There are two primary types of solar PV panels currently available for utility-scale solar energy facilities, which use different semiconductor materials to generate electricity from the sun.
Crystalline silicon panels are currently the most common type of panel. These types of panels use a crystal lattice of silicon atoms to convert sunlight into electricity. Silicon is the second most abundant material on Earth (after oxygen) and the most common semiconductor used in computer chips. It is nontoxic. (Source: U.S. Department of Energy, “Solar Voltaic Cell Basics.” https://www.energy.gov/
The other primary type of solar panel technology used today is called thin-film technology. Thin-film panels use cadmium telluride (CdTe) as the semiconductor material. Thin-film solar panels are made by painting exceptionally thin layers of CdTe (about 3% of the thickness of a human hair) on glass, and then sandwiching the material under another layer of glass. CdTe is a stable crystalline compound formed from cadmium
and tellurium. It behaves very differently than cadmium alone or other cadmium-based compounds. It is chemically stable, insoluble in water, and it has an extremely high melting point (1,906°F) and boiling point (1,922°F). All of these factors make it highly unlikely that cadmium will ever escape the panel. Furthermore, the vapor pressure of CdTe at ambient conditions is zero, so it is impossible for any vapors or dust to be generated when using CdTe PV modules.
Finally, there is simply so little CdTe in thin-film panels that even in modeled worst-case scenarios, the amount of cadmium that could theoretically leach into the soil from a thin-film solar energy facility would be far lower than the nation’s strictest health screening values and 400-6,000 times lower than the amount of cadmium that regularly leaches from common phosphate fertilizers used regularly by American farmers. To date, more than 50 peer reviewed papers from leading institutions around the world have confirmed the safety of CdTe solar technology during normal operation, fires, module breakage, and end-of-life recycling and disposal.
(Source: Bonnet, D., & Meyers, P., “Cadmium-telluride—Material for thin film solar cells,” Journal of Materials Research 13, no. 10 (1998), pp. 2740-2753)
(Source 2: V. Fthenakis and K. Zweibel, “CdTe PV: Real and PerceivedEHS Risks,” National
Renewable Energy Lab (May 2003))
(Source 3: Sinha, Parikhit et al. “Fate and transport evaluation of potential leaching risks from cadmium telluride photovoltaics.” Environmental toxicology and chemistry vol. 31, 7 (2012), pp. 1670-5)
(Source 4: First Solar, “Sustainability Documents.”)