“Any form of energy production has a dirty side, and solar is no exception, but I do think we tend to hold solar manufacturers to higher standards,” says Dustin Mulvaney, an assistant professor at San Jose State University who specializes in life-cycle analysis of solar energy. “Unlike conventional fossil-fueled technologies, solar power does not produce harmful greenhouse gasses or other air pollutants during operation. The concerns with the chemicals are at the beginning and end of the module’s lifecycle.”
According to the U.S. Energy Information Administration, nuclear, hydro, wind, and solar sources met 18% of total U.S. energy consumption, yet produced none of the country’s energy-production-related carbon dioxide emissions. Conversely, coal accounted for 20% of the energy consumption, with 34% of the emissions; petroleum provided 36% of the energy consumption, with 42% of the emissions; and natural gas provided 26% of the energy consumed, with 24% of the emissions.
A 2008 study—led by environmental engineer Vasilis Fthenakis, a senior scientist at Brookhaven National Laboratory in Upton, New York, and the director of the Center for Life Cycle Analysis at Columbia University—gathered air-pollution emissions data from 13 PV cell manufacturers in Europe and the United States for two years (2004–2006). The solar cells included four major commercial types: multicrystalline silicon, monocrystalline silicon, ribbon silicon, and cadmium telluride thin-film. For each technology, the complete life-cycle atmospheric air-pollution emissions were estimated by adding the direct and indirect electricity and fuel use associated with mining and production of materials, and manufacturing for PV cells, PV modules, and system components.
According to the life-cycle analysis, producing electricity from solar cells reduces air pollutants by about 90% compared to burning fossil fuels for electricity. Replacing grid electricity with central PV systems presents signiﬁcant environmental beneﬁts. For example, electricity generated by cadmium telluride (CdTe) PV modules reduces greenhouse gas emissions, heavy metals, and radioactive emissions by 89% to 98% compared to burning fossil fuels for electricity. For rooftop dispersed installations, such pollution reductions are expected to be even greater, since the loads on the transmission and distribution networks are reduced, and part of the emissions related to the life-cycle of these networks are avoided. Additionally, the study notes that emissions of cadmium from the life cycle of CdTe PV are 90 to 300 times lower than those from coal power plants with optimally functioning particulate control devices. [Complete study]
A 2012 study—“Renewable Electricity Futures Study”—from the National Renewable Energy Laboratory also found that “high renewable electricity futures can result in deep reductions in electric sector greenhouse gas emissions and water use.” Specifically, at 80% renewable electricity generation by 2050, annual generation from both coal-fired and natural gas-fired sources would be reduced by about 80%, resulting in reductions in annual greenhouse gas emissions of about 80% (on a direct combustion basis and on a full life-cycle basis) and reductions in the water use by the power sector of roughly 50%. At this level of electricity production by renewables, the study projects that gross land-use impacts associated with renewable generation facilities, storage facilities, and transmission expansion will total less than 3% of the land area of the contiguous United States. [Complete study]
While there is a need to further reduce the chemicals used in PV module manufacturing and improve end-of-life disposal practices, the leading alternatives for electricity production—coal, nuclear, and natural gas—pose even greater concerns on the production side.
Natural gas is touted as the “cleaner” alternative to coal, and while its combustion emits significantly lower levels of carbon dioxide and sulfur dioxide than the combustion of coal or oil, the production of natural gas creates other serious environmental problems. The hydraulic fluid used to fracture the wells (“fracking”) contains hazardous chemicals that can be released by spills, leaks, faulty well construction, or other exposure pathways. Fracking also produces large amounts of wastewater that contains dissolved chemicals and other contaminants.
Meanwhile, coal mining and oil drilling results in land and ecosystem destruction, as well as water pollution, and poses high occupational risks for workers. In 2011, coal mines in the United States produced more than 1.1 billion tons of coal. Burning this coal in power plants generated more than 130 million tons of coal combustion residuals (CCRs)—including fly ash, bottom ash, boiler slag, and flue-gas desulfurized gypsum. That’s 130 million tons of waste in one year compared to 23 thousand tons of solar waste generated over five years.
Ironically, the solar industry is catching heat for following hazardous waste protocols (see “News & Notes: Greener Module Manufacturing” in HP157), while waste from the coal industry remains largely unregulated, even though coal combustion byproducts contain a broad range of carcinogenic metals, including mercury, selenium, and cadmium. Currently, CCRs are excluded from federal hazardous waste regulations under the Resource Conservation and Recovery Act (RCRA). At the state level, regulations governing the disposal of CCRs vary widely.
When a retaining wall broke at the Tennessee Valley Authority's Kingston facility in December 2008, a massive coal ash spill flooded more than 300 acres of land, damaging homes and property. The materials flowed into the Emory and Clinch rivers, filling large areas of the rivers and resulting in fish kills. This event—one of many dangerous accidents involving coal production—motivated the U.S. Environmental Protection Agency (EPA) to revisit CCR waste regulations. Six years later, the EPA is proposing first-ever national rules for the disposal of coal ash by electric utilities and independent power producers.
Last but not least, there’s nuclear power. While nuclear power generation itself does not contribute to airborne emissions of carbon dioxide, plant construction and the entire nuclear fuel cycle require massive amounts of fossil-fuel—mostly for the mining, purification, and eventual long-term storage of uranium and the reactors’ byproducts. If starting the process with low-quality uranium-bearing ore, the total amount of carbon dioxide produced approaches that of a equivalent-sized gas-fired power plant. Nuclear waste is a solid waste that must be carefully stored because it contains radioactive material. Fall-out from disasters at Fukushima and Chernobyl nuclear plants, and the recent radioactive leaks at Washington state's Hanford Nuclear Reservation, pretty much say it all.
The bottom line: Even with its flaws, solar power is still one of the cleanest and greenest options available today. The key is to do your part to push the industry to do better on the production side.