As Chinese module production has ramped up in the past two years, clean manufacturing techniques are struggling to keep up. The Washington Post reported in March 2008 that a Chinese plant manufacturing purified polysilicon—the major crystalline PV module input—improperly disposed of tons of silicon tetrachloride, a toxic by-product (4 tons of silicon tetrachloride are produced for each ton of polysilicon). The toxic waste was reportedly being dumped on fields in villages neighboring the plant, making the soil infertile and potentially creating clouds of poisonous hydrogen chloride gas. There is a recognized, safe, nonhazardous process for recycling this by-product, but the high-heat recycling process nearly doubles per-ton production costs. Doubtless, this particular manufacturer was trying to save time and money by avoiding recycling, with a high social and environmental cost.
Concerns have also been raised about the newer generation of thin-film cells manufactured with cadmium or indium. Cadmium is a naturally occurring metal, and it is also a by-product of zinc refining. However, it can be extremely toxic to humans. Short-term exposure causes vomiting and fever, while long-term effects include kidney and lung damage. PV manufacturers claim that the cadmium used in PV modules is entirely encapsulated, so will pose no health dangers to consumers, and can be recycled at the end of the modules’ life spans. However, considering the lax regulatory environment in some countries, the health of the industrial workers and the communities surrounding the manufacturing plants must also be considered. Indium, like cadmium, is another thin-film input that comes mainly from zinc ore. Indium has received some publicity due to a perceived danger of supply shortages, and plants in China (where 40% of the world supply of indium comes from) have been shut down in the past due to pollution concerns.
While there is no doubt that PV modules can provide decades of nonpolluting renewable energy, questions about the environmental impact of manufacturing PV modules should go hand in hand with questions about the return on energy invested in modules. Modules that rely on less energy-intensive manufacturing processes and use less raw material offer lower embodied energy and a shorter payback path to clean, free energy.
However, awareness of environmental shortcuts that make manufacturing less energy-intensive, but create additional pollution (such as the improper recycling of by-products) is also important. One proposed solution is an organization modeled along the lines of the Forest Stewardship Council, which, through a chain of custody, certifies wood as coming from properly managed forests. A “sustainable PV” stamp could include calculations of embodied energy, and assure consumers that the manufacturing supply chain was well regulated.
While addressing these issues is important, it shouldn’t overshadow the overall positive effect of using PV (or other renewably generated) electricity. Electricity derived from coal and natural gas will never outweigh the energy and continual resources required to produce it. Additionally, there are the associated environmental impacts of global warming and air, water, and soil pollution due to the emissions from fossil-fuel based power plants, and the environmental impacts of mining, drilling, and transporting coal and natural gas. Unlike conventional energy sources, PV systems produce clean electricity for decades after achieving their energy payback in three or fewer years—this is truly the magic of PV technology.