A CO2 battery. It may sound crazy, but this is the thermodynamic energy storage project developed by the Italian start-up Energy Dome. The idea? Store CO2 in the form of gas in a huge dome and use it as an electricity storage solution. In “charge”, the gas is extracted and compressed in liquid form. To restore the stored energy, this liquid CO2 is heated until it returns to its original shape. In the process, the company arranges to spin a turbine that generates electricity. This is the basis of an already well-documented technique of compressed air energy storage.
Renewable energies being, by nature, intermittent – unlike power stations which are controllable – their electricity production must be stored if we want to be able to use it to supply the network offline. When it comes to storing the energy created by photovoltaic installations, it is usually traditional lithium-ion batteries that are used. But Energy Dome believes its CO2 battery is the perfect companion for wind farms, giving them greater flexibility. This is why its first partner is none other than Ørsted, a Danish renewable energy giant and operator of the largest offshore wind farm in the world.
Together, they are currently designing the plans for a CO2 energy storage plant with a capacity of 20 MW, capable of supplying electricity to the grid for ten consecutive hours. Its construction could begin in 2024 and, if successful, several sites of the same type could grow across Europe.
“We consider the CO2 battery solution to be a very promising alternative for long-term energy storage”, enthuses Kieran White, vice-president of Ørsted. As for the engineer Claudio Spadacini, boss and founder of Energy Dome, he explains that he had this idea because CO2 liquefies easily at low temperatures (from 31.1°C, with a pressure of at least 5.2 bar). “As a result, it is possible to store a large reserve of energy in relatively compact installations, which makes this technology very interesting from an economic point of view”he says.
This solution would indeed be much less expensive – and harmful to the environment – than the use of massive lithium batteries. Lithium whose extraction and transformation conditions are problematic. The CO2 battery is made with turbines and compressors, and requires traditional steel, a concrete base and resistant canvases. About forty start-ups are currently working on equivalent solutions around the world, each with their own technical specificities, but the young shoot Energy Dome has already been spotted by certain specialized funds and cited among the innovations to be followed by Bloomberg.
As for imagining the installation of miniature CO2 batteries to power buildings or houses equipped with solar panels or wind turbines, we are not there yet, the technology requiring a lot of space on the ground and a permanent control of exploitation to optimize performance and avoid accidents.