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  • Donald J. Pagel

Carbon Dioxide Isn’t the Only Greenhouse Gas

Carbon dioxide (CO2) is the main culprit behind global warming both because it is a potent “greenhouse” gas that traps heat in the earth’s atmosphere, and because of the large quantities that are released into the atmosphere by human activities. In 2017, 82% of U.S. greenhouse gas emissions were CO2. The goal of the Paris Climate Change Agreement is to keep global warming well below a 2°C rise above pre-

industrial temperature levels, and to strive to keep this temperature rise below 1.5°C. To achieve the 1.5°C goal, it is estimated that global CO2 emissions will have to be cut by about 45% from 2010 levels by 2030 and reach net zero by 2050.

Reducing CO2 emissions by this amount will be a monumental task. However, there are other greenhouse gases, like SF6, CH4, CF4, N2O, HFC-134, CFC-11, PFTBA (and many others), that contribute to global warming. Reducing the release of these gases into the atmosphere would increase the chances of reaching the Paris Agreement goals. Like CO2, many of these other greenhouse gases are emitted by important industrial processes, so a practical way to reduce their contribution to global warming is to find less damaging substitutes for these gases. The case of sulfur hexafluoride (SF6) provides a useful example of this approach.

SF6 is a chemically inert, nonflammable, dielectric gas that is very effective at quenching electrical arcs. This makes it useful in certain types of electrical equipment to prevent fires, such as in gas insulated switchgear (GIS) that is used to safely connect equipment to the power grid. Unfortunately, SF6 has a global warming potential of 23,500 (based on 100 years) which means that it is 23,500 times more potent as a greenhouse gas than CO2, and SF6 remains in the atmosphere for about 3200 years. A recent BBC article explains how GIS equipment is used in the electrical power grid and why even renewable energy sources like wind turbines and solar panels use GIS equipment. The BBC article estimates that leakage of SF6 from GIS equipment in Europe alone is the greenhouse equivalent of putting 1.3 million cars on the road every year.

So, are there substitute chemicals or technologies that can replace SF6 in GIS equipment that are more environmentally friendly? Yes. In 2016, the Swiss utility company ewz commissioned a pilot substation in Zurich, Switzerland using GIS equipment designed by ABB that uses a Novec™ 5100 dielectric fluid mixture in place of SF6. According to the 3M Company, Novec™ 5100 and Novec™ 4710 dielectric fluids are two promising nonflammable, arc quenching chemicals suitable for use in GIS equipment, These chemicals have global warming potentials of <1 and 2100, respectively, persist in the atmosphere for only 0.04 years and 30 years, respectively, and have ozone depletion potentials of zero. So, on paper, both of these look like promising replacements for SF6.

More recently, PG&E in California announced a plan to phase out the use of SF6 in all high-voltage GIS equipment. After considerable review, PG&E decided to use a replacement called “dry air/vacuum” technology that does not require an insulating greenhouse gas at all. The dry air/vacuum technology has zero global warming potential, no toxic byproducts, and is already installed in many GIS systems around the world. So, alternatives to SF6 GIS technology do exist. It seems that the biggest problem is how fast can the global installed base of SF6 GIS technology be replaced with the alternatives.

The SF6 example demonstrates that there are greenhouse gases other than CO2 that contribute to global warming, and that the technology that uses these other greenhouse gases can be made significantly more environmentally friendly. Of course, getting industries around the world to minimize the release of greenhouse gases will not be easy, but technology got us into the global warming mess and smarter technology will have to get us out of it.

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