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Hydrogen stores should go underground

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Salt caverns such as the one depicted here could provide a low-cost solution for the geologic storage of hydrogen
Salt caverns such as the one depicted here could provide a low-cost solution for the geologic storage of hydrogen

US researchers have concluded hydrogen for fuel cell vehicles and grid generation should be stored underground in the future

Hydrogen fuel for vehicles, electricity generation and heating systems should be stored in large underground caverns in the future instead of above ground, US researchers have concluded.

Hydrogen for fuel cell vehicles and electrolyser systems on electrical grids for power-to-gas applications will require large-capacity, cost-effective hydrogen storage if use of the gas increases in the future. 

The study, conducted by the Sandia National Laboratories and published this week in the the International Journal of Hydrogen Energy concludes that underground storage has several advantages over above ground storage in tanks.

According to the scenario described in the study, vast quantities of hydrogen could be kept underground in salt caverns, other natural geological features or man-made stores, and piped to cities during times of peak demand for fuel.

Storage of hydrogen gas above ground currently requires tanks, which cost three to five times more than geologic storage. Underground storage also offers advantages in volume. Anna Snider Lord, the study’s principal investigator from Sandia, said: “Above-ground tanks can’t even begin to match the amount of hydrogen gas that can be stored underground.”

Oil and gas are already stored geologically. Researchers used computer modelling and analysis of existing oil and gas storage and distribution systems to work out the demand and costs of hydrogen storage. This included looking at depleted oil and gas reservoirs, aquifers, salt caverns and hard rock caverns in the US.

However, Lord said there were several challenges remaining to be addressed, including permeability of various geologic formations.

Depleted oil and gas reservoirs and aquifers initially seem the most economically attractive options, she said: “Just looking at numbers, because they can hold such a larger volume relative to any cavern you create, they look cheaper. But, because hydrogen is a smaller molecule than methane, for example, it has the potential to leak easier and move faster through the rock.”

Depleted oil and gas reservoirs and aquifers could leak hydrogen, and cycling – filling a storage site, pulling hydrogen out for use and refilling the site – can’t be done more than once or twice a year to preserve the integrity of the rock formation, she added.

With a salt cavern or hard rock cavern, “there are no permeability issues, there’s really no way anything can leak,” she said. “You can bring more product in and out, and that will, in the long run, decrease your costs.”

Hard rock caverns are relatively unproven, but salt caverns, which are created 1,000 to 6,000 feet below ground by drilling wells in salt formations, pumping in undersaturated water to dissolve the salt, then pumping out the resulting brine, are used more extensively and already store hydrogen on a limited scale, Lord said.

The researchers hope the study will lead to demonstration projects to develop the viability of underground hydrogen storage. Salt caverns are the logical choice for a pilot project due to their proven ability to hold hydrogen, Lord said. Environmental concerns such as contamination could also be further analysed.

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