Trona or Salt? Choosing the Rock That Holds Our Hydrogen
Salt caverns are the proven home for underground hydrogen — but Wyoming sits on something different. A visual tour of how trona stacks up against salt as host rock.
Hydrogen is easy to make and hard to keep. It carries plenty of energy per kilogram, but it is extraordinarily light and stubborn to compress, so storing a useful amount means handling enormous volumes. Above ground, that gets expensive fast. The cheapest place to put a lot of hydrogen is the same place we already store natural gas: deep underground, inside engineered caverns.
The catch is that not every rock makes a good cavern. The host formation has to be impermeable enough to hold gas for months, strong enough not to collapse, and soluble enough that we can carve a cavity into it by pumping in water. For decades the answer has been bedded or domal salt. But Wyoming — a state with big hydrogen ambitions — sits on a different evaporite entirely: trona.
So which rock should hold our hydrogen? Let’s look.
Meet the candidates
Salt caverns are the benchmark. Halite — ordinary rock salt, NaCl — is about as simple as a mineral gets. Trona is its more complicated cousin: sodium sesquicarbonate, a mix of carbonate, bicarbonate, sodium, and water locked into one crystal.
Trona (sodium sesquicarbonate) is chemically richer than halite — it carries carbonate, bicarbonate and structural water. That extra chemistry makes it far more soluble, which shapes how its caverns are leached and how they behave.
That extra chemistry matters. Trona is far more soluble than halite, which changes how a cavern is leached and how the rock behaves once gas is cycling in and out of it.
A cavern, cross-sectioned
Both rocks are mined the same clever way: drill a well, inject fresh water, dissolve the rock, and pull the brine back out. What’s left is a void — the cavern — which is then filled with hydrogen. A cushion of gas stays permanently to hold the cavern open; the rest is cycled.
Pressure as a fraction of the lithostatic load at cavern depth (~0.0226 MPa/m). Geometry is illustrative: salt hosts deeper, thicker caverns; trona beds are shallower, thinner, and more soluble.
The pressure bar is the heart of cavern engineering. Run the cavern too empty and the surrounding rock slowly squeezes the void shut (creep closure). Run it too full and you risk fracturing the rock or breaching the caprock above. The art is staying in the green band — and that band is set by the rock’s strength and the depth of the cavern.
Head to head
Put the two rocks side by side and the trade-offs come into focus. Salt wins on the things that make engineers comfortable: it’s strong, gas-tight, and we have half a century of operating experience. Trona’s edge is abundance in the right place — and that turns out to matter a lot.
Qualitative 0–100 scores, larger is more favourable for that property. Hover an axis for values. Salt leads on maturity and gas-tightness; trona wins on regional abundance in Wyoming.
Trona is more soluble (faster to leach, but trickier to keep stable), mechanically weaker, and largely unproven for gas storage. On paper, salt is the safer bet almost everywhere. Almost.
Why Wyoming cares
Here’s the twist. Wyoming wants to produce and store hydrogen as part of the Western interstate hydrogen economy — and the rock it has in greatest abundance isn’t deep salt. It’s trona. The Green River Basin holds the largest known trona deposit on Earth.
Tap the basin or a city to learn more. Outline is schematic.
If you want to store hydrogen where Wyoming will make it, you can either transport gas long distances to suitable salt, or learn to use the trona that’s already underfoot. That economic reality is exactly why trona caverns are worth studying seriously, even though salt is the easier engineering answer.
So, trona or salt?
For now, salt remains the gold standard — proven, strong, and gas-tight. But trona is too abundant in the wrong-for-salt, right-for-hydrogen places to ignore. The open questions are about its mechanics: how fast it creeps, how tightly it holds gas over many cycles, and how shallow, thin beds limit cavern size. Answer those, and a great deal of Wyoming’s subsurface becomes available for clean-energy storage.
Sources & further reading
- Sheikheh, S., Rabiei, M., Rasouli, V. — Comparison of Salt and Trona Caverns for Hydrogen Storage, SMRI Spring 2023 Technical Conference. ResearchGate
- U.S. Geological Survey — Mineral Commodity Summaries: Soda Ash (Wyoming’s Green River Basin as the world’s largest trona deposit and the main source of natural soda ash).
- Caglayan, D. G., et al. (2020) — Technical potential of salt caverns for hydrogen storage in Europe, International Journal of Hydrogen Energy.
- Tarkowski, R. (2019) — Underground hydrogen storage: Characteristics and prospects, Renewable and Sustainable Energy Reviews.
Numbers in the interactive figures are illustrative — chosen to make the physics legible, not to report specific site data.