Project Summary
It will expand on the learnings from discovery phase which reviewed the current/future regulations developing future-proof recommendations for replacingSF6 by assessing the techno-economic performance of different intervention options.
SF6 leakage rates will be analysed to identify the most suitable interventions. Alternative low carbon SF6 disposal methods will be explored with laboratory-scale testing. Site handling of SF6-alternatives especially the gas-blends and complexity with mixture-ratio tolerance will be investigated.
The outcomes of the project will be to increase knowledge of the different intervention options, reduce any risks associated with the large-scale demonstration in the beta phase and key recommendations for industry.
Innovation Justification
UK targets of 50GW offshore wind by 2030, combined with growing electrification of heat and transport, will require a radical transformation of National Grid Electricity Transmission (NGET) electricity transmission system. An extensive reinforcement of existing networks is necessary, where compact-sized GIS play a crucial role. Sulphur hexafluoride (SF6) is widely used in GIS due to its excellent insulation performance, fault interruption capability and chemical stability. The significant global warming potential (GWP) of SF6, 24,300 times greater thanCO2, means that its ongoing use is a critical obstacle to the national need of achieving Net Zero by 2050. Environmentally friendlier alternatives are vital to facilitate an expediated the transition to sustainable electricity networks.
Despite industry-wide consensus that reduction/elimination of SF6 inventory is crucial to reach Net Zero, there is a glaring gap that no roadmap has been developed outlining the key steps to achieve 'SF6-free' by 2050. Recent development in SF6 replacement focused on new equipment optimised by manufacturers. However, replacing all existing assets worldwide with new-builds is time-intensive and impractical to achieve the environmental emission target.
This work is timely as the new EU F-gas draft regulation defined prohibition dates for new SF6 equipment in 2026-2031 covering all voltage levels. For equipment rated ≥145kV used in NGET's network, the proposed prohibition date for new SF6 equipment by the new EU F-gas draft regulation is 1st January 2031, which also proposed drastic restriction on alternatives with GWP ≥10. Furthermore, there is increasing spotlight and discussion for banning Per- and polyfluoroalkyl substance (PFAS) in Europe. This will affect the majority of current SF6 alternatives which signifies the importance of this project. It is recognised by policymakers that these drastic propositions may be impractical for equipment ≥145kV due to their technical requirements and safety critical functionality to the security of electricity supply. These risks provide opportunities for better management of existing SF6assets and recently installed substations using SF6-free solutions through identification of solutions that facilitate recycling and reusing existing gas inventory. Although not considered in the current F-gas regulation, the incineration and final disposal of fluorinated gases such as SF6 adopting an environmentally sound approach could be crucial to enable a 'circular economy approach' in the eventual phase-out of SF6.
Due to safety critical functionality of the electricity network, further technical unknowns must be addressed to de-risk solutions. The proposed project will develop new SF6 replacement interventions and de-risk the solutions through demonstration of the solutions using a representative test system at University of Manchester and in a substation environment at Deeside. Highlights of the novel within the proposal are:
1. The first holistic SF6 replacement strategy from new-build to SF6 end-of-life towards developing a UK 2050 SF6-free roadmap.
2. The first multi-partner investigation into the practical challenges of recycling and refilling aged gas mixture in the event of having incorrect mixture ratio.
3. Validate experimentally in a laboratory scale novel method for incinerating SF6that are significantly less carbon intensive than conventional thermal degradation process.
4. Develop a techno-economic analytical tool to be verified using two substations as case studies that can facilitate mass roll-out of SF6 replacement strategy.
These interventions will inform NGET's Responsible Business Charter that sets out their commitments to reduce SF6 emissions by 50% in 2030 and reach NetZero by 2050. This project will provide the necessary SF6 replacement expertise and innovative 'use-inspired' technological approaches to demonstrate the viability of different proposed solutions in the alpha phase. The implementation in subsequent Beta phase will also target technology translation down to lower voltages that will bring major environmental and technological development cost saving for GB distribution network operators.
Impacts and Benefits
The benefits already realised through the delivery of the Discovery Phase are a synthesis of work carried out in other innovation projects to gain an overall understanding of their importance in strategies to reduce the impact of SF6leakage in GB and described how upcoming F-gas regulations are likely to impact networks in the future. Based on our initial evaluation, alternative methods for disposing of SF6 have the potential to lower energy consumption. This finding calls for additional investigation and confirmation of the calculations. The techno-economic analysis also showed that the lowest cost options, once you factor in the societal and organisational cost of carbon, differ from substation to substation, depending on the profile of equipment. Consequently, there is a demonstrable need for an overarching strategy for reducing the impact of SF6 leakage from assets in GB.
Our pre-innovation baseline is that while networks are already putting in place strategies to remove SF6 from their network, there remains a need to build up the body of knowledge and evidence on leak mitigation measures and non-SF6alternatives to ensure networks recommend the optimal intervention at the optimal time for each asset. This will ensure that networks find the most economically effective route to remove SF6 on the most optimal timeline.
Financial - cost savings per annum on energy bills for consumers
Financial benefits to consumers manifest through savings in the long-term overall cost of removing SF6 up to 2050 over current strategies. Our strategy will lead to more optimal decisions on when and how to intervene to mitigate the impact ofSF6 emissions. Our Discovery Phase techno-economic analysis has calculated the NPV for the different intervention options available at two example substations owned by NGET. By comparing the difference in costs between the optimal solution and the second best solution we have estimated the potential saving associated with making better decisions on which intervention is best. Applying these savings across all SF6 GIS, of which NGET have approximately 100, gives a saving to the consumer of ~£33 million.
Environmental - carbon reduction - direct CO2 savings per annum
Direct environmental benefits can be tracked through the quantity of SF6 removed from assets and SF6 annual emission reductions. Our techno-economic analysis showed that *Interventions that lead to fewer SF6 emissions generally have a lower overall cost. Conversely, the more SF6 emissions generated, the higher the overall costs. Interventions at the two substations analysed were able to reduce lifetime emissions by 175,000 tonnes and 107,000 of CO2 equivalent compared with a base case, do nothing approach. This result shows the significant potential for interventions to reduce direct CO2 emissions, particularly if this is scaled up to include all SF6 GIS.
Financial - future reductions in the cost of operating the network
In Discovery, we estimated that the current method of high-temperature incineration of SF6 is approximately 10 times more energy intensive than a different low-carbon method of disposal. While this result demonstrates the potential for it to reduce energy consumption it also shows promise that alternative methods may also bring down cost. This topic will be explored further in the techno-economic analysis in the Alpha phase.
Finally, this project will bring significant whole system benefits. The UK government's target of 50 GW offshore wind by 2030 will require significantly more compact substations that would typically have used SF6 because offshore settings are typically heavily space constrained. Increasing the body of knowledge for non-SF6 alternatives in these settings is vital to ensure that these offshore wind targets are delivered in an environmentally sustainable way.
