Experimental study of carbon dioxide as working fluid in a closed-loop compressed gas energy storage system

Abstract

This paper investigates the utilization of carbon dioxide gas available in mass pressurized storage caverns as a working fluid for a modular low pressure compressed gas energy storage (CGES) system. The system is made up of three 7 L cylinders that discharge into an air turbine to convert the system potential energy into kinetic and eventually into electricity through an onboard generator. The operating pressures are kept low (around 3 bar) in order to maintain the adiabatic operational assumption and not necessitate the usage of heat exchangers. The gas is then rerouted back into the storage cavern after expansion. The reported energy conversion efficiency is 46.2% for the three active cylinders operating in tandem and 76.4% for them operating in unison. The main advantage of the proposed system is its flexibility to function under high power density for the latter or high energy density requirements for the former arrangement, respectively. This level of discharge control allows the system to serve in ranges that previously required independent storage systems addressing narrow power/energy density needs. This charge/discharge cycle takes advantage of the availability of the stored and pressurized carbon dioxide, which is denser than air and hence produced higher power output and required 65% less space than its air-operated counterpart.