Hydrofluoric acid is used to etch and remove oxidation from semiconductors, and discharged into the wastewater. While the acid can be neutralized and the wastewater treated to remove the pollutants, the industry is exploring alternatives for hydrofluoric acid etching. “Other chemicals and thermal processes could be used, but they are more expensive and not commercially proven at this point. Companies have described efforts to reduce hydrofluoric acid and better treat wastewater containing it, but it remains an essential input for making silicon-based PV,” Mulvaney says.
Lead is used to solder PV electrical components, but there has been an industry push to use lead-free or tin-lead alternatives, with lower toxicity levels. Some manufacturers—including SunPower, Mitsubishi Electric, and Trina Solar—offer lead-free or low-lead content modules.
A key concern is that photovoltaic manufacturing and production processes require large amounts of water that discharge different pollutants such as hydrogen fluorides, suspended solids, mixed acids, silicon dioxide, and high oxide particles. Demonstrating the need for chemical reduction plans, a study that appeared in the March edition of the Desalination and Water Treatment Journal explored wastewater treatment options for PV manufacturing, and noted that wastewaters produced by PV manufacturing are “highly toxic and contain high concentrations of fluoride.”
Newer thin-film technologies use less semiconductor material, but there are also health and environmental concerns related to these technologies. The more-popular thin-film technologies—cadmium telluride (CdTe) and copper indium gallium selenide (CIGS) mainly used in large commercial PV installations—contain cadmium, a carcinogen that is considered highly toxic by the EPA and Occupational Safety and Health Administration (see “Abound Solar Spoils” sidebar).
Cadmium is banned by the European Parliament’s Restriction of the Use of Certain Hazardous Substances (RoHS), which requires by law that certain hazardous substances, including lead, mercury, and cadmium, be replaced with safer alternatives in electrical and electronic equipment. CdTe thin-film PV modules are explicitly allowed by RoHS to contain unlimited cadmium, even though cadmium is restricted in all other electronics. This exemption is why thin-film companies like First Solar are able to sell their CdTe modules in Europe. Proving what is possible, Japan-based Solar Frontier has developed copper indium selenide (CIS) thin-film solar modules that are cadmium- and lead-free.
On the production side, there’s also the energy used by solar manufacturing facilities to factor into the equation. While there is some PV manufacturing accomplished largely with solar power, the most energy-intensive processes—polysilicon manufacturing, for example—are often upstream and rarely powered by renewable energy, Mulvaney says.
As of 2014, EU’s Directive on Waste in Electrical and Electronic Equipment (WEEE) will also apply to PV modules, and require solar manufacturers to operate recycling and recovery programs for their products. Currently no such federal mandate exists in the United States.
Part of the problem, says Sheila Davis, executive director for the SVTC, is that the “universal waste” laws that govern hazardous waste disposal vary by state. “What is considered hazardous waste in one state may not be in another. That makes it difficult to regulate and ensure that all modules are being manufactured, and disposed of, safely,” she says.
California’s standards are known to be more strict than most states, and, in some cases, surpass the federal government’s regulations. The state’s standards are nearly identical to those at the federal level, but the state applies the standards to more wastes. Dry-cell alkaline batteries, for one, are considered hazardous waste in California, but not at the federal level.