John Endres: Silicon melting process clouds “green” claim for solar modules

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By John Endres

The proposed PacWest/HiTest silicon smelter in Newport, Wash., was touted as a “green” facility because part of its product, metallurgical silicon, would be further refined for use in silicon solar panels. “Smelting” involves the extraction of a metal from its ore, and “refining” involves the purification of an extracted metal. It was originally claimed that 50% of the smelter’s silicon would be used for solar panels, but it was later suggested that only 5% would be used by REC Silicon’s Moses Lake refinery for solar panels. Most metallurgical silicon is used in the metal alloy and chemical industries, and only a small percentage is further refined to meet the high purity requirements for electronics and solar panels.

Silicon smelters have an enormous power requirement and heavily pollute industrial plants. According to the Washington Department of Ecology, the proposed smelter would include two submerged arc furnaces and a 157-foot-tall emissions stack; and the estimated annual material would include 170,000 tons of quartzite rock (silica), 150,000 tons of blue gem coal and charcoal, and 130,000 tons of wood chips to extract 73,000 tons of metallurgical-grade silicon per year. Estimated annual emissions would include over 766,000 tons of greenhouse gases per year, plus tens to hundreds of tons of other carbon poisons per year. According to 2020 data from the EPA’s Greenhouse Gas Reporting Program, the proposed smelter would be about the 12th highest industrial greenhouse gas emitter in Washington state.

A constant supply of 105 megawatts of electricity – more than 900 million kilowatt hours per year – would be required to generate the intense heat required to obtain molten quartz mixed with carbon reductants. According to the US Energy Information Administration, the average US home uses about 11,000 kilowatt hours per year. The annual electricity consumption of the smelter would be enough to power more than 80,000 average households per year.

The smelter’s “carbothermic reduction process” uses carbon from coal, charcoal and wood chips in a reaction with silicon dioxide to yield carbon dioxide and elemental silicon. Molten silicon is collected from a furnace taphole, and carbon dioxide and other greenhouse gases and pollutants are emitted into the atmosphere.

How can a heavy industrial facility producing a product only a fraction of which is used for solar panels be considered a “green” facility? Scientific papers describing methods for calculating the carbon footprint of solar panels revealed some surprising and worrying issues:

• The carbon footprint values ​​of silicon solar panels reported in the reviewed literature do not include the silicon melting process, which is confusing since silicon is the critical component of silicon solar panels.

• Carbon footprint calculations use a process known as life cycle analysis and life cycle inventory. These methods are highly subjective, produce conflicting and incomparable results, are not subject to a uniform standard method, and are typically performed by industry rather than independent bodies.

• According to the Intergovernmental Panel on Climate Change (IPCC), greenhouse gas emissions from biomass sources (woodchips, charcoal, etc.) are not accounted for at the point of combustion in energy and industrial sectors, including smelting. But we all know that burning wood and charcoal produces smoke (carbon dioxide and other gases). A number of reviewed articles question the IPCC’s biomass accounting methodology.

• The loss of carbon sink due to the harvesting of trees for wood chips and charcoal used in the smelting process is not included in the carbon footprint of silicon solar panels. It can take decades to more than 100 years to replace the carbon sink loss caused by tree harvesting.

• A clear and quantifiable definition of “green” does not exist and “greenwashing” is an ongoing problem.

• Using the raw material and emissions amounts provided for the proposed smelter, the impact of silicon smelting on the carbon footprint of solar panels was estimated, suggesting that silicon solar panels account for more atmospheric carbon dioxide than they save. Excluding the silicon smelting process from solar panel carbon footprint calculations undermines the integrity of the silicon solar panel industry and calls into question the “green” claim of proposed silicon smelting, as well as the “green” claim of silicon solar panels.

We are facing a climate crisis. If we don’t manage the environmental impacts of our operations with the utmost integrity and transparency, we will face ever-increasing challenges to our quality of life.

John Endres of Newport has degrees in Conservation Technology and Botany. He has worked in forestry, plant genetics research and production and research in protein biochemistry.

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