Vast salt caverns designed to store hydrogen are to be excavated under Britain’s biggest former naval base as part of plans to bolster the country’s energy security

UK Oil & Gas (UKOG), the company behind the scheme, has said it will seek planning permission within months. 

Each the size of St Paul’s Cathedral, the 19 caverns will be dug under Portland Harbour in Dorset and filled with enough hydrogen to fuel a power station for days. The hydrogen contained in the caverns will be reserved for emergency use and called upon when wind and solar farms are not generating enough energy to keep Britain’s lights on.

Stephen Sanderson, UKOG’s chief executive, said: “Portland Port is ideally situated for the construction of large salt caverns as it overlies a 450-metre thick, high-quality rock salt.”

The harbour’s anticipated new role storing hydrogen relies on a rock known as halite or rock salt. 

A massive layer of this has been found two miles beneath the surface – where it has been buried for at least 200 million years. Salt is highly soluble so the fact it has lasted so long shows the rock has no water running through it –  making it highly stable and suitable for storing hydrogen.

Matt Cartwright, UKOG’s commercial director, said the caverns would be created by drilling wells into the salt and then injecting fresh water to dissolve the rock. UK Energy Storage, a wholly-owned subsidiary of UKOG, will oversee the project.

Each cavern is set to be 85 metres in diameter and 90 metres high with a capacity of 320,000 metres cubed, which is roughly twice the volume of St Paul’s Cathedral.

A spokesman for UKOG said the company was moving away from oil and gas and saw a much bigger future in renewable energy.