How Are Solar PV Modules Tested for Toxicity?
9.57 million tonnes of PV panels are expected to reach their end-of-life (EOL) by 2050. It’s exciting to see the launching of large-scale PV development plans throughout the United States. As we develop these massive utility-scale solar projects, we must consider how we will responsibly recycle these panels after reaching the end of their life, or if a repowering is needed, or if a severe weather event requires clean-up and recycling management. Solar panels must be disposed of or recycled to ensure environmental safety.
A critical step in this process is determining the toxicity of the modules to ensure compliance with regulations such as the Resource Conservation and Recovery Act (RCRA). To identify potential environmental hazards, the leaching potential of harmful metals needs to be tested. The EPA’s Toxicity Characteristic Leaching Procedure (TCLP) is the standard method used for this testing.
Our team wanted to educate and provide a guide on how to properly sample solar PV modules for toxicity testing, following the guidelines outlined in the ASTM E3325-21 standard. We use this standard at Solar eWaste Solutions, which focuses on preparing representative and repeatable samples for testing and ensuring that results are accurate and reliable.
Introduction to PV module sampling
Solar PV modules contain various materials, including metals like cadmium, lead, silver, and arsenic, which may leach into the environment if improperly disposed of, for example, in a landfill. As more solar modules increasingly reach end-of-life, there is a pressing need to understand their toxicity potential. The TCLP process is used to simulate landfill conditions to determine the risk of toxic substances seeping into the environment.
The ASTM E3325-21 standard provides a method for extracting, preparing, and testing representative samples of solar PV modules for toxicity. This method focuses specifically on crystalline silicon (c-Si) and cadmium telluride (CdTe) PV modules since these types are the most common in the market. Though other technologies could also fit, the emphasis is on these two due to their popularity.
Process overview
The ASTM E3325-21 standard gives a clear set of steps to follow when extracting and preparing PV module samples for toxicity testing, using the EPA’s TCLP test. This approach ensures that sampling sampling stays consistent and that results aren’t influenced by any unintentional bias.
Sample extraction method – waterjet cutting
The ASTM standard suggests using waterjet cutting over mechanical methods as the preferred sample extraction method for PV modules. Waterjet cutting is preferred because it produces more consistent results by slicing PV module laminates into uniform 9.5 mm squares, all while keeping the layers, like the glass, encapsulant, and backsheet, intact. Waterjet cutting ensures that the laminate areas of the PV module are sliced into square pieces, typically 9.5 mm by 9.5 mm, without separating the layers of the module, such as the glass, encapsulant, and backsheet.
1. TCLP Testing for harmful metals
The extracted samples are tested for eight distinct metals using various EPA methods.
- Mercury (Method 7470A)
- Arsenic, Barium, Cadmium, Chromium, Lead, Selenium, Silver (Method 6010C)
2. Applicable PV technologies
The standard focuses on crystalline silicon (both mono and polycrystalline) and cadmium telluride PV modules. It includes sampling of the laminate area, excluding non-relevant parts such as aluminum frames or junction boxes, which are already covered by recycling protocols.
Step-by-step sampling plan
The following steps outline the proper process for sampling solar PV modules for toxicity testing:
1. Pre-sampling calculations
Before extracting samples, a thorough calculation of the total laminate area of the PV module is necessary. This involves knowing the module’s dimensions and dividing it into relevant areas, such as:
- Cell area
- Cell-ribbon area
- String-ribbon area
- Non-cell/non-ribbon area
For crystalline silicon modules, each area must be calculated proportionally to the overall module area.
2. Sample size and weight
- The total weight of all samples must be at least 100 grams for TCLP testing, with an additional 5-10 grams for pH testing.
- Each sample piece must measure 9.5 mm by 9.5 mm, and the particle size must be representative of conditions in a landfill.
3. Waterjet cutting
Send the PV module to a waterjet cutting facility to extract samples from the laminate area. The waterjet ensures precision in cutting, avoiding separation of the layers within the module.
Two cutting steps are involved:
- Initial linear strips are cut from different areas of the laminate.
- These strips are further cut into square pieces measuring no more than 9.5 mm on each side.
4. Rinsing and drying samples
Once the samples are extracted, they must be rinsed in deionized water and dried in a convection oven at 50°C for at least four hours. This step ensures that no contaminants affect the accuracy of the TCLP test results.
5. Grouping and weighing samples
After drying, group the samples according to the areas they were removed from (cell area, cell-ribbon area, string-ribbon area, etc.). Each group must be weighed separately to ensure that the sample sizes are proportionate to the total laminate area.
6. Submit for TCLP Testing
Once the samples are prepared and verified for the correct weight and size, they can be submitted for TCLP testing. Be sure to include 100 grams of sample pieces for the leaching test and an additional 5-10 grams for pH testing.
7. Data interpretation
After the TCLP test is complete, the concentrations of metals in the leachate will be reported. If any metal exceeds the EPA’s allowable limits, the module must be classified as hazardous waste and disposed of accordingly. If all concentrations are within acceptable ranges, the module can be disposed of in a regular landfill.
Are your panels being sampled for hazardous waste when you send them off to be recycled? Sampling solar PV modules for toxicity is a critical step in ensuring that the end-of-life disposal of these modules is environmentally safe. By following the guidelines outlined in ASTM E3325-21, solar developers, recyclers, and waste management facilities can ensure that their sampling practices are consistent and reliable. The use of waterjet cutting, proper sample preparation, and compliance with TCLP guidelines are essential to obtaining accurate results that protect the environment and public health.
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