GWh Level Renewable Energy Storage and Supply using Liquid CO₂

A novel energy storage system is proposed to deliver GWh or more of electric energy from an intermittently available energy source. The system is a closed loop cycle that transforms carbon atoms between liquid carbon dioxide and liquid methane. Methane is associated with the highest energy content per mole carbon. Therefore, for a given power, it requires the least amount of carbon circulation in the cycle. Both carbon dioxide and methane are stored as liquids, thereby avoiding the challenges associated with storing gases. In each case, the electrical power required for liquefaction is minimized by integrating the vaporization and liquefaction steps of carbon dioxide and methane. This means that the refrigeration available from vaporizing liquid carbon dioxide is used in the liquefaction of methane and the refrigeration available from vaporizing liquid methane is used in the liquefaction of carbon dioxide.