Clean energy journalism for a cooler tomorrow

Energy Dome is the rare long-duration storage firm that’s moving fast

The Italian firm landed a deal for a 100MWh plant just two years after launch.
By Julian Spector

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(Energy Dome)

Many companies are competing to store clean electricity cheaply for many hours. Exceedingly few of them get to market quickly.

But that’s exactly what one Italian startup is on the cusp of pulling off. Energy Dome secured its patents and formally launched in 2019. Last week it closed an $11 million Series A funding round. If a commercial demo project on the island of Sardinia is successful next year, the company will then break ground on a 100-megawatt-hour storage project for A2A, a utility serving 2 million customers in Italy.

That’s a markedly faster path from launch to major project than pretty much any other long-duration storage contender. Many startups commercializing the long-simmering flow battery technology, for instance, toiled at the laboratory bench for a decade without breaking even the megawatt threshold on their installed projects. Lab science takes years, even if the basic premise is well characterized, as it is with flow batteries.

Under the dome

But Energy Dome didn’t have to bother with years of scientific research. Its innovation is in how it sticks together preexisting equipment to store large amounts of clean energy.

Buying off the shelf” means Energy Dome doesn’t need to build its own factory — it just purchases equipment from established suppliers. It can also rely on performance guarantees from those vendors.

By making use of off-the-shelf technologies, they face less technology risk than many more exotic long-duration storage options,” said engineering professor Jesse Jenkins, who researches technologies to decarbonize the grid at Princeton University.

The eponymous dome refers to a structure that stores carbon dioxide. It’s not an underground salt dome (a geological structure currently used to store gases at much larger scale), but rather an inflatable above-ground membrane that CEO Claudio Spadacini likens to a winter tennis-court bubble.

(Energy Dome)

Let’s say there’s cheap solar or wind power flooding a regional grid. An Energy Dome plant could use that electricity to pull CO2 from the dome and pressurize it.

Pressurizing the gas generates considerable heat, which gets absorbed by thermal storage (kind of like a fancy thermos for keeping things hot), while the carbon dioxide gets stored in liquid form at ambient temperature. To release or discharge the stored energy, Energy Dome converts the liquid back to gas and warms it with the stored heat. The hot gas turns a turbine and generates electricity for use on the grid. The whole system is closed, so the carbon dioxide never leaves the facility.

Our process is really simple, almost obvious,” Spadacini explained to me at the Energy Storage Association conference in Phoenix last week.

If that assessment makes you feel ignorant or provincial, I must confess that I too once overlooked the energy-storing potential of carbon dioxide liquefaction and re-gasification. So had the rest of the energy storage industry, judging by the dearth of companies pursuing it. The venture with the closest approach is probably Highview Power, which stores energy by liquefying air, though the engineering details of the two processes differ.

It turns out that CO2 has some fundamental attributes that make it a good fit for this role.

Compressing or liquifying CO2 is relatively easy to do at close to atmospheric pressures and ambient temperatures, in comparison to hydrogen or air,” said Rebecca Ciez, an engineering professor at Purdue University specializing in energy storage technologies.

The design also builds off years of experience working with similar machinery. Spadacini previously founded a geothermal energy company called Exergy, which built 500 megawatts of generation before being sold to a Chinese industrial interest. Spadacini also founded Sebigas, which built 84 biogas plants worldwide and utilized the same membrane for storing the gas that Energy Dome now employs.

We have a reputation as a team,” Spadacini said. We did something real.”

That experience helped Energy Dome move quickly in finding its first customer. Italian utility A2A — which is also a strategic investor in Energy Dome — owns and operates fossil-fueled and renewable power plants and is looking for new ways to address the mismatch between demand and supply from those sources.

A2A has a location picked out for its Energy Dome project: a brownfield site that previously hosted a power plant. That means construction can move quickly. The remaining item to be checked off the list, Spadacini said, is verification of Energy Dome’s 2.5-megawatt/4-megawatt-hour demo project, now under construction in Sardinia. That should be operational in February, according to the CEO.

Energy Dome also received Series A funding from Barclays’ Sustainable Impact Capital, multifamily office Novum Capital Partners, and Third Derivative, an accelerator for climatetech startups created by think tank RMI and New Energy Nexus. (Canary Media is an independent affiliate of RMI.)

A more efficient system

Energy Dome boasts a strength in an area where many long-duration storage ventures are weak: round-trip efficiency.

That’s the measure of how much energy is lost in the process of putting electricity into storage and pulling it out again. Lithium-ion batteries do pretty well — a 2019 U.S. government analysis of large grid batteries found they recovered 82 percent of the input energy on average. But they suffer on cost-effectiveness for longer durations of discharge, meaning you’d be hard-pressed to use lithium-ion for, say, a battery plant that discharges for 12 hours or more.

Technologies optimized for cost-effective long-duration storage often suffer on round-trip efficiency, posting as low as 40 or 50 percent. Evangelists for those companies typically argue that they’ll store power so cheaply over long periods of time that losing much of the energy won’t impact their effectiveness. But wasting energy is clearly a bug, not a feature.

Energy Dome says it will deliver 75 percent round-trip efficiency. That’s the sort of claim that needs to be vetted by third parties in field tests. But the figure is based on the performance guarantees from the manufacturers that supply the key compressors and expanders, Spadacini said.

The startup says it can deliver four to 24 hours of storage, meaning it could store solar generation to run a clean grid through the night or buffer gaps in renewables production from day to day. This type of offering doesn’t fit neatly into the contracting structures the electricity sector is familiar with today — a business challenge facing all long-duration storage aspirants.

That’s why it’s significant that Energy Dome found a utility customer that’s looking ahead to how the grid is changing and is willing to take a chance on a new type of grid infrastructure.

Ultimately, cost is the key challenge for any long-duration technology, Jenkins said.

To truly serve as a substitute for firm generation and reach a really impactful scale, long-duration storage needs to be super cheap, on the order of $1 to $10 per kilowatt-hour,” Jenkins said, based on his modeling on the topic.

It’s not yet clear how cheap Energy Dome can get within the constraints of its gas enclosure. Storage in underground caverns offers far more volume, which makes the unit cost cheaper. But that approach is limited to places with the right geological formations.

If CO2-filled tennis bubbles beat out lithium-ion and other competitors for up to 24 hours of storage, that could make for a profitable and prolific company. Whether or not that’s enough to solve the systemwide challenge of 24/7 clean energy is a different matter. 

Julian Spector is a senior reporter at Canary Media. He reports on batteries, long-duration energy storage, low-carbon hydrogen and clean energy breakthroughs around the world.