After decades of being hailed as the energy
vector of the future, hydrogen is finally becoming a viable alternative to
fossil fuels. A combination of improved technology, lower costs and extended
infrastructure has pushed the idea of a hydrogen economy out of think tanks and
onto national energy agendas. By 2050, studies suggest that green hydrogen
could supply up to 25% of the world’s energy needs.
But with increasing demand also comes a need for greater storage capacity.
Hydrogen can be stored physically as either a gas or a liquid. While storage of
hydrogen as a gas typically requires high-pressure tanks, an old storage method
is gaining traction as demand increases: underground salt caverns.
HOW DOES IT WORK?
Salt caverns are artificial cavities in underground salt formations. These are
created by drilling into the salt dome, typically 400-1,000 meters below the
surface, and injecting the rock with water that dissolves the salt. The resulting
brine is extracted, leaving a large cavity where hydrogen can be stored. While
there are other methods for large-scale underground storage — such as exhausted
oil and gas fields or aquifers (an underground layer of water-bearing permeable
rock) — caverns have a number of advantages:
- Robust As hydrogen has a very low volumetric
energy density, the gas is typically compressed before storage. Depending on
the depth, salt caverns can be operated with a pressure of up to 200 bar and
thus allow for the storage of high volumes of gas.
- Resilient Salt caverns are impervious to gases
and the walls are resilient to reservoir degradation. For example, the first
hydrogen cavern was constructed in the UK in 1972 and is still in operation
- Clean Many of today’s applications, such as
fuel-cell vehicles, require ultra-pure hydrogen. Salt caverns, which are almost
completely hermetic, are very clean and bring a minimum risk of gas
contamination by impurities.
- Affordable Underground caverns remain comparably
cheap to construct, with some studies suggesting a ten-fold cost advantage to
aboveground tanks. In addition, there is very little exploration work required
as many salt structures are already known from previous oil and gas as well as
- Flexible The salt structures also allow for a
lot of flexibility in injection and withdrawal cycles, which means they can
even be used to cover daily demand peaks.
- Lack of research As there is still a limited
number of salt caves around the world in use for storing hydrogen, some
researchers point to a need for more research of its viability. For example,
caverns tend to close up over time, which is accelerated if regularly filled
and emptied with gas.
- Purity One potential issue that can arise is
that humidity could be added during the creation of the cavity, which could
undermine the purity of the gas.
- Geographical scarcity The main known drawback
of salt caverns is scarcity. While there are currently some 2,000 caverns in
North America used to store various energy carriers, most upcoming projects are
located in a handful of European countries with large salt deposit, like
Germany, the UK, Ireland, France, the Netherlands, and Denmark. Otherwise, most
other countries have minor or no deposits at all.
PROJECTS AND INNOVATIONS
In the U.S., some 200 kilometers south of Salt
Lake City, engineers are working on what will become the world’s largest
storage facility for 1,000 megawatts of clean power, partly by storing hydrogen
in underground salt caverns.
- The Advanced Clean Energy Storage
project, a joint venture between Mitsubishi Power and Magnum Development, will
take excess power generated from hydroelectric, geothermal, solar and wind and
electrolyse it into hydrogen for storage in the salt caverns, where it can
later be used for power, industrial and transport applications.
- Scheduled for operation by 2025,
the first phase will provide 150,000 MWh of renewable power storage capacity
— enough to power 150,000 households for one year.
- The project was recently invited
to apply for up to $595 million in loans from the US Department of Energy’s
Loans Program Office.
A government-funded German consortium of more
than a 100 companies plans to build a salt cavern in Saxony-Anhalt with about
150,000 MWh of energy from wind power-generated hydrogen.
- If the project is approved, the
Hydrogen Power Storage and Solutions East Germany (HYPOS) could be continental
Europe’s first hydrogen storage cavern.
- More broadly, the project aims to
produce green hydrogen on an industrial scale, as well as to build an extensive
network of distributor networks and storage stations across Germany to make
hydrogen available to all regions.
Spearheaded by ENGIE-subsidiary Storengy, a consortium of French companies have
launched the first EU-funded project aiming to demonstrate large-scale
underground storage of green hydrogen in salt caverns.
- With a budget of €13 million, the
HyPSTER project (Hydrogen Pilot Storage for large Ecosystem Replication)
— a 2021 Innovation Trophy nominee — will take place in the southern
French area of Etrez that is already used for natural gas storage in salt
- Initially, a renewable-energy
powered, 1-MW electrolyser will produce 400 kg of hydrogen per day to be
stored, which will eventually be ramped up to 44 tons of total hydrogen storage
— enough to meet the daily need of 1,760 fuel-cell buses.
Etrez is a strategic area for green-hydrogen
development due to neighboring large-scale projects like the Zero Emission
Valley in the Auvergne-Rhône-Alpes region, as well as the construction of
hydrogen production and distribution stations in Burgundy-Franche-Comté.