Diego De La Fuente, Rachel A. Meidl and Michelle Michot Foss
As interest grows in wind, solar and electric vehicles, we will see a concurrent shift towards electrification. Penetration of energy storage and greater reliance on electrification for industrial processes will supplement enlargement of power grids with high and ultra-high voltage transmission lines, substations, and other infrastructure. While the promise of electrification is in part climate related and to address energy poverty, the lack of data and uncertainty around life cycle impacts highlights the need for an honest accounting of systems-level vulnerabilities, trade-offs and risk-shifting along the value chain.
Here we focus on only one of many distinct mitigation challenges that such honest accounting will need to consider:a synthetic, relatively obscure, and odorless gas: Sulfur Hexafluoride (SF6).
In 1997, the Kyoto protocol identified SF6as one of the six main greenhouse gases (GHG). Not without a good reason: SF6is the most potent GHG known to humanity, with awarming potential 23,900times that of carbon dioxide (CO2)and atmospheric residence of up to3,200 years.
Should we worry?
Although SF6contributes only around 0.8% of CO2-equivalent modeled global warming, its potency andatmospheric lifetime persistence of 3,200 yearsnecessitates action. The atmospheric concentration of SF6has increased rapidly over time, primarilydriven by demand for gas-insulated electric switchgear in developing countries. The annual emissions raterose from about 7.3 gigagrams or Gg estimated in 2008 to about 9.04 Ggin 2018, an increase of 24% over the course of the decade. For reference, 9 Gg of SF6equates to GHG emissions of approximately44 million passenger vehiclesdriven for one year, or226 billion pounds of coal being burned. Similarly, the global mean concentration of SF6has increased steadily since tracking began in 1995 from approximately3.5 parts per trillion or ppt to 10.5 pptin 2021 (to date), a three-fold increase over the course of 25 years. The largest year over year increase occurred in 2017-2018 and amounted to 0.35 ppt.
In addition, those numbers may be actually much higher. Even though United Nations Framework Convention on Climate Change (UNFCC) partners are expected to report their GHG emissions, countries such as China, India and South Korea have notreported emissions of SF6. China itself is believed to be responsible for36% of global SF6emissions. Even somedeveloped countries, including the U.S. and UK, may grossly underestimate their output. In all, the discrepancy between the actual SF6emissions and what is reported might range between2.5 Gg to 5 Gg from 1990-2018.
MORE FROMFORBES ADVISOR
The issues of growing SF6 emissions and their underreportingareparticularly problematic as countries at all levels of developments push for electrification of their economies.
How is SF6related to electrification?
Unique chemical properties of SF6make it agreat electrical insulator. It is highly stable, non-toxic, non-flammable, electronegative, and has excellent arc-quenching properties. SF6replaced polychlorinated biphenyls (PCBs), which governments phased out and eventually banned due to concerns about dioxins. SF6was widely adopted as an alternative to oil and air for insulating mid- and high-voltage electrical equipment.Around 80%of all SF6produced worldwide is used in the electric power industry. SF6isused in gas-insulated switchgearfor wind turbinesto prevent overloading and short-circuiting. SF6also is found ingas-insulated transmission lines, local distribution systems for safe delivery of electricity and transformers,and in themanufacturing photovoltaic panels. In electronics, SF6is used insemiconductordevices found in cell phones, computers, and batteries for electric vehicles.
Over time, SF6can leak during manufacturing, shipping, and storage of SF6equipment and cylinders and duringinstallation, operation, maintenance, decommissioning, disposal or recyclingof gas-insulated equipment.
What are existing rules?
As might be expected from lack of reporting, policy and regulatory approaches to SF6management are not widespread. In the U.S., legislation does not cover all segments of the SF6life cycle and few states have rules related to SF6management. California discourages use of SF6by requiring that emissions rates from equipmentmay not exceed 1% (reduced from 10% in 2011). Massachusetts state lawlimits the annual leakage rate of equipment to 1%while equipment owners must comply with pre-established maintenance and recording procedures. Washington, Oregon, and New Jersey have reporting requirements for SF6that allows for stringent emissions tracking.
The U.S. Environmental Protection Agency (EPA) mandates SF6reporting for equipment with nameplate insulation capacity of 17,820 pounds or more. In 1999, EPA established avoluntary partnershipwith the power industry to reduce SF6emissions. The partnership has helpedreduce SF6emissions by 74%as of 2018.
The European Union has also taken steps to reduce SF6emissions, acknowledging that the fluorinated gases (F-gases) group has the strongest potential greenhouse effect with emissions doubling from 1990 through 2014.Current legislationcalls for overall F-gas emissions reductions of two-thirds, to 2014 levels, by 2030. SF6is prohibited from use in magnesium die-casting alloys and during filling vehicle tires. In 2020, the EU released areportindicating intentions to phase out SF6in electric power systems.
What are SF6mitigation strategies?
Because SF6emissions can occur throughout the entire electric power infrastructure life cycle and as electrification expands to new technologies and applications, both sources and diversity of emitters will increase. Thestrongest reductions come from improving management practices. Upgrading and modernizing existing protocols and standard operating procedures throughout the SF6supply chain helps reduce emissions. Establishing a life cycle approach ensures gas inventory tracking and accounting; leak detection and repair; proper recovery, recycling and disposal of SF6and equipment; management of SF6acquisitions; equipment upgrades and replacement; and proper decommissioning. Instituting such practices through expanded regulatory partnerships could drastically reduce emissions and increase accountability.
What are the alternatives?
Although many gases have been explored as viable alternatives to SF6, there is no proven, commercial alternative yet. SF6has unique attributes as an electrical insulator and substitutes must also be non-flammable, non-corrosive, readily available, safe to handle and non-toxic.
When considering potential viable alternatives to SF6, it is important to take a systems level approach and consider full life cycle effects in order to understand sources of risks, how risks will shift, and how to mitigate them.
Trifluoroiodomethane,CF3I, with similar dielectric properties, is one possibility. However, CF3I is carcinogenic, mutagenic, and reprotoxic. It also causes oxidation and corrosion to electrical equipment.CO2by itself or mixed with oxygen,CO2/O2, is another. CO2/O2has a much larger potential environmental footprint than equivalent SF6units. Other alternatives used or attempted includemixturesof SF6 with nitrogen, SF6/N2and different fluorinated gases but few meet the replacement criteria. Proprietary options are in development.General Electric offers “g3”, otherwise known as “green gas for grid.” g3 has similar performance metrics to SF6and can function at high voltages (up to 420 kV). Currently, three utilities use g3: National Grid (UK), Scottish Power Energy Networks (UK), and Axpo (Switzerland).ABB has produced a five carbon, C5, fluoroketone/air gas compoundwith a global warming potential 99.99% lower than SF6. The company is phasing this product into its existing switchgear platforms. Thus far ABB’s
What is SF6systems-level accounting?
A fundamental question is how best to ensure honest accounting of systems-level impacts, risks, trade-offs, and vulnerabilities. Are manufacturers, shippers, owners, operators, and those involved in decommissioning, recycling and disposal incorporating mitigation techniques into their management plans? Development and deployment of substitutes will take time.Meanwhile, the push is on to accelerate access to electric power in the quest to address climate issues and alleviate energy poverty. In light of those goals, it will be even more imperative that SF6emissions or environmental consequences of substitutes are truly sustainable and balanced throughout the system. Additionally, a well-established regulatory framework that has consistent accountabilities across the global SF6supply chain will be essential for a transparent system that will situate us on path towards sustainability.
Diego De La Fuente, is Student Research Assistant at Rice University’s Baker Institute for Public Policy-Center for Energy Studies.
Rachel A. Meidl, LP.D., CHMM, is the fellow in energy and environment at Rice University's Baker Institute-Center for Energy Studies.
Michelle Michot Foss is Fellow in Energy, Minerals & Materials at Rice University’s Baker Institute for Public Policy-Center for Energy Studies.