Already in August 2022, Tagesschau reported under a sensational headline about the greenhouse gas SF6 as a "climate killer in wind turbines". But is sulphur hexafluoride really so harmful to our environment in wind turbines? We have looked into the issue and will provide clarification.
Sulphur hexafluoride, or SF6 for short, is indeed a climate-damaging gas. Just one kilogram of it is as harmful as about 23,000 kilograms of carbon dioxide . "This climate killer is almost always found in the electrical switchgear of a wind turbine," reports the ARD magazine "Plusminus." What the report does not mention, however, is that SF6 gas is not only used in wind turbines, but also in other industries, including medical technology. This is because the gas has special properties: it insulates the lines in switchgear and prevents the formation of light arcs when switching. This allows the systems to be built relatively compactly.
As sulphur hexafluoride is used in a closed system in the context of wind turbines, only very small amounts of SF6 enter the atmosphere. When considering the SF6 emissions from all industries, they are as harmful to the climate as a total of three million tonnes of carbon dioxide. This was the result of calculations by the Federal Environment Agency for the year 2020. The quantity corresponds to a share of 0.4 percent of the total greenhouse gas emissions in Germany.
Prokon is aware of this issue - and actively seeks alternatives. "In our substations, we have been using SF6-free, air-insulated switchgear for some time," says Hauke Henningsen, an electrical engineer at Prokon. However, the larger design of air-insulated systems may not be possible for all applications, according to Henningsen. Therefore, Prokon is considering switching to the more expensive but more sustainable vacuum-insulated systems in the future. However, the cooperative does not have influence over the technology in all trades.
Sulphur hexafluoride, or SF6 for short, is a gas that is colourless, odourless, and about five times heavier than air. It is used in a variety of ways, including in the production of semiconductor components, as a protective gas in magnesium extraction, and as an insulating gas in switchgear. However, SF6 has a significant drawback: it is extremely harmful to the climate. One kilogram of the gas is approximately as damaging as 23,000 kilograms of carbon dioxide.
SF6 gas is used, among other things, in wind turbine switchgear. However, it is not only utilised in the context of wind energy systems but also in the construction of any type of switchgear. In the past, SF6 was also used in soundproof windows, tennis balls, shoe soles, or car tyres, but this usage is no longer permitted today.
In the construction of wind turbines, SF6 supports a compact design. In medical technology, sulphur hexafluoride is used as a contrast agent for detecting liver metastases. In ophthalmology, SF6 is mixed with air and used to treat retinal detachment.
In the typical switchgear used in wind turbines, between three and five kilograms of SF6 are contained. Less than 0.1% escapes from the system each year, as these systems are encapsulated – over a lifespan of 20 years, this amounts to less than 2% .
Although the likelihood is very low, it can happen that the gas fully escapes, for instance, if the system catches fire or is otherwise severely damaged. However, it helps to put this into perspective to make an assessment. If three kilograms of SF6 escape, which is known to be 23,000 times more harmful to the climate than COâ‚‚, the scientist Stefan Holzheu notes that this would release 3.4 tonnes of COâ‚‚e per year, which must be weighed against the 10,000 tonnes of COâ‚‚e saved per year. In newer systems, vacuum-insulated switchgear is increasingly being used to eliminate this risk entirely.
The SF6 emissions from all sectors combined are as harmful to the climate as three million tonnes of carbon dioxide. This was the result of calculations by the German Environment Agency for the year 2020. This amount corresponds to a 0.4 percent share of greenhouse gas emissions in Germany .
When a wind turbine is dismantled, certain regulations must be observed. The gas is either extracted or disposed of with documentation, neutralised, or reprocessed for reuse.
In still air, the gases would separate and prevent rising. However, due to the turbulence and mixing, the gases are blended and carried into the atmosphere. The gas absorbs sunlight, which causes the atmosphere to warm.
Carbon dioxide (COâ‚‚) can still be detected in the atmosphere for 15 to 40 per cent after 1,000 years. The complete breakdown of COâ‚‚ would take several hundred thousand years.
The half-life of methane in the atmosphere is around 12.4 years, significantly shorter than that of COâ‚‚. However, this gas is 25 times more effective than carbon dioxide.
F-gases, including SF6, take more than 3,000 years to fully break down and become inactive .
The so-called Kyoto Protocol reports annually what percentage of greenhouse gases are present in the atmosphere. In 2020, greenhouse gases in Germany were composed of 87.1% carbon dioxide, 6.5% methane, 4.6% nitrous oxide, and around 1.7% F-gases, including SF6.
The topic of sulphur hexafluoride in wind turbines is by no means new and was thoroughly examined as early as 2019. Furthermore, discussions on its use have been ongoing for decades. The devastating consequences of a potential leak cannot be denied, but it is important to note that the majority of SF6 emissions are not due to switchgear installations, but rather to sources such as soundproof windows where the gas can escape freely during disposal. Referring to SF6 as a 'climate killer in wind turbines' is therefore unfounded – a fact clearly supported by the data from the Environment Agency.
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