A Scottish green energy storage firm has unveiled plans to construct hundreds of purpose-built underground hydrogen storage shafts.

Edinburgh-based underground energy storage specialists Gravitricity has hailed signing a memorandum of understanding with infrastructure major VSL Systems UK to complete the design of below-ground lined rock shafts.

The partners plan to build a scale demonstrator in the next 24 months ahead of commercial roll-out.

Gravitricity believes its storage technology – known as FlexiStore – is a “goldilocks” solution to the future challenge of green hydrogen storage, offering a system that is "larger and more secure" than above-ground hydrogen storage, but also more flexible than subterranean salt caverns, which it said are "the two most commonly-proposed alternatives".

HeraldScotland: How it works and where it goesHow it works and where it goes (Image: Gravitricity)

The shaft would be six metres in diameter and 365 metres deep and lined with steel. A single store would hold up to 100 tonnes of green hydrogen, the firm said.

It also said 1,000 sites would meet a quarter of the UK predicted 2050 hydrogen storage needs.

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It has identified a number of sites for the pilot project and is in discussion with site owners after recently completing a £300,000 feasibility study, conducted with ARUP and funded by the UK Government’s BEIS HySupply programme, which showed "it is technically and commercially feasible to store large amounts of compressed hydrogen in an underground lined rock shaft".

It claims the stores can be constructed where required, and is now seeking funds to build the demonstrator.

Once complete Gravitricity then plans the roll-out of "hundreds of purpose-built sites nationwide".

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Charlie Blair, managing director of Gravitricity, said that green hydrogen “will be a vital fuel of the future” in industrial applications and heavy transport.

“Purpose-built lined rock shafts will be the safest and most affordable way to store large volumes of hydrogen near to where it will be required,” said Mr Blair. “It is difficult to transport hydrogen. It therefore makes sense to locate hydrogen storage systems close to sources of renewable power – which can generate green hydrogen – and to potential users.  

“At present, the main proposals for storage are underground salt caverns and above ground storage. Salt caverns offer scale, but very little flexibility – they only exist in certain locations; whilst above ground systems lack scale."

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He added: “We believe we have a ‘Goldilocks’ solution which can be delivered safely and affordably to meet the growing hydrogen economy’s needs.”

Peter Hughes, managing director of VSL UK, said it aims to “deliver these pioneering ground engineering solutions for renewable energy generation and storage”.

Gravitricity is also in advanced discussions with Cumbrian steel specialists Bendalls Engineering to fabricate the linings for the rock shafts.