Hydrostatically compensated caes system having an elevated compensation liquid reservoir
A hydrostatically compensated compressed air energy storage system may include an accumulator disposed underground and a compressor/expander subsystem in fluid communication. A compensation shaft may extend between an upper and a lower end and define a shaft depth. An upper end wall can cover the upper end of the shaft. A compensation liquid reservoir can be offset above the upper end wall by a reservoir elevation that is at least about 15% of the shaft depth. A compensation liquid flow path may extend between the compensation liquid reservoir and the accumulator and can include the compensation shaft and a liquid supply conduit extending between the compensation liquid reservoir and the upper end of the compensation shaft whereby a total hydrostatic pressure at the lower end of the shaft is greater than a hydrostatic pressure at a depth that is equal to the shaft depth.
1. A hydrostatically compensated compressed air energy storage system comprising:
a) an accumulator disposed underground and comprising an interior for containing a layer of compressed air above a layer of compensation liquid;
b) a compressor/expander subsystem in fluid communication with the accumulator interior via an air flow path and configured to selectably convey compressed air into the accumulator and to extract air from the accumulator;
c) a compensation shaft extending between an upper end that is proximate a surface of a ground and a lower end that is proximate and in fluid connection with the accumulator and defining a shaft depth, an upper end wall being configured to cover the upper end of the shaft and to isolate an interior of the compensation shaft from the ambient atmosphere;
d) a compensation liquid reservoir spaced apart from the accumulator and offset above the upper end wall by a reservoir elevation that is at least about 15% of the shaft depth;
e) a compensation liquid flow path extending between the compensation liquid reservoir and the accumulator, the liquid flow path comprising the compensation shaft and a liquid supply conduit extending between the compensation liquid reservoir and the upper end of the compensation shaft whereby a total hydrostatic pressure at the lower end of the shaft is greater than a hydrostatic pressure at a depth that is equal to the shaft depth;
wherein the system is operable in at least:
a charging mode in which the gas compressor/expander subsystem is configured to covey compressed air at an accumulator pressure into the layer of compressed air within the accumulator which then displaces a corresponding volume of compensation liquid from the layer of compensation liquid within the accumulator out of the accumulator via the compensation liquid flow path thereby maintaining the layer of compressed air at substantially the accumulator pressure during the first charging mode; and
a discharging mode in which the gas compressor/expander subsystem is configured to extract compressed air from within the accumulator which then enables a corresponding volume of compensation liquid to enter the accumulator via the compensation liquid flow path thereby maintaining the pressure within the accumulator at substantially the accumulator pressure during the discharging mode.
2. The system of claim 1 , wherein the liquid supply conduit is connected to an opening in the upper end wall of the compensation shaft.
3. The system of claim 1 , wherein the liquid supply conduit is connected to an opening in a sidewall of the shaft, proximate the upper end of the compensation shaft.
4. The system of claim 1 , wherein the compensation liquid reservoir comprises at least one of an enclosed tank, an open containment region and a body of water.
5. The system of claim 4 , wherein the compensation liquid reservoir is supported at the reservoir elevation by a reservoir support apparatus.
6. The system of claim 5 , wherein the reservoir support apparatus comprises a portion of the ground.
7. The system of claim 1 , wherein the reservoir elevation is at least 20% of the shaft depth.
8. The system of claim 7 , wherein the reservoir elevation is between about 20% and about 50% of the shaft depth.
9. The system of claim 1 , wherein the reservoir elevation is between about 50 m and about 250 m.
10. The system of claim 9 , wherein the reservoir elevation is between about 100 m and about 200 m.
11. The system of claim 1 , wherein the shaft depth is at least 300 m.
12. The system of claim 11 , wherein the shaft depth is between about 400 m and about 500 m.
13. The system of claim 1 , wherein a sum of the shaft depth and the reservoir elevation is at least 500 m.
14. The system of claim 1 , wherein the shaft depth is measured in a downward direction from the upper end wall of the shaft and the reservoir elevation is measure in an opposing, upward direction from the upper end wall of the shaft.
15. The system of claim 1 , wherein the accumulator pressure is between about 40 and about 70 bar.
16. The system of claim 15 , wherein the accumulator pressure is between about 50 and about 60 bar.
17. The system of claim 1 , wherein the total hydrostatic pressure is at least 80% of the accumulator pressure.
18. The system of claim 17 , wherein the total hydrostatic pressure is at least 95% of the accumulator pressure.
19. The system of claim 1 , wherein the total hydrostatic pressure is the hydrostatic pressure at a depth that is equal to the shaft depth plus the reservoir elevation.
20. The system of claim 1 , wherein the compensation liquid comprises at least one of water, brine, oil and a combination thereof.