Compressed carbon dioxide energy storage

Compressed carbon dioxide energy storage can be used to store electrical energy at grid scale. The gas is well suited to this role because, unlike most gases, it liquifies under pressure at ambient temperatures, so occupies a small volume. Energy Storage News reported that it will be "a cheaper form of energy storage than lithium-ion batteries".[1]

Process

A 100MWh store requires about 2000 tonnes of carbon dioxide (CO2). At the start of the process, CO2 gas is stored at atmospheric pressure in a large expandable fabric container, like those used to store biogas, housed within an inflatable protective dome.

To store energy, the gaseous CO2 is compressed to around 70 bar, which heats it to around 400 °C. Passing it through a heat exchanger and a thermal store cools the supercritical carbon dioxide gas enough to liquify it. The liquid CO2 can be stored in this state indefinitely in pressurised cylinders.

When energy is required, the CO2 is passed back through the heat exchanger, where it is warmed by recovering heat from the heatstore and reverts to high-pressure gas. The gas is used to drive a turbine to generate electricity as it passes back into the low pressure store, completing the closed cycle. [2][3]

Advantages

Liquid carbon dioxide can be stored at ambient temperatures, unlike Liquid air energy storage (LAES), which must keep liquid air cold at −192°C, though the CO2 does need to be kept pressurised.

Liquid CO2 has a much higher energy density (66.7 kWh/m3), than compressed air in typical to compressed-air energy storage (CAES) systems (2-6 kWh/m3), meaning the same energy can be stored in a much smaller volume.[4]

All the components of the system are readily available: gas storage domes are used in biogas production; the compressors and heat exchangers are used in the oil and gas industries; the turbine is similar to a medium pressure steam turbine.[1]

Disadvantages

The gas domes take up land - approximately 6% of the land area of a matching solar farm.[1]

Carbon dioxide is an odourless asphyxiating gas that is heavier than air. A catastrophic rupture of a storage dome in, say, a hurricane would disperse the gas harmlessly,[1] but a rupture in still air, through accident or sabotage, could be more problematic.

Energy Dome

The start-up company Energy Dome built a 2.5 MW/4 MWh demonstrator plant in Sardinia, for the Italian utility company A2A, which came into operation in June 2022. Opportunities are being explored for production of standardised 20 MW/200 MWh energy storage units in conjunction with wind energy supplier Ansaldo. The company claims a round trip efficiency of 75% and a projected cost of EUR220/kWh of storage capacity, which is half that of Li-ion batteries.[1][5]

References
  1. Andy Colthorpe (12 April 2023). "Energy Dome: Turning a greenhouse gas into a cheaper form of energy storage than lithium-ion batteries". Editors blog. Energy Storage News. Retrieved 16 April 2023.
  2. Justine Calma (12 Oct 2022). "Meet the CO2 battery cozying up with a wind energy giant". The Verge. Retrieved 16 April 2023. t faces stiff competition, but the CO2 battery has some unique strengths that could accelerate the transition to clean energy
  3. Mr. Simone Maccarini (2021). "The Carbon Dioxide for energy storage applications" (PDF). DoE. Thermochemical Power Group, University of Genoa (italy). Retrieved 16 April 2023.
  4. "Our Technology". Corporate website. Energy Dome. Retrieved 16 April 2023.
  5. "CO2 battery licensed by Energy Dome". Power generation: news and insights. Ansaldo Energia. Retrieved 16 April 2023.
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