Project Summary

The Hybrid Storage System will enable safe and efficient storage of hydrogen on operational sites using an optimised approach to hydrogens physical state against production and demand profiles.

Innovation Justification

Preparing for a Net Zero Power System
Green hydrogen production is a low stability system in that the production relieson the weather (wind/solar) and/or constraints in the electricity network making ithard to align production and use of hydrogen. Having an efficient optimisedstorage system means that hydrogen can be produced during periods of highrenewable generation and stored, reducing the overall cost of hydrogen.

Learnings from Previous Projects
The NIA project 'Hydrogen Fuel Gas for NTS Compressors' looked at on sitehydrogen production and storage options for fuelling gas turbines. It concludedthat a compressed gas store of over 11 tonnes would be required alongside a Tier1 COMAH permit which comes with considerable resource and cost to achieve.This has driven the need for an alternative and solid state storage could meet thestorage requirements whilst avoiding entering COMAH regulations, as thehydrogen is stored as a chemical compound and the safety requirements for thatcompound would apply.

Working with Stakeholders
The project has engaged with National Gas Transmission internal teams includingSubject Matter Experts in Rotating Machinery, Operations and Policy andRegulation to help define the system requirements, as well as other networks tounderstand their needs. The project has also engaged with other SIF projects toshare knowledge and experience, including UKPN's Connectrolyser and NGT's Waste Heat Recovery projects.

Innovation
This project is innovative in its approach by hybridising solid and gaseous storageto resolve the limitations of the different hydrogen storage systems. The proposedsolid state hydrogen storage technology stores hydrogen more efficiently, safelyand at a lower cost than compressed gas. The hydrogen forms a chemical bondwith the metal forming a metal hydride, meaning the safety requirements wouldapply to the metal hydride rather than hydrogen itself. The system includes aninnovative machine learning platform (HyAI) using reliable algorithms whichpredict energy generation/storage /demand to optimise operations across thevalue chain. This project will also consider the opportunity to expand the scale ofthe solid-state system and utilise novel methods to improve release ratesalongside the use of gaseous storage.

State of the Art
For small scale hydrogen storage, the current options include compressed gasstorage, liquid storage and carriers such as ammonia. Compressed gas storage iswell established and more suited to short term storage but comes with associatedsafety considerations. Carriers allow hydrogen to be stored as another chemicalsuch as ammonia or liquid organic hydrogen carriers. Liquid allows for easiertransport and storage but the efficiencies of these technologies are low due to thehigh temperatures require to release the hydrogen.
TRL
Currently 4-6, moving to 7
IRL
Currently 1, moving to 4-5
CRL
Currently 1-2, moving to 4-5

Project Size and Scale
The demonstration will take place on a low utilisation compressor station, reducingthe CAPEX on equipment and minimising disruption, whilst allowing the increasedefficiencies to be demonstrated on an active site. The project will consider differentsites on the NTS to better understand the business case and wider roll out of thesolution.

BAU
The key technology to be demonstrated is at low TRL (solid state storage 4-6),and funding the demonstration through innovation funding reduces the risk of theproject. Additionally, hydrogen activities are not currently funded through businessas usual funding.

Counterfactuals
Compressed gas hydrogen storage is an option for our application, but wouldrequire additional safety considerations which could be prohibitively costly for botha demonstration and roll out across the network. COMAH permit application feescould be as much as £1m per site, excluding ongoing annual fees.

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Impacts and Benefits

Pre-innovation baseline
In order to quantify the financial benefits of a hybrid storage system a baseline of acompressed gas storage system will be compared against the novel design.Consideration of the wider financial and environmental benefits that hybrid storageenables with the use of hydrogen for compression to meet emission reductiontargets will also be necessary.

Financial Benefits
Significant upfront and ongoing costs are associated with COMAH certification tostore \>5t compressed hydrogen. These costs will be further explored as theproject progresses but are in the order of £800k initially followed by an additional£150k/year for ongoing interventions per site. If large amounts of hydrogenstorage were required across all 12 compressor stations with Avon gas turbines(in order to meet the Medium Combustion Plant (MCP) Directive for low emissionsin 2030), this has the potential to cost £9.6m in addition to yearly costs of £1.8m,increasing the network operation costs. It should also be highlighted that there areadditional implications for COMAH sites including an increased presence in policepatrols and rapid response to perceived threats, therefore an increase in thenumber of sites classified this way will affect the wider area as well.

At high utilisation individual sites such as those identified in the discovery project,the implementation of on-site hydrogen production via electrolysis with hybridstorage also offers the potential to reduce initial CAPEX costs by £6m from£26.5m to £21.4m when compared to on-site hydrogen production withcompressed gas storage only.
More widely, there are currently 30 Avon gas turbines on the NTS which areearmarked for replacement in order to meet the MCP Directive as no alternativelow emissions retrofit technology (such as DLE) will be ready by 2030. If theseunits can be repurposed for hydrogen by 2030 (which would also necessitateadequate hydrogen storage and supply), National Gas could avoid replacing theseunits at a cost of ~£60m each, or £1.8Bn in total.

Environmental - System Emissions
In 2021, Avon gas turbines at compressor stations emitted around 106,000 tonnesof CO2 from burning natural gas. If the fuel gas contained 20%vol hydrogen thiswould decrease emissions by around 7%, or alternatively could eliminate CO2completely if 100% hydrogen is used as the fuel gas. In the highest utilisationscenarios, using 100% green hydrogen could result in significant CO2 emissionssavings of up to 12,000t per year per compressor. Using green hydrogen fromelectrolysis would mean there would be no indirect CO2 associated with the hydrogen production.

Safety Benefits
Deployment of solid state storage could be safer than having significantcompressed gas storage on site, with lower risks and hazards associated withlower operational pressures. Additionally, the ventilation of the units is such thatthe lower explosive limit (LEL) of hydrogen may not be reached, and the systemcould avoid being classed as ATEX, which would reduce costs.

Benefit Synergies
A broader understanding of the wider system benefits (for efficient on-site H2production and storage) will be achieved through working in conjunction with otherSIF projects including HyNTS Waste Heat Recovery, SGNs Carnot Gas Plantapplication & UKPNs Connectrolyser to ensure alignment and that the value of thesynergistic benefits is articulated, as such each energy network is supportingthese Alpha submissions to ensure collaboration.

Initial benefits will be seen during the beta phase, once the demonstration site isoperational, however most benefits will occur once the system has been deployedacross multiple operational sites. We believe this could be achieved through the Project Union timeline of between 2026 and the early 2030s for the gas transmission network.