantities of new materials than the 35-year baseline scenario.

The researchers noted three significant trends in material flows:

• Long-lived modules not only reduce demand for new material but also provide a longer grace period in which to develop and implement end-of-life recycling or remanufacturing processes, as it will be longer until they begin to retire.
• Shorter-lived modules must achieve high rates of recollection and recycling/remanufacturing to avoid consuming additional new materials.
• Glass composes the majority (by mass) of today’s PV modules. When developing recycling or remanufacturing processes, it will be important to consider PV glass to ensure a steady supply of high-quality glass in addition to silicon and metals.

“Longer module lifetimes make it easier to achieve our PV deployment goals for decarbonization,” said Teresa Barnes, an author of the article and manager of NREL’s PV Reliability and System Performance Group. “We can avoid excess replacements and additional manufacturing by building systems right the first time. Recycling short-lived modules sound attractive, but our mass balance and capacity calculations show it might limit PV capacity. Our upcoming research on energy balance should further guide us toward the most sustainable and successful pathways for PV deployment.”

The NREL team uses a tool it created called PV in the Circular Economy (PV ICE) to model the flows of PV materials through 2050. The PV ICE tool allows researchers to obtain the latest data from the PV industry to model the flow of PV materials over the next several decades. This helps them to predict the effects of different market trends, technological developments, and government policies.

The open-source tool has two main areas. First, it collects the key properties of today’s PV modules — and predictions for future modules, including the quantities of different materials they contain, their expected lifetimes, and their power conversion efficiencies. The second is it tracks how these modules, materials, and the energies they contain will move through the PV life cycle.

Focusing on material demand and life cycle waste, this article followed the flow of mass for various module materials. The PV ICE tool will soon be able to consider other factors, such as energy flows, environmental impacts, and social implications.

Source: nrel.gov