Energy Dome and its carbon dioxide batteries

The global push for renewable energy sources like solar and onshore wind power has created a challenge: these energy sources are intermittent, meaning their output fluctuates depending on weather conditions such as sunlight or wind availability. This intermittency disrupts the balance between energy supply and demand on the electrical grid. To address this issue, long-duration energy storage solutions are becoming essential. These systems store excess energy generated during peak production times and release it when demand is high or production is low. Energy Dome, a company founded in 2020 and based in Milan, Italy, has developed a technology to meet this need by using compressed carbon dioxide (CO₂) to store energy for up to 24 hours, smoothing out the gaps in renewable energy supply.

Energy Dome’s technology relies on a large white dome, covering an area equivalent to seven soccer fields, which holds approximately 2,000 metric tons of carbon dioxide gas. The process begins when excess energy from renewable sources, such as a solar farm, is available. Compressors squeeze the CO₂ gas, turning it into a liquid that is stored in carbon-steel tanks. This compression generates heat, which is captured and stored using a proprietary thermal storage material. When electricity is needed, the liquid CO₂ is released and warmed using the stored heat, converting it back into a gas. This gas then passes through a turbine to generate electricity before flowing back into the dome to repeat the cycle. Unlike traditional compressed air energy storage, which requires specific underground geological formations, Energy Dome’s system can be deployed anywhere, making it more scalable globally.

Energy Dome launched its first commercial plant in Sardinia, Italy, in 2025. This facility has a storage capacity of 200 megawatt-hours (MWh), which is enough to power approximately 18,000 Italian homes for 10 hours. The plant demonstrates the technology’s viability and serves as a proof of concept for future projects. The company’s approach uses existing, commercially available equipment such as compressors and storage tanks, which simplifies scaling and reduces costs. Energy Dome has plans to expand its operations significantly, with projects totaling 30 gigawatt-hours (GWh) of storage capacity across five continents, including a 200 MWh plant in Ireland scheduled for completion in 2028 in partnership with Google.

Lithium-ion batteries are currently the dominant technology for short-duration energy storage, typically up to four hours. However, for longer durations, such as eight hours, the cost of lithium-ion systems increases significantly because more battery cells are required. Energy Dome claims its technology is 10% to 15% cheaper than lithium-ion batteries for an eight-hour storage system, with even greater cost advantages for longer durations up to 24 hours. This cost efficiency is attributed to the use of standard industrial components, which reduces both capital and operational expenses. Energy Dome’s plants, either operational or under contract, currently offer eight or 10 hours of storage capacity, positioning the company as a competitive alternative for medium to long-duration energy storage.

While Energy Dome’s technology offers cost benefits, it is less efficient than lithium-ion batteries. The system has a roundtrip efficiency of about 70%, meaning it returns 70% of the stored energy to the grid. In comparison, lithium-ion batteries typically achieve around 90% efficiency. However, Energy Dome’s efficiency is higher than some other long-duration storage technologies, such as iron-air batteries, which have an efficiency of approximately 50%. Additionally, Energy Dome offers a version of its system that integrates natural gas turbines, replacing internal heat storage with waste heat from the turbines. While this improves efficiency, it also results in greenhouse gas emissions from the natural gas combustion, which may not align with the goal of reducing carbon footprints in energy storage.