Mechanisms of Geologically Stored CO2 for Energy Storage

Abstract

Carbon dioxide-Bulk Energy Storage (CO2-BES) is a bulk energy storage technology that uses carbon dioxide (CO2) in sedimentary basin geothermal resources to time-shift electricity production. Here, we investigated how the charging and discharging cycles affect the power storage capacity and power output capacity of a CO2-BES facility. We simulated the operation of CO2-BES with seven different operating cycles for fourteen years. Our results suggest that continuous charging and discharging cycles do not change the rate of heat depletion of the geothermal resource. But the power storage capacity and the power output capacity are affected because they rely on the magnitude of the overpressure. If, in a cycle, the duration of electricity dispatch is greater than the duration of electricity storage, overpressure may eventually deplete and a CO2-BES facility may cease to be operational. If idle periods where electricity is neither charged nor discharged are included in the cycle, there is a small increase in power output capacity and a small decrease in power storage capacity. In general, if electricity is dispatched and stored for equal amounts of time, the duration of dispatch/storage and of the idle period does not affect the power output capacity or the power storage capacity. As a result, as long as the cycles consist of equivalent charging and discharging durations throughout the lifetime of the facility, the length of those durations and frequency of idle periods could be based on financial incentives (e.g., diurnal variations in electricity prices), rather than process-level factors like the potential for heat or pressure depletion.

Keywords: CO2 for energy (storage), GHGT-14