Key Components
The Key components
CO2
Carbon Dioxide (CO2) is the working fluid employed in the CO2 Battery, manipulated between gaseous and liquid phase in a closed thermodynamic transformation. CO2 is the best fluid from a thermodynamic point of view as it can be stored as compressed liquid at atmospheric temperature, without the need for cryogenics equipment (as for LEAS) or site dependent underground caverns (as for A-CAES).
Dome
The dome is our key-component. It is composed of two membranes: an internal membrane, which stores the CO2 in atmospheric conditions and an external membrane, which is an air-supported structure used to protect the internal one from atmospheric agents. The dome allows to have a closed thermodynamic transformation: the CO2 that is sucked from the dome and compressed during the charge phase, is then returned back during the discharge after expansion in the turbine.
Turbine
The turbine is a medium pressure steam turbine. It is a multistage rotating machine, with the main goal to expand the compressed gaseous CO2 coming from the TES during the discharge phase. Mechanical power is produced exploiting the pressure and temperature energy (“enthalpy”) of the CO2 and converted into electrical power thanks to the generator, injecting electricity back into the grid. The low pressure CO2 is then discharged in the dome to close the cycle.
Compressor
The compressor is an integrally geared multistage compressor. It is made of multiple rotors (the pinions), each one connected to a gear rotating at different speed to optimize the fluid-dynamics, hence the efficiency of the compressor. The function of the compressor is to compress the CO2 coming from the dome during the charge phase. The power needed for the compression is provided by the motor.
Motor/Generator
The apparatus is a standard 4-poles synchronous machine used to drive the compressor by absorbing electrical power from the grid during the charge phase; and to convert the mechanical power produced at the shaft by the turbine into electrical power to be discharged to the grid during the discharge phase. Being a synchronous machine, it contributes to grid inertia and voltage regulation (reactive power)
Thermal Energy Storage
The thermal energy storage is a key component of the CO2 Battery:
a) It stores the heat generated during the adiabatic compression of the CO2 in the compressor during the charge phase.
b) It discharges the heat previously stored during the charge phase and allows therefore to heat the compressed gaseous CO2 up to high temperature, hence enthalpy, in order to expand in the turbine and produce power with high RTE
CO2 Tanks
The CO2 Tanks are carbon steel pressure vessels used to store the compressed liquid CO2 during the charge phase, allowing its release during the discharge phase. Storing CO2 in pressurized liquid form allows to achieve a high volumetric energy density (kWh/m3) on the high pressure side of the cycle.
