Compressed gas energy storage system

Abstract

Embodiments of the present invention use compressed air to store and deliver electrical, mechanical, and/or thermal power with high round-trip efficiency. Various embodiments may be scalable for use in a variety of environments—from wind farms to power plants to motor vehicles. An energy storage system according to the present invention can operate as a stand-alone storage system that connects electrically to the grid, it can be tightly integrated with a wind turbine, and/or it can be co-located with a thermal power generation facility and operate with even higher efficiency by scavenging low-grade waste heat.

What is claimed is: 
     
         1 . An apparatus comprising:
 an expander comprising an inlet valve configured to receive a pressurized gas, the expander further comprising an element configured to introduce liquid to effect gas-liquid heat exchange with gas being expanded;   a proportional-integral-derivative (PID) controller configured to adjust a timing of the inlet valve to close when a percentage of the expander filled is a quotient of downstream and upstream pressures;   a gas-liquid separator configured to separate the liquid from a gas-liquid mixture received from the expander; and   an insulated thermal storage unit in thermal communication with the separated liquid.   
     
     
         2 . An apparatus as in  claim 1  wherein the insulated thermal storage unit is configured to store the separated liquid. 
     
     
         3 . An apparatus as in  claim 1  wherein the insulated thermal storage unit is configured to store a second liquid in thermal communication with the separated liquid through a heat exchanger. 
     
     
         4 . An apparatus as in  claim 3  wherein the second liquid is maintained at a lower pressure than the gas-liquid mixture. 
     
     
         5 . An apparatus as in  claim 3  wherein the separated liquid and the second liquid comprise water. 
     
     
         6 . An apparatus as in  claim 3  wherein the separated liquid comprises water and the second liquid comprises an oil. 
     
     
         7 . An apparatus as in  claim 1  wherein the inlet valve is configured to receive the pressurized gas from a compressed gas storage unit. 
     
     
         8 . An apparatus as in  claim 7  wherein inlet valve comprises an active valve having a valve timing changed as the compressed gas storage unit depletes. 
     
     
         9 . An apparatus as in  claim 1  wherein the inlet valve is configured to receive the pressurized gas from a higher pressure expansion stage. 
     
     
         10 . An apparatus as in  claim 1  wherein the expander comprises a reversible compressor/expander. 
     
     
         11 . An apparatus as in  claim 10  wherein the insulated thermal storage unit is in thermal communication with a heat source when the reversible compressor/expander is operating as an expander. 
     
     
         12 . An apparatus as in  claim 11  wherein the heat source is internal. 
     
     
         13 . An apparatus as in  claim 11  wherein the heat source is external. 
     
     
         14 . An apparatus as in  claim 10  further comprising a second insulated thermal storage unit configured to be in thermal communication with the separated liquid when the reversible compressor/expander is operating as a compressor. 
     
     
         15 . An apparatus as in  claim 14  wherein the second insulated thermal storage unit is in thermal communication with a heat source. 
     
     
         16 . An apparatus as in  claim 10  further comprising a second insulated thermal storage unit configured to be in thermal communication with liquid separated by a second gas-liquid separator when the reversible compressor/expander is operating as a compressor. 
     
     
         17 . An apparatus as in  claim 10  wherein the insulated thermal storage unit comprises a moveable partition defining,
 a first chamber receiving the separated liquid when the reversible compressor/expander is operating as a compressor, and 
 a second chamber receiving the separated liquid when the reversible compressor/expander is operating as an expander. 
 
     
     
         18 . An apparatus as in  claim 10  wherein the reversible compressor/expander is in selective communication with a Variable Frequency Drive (VFD). 
     
     
         19 . An apparatus as in  claim 1  wherein a majority of the gas-liquid heat exchange is sensible heat. 
     
     
         20 . An apparatus as in  claim 1  wherein the element comprises a pre-mixing chamber.