The UK Government has made a commitment to deliver a hydrogen economy as a means to decarbonise heating and heavy transport. This was most recently highlighted in the Government’s “Ten-point plan for a green industrial revolution” and the recent Energy White Paper “Powering our net zero future”. In this blog, Professor Kevin Taylor, from the Manchester Environmental Research Institute, lays out the role of the sub-surface in both hydrogen storage and carbon capture – both crucial strands of the UK’s net zero ambitions.

• Most hydrogen production currently generates CO₂ as a by-product, which needs to be stored via carbon capture and storage.
• Once produced, hydrogen gas will also need the be stored temporarily or seasonally to address demand fluctuations.
• The sub-surface can meet both of these roles using existing natural formations, such as deeply buried sandstones offshore or salt caverns in Cheshire.
• Policymakers must implement a nation-wide pilot programme to identify more suitable sites, and ensure the UK has the skills and infrastructure needed to make sub-surface storage a reality.

The government’s commitment to a hydrogen economy has led to promises of a number of hydrogen networks in the UK, a potential “hydrogen town” by the end of the decade, and of greater investment across the energy sector to meet these targets. However, this ambition is not without its challenges and risks. As a geoscientist, it is clear to me that two aspects where we will need significant and rapid investment, leading to development and implementation of technology, are at the end of the hydrogen economy chain – underground (or geological) capture and storage (CCS) – and the very likely need to temporarily store hydrogen in the sub-surface to buffer intermittent energy demands. While on the face of it these appear to be different challenges, they share a great deal in common.

Currently, most of the global production of hydrogen is manufactured from coal (so-called brown hydrogen). This process not only fuels the coal economy, but also produces significant amounts of CO₂ as a by-product. An alternative source is through the manufacture of hydrogen from natural methane gas, via a process called steam methane reformation; so-called grey hydrogen. While this is “cleaner” than brown hydrogen, it still produces CO₂ as a by-product.  Much store has been placed, at least in the next two decades, in burying this CO₂ in the ground (carbon capture and storage – CCS), thereby locking the CO₂ away long-term (blue hydrogen). The ultimate goal, of course, is for green hydrogen to be produced utilising renewable energy sources and the electrolysis of water, which releases no CO₂. However, the economics of green hydrogen production, and the relative abundance and cheaper availability of producing it from methane, has led many to conclude that CCS will need to be a key part of the hydrogen economy supply chain for the foreseeable future.

Why use the sub-surface for storage and disposal?

To many the sub-surface has traditionally been associated with the extraction of fossil fuels, and so it is not immediately seen by the public to be part of the solution to meeting net zero. However, the sub-surface can and should play a key role in safely disposing of CO₂. We know that two potential parts of the sub-surface could hold and retain CO₂; either spent oil and gas reservoirs, or deep saline aquifers. Currently, the UK has no active CCS sites operational – plans to invest in CCS pilot sites were abandoned in 2015 due to insufficient fiscal support from the previous government. In contrast, there have been a number of successful CCS projects in the Norwegian sector of the North Sea (eg the Sleipner CCS site) and new projects have recently been announced (such as the Northern Lights Project). According to the IEA, globally, there are still only around 20 projects in commercial use, but in the last three years, plans for more than 30 commercial carbon capture facilities have come forward, representing a potential investment of about $27bn (£20.7bn). The UK, for example, has announced two new projects in Teesside and Humberside involving consortia of energy and engineering companies.

The ability of the sub-surface to trap gas has also led to proposals for the temporary sub-surface storage of hydrogen, in order to off-set fluctuating/seasonal demand.  These could be simple engineered tanks buried in the ground, but why go to the expense of this when rocks in the sub-surface have the capability to have gases pumped in and pumped out, as evidenced by a number of existing gas storage projects in the UK and wider. A recent assessment has suggested that gas fields under the North Sea could provide this storage. Here, the northwest of England could also help to offer sub-surface storage solutions with the presence of highly suitable mined-out salt caverns in Cheshire.

Integration in the northwest of England.

The northwest of England has a hydrogen economy project that is being developed with a clear ambition to deliver both hydrogen and a path to net zero by burying CO₂ produced via hydrogen production, and utilising temporary hydrogen storage in the sub-surface. Sites that may be suitable for the former have been identified in the sub-surface under the Irish Sea, where there are existing hydrocarbon gas sub-surface storage systems, in addition to the already mentioned potential for hydrogen storage in Cheshire salt caverns.

It is clear that the sub-surface is a key player in the hydrogen economy, and geoscience and engineering technology and skills, which already exist in many parts of the energy sector, will be critical to delivering the hydrogen economy promised by the UK Government. Policymakers should work with established experts in this field, such as oil and gas geologists and engineers, to reduce the skills gap needed to properly utilise the potential of the sub-surface.

The northwest of England is in an excellent position to take advantage of key areas beneath our feet. Investment and research towards better understanding this sub-surface domain – and how it will behave when gases are pumped into, stored and retrieved from it – will be needed here in the form of research pilot sites where independent and verifiable trials can take place are needed. Again, the northwest of England has a head-start in this. The British Geological Survey, together with the UKRI, have planned a UK Geoenergy Observatory in Cheshire, (UKGEOS) which will use data from lab studies on rock core from the sub-surface, combined with 3D mapping and in-situ real time monitoring data to reduce uncertainties. But given the variable geology of the sub-surface, both regionally and nationally, a policy of wider study should be a priority. We are on the road to hydrogen, but there is much to be done if we are to realise this exciting potential.

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