Gigantic underground hydrogen storage facilities can secure the energy supply
Wind and solar power produce energy unevenly. To ensure a stable supply, we must store enormous amounts of energy. NGI researchers point to the ground beneath our feet as part of the solution.
Large underground rock caverns can play an essential role in future energy systems, whether for energy storage or other critical societal purposes. ( Photo: NGI)
The green transition requires more than just producing renewable power. Because the sun does not always shine and the wind varies, it is necessary to store energy for later use. Hydrogen is highlighted as a key solution because it can serve as a large-scale energy carrier.
“Hydrogen can function like a giant battery. We are talking about terawatt-hours, enormous amounts of energy that can balance supply when we need more than solar and wind can provide,” says Bahman Bohloli, researcher at the Norwegian Geotechnical Institute (NGI).
Together with his colleague Tore Ingvald Bjørnarå, he is working to address the challenges associated with large-scale hydrogen storage. While batteries are best suited for short-term storage, industry and society need storage capacity that can last across seasons. The solution involves moving energy down into geological formations.
Production method defines the label
Hydrogen is an invisible gas, but it is often classified using colour codes based on how it is produced. Green hydrogen is produced from renewable energy, while blue hydrogen is made from natural gas with carbon capture. The system is extensive.
“There are already many colour variants, and there is probably room for many more. For example, we have pink hydrogen when the energy comes from nuclear power, and orange hydrogen when it is produced through natural processes,” says Bjørnarå.
Regardless of how hydrogen is produced, it differs fundamentally from electricity in terms of distribution.
“Electricity can be produced on demand. Hydrogen is a fuel that must be produced and then stored,” Bohloli points out.
Requires enormous storage volumes
The need for storage capacity is massive. DNV estimates that hydrogen will cover three to four percent of global energy demand by 2050. This requires infrastructure far beyond what surface tanks can handle.
“If we look at Europe, we are talking about around 20 million tonnes of hydrogen per year. If 20 percent of this needs to be stored, that corresponds to between 200 and 400 large caverns,” says Bohloli.
A cavern is a man-made underground cavity. Internationally, salt caverns are the most common method. These are created by pumping water into salt formations to dissolve the salt, leaving an empty chamber behind.
“The caverns can be enormous. We are talking Eiffel Tower scale. They can be several hundred metres high and have a diameter of 50 to 100 metres,” says Bohloli.
Norwegian rock caverns and material challenges
Since Norway lacks the necessary salt formations, rock caverns, or porous offshore formations, domestically, rock caverns are the most relevant storage options. Hydrogen storage, however, presents specific technical challenges. Hydrogen atoms are tiny and can penetrate the materials used for containment.
“Hydrogen penetrates the metal structure and weakens it from the inside, making the steel brittle and prone to cracking,” Bjørnarå explains.
Infrastructure, including pipes and valves, must therefore be designed and maintained to withstand this stress. NGI is also researching so-called cryogenic storage, in which hydrogen is cooled to a liquid to reduce its volume.
“Then we are talking about temperatures close to absolute zero, around minus 250 degrees Celsius. We do not yet fully understand how cement, steel, and rock behave at such low temperatures,” says Bjørnarå.
Safety at depth
Many people remember chemistry class in lower secondary school, when the teacher mixed hydrogen with oxygen in the right proportions and held a match to it, the so-called oxyhydrogen gas exploded with a bang. It is precisely this explosive combination that engineers aim to avoid when storing hydrogen. Hydrogen is highly flammable when exposed to oxygen, which is why underground storage is considered safer than surface storage.
If a leak were to occur from an underground facility, the gas would rise upwards and disperse into the atmosphere as a clean release, rather than accumulating as an explosive cloud at ground level. Experience from facilities in the UK and the United States, which have operated safely since the 1970s, confirms that the risk is low.
Gas extraction itself is based on simple physics.
“Think of the cavern as a gigantic pressure vessel. When we pump gas in, we build up enormous pressure. When we later need the energy, it is this overpressure that drives the gas back up to the surface,” Bjørnarå explains.
The need to extract the gas will vary. This is where the link to industry lies. While batteries are excellent for passenger cars, they fall short for heavy transport, ships, and smelters. Since wind turbines and solar panels do not deliver energy evenly, we need a giant battery that can dispense energy when nature takes a break.
“We are in the middle of an energy transition in which hydrogen will play a key role in decarbonising heavy industry. Our job is to ensure that the technical solutions underground are safe enough to support society’s needs above ground,” Bahman Bohloli concludes.
Bahman Bohloli
Principal Researcher Energy Geomechanics and Geophysics bahman.bohloli@ngi.no+47 469 87 338
Tore Ingvald Bjørnarå
Head of Section Energy Geomechanics and Geophysics Energy Geomechanics and Geophysics tore.ingvald.bjornara@ngi.no+47 908 59 184