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 is projected to be between 0.17 and 1 million tons. For context, this is part of the 200 million tons of solid waste generated in the U.S. every year, excluding recycled and composted materials. Most of the end-of-life issues currently arise from weather damage and installation mistakes, but some consumers and plant operators may opt to upgrade their panels before the warranty period is over or in response to advancements in technology.

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While recycling processes for cadmium telluride and silicon PV modules exist, the total cost of recycling in the U.S. presently exceeds the cost of landfill disposal. Emphasizing PV end-of-life management is vital for the U.S. Department of Energy Solar Energy Technologies Office (SETO) to minimize solar energy's environmental impacts and ultimately enhance its affordability. Learn more about SETO's goals.

SETO Research in PV End-of-Life Management

SETO is actively funding research designed to create new materials and components that can enhance the durability of PV products, reduce energy intensity during production, and facilitate recycling. Additionally, these efforts are focused on exploring practices that improve insights into the environmental impacts, aiming to circumvent unintended pollution or health risks. SETO's Photovoltaics End-of-Life Action Plan lays out a comprehensive five-year strategy to assert safe, responsible, and cost-effective end-of-life practices.

Through the Materials, Operation, and Recycling of Photovoltaics (MORE PV) Funding Program, SETO has backed four projects addressing technological enhancements to mitigate these challenges while taking a holistic view of the entire PV lifecycle—from material selection and installation through to operation and end-of-life considerations.

Furthermore, SETO supports multiple projects under the Fiscal Year Photovoltaics Research and Development (PVRD) Funding Program that strive to limit precious metal usage such as silver in solar modules. These projects are also focused on developing efficient techniques for materials separation in PV recycling, enhancing supply chain resilience, and decreasing the environmental impacts of PV modules that are disposed of.

NREL has conducted lifecycle analyses of PV modules and explored cost models for module recycling funded by SETO. They also coordinate sustainability initiatives for the International Energy Agency Photovoltaic Power Systems (IEA-PVPS) program, prioritizing recycling research and analysis, PV module lifecycle assessments, safeguarding environmental health during PV manufacturing, and publishing extensive reports on end-of-life management for PV panels. Additionally, NREL has been supported by SETO to evaluate state and local regulations concerning end-of-life modules.

NREL has released the first global assessment of efforts aimed at recycling PV modules, highlighting optimal disposal management strategies. Insights gathered from IEA-PVPS were used to guide manufacturers and stakeholders in understanding the recycling requisites for PV hardware, along with initiatives to design reusable modules and equipment. The report highlights the pressing need for continued investment in R&D, particularly in silicon purification processes, waste reduction in manufacturing, and decreasing recycling costs, among other critical areas.

Additional awards:

• Numerous projects in the SETO Small Innovative Projects in Solar funding program are geared toward enhancing PV technologies' reuse and recycling processes.
• In [year], SETO allocated $700,000 to EnergyBin, a company that has established an online marketplace for solar-industry overstock and hard-to-find components, promoting the reuse of decommissioned materials at discounted prices.
• In [year], SETO granted $900,000 to SRI International to develop a more effective method of recycling silicon waste generated during the wafer-cutting process back into PV-grade silicon.
• In [year], SETO awarded $150,000 to NREL to analyze PV end-of-life management and evaluate the success of designs aimed at simplifying module and equipment reuse.
• Collaborating with the Energy Department’s Advanced Manufacturing Office, SETO is funding a project at NREL to establish a certification for sustainable modules alongside recyclable design initiatives.

Search the Solar Energy Research Database to discover individual SETO-funded projects.

Additional Resources

For further insights into PV research and solar energy initiatives within SETO, along with current and past funding programs, click here.

From pv magazine USA

Residential solar panels are typically sold with extensive loans or leases, with homeowners often signing contracts for 20 years or more. However, what is the actual lifespan of these panels and how robust are they in real-world conditions?

The lifespan of panels varies based on several factors, including climate conditions, module type, and the racking system used, along with others. While there isn't a fixed 'end date' for panels, a decrease in productivity over time may prompt equipment upgrades.

For homeowners pondering whether to retain their panels for 20-30 years or consider upgrades down the line, closely monitoring energy output levels can inform better choices.

Degradation

Loss of output due to degradation typically settles around 0.5% each year according to the National Renewable Energy Laboratory (NREL). Manufacturers generally regard 25 to 30 years as a marker at which noticeable degradation may warrant replacement. The industry standard for manufacturing warranties on solar modules hovers around 25 years, according to NREL.

With a 0.5% annual degradation benchmark, a panel aged 20 years can still produce roughly 90% of its initial output capacity. The quality of the panel can influence degradation as well; for instance, NREL indicates that leading manufacturers like Panasonic and LG have degradation rates near 0.3% annually, whereas some brands may degrade as rapidly as 0.80%. After 25 years, high-quality panels could maintain 93% of their original performance, compared to lower-quality panels potentially outputting as little as 82.5%.

(Read: 'Researchers assess degradation in PV systems older than 15 years')

A considerable portion of degradation results from potential induced degradation (PID). This issue, while not universal across all panels, occurs when the module's voltage potential and leakage current facilitate ion movement within the semiconducting material and other module components, thus diminishing power output capacity.

Manufacturers often utilize PID-resistant materials in their glass, encapsulation, and diffusion barriers to combat this problem.

Moreover, all panels inherently experience light-induced degradation (LID), where initial exposure to sunlight reduces efficiency temporarily. LID varies in intensity according to crystalline silicon quality but generally results in a one-time efficiency loss between 1-3%, according to testing laboratory PVEL.

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Weathering

Weather conditions significantly influence panel degradation, with heat being a crucial factor affecting both performance and long-term efficiency. Ambient heat can adversely impact electrical components according to NREL. By referencing the manufacturer's data sheet, a panel's temperature coefficient can be identified, clarifying the panel’s efficiency in high-temperature scenarios.

The coefficient illustrates how much efficiency diminishes for every degree Celsius above the standard temperature of 25 degrees Celsius. For instance, a temperature coefficient of -0.353% indicates that for each degree Celsius rise, 0.353% of efficiency is lost.

Thermal cycling contributes to panel degradation, with materials expanding in warm conditions and contracting in cooler ones. Over time, this cycle can lead to microcracking, further diminishing output.

In an annual Module Score Card study, PVEL assessed 36 operational solar projects in India and observed significant impacts from heat degradation. The average annual degradation rate across the projects stood at 1.47%, while arrays in colder regions showed degradation rates near 0.7%.

Caring for installation helps mitigate heat-related issues. Panels should be mounted a few inches above the roof to promote convective airflow beneath and keep them cool. Additionally, lighter materials can be adopted in panel construction to limit heat absorption, and sensitive components like inverters should be placed in shaded areas, as suggested by CED Greentech.

Wind is another weather factor that can affect solar panel integrity. Strong winds may induce flexing, a phenomenon referred to as dynamic mechanical load, which can produce microcracks and lower output. Certain racking solutions are designed to endure high-wind conditions, stabilizing panels against strong upward forces and curtailing microcracking. Typically, the manufacturer's data sheet will indicate the maximum winds against which the panel can be rated.

Snow can similarly cover panels during intense storms, resulting in limitations on output. Though snow tends to slide off the panels due to their slick surfaces, a homeowner may opt to clear accumulated snow, an action that must be performed carefully to prevent scratching the glass and compromising output.

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

Degradation is a routine, unavoidable aspect of a panel's lifespan. Though thoughtful installation, mindful snow clearance, and careful panel cleaning can enhance performance, solar panels are fundamentally stable technology with no moving components, necessitating minimal maintenance.

Standards

To ensure durability and optimal performance over time, solar panels must undergo rigorous standards testing for certification. Both mono- and polycrystalline panels are assessed under the International Electrotechnical Commission (IEC) standards.

According to EnergySage, IEC 61215 standards require panels to be evaluated for electrical characteristics like wet leakage currents and insulation resistance. Mechanical load tests assess stress from wind and snow, while climate tests ensure resistance to hot spots, UV exposure, humidity-freeze cycles, damp heat, hail impact, and various other environmental exposures.

IEC 61730 standards also determine performance metrics at standard test conditions, including temperature coefficients, open-circuit voltage, and maximum power output.

Additionally, a common logo found on panel spec sheets is provided by Underwriters Laboratories (UL), which implements its own standards and testing protocols that encompass climatic and aging tests in conjunction with comprehensive safety evaluations.

Failures

Solar panel failures are infrequent occurrences. A NREL study evaluating over 50,000 systems installed across the United States since 2010 revealed a median annual failure rate of just 5 panels per 10,000.

Failure rates have decreased significantly over time; installations prior to 2010 exhibited double the failure rate observed in post-2010 systems.

(Read: 'Top solar panel brands in performance, reliability and quality')

It's worth noting that system downtime is usually not linked to panel failures. In fact, a study conducted by kWh Analytics identified that 80% of solar plant downtime arises from malfunctioning inverters, the crucial component responsible for converting DC output from panels to usable AC electricity. The next installment of this series by pv magazine will delve into inverter performance.

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