Compression of energy storage gases is not new: for decades, several facilities around the world have been pumping air into huge underground pressure cavities and then using it to generate electricity at a natural gas power plant. But the Energy Dome turned to carbon dioxide because of its physics.
Carbon dioxide, when squeezed to a sufficiently high pressure, turns into a liquid that air does not do unless it is cooled to ultra-low temperatures. Liquid carbon dioxide can be stored in smaller steel tanks near where renewable energy is generated and used.
In the design of the Energy Dome, a flexible membrane keeps carbon dioxide in a huge dome at low pressure. When there is excess electricity, the gas passes through a compressor to reach high pressure. This process also generates heat, which is also stored.
Then, when energy is needed, the accumulated heat is used to heat the carbon dioxide, which decompresses and rotates the turbine, generating electricity.