Italian start-up Energy Dome says that its new long-duration “CO2 battery” system, which only uses off-the-shelf equipment will achieve a levelised cost of storage (LCOS) of $50-60/MWh in the next few years.
That would be more than twice as low as the LCOS of lithium-ion batteries — $132-245/MWh, according to Lazard — and almost twice as cheap as current long-duration storage market leader Highview Power’s CRYObattery ($100/MWh, according to a 2019 interview with Recharge).
Chief executive Claudio Spadacini tells Recharge that Energy Dome's thermodynamic liquid-CO2 system has a round-trip efficiency of 75-80% — higher than any other long-duration energy storage technology currently on the market, including liquid-air, compressed-air and gravity-based solutions.
“We have calculated an LCOS which is already below $100/MWh with the first commercial plant we are going to build, which is 25MW/200MWh — our standard module,” says Spadacini.
“But we have a projection that we can reduce the cost of the technology quite fast. So we are aiming to be far below $60/MWh in a few years, close to $50/MWh.”
But in an increasingly competitive, fast-moving sector, Energy Dome's technology might not be the cheapest energy storage on the market once it is commercialised.
And only last week, US start-up Form Energy claimed that its 100-hour iron-air battery would achieve an LCOS of less than one-tenth the cost of lithium-ion — but it has not said when, and its technology is yet to be proven outside of a laboratory.
How it works
The CO2 battery utilises aspects of thermal energy storage, which stores electricity as heat, and compressed-air and liquid-air systems, which reduces the volume of air (by compressing/condensing it) and then generates electricity by allowing it to rapidly expand to its natural state, with the whoosh from that expansion driving a power-generating turbine.
In Energy Dome’s system, carbon dioxide is compressed at a pressure of 60 bar which heats the gas to 300°C liquid. The heat is then extracted and stored in “bricks” made of steel shot and quartzite for later use, cooling down the CO2 to an ambient temperature. The gas is then condensed into liquid form and stored in carbon-steel tanks.
When electricity is required, the liquid CO2 is run through an evaporator to turn it back to a pressurised gas, which is then warmed up back to 290-300°C causing the stored heat. The gas is then introduced into an expansion turbine, where it rapidly expands at atmospheric pressure to drive a power-generating rotor, with the uncompressed CO2 then stored in a flexible dome — hence the company name — at ambient temperature and pressure for later re-use.
Spadacini explains that Energy Dome uses CO2 because it can be converted into liquid under pressure at 30°C, compared to minus 150°C for air. Highview Power’s liquid-air battery therefore has to use cryogenic technology to liquefy air, but the Energy Dome system requires far less power, resulting in cheaper costs and a higher round-trip efficiency, the company says.
“This idea… is fully new and fully innovative, but really based on off-the-shelf components,” says Spadacini. “So we just put together existing components and this is key in order to go to the market.”
It does mean that rather than using the surrounding air, a large inflatable gas holder — ie, the dome — is needed to store the CO2 in a closed system. But this is a low-cost component, requiring little more than a strong but flexible PVC-coated textile, which is already manufactured for use in biogas plants.
He explains that an inflatable dome is required, rather than a solid steel tank, because the CO2 has to be at a constant pressure.
“If you have a sealed tank and you take gas out of that, you reduce the pressure. In the dome, the geometry adapts to the amount of gas we have inside and the pressure remains constant. This is a key feature of the system.”
Spadacini adds: “The system is totally closed. We don’t consume any CO2, it’s just the working fluid that goes back and forth… for the life of the system, over 25 years. So we have no emissions in the atmosphere.”
The Italian explains that the CO2 battery system will be modular and scalable to any size required, as any number of individual components can be added.
“We are looking to build multiples of standard sizes — that can be 50MWh, 100MWh, 200MWh,” he says.
“So we have a standard design for the liquid CO2 vessel, and you can just use 10, 20 or 50 of those, but production is modularised. And on the other side, that we have 10MW or 25MW compressors, and we have 10MW to 25MW or a 50MW expansion turbine
“This means that owners can optimize the design by using the most appropriate charge or discharge rate, depending on their application. As to the dome, depending on the MWh storage capacity, the dome will be larger or smaller, or multiple domes can be built for capacities in excess of 200MWh.”
Spadacini describes the company’s “sweet spot” as eight to ten hours of storage, as that is the “best match” for wind and solar farms, in order to enable them to have dispatchable output 24 hours a day.
The system could also be used more centrally on the electricity network to store renewable energy and provide ancillary services to the grid,” he adds.
To date, the 18-month-old company has only built a small pilot plant for the thermal energy storage part of the system, but it is constructing a 2.5MW/4MWh commercial demonstration facility on the Italian island of Sardinia this year, which will be put into operation in January or February 2022.
The engineer explains that Energy Dome does not want to build projects itself.
“We don’t have the capability to grow as fast as the market requires,” he says. “So our model is to license the technology to EPC companies or IPPs, utilities, the final user, because that is the best way for us to expand geographically and by sector.
“The time to market is key in this fast-transforming world.”
Energy Dome has already signed a commercial agreement with Italian gas-focused power-generation equipment supplier Ansaldo Energia to bring to market the CO2 battery — as well as a sister system, the CO2 ETCC (see panel below).
“We are also discussing other commercial agreements and licensing with other large OEMs in the oil & gas sector, in the steel sector, in the green chemistry sector, and also in the mining sector. So we are getting a lot of interest.
“We are building a very nice and potentially big pipeline of projects.”
Energy Dome is currently attempting to raise €10m in a Series A investment round, for which it is already in talks with institutional investors and venture capital firms. The money would be used to which would be used to complete the commercial demonstration plant and cover company outgoings, Spadacini explains.
“We believe that the potential growth of the company is really high, for two reasons — because we have very competitive performances and costs,” he says.
Energy Dome has devised a separate, but similar system that it calls the CO2 Energy Transition Combined Cycle (ETCC), which combines gas-fired power production with large-scale long-duration energy storage.
"[This] unique system... reaches unprecedented gas to power efficiency and at the same time operating in a very flexible way being able to switch from absorbing and storing energy from the grid to full power production in a matter of seconds," says Energy Dome.
The company explains that the ETCC system would, effectively, increase the efficiency of combined-cycle gas turbine plants from 55% to 85%, and reduce fuel costs on each stored kWh of energy by 35-40%.