SYSTEMS AND METHODS FOR FOAM-BASED HEAT EXCHANGE DURING ENERGY STORAGE AND RECOVERY USING COMPRESSED GAS

1 .- 434 . (canceled)

435 . A method of energy storage and recovery utilizing a power unit comprising a cylinder assembly for at least one of the compression of gas to store energy or the expansion of gas to recover energy, the method comprising:

compressing gas in the power unit; and

at least one of prior to or during the compression, (i) withdrawing heat-transfer liquid from a first thermal well at a first temperature, and (ii) introducing the heat-transfer liquid into the gas to exchange heat therewith, the heat exchange bringing the heat-transfer liquid to a second temperature higher than the first temperature;

transferring the compressed gas to a compressed-gas store; and

transferring the heat-transfer liquid at the second temperature to at least one of the compressed-gas store or a second thermal well discrete from the first thermal well.

436 . The method of claim 435 , further comprising:

transferring compressed gas from the compressed-gas store to the power unit;

expanding the compressed gas in the power unit; and

at least one of prior to or during the expansion, (i) withdrawing heat-transfer liquid from at least one of the compressed-gas store or the second thermal well, and (ii) introducing the heat-transfer liquid into the gas to exchange heat therewith; and

transferring the heat-transfer liquid to the first thermal well.

437 . The method of claim 436 , wherein expanding the compressed gas in the power unit comprises expanding the compressed gas in a first stage and a second stage each spanning a different pressure range.

438 . The method of claim 437 , wherein (i) heat-transfer liquid is withdrawn from the compressed-gas store at least one of prior to or during expansion in the first stage and (ii) heat-transfer liquid is withdrawn from the second thermal well at least one of prior to or during expansion in the second stage.

439 . The method of claim 436 , wherein the heat exchange between the gas and the heat-transfer liquid at least one of prior to or during the expansion renders the expansion substantially isothermal.

440 . The method of claim 436 , wherein introducing the heat-transfer liquid into the gas at least one of prior to or during expansion comprises spraying the thermally conditioned heat-transfer liquid into the gas.

441 . The method of claim 436 , wherein introducing the heat-transfer liquid into the gas forms a foam comprising the heat-transfer liquid and the gas.

442 . The method of claim 441 , further comprising separating at least a portion of the foam into gas and heat-transfer liquid prior to transferring the heat-transfer liquid to the first thermal well.

443 . The method of claim 435 , wherein compressing the gas in the power unit comprises compressing the gas in a first stage and a second stage each spanning a different pressure range.

444 . The method of claim 443 , wherein (i) heat-transfer liquid is transferred to the compressed-gas store after or during compression in the first stage and (ii) heat-transfer liquid is transferred to the second thermal well after or during compression in the second stage.

445 . The method of claim 435 , wherein the heat exchange between the gas and the heat-transfer liquid at least one of prior to or during compression renders the compression substantially isothermal.

446 . The method of claim 435 , wherein introducing the heat-transfer liquid into the gas at least one of prior to or during compression comprises spraying the thermally conditioned heat-transfer liquid into the gas.

447 . The method of claim 435 , wherein introducing the heat-transfer liquid into the gas at least one of prior to or during compression forms a foam comprising the heat-transfer liquid and the gas.

448 . The method of claim 447 , further comprising separating at least a portion of the foam into gas and heat-transfer liquid before transferring the heat-transfer liquid at the second temperature to at least one of the compressed-gas store or a second thermal well discrete from the first thermal well.

449 . The method of claim 435 , further comprising storing, in the second thermal well, waste thermal energy produced by the power unit.

450 . The method of claim 435 , further comprising exchanging thermal energy between the surrounding environment and at least one of the first thermal well or the second thermal well.

451 . The method of claim 450 , wherein thermal energy is exchanged with the surrounding environment while the power unit is neither compressing nor expanding.