Solar panels contain several hazardous materials, most notably lead, cadmium, and tellurium in the photovoltaic cells themselves, plus smaller amounts of other heavy metals like copper and tin in the wiring and solder. The exact mix depends on the type of panel. Standard crystalline silicon panels, which make up the vast majority of installations, primarily raise concerns about lead in their solder connections. Thin-film panels add cadmium and tellurium to the list. Newer technologies not yet widely deployed introduce additional risks, particularly from water-soluble lead compounds.
Lead in Standard Silicon Panels
The most common hazardous material in conventional solar panels is lead, used in the solder that connects individual cells. While the amount per panel is small, it adds up across millions of installations. When panels are crushed or broken in a landfill, lead can leach into groundwater over time.
The EPA uses a standardized leaching test (called TCLP) to determine whether waste materials qualify as hazardous. About 8% of panels built with traditional manufacturing techniques have leached lead above the EPA’s 5 mg/L threshold in testing. The good news: panels built with newer manufacturing methods, including wire interconnect technology and glass-on-glass construction, have not exceeded that limit in any tested samples. Still, the EPA notes that waste panels containing heavy metals like lead and cadmium may fail this leaching test, which means they could be classified as hazardous waste under federal law.
Cadmium and Tellurium in Thin-Film Panels
Thin-film solar panels, particularly those made with cadmium telluride (CdTe), contain two elements with well-documented toxicity. Each square meter of panel holds roughly 0.84 grams of cadmium and 0.89 grams of tellurium. That’s a tiny fraction of the panel’s total weight (about 0.004% each), but cadmium is regulated as a toxic substance. The EPA sets its maximum allowable level in drinking water at just 0.005 milligrams per liter.
Cadmium telluride can cause severe lung inflammation and scarring when inhaled as fine particles. In animal studies, aerosolized particles just 2 to 3 micrometers across were lethal at relatively low concentrations. Tellurium, while not federally regulated in drinking water, has been linked to kidney, heart, lung, and skin damage in both animal studies and limited human case reports. Under normal operating conditions on a rooftop, these materials are sealed within the panel and pose no exposure risk. The concern is what happens when panels break, burn in a fire, or end up in landfills where rain can slowly dissolve the compounds.
Gallium Arsenide in High-Efficiency Cells
A smaller category of solar cells uses gallium arsenide, a semiconductor compound that contains arsenic. These cells are expensive and mostly found in space applications and concentrated solar power systems rather than residential rooftops. The primary hazard comes during manufacturing rather than from the finished panel. Arsine gas, used as a feedstock in production, is extremely toxic. Workers and surrounding communities face potential exposure if the gas is accidentally released.
The solid gallium arsenide waste left over from manufacturing is classified for hazardous waste landfills. These residues can release toxic fumes if burned, and the compounds cause acute and chronic health effects through inhalation, ingestion, and skin contact. For the average homeowner, gallium arsenide panels are unlikely to be relevant, but they represent a real occupational and environmental hazard at the industrial scale.
Lead in Next-Generation Perovskite Cells
Perovskite solar cells are an emerging technology not yet widely commercialized, but they deserve mention because their lead problem is fundamentally different from what’s found in traditional panels. A perovskite module contains about 0.4 grams of lead per square meter, a modest amount. The critical difference is that this lead exists in a water-soluble form.
When perovskite materials degrade, they react with moisture to produce lead iodide, which dissolves readily in water. Research published in iScience found that lead absorption from perovskite-contaminated soil was actually higher than from soil contaminated with lead iodide alone, suggesting the perovskite form poses an elevated risk. If these panels eventually reach mass production, their disposal and breakage scenarios would require stricter containment than current silicon panels need.
Hazards From Manufacturing
Some of the most significant hazardous materials associated with solar panels never end up in the finished product. They’re byproducts of the manufacturing process. Producing polysilicon wafers, the foundation of most solar cells, generates silicon tetrachloride and hydrofluoric acid. Both are dangerous: silicon tetrachloride reacts violently with water to produce hydrochloric acid and silica, while hydrofluoric acid is one of the most corrosive substances used in industrial chemistry. A 2014 report in Nature flagged inadequate treatment of these waste streams as an ongoing pollution concern, particularly at manufacturing facilities with lax environmental controls.
Nitrogen trifluoride, a gas used to clean manufacturing equipment during production of thin-film photovoltaic cells, is a potent greenhouse gas with a global warming potential 17,200 times that of carbon dioxide on a 100-year timescale. It persists in the atmosphere for roughly 569 years. The photovoltaic industry accounts for only about 3% of global nitrogen trifluoride consumption (semiconductor and display manufacturing use the rest), but its contribution is worth noting in a full accounting of solar panel hazards.
What Happens During a Fire
When solar panels burn, the primary gases released are carbon monoxide and carbon dioxide from the plastic backing and encapsulant materials. In controlled fire tests, CO concentrations reached up to 522 parts per million under high heat conditions. While these levels are not trivial for firefighters working in close proximity, researchers noted that the CO and CO2 output from photovoltaic modules is relatively low compared to other building materials. The greater concern in a fire is the potential release of heavy metal particles, particularly from cadmium telluride panels, as fine particulate matter that can be inhaled or settle into surrounding soil.
Recycling and Disposal
Solar panels are not universally classified as hazardous waste under federal law. Whether a specific panel qualifies depends on the results of the EPA’s leaching test. Panels that pass can go to regular landfills in most states. Panels that fail must be handled as hazardous waste under the Resource Conservation and Recovery Act (RCRA). Some states, notably California, treat all solar panels as hazardous waste regardless of test results.
Recycling facilities recover the valuable and hazardous materials through a combination of chemical and electrical separation techniques, extracting silver, tin, lead, copper, and purified silicon. The recycling infrastructure for solar panels is still limited compared to the volume of panels approaching end of life. Most residential panels installed in the early 2000s have warranties of 25 to 30 years, meaning a significant wave of panel waste is expected in the coming decade. How well the recycling industry scales up will determine whether these hazardous materials are recovered or end up in landfills.