A newly proposed megaproject could put Utah on the map for cutting-edge energy storage execution.

The Advanced Clean Energy Storage project, announced Thursday, would install 1,000 megawatts of energy storage capacity, for an undisclosed energy duration. Mitsubishi Hitachi Power Systems (MHPS) will supply the power equipment, while partner Magnum Development brings control of a salt cavern formation conveniently located near the transmission hookup at the Intermountain Power Project.

In recent months, the title for largest proposed storage project has slipped from developer to developer like a greased pig, but MHPS wants to serve up a different kind of bacon.

Instead of opting for the conventional lithium-ion battery design, the company selected a roster of exotic technologies with limited exposure to commercial operation: compressed air energy storage (CAES), flow batteries, renewable hydrogen and solid-oxide fuel cells.

"This is the first large-scale, long-duration storage initiative announced in the U.S. in recent years," said Ravi Manghani, head of energy storage research at Wood Mackenzie Power & Renewables. "Long-duration storage will be critical for a decarbonized future."

CAES stores excess grid power by compressing gas into an enclosed space, and releasing it to generate power via a turbine. The bigger the vessel, the greater the storage capacity, so salt caves make an ideal location. The oil and gas industry regularly uses this sort of geology for storing its wares.

That specific geological need also explains why CAES works almost nowhere in the world. It's hard for developers to find and gain the rights to workable formations, but that appears to be what Magnum has already done. The announcement notes that the company already has five salt caverns in use for liquid fuels storage, and is developing additional sites for CAES and hydrogen storage.

CAES suffers from lower roundtrip efficiency than mainstream battery technologies, but it can deliver power for far longer than the most efficient batteries on the market.

A handful of venture-backed startups have attempted and failed to improve that efficiency or miniaturize the container for the air. Canadian company Hydrostor has made headway with demonstrations of a process that pumps air into waterlogged mineshafts.

The most recent large-scale CAES plant, Alabama's 110-megawatt McIntosh facility, came online in 1991, which says a lot about the state of this market. Its immediate predecessor arrived in 1978 in Huntorf, Germany. That said, McIntosh can deliver its full power rating for up to 26 hours, something no lithium-ion plant can achieve.

Flow batteries similarly make sense on paper but have achieved limited commercial deployment. Rather than using mass-produced lithium-ion cells, flow systems circulate liquid electrolytes to charge and discharge. Their proponents claim the technology is less likely to catch fire and will last longer than lithium-ion systems.

Flow venders have to convince customers that they will still be around for the multi-decade lifespan of the devices. That's a hard sell to financiers as well. But having a brand like Mitsubishi Hitachi stand behind the technology would be a major vote of confidence.

The mechanics of hydrogen are better understood, but utilizing this substance for grid storage would be a new development.

Excess renewable generation can synthesize hydrogen, which can be stored and used as an energy source later on. MHPS says it has engineered a gas turbine that runs on a mix of natural gas and hydrogen, lowering the carbon emissions. The company hopes to transition to fully hydrogen-powered turbines over time.

“When we add gas turbines powered with renewable hydrogen to a hydrogen storage salt-dome, we have a solution that stores and generates electricity with zero carbon emissions,” said Paul Browning, president and CEO of MHPS Americas, in a statement.

As for location, it appears largely driven by geography, namely the location of the salt caves plus transmission infrastructure and access to potential clean energy plants.

Utah generated 86 percent of its electricity from coal and gas in 2017, according to the Energy Information Administration. It does have a rapidly growing solar sector, with 1,627 megawatts installed. 

In justifying its choice of Salt Lake City to host the major Solar Power International trade show, the Solar Energy Industries Association called it "an obvious choice...as this booming market has soared into the top-10 solar state ranks."



For current data on the growing U.S. energy storage market, see the most recent Energy Storage Monitor executive summary.