When Wisconsin’s largest coal plant, the Columbia Energy Center, closes in the next few years, a carbon dioxide-filled “battery” developed by the Italian company Energy Dome will take its place.
The installation is billed by its backers as a potentially crucial development in the renewable energy transition. The European Investment Bank announced at the COP28 climate conference this month that it is backing a similar project by the same company in Italy.
The balloon-like facility will use electricity to compress carbon dioxide when demand is low. When demand is higher, it can generate electricity by letting the carbon dioxide expand to drive a turbine.
While energy storage can lower emissions, renewable energy advocates say the climate benefits depend on whether the projects also drive development of wind and solar. A single pilot project is unlikely to do so, but a successful test could show new ways to manage those variable sources in the future that don’t require natural gas as a “bridge fuel.”
“Right now we have nothing that can buffer a 4 megawatt solar field,” said Oliver Schmitz, director of the Grainger Institute of Engineering at the University of Wisconsin-Madison and a technical adviser on the Energy Dome project. “If we show this works now using whatever energy mix we have, we have the certainty” to deploy more renewables paired with it in the future.
Last year, Wisconsin got 37% of its electricity from natural gas and 36% from coal, according to the Energy Information Administration. Nuclear provided 16% of electricity used in Wisconsin, and non-hydro renewables provided less than 1%, according to the EIA. These energy sources will largely power the battery until the state’s energy mix changes drastically.
A goal of Wisconsin’s Energy Dome, slated to be the first commercial-scale application of the technology, is to drive more renewable development, according to Alliant Energy, the utility that co-owns the Columbia coal plant.
“The expansion of energy storage infrastructure is key to accelerating the transition to cleaner, more sustainable renewable energy,” said Alliant Energy spokesperson Tony Palese. “As we retire older fossil fuel facilities and add additional renewable resources to our generation portfolio, energy storage solutions help to ensure system reliability and meet customer needs.”
But the 20-megawatt Energy Dome alone won’t likely drive new renewable development. Even if the project is successful and more Energy Domes are built, as Palese said is possible, some other challenges still would stand in the way.
Alliant Energy is the largest utility owner-operator of solar in Wisconsin, with over 250 megawatts deployed and 839 megawatts more slated for completion by mid-2024. Since Wisconsin is part of the MISO grid (Midcontinent Independent System Operator), the Energy Dome also pulls from a system where renewables are expanding quickly, but also plagued by a clogged interconnection queue, transmission constraints and other issues.
Alliant owns 1,700 megawatts of wind across Wisconsin, Iowa and Minnesota within the MISO grid, Palese noted, and is also expanding solar in Iowa. Meanwhile, in the future an Energy Dome could draw energy directly from wind or solar farms rather than the grid, Palese added.
“As we operate and evaluate various aspects of the Energy Dome system’s performance, we envision it could become a model for additional energy storage development for grid applications or directly connected to wind or solar developments,” Palese said.
Citizens Utility Board executive director Tom Content said the board would likely support the project only if it is genuinely aimed at expanding renewable deployment, and he would oppose any new natural gas generation to feed the Energy Dome.
“Energy storage technologies beyond lithium-ion batteries are being actively studied and can be key elements of the nation’s energy future,” he said. “It’s encouraging to see innovative concepts such as this get funding to be explored, proven and become more economical over time.”
A promising pilot
In September, Alliant Energy received a grant of up to $30 million from the U.S. Department of Energy to develop the Columbia Energy Storage Project. It will cover 12 acres of the coal plant site south of Portage, Wisconsin, including a large dome holding a balloon that can inflate and deflate as carbon dioxide is compressed and decompressed inside it.
When wind or solar power is abundant, the energy can be used to compress carbon dioxide gas into a liquid. When extra energy is needed, the liquid will be allowed to decompress, turning back into gas and powering a turbine to generate enough electricity to power up to 20,000 homes.
The dome and balloon are part of a closed-loop system, meaning no carbon dioxide will be released, and no carbon dioxide delivery is needed after the initial setup. The project will tap into the grid infrastructure already onsite at the 1,112-megawatt coal plant, the last coal plant in Alliant’s fleet.
This is billed as the first-ever test of the technology at commercial scale. A much smaller 2.5 megawatt project is operating in Sardinia, Italy, where a new 20-megawatt Energy Dome is planned.
The Wisconsin project will explore whether the high efficiency rate of up to 75% achieved at the small project can be replicated when a much larger volume of gas is compressed. Carbon dioxide is especially suited for such an application since, unlike other gases, it can be liquified at ambient temperatures.
Mike Bremel, Alliant director of engineering and customer solutions, said Alliant put out a request for information on battery storage proposals in spring 2022, seeking projects that could provide 10 hours or more of reliable energy.
“Energy Dome was at the top of our list, basically because of its round-trip efficiency of 75%, and even more importantly the fact that it’s a really simple process that uses off-the-shelf components,” Bremel said. “The compression of CO2 to liquid has been done for over a century. It’s a reliable process that the industry and folks understand.”
Alliant was planning on a capital outlay of about $5 million, he said, whereas about $60 million would be needed for the Energy Dome project.
Around Thanksgiving of 2022, the company “stumbled upon” notice of a DOE Office of Clean Energy Demonstrations grant specifically for long-duration energy storage projects, Bremel said. The grant allows the project to move forward as a 50% cost-share between the federal government and Alliant as well as the two other utilities that own the Columbia Energy Center, WEC Energy Group and Madison Gas and Electric.
Used to buffer renewable energy production
Eight other projects received DOE grants, including one developing iron-based batteries at retiring coal plants in Minnesota and Colorado; and one using zinc bromide batteries in tandem with renewables in Manitowoc, Wisconsin. Bremel noted that Energy Dome was the only mechanical energy storage technology selected; the others involve thermal or chemical (battery) energy storage.
Schmitz said that compared to the many energy storage systems he’s studied — including lithium ion and flow batteries, thermal systems, molten salt — “this one is a huge storage solution at scale.”
Compared to batteries that involve precious metals and potentially other supply chain challenges, the Energy Dome can be built on-site using domestically sourced technology, including as many components as possible from Wisconsin, Bremel said. If the project is successful, more similar domes may be built on the Columbia coal plant site, he added.
“Because it does use up substantial amounts of space, it’s pretty well-suited for rural solutions, rural resiliency,” said Bremel, noting a local microgrid could be built around the energy storage.
The utilities will be studying how the project can be used for load-following, providing less energy than its total capacity at a given time and extending how long it can provide energy.
“We could potentially have twice the duration,” Bremel said. “Once we understand this project more, there is potential to marry several domes to a single generation and compression source.”
Plans for operation in 2026
There has been much public concern about carbon dioxide pipelines and carbon sequestration, including in light of the disaster in Satartia, Mississippi, during which a carbon dioxide pipeline ruptured, the gas displaced oxygen and scores of people were sickened.
But Bremel said the dome poses little risk. There will be sensors to detect leaks in and around the facility, and “in the event there was a leak at the gas stage, it’s not going to leak at a very fast rate because it is at atmospheric pressure — it’s not at thousands of PSI” as in a pipeline, Bremel said.
He said the project also involves very little environmental impact, including after its decommissioning expected after 25 to 30 years. Concrete will be poured around the dome perimeter, and the land directly underneath will be relatively untouched, Bremel said. The largely steel and plastic components can be recycled.
Alliant plans to seek needed approvals from the state Public Service Commission in the first half of 2024 and hopes to begin construction in 2025 and operation in 2026.
The University of Wisconsin, which works with Alliant through its Clean Energy Community Initiative, is helping lead a community engagement process and development of a community benefits agreement, conditions of the DOE grant.
“There is supposed to be a two-way engagement around energy justice, environmental justice, workforce and good jobs,” Schmitz said. “Communities guide the process, bring in their priorities and concerns.”
Madison Area Technical College will help develop a clean energy jobs pipeline around the storage project, building on its role leading a national consortium of community college energy programs. And University of Wisconsin faculty will likely study issues like whether the dome impacts birds, Schmitz said.
Schmitz noted that the Energy Dome itself won’t create many jobs after construction is done since “it is very low maintenance, very reliable.” But clean energy advocates hope the large dome’s presence will help raise awareness about clean energy more generally and encourage locals to work in the clean energy economy. That means the benefits for renewable deployment could go beyond the role of bridging intermittency.
“The best thing that can happen is visible projects like this have an immediate impact because they excite potential workers to think about this sector,” Schmitz said. “Maybe they become a solar installer or wind technician. Our workforce is strong on manufacturing and building things, so we want to upskill people into the clean energy domain.”
