End-of-Life Management for Solar Photovoltaics

Why Is PV End-of-Life Management Important?

According to the International Renewable Energy Agency, cumulative end-of-life PV waste in the United States in is projected to be between 0.17 and 1 million tons. To put that in perspective, there are 200 million tons of solid waste, excluding recycled and composted materials, generated in the United States each year. While weather damage and installation errors cause most end-of-life issues now, some consumers and plant operators may choose to upgrade their panels before the warranty period expires or to take advantage of technological improvements.

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Recycling processes for cadmium telluride and silicon PV modules exist, but in the U.S., the total cost of recycling is greater than the cost of disposing in a landfill. Focusing on PV end-of-life management will help the U.S. Department of Energy Solar Energy Technologies Office (SETO) reduce the environmental impacts of solar energy and ultimately make solar energy more affordable. Learn more about SETO&#;s goals.

SETO Research in PV End-of-Life Management

SETO funds research to develop new materials and designs that can make PV products longer-lasting, less energy-intensive to produce, easier to recycle, and even less polluting at the end of life. New practices can improve understanding of environmental impacts to prevent unintended pollution or human health effects. SETO's Photovoltaics End-of-Life Action Plan outlines a five-year strategy to establish safe, responsible, and economic end-of-life practices.

SETO funds four projects in the Materials, Operation, and Recycling of Photovoltaics (MORE PV) Funding Program that support technology improvements to reduce these challenges with a holistic view of all stages of the PV lifecycle&#;from the material needs and installation to operation and end of life. 

SETO funds several projects in the Fiscal Year Photovoltaics Research and Development (PVRD) Funding Program that work to reduce the use of precious metals like silver in solar modules, develop designs and materials separation techniques for PV recycling, which will result in a more resilient supply chain, and lower the environmental impacts of PV modules entering the waste stream.

SETO has funded projects at the National Renewable Energy Laboratory (NREL) on life-cycle analysis of PV modules and cost models for module recycling. SETO also funds NREL to coordinate PV sustainability efforts for the International Energy Agency Photovoltaic Power Systems (IEA-PVPS) program. These efforts focus on recycling research and analysis, assessing the life cycle of PV modules, improving environmental safety and health in PV manufacturing, and publishing reports on end-of-life management for PV panels. SETO has also supported NREL to survey state and local policies related to end-of-life modules.

NREL published the first assessment of worldwide efforts to recycle PV modules and identified the best ways to manage disposal. The researchers investigated lessons learned from IEA-PVPS to help inform manufacturers and other stakeholders about recycling requirements for PV hardware and efforts to design reusable modules and other equipment. The report finds that more research and development is needed in silicon purification processes, methods to avoid waste in manufacturing, lowering recycling costs, and other areas.

Additional awards:

• Several projects in the SETO Small Innovative Projects in Solar  funding program are working to improve reuse and recycling processes of PV technologies.
• In , SETO awarded $700,000 to EnergyBin, a company that created an online marketplace for solar-industry overstock and hard-to-find components. This marketplace allows decommissioned materials to be reused, in the form of discounted, warrantied solar project components from vetted, reputable sources. This gives new life to old materials while reducing project construction and maintenance costs.
• In , SETO awarded $900,000 to SRI International, an independent nonprofit research organization, to develop a more efficient process to recycle the silicon waste generated by the wafer-cutting process into PV-grade silicon.
• In , SETO awarded $150,000 to NREL to analyze PV end-of-life management and the effectiveness of efforts to design modules and other equipment for easier reuse. 
• Together with the Energy Department&#;s Advanced Manufacturing Office, SETO is funding a project at NREL focused on developing a certification for sustainable modules and designing recyclable modules.

Search the Solar Energy Research Database to learn more about individual SETO-funded projects.

Additional Resources

Learn more about PV research, other solar energy research in SETO, and current and former funding programs.

From pv magazine USA

Residential solar panels are often sold with long-term loans or leases, with homeowners entering contracts of 20 years or more. But how long do panels last, and how resilient are they?

Panel life depends on several factors, including climate, module type, and the racking system used, among others. While there isn&#;t a specific &#;end date&#; for a panel per se, loss of production over time often forces equipment retirements.

When deciding whether to keep your panel running 20-30 years in the future, or to look for an upgrade at that time, monitoring output levels is the best way to make an informed decision.

Degradation

The loss of output over time, called degradation, typically lands at about 0.5% each year, according to the National Renewable Energy Laboratory (NREL).

Manufacturers typically consider 25 to 30 years a point at which enough degradation has occurred where it may be time to consider replacing a panel. The industry standard for manufacturing warranties is 25 years on a solar module, said NREL.

Given the 0.5% benchmark annual degradation rate, a 20-year-old panel is capable of producing about 90% of its original capability.

Panel quality can have some impact on degradation rates. NREL reports premium manufacturers like Panasonic and LG have rates of about 0.3% per year, while some brands degrade at rates as high as 0.80%. After 25 years, these premium panels could still produce 93% of their original output, and the higher-degradation example could produce 82.5%.

(Read: &#;Researchers assess degradation in PV systems older than 15 years&#;)

A sizeable portion of degradation is attributed to a phenomenon called potential induced degradation (PID), an issue experienced by some, but not all, panels. PID occurs when the panel&#;s voltage potential and leakage current drive ion mobility within the module between the semiconductor material and other elements of the module, like the glass, mount, or frame. This causes the module&#;s power output capacity to decline, in some cases significantly.

Some manufacturers build their panels with PID-resistant materials in their glass, encapsulation, and diffusion barriers.

All panels also suffer something called light-induced degradation (LID), in which panels lose efficiency within the first hours of being exposed to the sun. LID varies from panel to panel based on the quality of the crystalline silicon wafers, but usually results in a one-time, 1-3% loss in efficiency, said testing laboratory PVEL, PV Evolution Labs.

For more FAQ of solar panelsinformation, please contact us. We will provide professional answers.

Weathering

The exposure to weather conditions is the main driver in panel degradation. Heat is a key factor in both real-time panel performance and degradation over time. Ambient heat negatively affects the performance and efficiency of electrical components, according to NREL.

By checking the manufacturer&#;s data sheet, a panel&#;s temperature coefficient can be found, which will demonstrate the panel&#;s ability to perform in higher temperatures.

The coefficient explains how much real-time efficiency is lost by each degree of Celsius increased above the standard temperature of 25 degrees Celsius. For example, a temperature coefficient of -0.353% means that for every degree Celsius above 25, 0.353% of total production capability is lost.

Heat exchange drives panel degradation through a process called thermal cycling. When it is warm, materials expand, and when the temperature lowers, they contract. This movement slowly causes microcracks to form in the panel over time, lowering output.

In its annual Module Score Card study, PVEL analyzed 36 operational solar projects in India, and found significant impacts from heat degradation. The average annual degradation of the projects landed at 1.47%, but arrays located in colder, mountainous regions degraded at nearly half that rate, at 0.7%.

Proper installation can help deal with heat-related issues. Panels should be installed a few inches above the roof, so that convective air can flow beneath and cool the equipment. Light-colored materials can be used in panel construction to limit heat absorption. And components like inverters and combiners, whose performance is particularly sensitive to heat, should be located in shaded areas, suggested CED Greentech.

Wind is another weather condition that can cause some harm to solar panels. Strong wind can cause flexing of the panels, called dynamic mechanical load. This also causes microcracks in the panels, lowering output. Some racking solutions are optimized for high-wind areas, protecting the panels from strong uplift forces and limiting microcracking. Typically, the manufacturer&#;s datasheet will provide information on the max winds the panel is able to withstand.

The same goes for snow, which can cover panels during heavier storms, limiting output. Snow can also cause a dynamic mechanical load, degrading the panels. Typically, snow will slide off of panels, as they are slick and run warm, but in some cases a homeowner may decide to clear the snow off the panels. This must be done carefully, as scratching the glass surface of the panel would have a negative impact on output.

(Read: &#;Tips for keeping your rooftop solar system humming over the long term&#;)

Degradation is a normal, unavoidable part of a panel&#;s life. Proper installation, careful snow clearing, and careful panel cleaning can help with output, but ultimately, a solar panel is a technology with no moving parts, requiring very little maintenance.

Standards

To ensure a given panel is likely to live a long life and operate as planned, it must undergo standards testing for certification. Panels are subject to the International Electrotechnical Commission (IEC) testing, which applies to both mono- and polycrystalline panels.

EnergySage said panels that achieve IEC standard are tested for electrical characteristics like wet leakage currents, and insulation resistance. They under go a mechanical load test for both wind and snow, and climate tests that check for weaknesses to hot spots, UV exposure, humidity-freeze, damp heat, hail impact, and other outdoor exposure.

IEC also determines a panel&#;s performance metrics at standard test conditions, including temperature coefficient, open-circuit voltage, and maximum power output.

Also commonly seen on a panel spec sheet is the seal of Underwriters Laboratories (UL), which also provides standards and testing. UL runs climactic and aging tests, as well as the full gamut of safety tests.

Failures

Solar panel failure happens at a low rate. NREL conducted a study of over 50,000 systems installed in the United States and 4,500 globally between the years of and . The study found a median failure rate of 5 panels out of 10,000 annually.

Panel failure has improved markedly over time, as it was found that systems installed between and demonstrated a failure rate double the post- group.

(Read: &#;Top solar panel brands in performance, reliability and quality&#;)

System downtime is rarely attributed to panel failure. In fact, a study by kWh Analytics found that 80% of all solar plant downtime is a result of failing inverters, the device that converts the panel&#;s DC current to usable AC. pv magazine will analyze inverter performance in the next installment of this series.

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