Italian company Energy Dome has opened the first of its remarkable grid-level energy storage plants, in Sardinia. These "CO2 batteries" can store renewable energy over long periods and release it quickly, at less than half the cost of big lithium batteries.
Large-scale energy storage is going to be required on an epic scale all round the world, as green energy begins to take over the world's power supply. Renewable energy is often generated at times and places where it's not needed, and a variety of grid-level storage technologies are jockeying for various energy market niches, each with their own strengths and weaknesses.
Energy Dome's batteries use huge domes with giant, flexible bladders full of carbon dioxide gas in them. It "charges" its battery by using energy to run electric compressors that squeeze the gas into smaller and smaller volumes, eventually condensing it into a liquid. This charging process creates waste heat, which is captured in a thermal energy storage system.
As long as the pressure is maintained, the carbon dioxide will happily sit there over the long term. When the energy is needed, the system uses its stored heat to evaporate the CO2, and a set of turbines harvests energy back out for the grid as the carbon dioxide expands back into the bladder dome.
The round-trip efficiency of this solution, says Energy Dome, is over 75 percent. In this regard, it can't compete with big lithium batteries. But cost is king in the energy sector, and the company has says its levelized cost of storage will be on the order of US$50-60 per MWh within a few years, much lower than the US$132-245 per MWh it costs to use lithium batteries.
There are solutions that store energy more cheaply, but they're typically slower to react to demand and more appropriate for longer-term seasonal energy generation and demand mismatches, where these CO2 batteries can operate closer to the instant response of lithium batteries, while storing energy for longer with less system degradation.