Project Summary

The project seeks to develop an economic, efficient, and holistic strategy for delivering an SF6-free electricity system that will support GB’s ambition to deliver a net-zero, resilient energy system.

The potency of SF6 released into the earth’s atmosphere has a significant effect on global warming. It is estimated that there are over 960 tonnes of SF6 currently insulating gas insulated switchgear (GIS) apparatus in GB substations. The SF6 in GIS switchgear continuously leaks into the atmosphere throughout its lifecycle and requires periodic top-ups and cleansing to maintain satisfactory insulating properties.

SF6 leakage contributes the second highest greenhouse gas emissions from transmission networks, after network losses. The transmission networks must develop a roadmap to being SF6-free by 2050. To understand how to achieve this, whilst deriving best-value to consumers, we propose to develop a strategy for the retrofill of existing switchgear apparatus with alternative lower-carbon-footprint insulating gases, programmes for reducing leakage in existing apparatus, and direct replacement of apparatus where it would not provide optimal value to retrofill with an alternative gas. The strategy would define the broad principles of decision-making for profiles of apparatus (age, scale, future planning requirements, footprint, leakage rates, etc.) across GB’s entire transmission system.

This project will analyse the current regulatory frameworks that govern the use of SF6 and lower-carbon alternative gases and deliver a desk-top study of proposed changes to the regulatory landscape, to deliver a strategy that is future-proof by assessing the techno-economic performance of each option. The overall strategy will be refined over the project lifecycle, and will comprise an exploratory analysis during Discovery phase, testing of solutions at Deeside Innovation Centre during the Alpha phase, and strategy development and deployment during the Beta phase.

The lead partner is National Grid Electricity Transmission (NGET) supported by the following project partners in the Discovery phase:

• SSEN Transmission as a transmission licensee.
• University of Manchester as an academic partner and expert in HVAC switchgear technologies and alternative lower-carbon-footprint insulating gases.
• DNV as project manager and techno-economic assessment experts.

In the Alpha and Beta phases, we anticipate additional partners would join the project, including:

• 3M as provider of alternative low-carbon gas solutions
• DILO as specialist in gas handling, including reconditioning, mixing and recovery of gases.

Each project partner has an interest in driving innovation and supporting the efficient roll-out of new infrastructure and delivering a resilient energy system which is net-zero ready.

Innovation Justification

Our energy system is undergoing a radical transformation. Government targets of 40 GW of offshore wind generation by 2030 and net zero emissions by 2050 present challenges to deliver the infrastructure needed to support increasing amounts of renewable energy and to facilitate a nationwide rollout of electric vehicles. The continued electrification of heat and transport will increase further demand on the electricity network. This will require an extensive uprating of existing electricity network infrastructure where power-dense gas-insulated substations (GIS) have an increasingly vital role to play. SF6, a gas with the highest known global warming potential (25,200 times greater than CO2), is the main insulation medium used in GIS because of its dual qualities of electrical insulation and arc interruption. Existing SF6 technology has provided industry with the ability to install compact high-voltage substations that occupy a volume as low as 5% of air-insulated substations at equivalent voltage level.

The SF6 inventory is expected to drastically increase in the coming years given the growth in renewable generation and uprating of existing electricity infrastructure. Some commercial equipment utilizing non-SF6 based solutions developed by manufacturers has been deployed, but user experience remains limited since the first installation at Sellindge in 2016, so there are many technical unknowns that require urgent further investigation. As the industry accelerating the development of SF6-free technology, we introduce a new challenge in the end-of-life treatment and eventual disposal of many thousands of tonnes of SF6. The current method of high temperature incineration of SF6 contained in its storage container is energy intensive and not carbon neutral. All these issues will inherently delay the Net Zero transition and introduce uncertainty into the safe operation of our energy systems.

This project focuses on developing a viable long-term strategy around (a combination of) the following possible solutions:

1. new-build replacement for substations at the tail end of the asset lifetime;
2. retrofilling existing SF6-designed equipment at the middle or early stage of their lifetime;
3. effective seal mitigation techniques applied on ageing assets to minimise direct SF6 release to atmosphere; and
4. effective end-of-life treatment and disposal of SF6.

This work will drive the changes necessary to transform our energy system towards a sustainable SF6-free electricity grid that is reliable and affordable for consumers.

Project Benefits

The principal benefit of this project is the facilitation of a net zero power system at the minimum achievable cost to the consumers, giving significant environmental and financial benefits:

Environmental benefits: Direct environmental benefits can be tracked through the quantity of SF6 removed from assets and SF6 annual emission reductions. Following the alpha and/or beta phase, the findings of the project will inform the replacement of possibly several tonnes of SF6 as the procedures recommended by the holistic SF6 replacement strategy move into BAU. If a conservative estimate of 10 GISs across GB identified by the holistic strategy could be retrofilled/replaced with SF6-free alternatives before 2035, this alone would result in an abatement of 1050 kg of SF6 emissions in the following 15 years assuming 700 kg of SF6 is removed from each GIS and a 1% leak rate. This is equivalent to more than £6bn in environmental savings using 2021 HMRC Green Book carbon costs, and is a low estimate for savings as the vast array of other SF6 assets excluding GISs is not considered.

Financial benefits: Financial benefits to consumers manifest through savings in the long-term overall cost of removing SF6 up to 2050 over current strategies, which for RIIO-2 are focussed on refurbishment and replacement with further SF6 equipment and do not consider retrofilling as a commercially available alternative. Exact savings will be quantified as the strategy develops and optimal strategies can be compared in terms of cost to the current strategy of leak reduction and replacement. However, considering the previously mentioned example future scenario, replacing 10 GISs with current new-build options for GISs would cost around £1.5bn, whereas retrofilling solutions would be estimated to cost an order of magnitude less at roughly £150m. This would result in a reduced cost of around £1.35bn to consumers, and would be in addition to significant time savings. Rapidly bringing these solutions to commercial availability through this SIF-funded project is therefore paramount. The holistic SF6 replacement strategy, and its associated techno-economic feasibility studies, will expedite the large-scale rollout of SF6-free options and optimise the choice of solution from all available options, not just retrofilling, for a varied profile of assets. This will echo recent stakeholder sentiment; a 2019 survey revealed that 60% of consumers would like National Grid to reach net zero ahead of the promised 2050, further encouraging the accelerated path to decarbonisation that is offered by this project.