Patent ID: 8272212

Claim:
A method of controlling the thermal efficiency of a compressed gas-based energy storage and recovery system, the compressed gas-based energy storage and recovery system including a gas compressor/expander device and a liquid management system, the liquid management system including a first hydraulic cylinder having a first working piston disposed therein for reciprocating movement in the first hydraulic cylinder, the first working piston dividing the first hydraulic cylinder into, and defining therewith, a first hydraulic chamber and a second hydraulic chamber, a second hydraulic cylinder having a second working piston disposed therein for reciprocating movement in the second hydraulic cylinder, the second working piston dividing the second hydraulic cylinder into, and defining therewith, a third hydraulic chamber and a fourth hydraulic chamber, the method comprising: fluidically isolating the first hydraulic chamber from a liquid source; establishing fluid communication between the first hydraulic chamber and the gas compressor/expander device; fluidically isolating the second hydraulic chamber from the gas compressor/expander device; establishing fluid communication between the second hydraulic chamber and the liquid source; moving the first working piston in a first direction to: a) reduce the volume of the first hydraulic chamber and displace a first volume of liquid contained therein to the gas compressor/expander device, and b) increase the volume of the second hydraulic chamber and receive therein a second volume of liquid from the liquid source; fluidically isolating the first hydraulic chamber from the gas compressor/expander device; establishing fluid communication between the first hydraulic chamber and the liquid source; fluidically isolating the second hydraulic chamber from the liquid source; establishing fluid communication between the second hydraulic chamber and the gas compressor/expander device; moving the first working piston in a second direction, opposite to the first direction, to: a) reduce the volume of the second hydraulic chamber and displace the second volume of liquid contained therein to the gas compressor/expander device, and b) increase the volume of the first hydraulic chamber and receive therein a third volume of liquid from the liquid source.