Systems and methods for energy storage and recovery using gas expansion and compression

Abstract

In various embodiments, energy-storage systems are based upon an open-air arrangement in which pressurized gas is expanded in small batches from a high pressure of, e.g., several hundred atmospheres to atmospheric pressure. The systems may be sized and operated at a rate that allows for near isothermal expansion and compression of the gas.

What is claimed is: 
     
         1 .- 20 . (canceled) 
     
     
         21 . A method of energy recovery, the method comprising:
 introducing compressed gas at a first pressure into a first cylinder assembly comprising a piston therewithin;   expanding the gas within the first cylinder assembly to a second pressure lower than the first pressure, thereby translating the piston within the first cylinder assembly;   converting the translation of the piston into rotary motion of a motor/generator outside the first cylinder assembly;   introducing heat-transfer fluid into the gas such that the heat-transfer fluid exchanges heat with the gas within the first cylinder assembly during expansion;   controlling operation of the first cylinder assembly (i) to enforce substantially isothermal expansion of gas therein and (ii) in response to at least one system parameter associated with operation of the first cylinder assembly; and   venting substantially all of the expanded gas at the second pressure from the first cylinder assembly to atmosphere.   
     
     
         22 . The method of  claim 21 , wherein the translation of the piston is converted into rotary motion by a transmission mechanism. 
     
     
         23 . The method of  claim 22 , wherein the transmission mechanism comprises a crankshaft. 
     
     
         24 . The method of  claim 22 , wherein the transmission mechanism comprises a crankshaft and a gear box. 
     
     
         25 . The method of  claim 22 , wherein the transmission mechanism comprises a crankshaft and a continuously variable transmission. 
     
     
         26 . The method of  claim 22 , wherein the transmission mechanism is connected to the piston by a shaft and a crosshead linkage. 
     
     
         27 . The method of  claim 22 , wherein the transmission mechanism varies torque for a given force exerted thereon. 
     
     
         28 . The method of  claim 21 , wherein the at least one system parameter comprises at least one of a fluid state, a fluid flow, a temperature, or a pressure. 
     
     
         29 . The method of  claim 21 , wherein the at least one system parameter comprises a position of the piston within the first cylinder assembly. 
     
     
         30 . The method of  claim 21 , wherein the at least one system parameter is monitored by at least one sensor. 
     
     
         31 . The method of  claim 21 , further comprising, prior to introducing gas into the first cylinder assembly, expanding gas from a third pressure higher than the first pressure to approximately the first pressure within a second cylinder assembly (i) comprising a piston therewithin and (ii) selectively fluidly connected to the first cylinder assembly. 
     
     
         32 . The method of  claim 31 , further comprising, prior to expanding gas within the second cylinder assembly, transferring gas from a compressed-gas reservoir to the second cylinder assembly at approximately the third pressure. 
     
     
         33 . The method of  claim 31 , wherein the piston within the first cylinder assembly and the piston within the second cylinder assembly are mechanically coupled to a crankshaft. 
     
     
         34 . The method of  claim 31 , further comprising (i) after expanding gas from the third pressure to the first pressure within the second cylinder assembly, expanding one or more additional portions of gas each from a pressure less than the third pressure to the first pressure within the second cylinder assembly, and (ii) maintaining a substantially constant power output of the motor/generator during the expansions notwithstanding the different initial pressures of gas. 
     
     
         35 . The method of  claim 21 , wherein gas at the first pressure is introduced into the first cylinder assembly from a compressed-gas reservoir storing gas at approximately the first pressure. 
     
     
         36 . The method of  claim 21 , further comprising (i) after expanding gas from the first pressure to the second pressure within the first cylinder assembly, expanding one or more additional portions of gas each from a pressure less than the first pressure to the second pressure within the first cylinder assembly, and (ii) maintaining a substantially constant power output of the motor/generator during the expansions notwithstanding the different initial pressures of gas. 
     
     
         37 . The method of  claim 21 , further comprising monitoring a temperature of the gas during expansion of the gas. 
     
     
         38 . The method of  claim 21 , further comprising monitoring a pressure of the gas during expansion of the gas. 
     
     
         39 . The method of  claim 21 , further comprising monitoring, during expansion of the gas, at least one of a position or a rate of movement of the piston. 
     
     
         40 . The method of  claim 21 , wherein introducing heat-transfer fluid into the gas comprises spraying heat-transfer fluid into the gas.