| Abstract |
The CO2-Plume Geothermal (CPG) power system can operate either as a baseload power source or as a dispatchable generator, making power when it is needed on the electric grid. Unlike wind and solar, which are intermittent power sources that operate only when the wind blows or the sun shines, geothermal heat is always available and can be extracted as needed to generate electricity. As wind and solar begin to constitute a larger portion of the electricity provided to the grid, there is an increased need to provide flexible power generation that makes up the difference between demand and this varying renewable supply. Thus, CPG is a carbon-neutral, renewable, flexible power generator that can fulfill this need. Unlike most geothermal technologies, CPG can be extended to be an energy storage system, termed CO2 Plume Geothermal Energy Storage (CPGES). To create one version of a CPGES system, a second shallow reservoir is added to the CPG system. CO2 is stored in this shallow reservoir in an intermediate state after power is generated but before the energy-intensive parasitic loads, which reduce the power plant’s overall output. When the generation and parasitic stages are separated by time, nearly the full gross turbine electric generation can be sent to the grid when power is needed. Later, when electricity is cheap, power is taken from the grid and used to cool (and sometimes pump or compress) the CO2. Thus, CPG is expanded into CPGES, adding energy storage to the electric grid. In this work, we describe a new type of CPGES, termed Earth Battery Extension II (EBE II), which uses a large surface storage tank, or gasometer, to store the CO2 at near-atmospheric pressure. This permits up 260 MWe of electricity to be generated during the battery discharge phase compared to 2.5 MWe for CPG alone. Additionally, the new CPGES system can be configured to produce solid CO2 (dry ice) that can be sublimated at near atmospheric pressure, providing a -78 °C heat sink that can be used for cooling purposes in general and, specifically, to cryogenically capture CO2 from the air. This CO2 can, in turn, be used to develop more such CPGES systems. If no heat sink is desired, the turbine can be optimized by including (additional) stages that result in increased electric power output without dry ice formation. |