DoD selects BWXT to build Project Pele prototype advanced microreactor; delivery to INL in 2024
EPA issues RFI on end-of-life management of batteries

DOE closes on $504M loan guarantee for world’s largest clean hydrogen and energy storage project

The US Department of Energy (DOE) closed on a $504.4-million loan guarantee to the Advanced Clean Energy Storage project in Delta, Utah (ACES Delta)—marking the first loan guarantee for a new clean energy technology project from DOE’s Loan Programs Office (LPO) since 2014. The loan guarantee will help finance construction of the largest clean hydrogen storage facility in the world, capable of providing long-term low-cost, seasonal energy storage, furthering grid stability.


ACES Delta is a joint venture between Mitsubishi Power Americas and Magnum Development.

The hub will initially be designed to convert renewable energy through 220 MW of alkaline electrolyzers to produce up to 100 metric tonnes per day of green hydrogen, which will then be stored in two massive salt caverns each capable of storing 150 GWh of energy.


Rendering of Advanced Clean Energy Storage salt cavern

Financed with support from the DOE loan guarantee, this facility will supply hydrogen feedstock to the Intermountain Power Agency’s (IPA) IPP Renewed Project—an 840 MW hydrogen capable gas turbine combined cycle power plant—that will initially run on a blend of 30% green hydrogen and 70% natural gas by volume starting in 2025 and will increase to 100% hydrogen by 2045.

The Advanced Clean Energy Storage hydrogen hub was announced in May 2019, and within three years was in the final stages of debt and equity closing. Currently, the hub has secured all major contracts including offtake; engineer, procure and construct (EPC) contractors; major equipment suppliers, and Operations and Maintenance (O&M) providers.

With the closing of this loan guarantee, LPO now has $2.5 billion in remaining loan guarantee authority for Innovative Clean Energy projects.



For that sort of capacity to cover seasonal intermittency etc you need chemical storage.
The means of storage depend on the application, and those who seek to broadly dismiss on 'first principles' hydrogen storage are mistaken.


For short term storage to cover hours and for frequency regulation, this sounds good to me:

Although it uses CO2, it is a closed system and so does not consume it.
It is more efficient to compress CO2 than liquid air, uses current tech and commercially available equipment, can be installed near point of use and hits 75-80% round trip efficiency.

Here is liquid air for comparison:

'IMechE says this process is only 25% efficient but it is massively improved by co-siting the cryo-generator next to an industrial plant or power station producing low-grade heat that is currently vented and being released into the atmosphere.'

In contrast this CO2 process works at ambient temperatures and gives comparable round trip efficiencies to batteries.

This looks to me better environmentally and cheaper than using batteries.

Gotchas, anyone? :-)


National Labs and Universities have been writing about CO2 CAES for decades



Well, they are building them now. Dunno why it took so long, any idea?



I could not spot with a quick google any links to the papers you are talking about.
Here is a paper from 2016 where they seem to think that this sort of energy cycle is innovative:

' Although, some research has been conducted on energy power cycle and energy 145 storage systems based on CO2 and liquid CO2' (line 145)
'Some research' does not sound like there were extensive investigations.

Of course, all this means is that I have not been able to track anything down, but there is nothing very obvious published on this particular approach.


I have located an article from when they started the build, in 2021:

A few bits more of info there:

' The engineering team guided by Mr. Claudio Spadacini, founder and CEO of Energy Dome is building a 2.5MW/4MWh first of a kind energy storage facility in Sardinia, Italy, expected to be launched in early 2022.

The plant, with a size of 2.5MWe and 4MWh, will be designed allowing for future storage expansion bringing it to 8MWh and above. The Demo Plant will use the same component parts as the full-scale commercial system of 25MW and 100MWh or 200MWh, effectively proving the readiness of this technology for the market.

This demonstration project is meant to be operated commercially and generate revenue by operating on the energy and ancillary services markets. Energy Dome technology provides outstanding performance, achieving a highly competitive Round Trip Efficiency (RTE) and Levelised Cost Of Storage (LCOS) for storage durations from 3 to 16+ hours, with little or no degradation over time.

Less than two years since its incorporation, Energy Dome will deploy the Demonstration Plant, by pioneering an innovative alternative to batteries for utility scale energy storage. Energy Dome’s technology is based on a completely new process which has been engineered and designed to use only existing and proven equipment. The team rose to the challenge to develop a solution that would not only be technologically and economically feasible now, but would also overcome the inherent limitations of Lithium Ion. Notably, the CO2 Battery poses no fire risk, uses no rare materials and marries a better performance with a lower capital cost, as compared to Li-Ion.'

And they think:
' The CO2 Battery Demo plant will both prove the efficiency of the technology and the capability of the technology to provide energy and regulation services on the electrical grid, by testing the technology at a relevant scale and by overcoming the technical risks, which mainly refer to the risk of component integration (TRL 9).'

IMO recognising component integration as a risk factor is a good tell-tale on their approach, as it is frequently ignored.

So we await data now they are running, and also I have not managed to dig out any concrete levelised cost figures.


Super Critical CO2 Storage does look like a good idea. Hydrogen Storage works best in Salt Caverns (we discussed this earlier here - The Mitsubishi ACES Delta Project can still be used for Ammonia production much like the Yara Freeport TX plant and today “Green Ammonia” is actually economical.
Super Critical CO2 can be stored in many places, e.g.geothermal wells, etc.
And “High Efficiency and Large-scale Subsurface Energy Storage with CO2‘


early interest in CAES until inception of engineering/construction on August 11, 1988


That link appears to be dead now, but there has certainly been a lot of interest in CAES for many years.
I was in contact at one stage with an engineer who had been involved in the field for year - he hated it, from memory due to issues keeping the equipment running with the greases etc needed to keep it running getting polluted.

The closed loop nature of the proposals Iinked will perhaps help in that?
And using liquid CO2 is a rather different ball game.



Great links as always!

Your links explain why they mention long term storage on the EnergyDome website, when their system of inflatable domes for decompressed gas are suitable for the grid fluctuation and diurnal storage they are initially targeting.

It should be easier, I am guessing, to get their system up and running without having to worry about variable geology and location, but it would test many of the components and systems needed for seasonal geological deployment.

Great efficiencies give this a real edge in my view.


Just to highlight it for casual readers of this thread, who may not care to follow the links, gryf has shown work on geological storage of CO2, making use of underground heat to up the electrical efficiency of of the cycle to above unity against electrical input and enabling long term storage.

Reading the link again it does not look as though they actually liquify the CO2 for their geological storage, just cool and compress it.


Read the Phys.Org link, according to Prof.Julio Meneghini”
“ From the water line itself, the distance from the surface to the sea floor is 2,000 to 3,000 meters in depth. That and other variables leave gas in what is known as the supercritical state.”
Also, Energy Dome discusses using Combined Cycle to enhance the efficiency of Waste Heat and Renewable Energy Sources (
Geothermal needs something like this particularly in California where Solar and Wind have a lower LCOE.
Super Critical CO2 has smaller turbines than Steam Turbines (up to 10x smaller for the same power). Siemens Energy discusses Waste Heat and sCO2 here:


Thanks gryf.

Ignorance of supercritical CO2 caused me to somewhat read past that.
However, wiki tells us:

' Despite the promise of substantially higher efficiency and lower capital costs, the use of sCO2 presents corrosion engineering, material selection and design issues. Materials in power generation components must display resistance to damage caused by high-temperature, oxidation and creep. Candidate materials that meet these property and performance goals include incumbent alloys in power generation, such as nickel-based superalloys for turbomachinery components and austenitic stainless steels for piping. Components within sCO2 Brayton loops suffer from corrosion and erosion, specifically erosion in turbomachinery and recuperative heat exchanger components and intergranular corrosion and pitting in the piping.[18]'

Some I am wondering if its use in the applications does not present substantial extra engineering challenges compared to the closed loop liquid CO2 EnergyDome have chosen for their early systems, as pumping supercritical CO2 down to substantial depths not only presents challenges in its own rights, but gives the opportunity for its high solvent capacity to pick up all sorts of complex nasties.

Of course, this is just a guess by an ill informed outsider, and should be treated as such.

The EnergyDome system does sound simpler and with less challenges for early systems though, and more controllable.


Compressed Air Energy Storage (CAES) was conceived as a peak-shaving measure for electric generating utilities in the peak-shaving measure for electric generating utilities in the 1970's


Thanks SJC

This is a bit different to compressed air though.


It is compressed air, the previous link was dead.


Energy Dome stores CO2 at the liquid state @ 70 bar. Supercritical CO2 starts at pressures (P) in excess of 73.8 bar at temperatures (T) higher than 31° Celsius (check the Siemens link and this Energy Dome link:
Spadacini probably keeps the pressure at that level for cost and engineering reasons.


Hi gryf

From my vast knowledge of supercritical fluids, gleaned in the last 10 minutes or so, they sound tricky in that environment.

I was interested to learn that that is what they use in the EcoCute heat pumps for low temperatures though - I used to have a regular, non CO2 heat pump in my old flat.

But servicing and maintaining those is hardly the issue that I imagine running a supercritical system for a major system like the pumped geothermal systems described in your link might present.



' It is compressed air'

? I am not sure what you are referring to. There are existing CAES systems, but the EnergyDome system does not use compressed air.

The only thing they are compressing and liquifying is CO2, with no nitrogen or oxygen, which is a totally different ball game.


According to Energy Dome patents (WO2021191786A1)
Plant and process for energy generation and storage
“The closed thermodynamic cycle (TC) can be sub-critical, super-critical or trans- critical and is actuated with the same machines of the Energy Storage (CTT) system”.


Thanks, gryf

Yeah, I had seen that in their info, I think, but did not really know what they were talking about.

But when I looked at the one they have built, they seem, wisely, to have kept it simple:

' Our proprietary technology is based on a closed thermodynamic transformation that, by manipulating CO2 between its gaseous and liquid phase, enables efficient and cost-effective energy storage.

In charging mode, the CO2 is drawn from an atmospheric gasholder, the Dome, compressed and then stored under pressure at ambient temperature in a high density supercritical or liquid state. When energy needs to be released, the CO2 is evaporated and expanded into a turbine, and then returned back to the atmospheric gasholder, ready for the next charging cycle.

By storing in the liquid phase at ambient temperature, we significantly reduce the typical storage costs associated with CAES (Compressed Air Energy Storage) without having to deal with cryogenic temperatures associated with LAES (Liquid Air Energy Storage).'

It sounds as though they have loads of headroom using supercritical CO2, underground storage etc to improve it, extend durations and so on.

I like that the early ones can be (relatively) simple though.


I should add that I thought reading through that they are currently taking the: 'or liquid' option! ;-)


Good PDF on C02 storage


Here's another one from more than two decades ago

They talk about storing 100 billion tons of C02
which is about 30 years of U.S. emissions in empty NG fields


Here's another one from a national lab almost 20 years ago

The comments to this entry are closed.