Process for Storing Energy as Compressed Gases in Subterranean Water Reservoirs Using High-Pressure Electrolysis

Abstract

A process for storing large amounts of energy underground in existing or artificial aquifers at very large scale using deep-water, high-pressure electrolysis. The process is intended for use as large scale storage for electrical power grids. When implemented at depths greater than roughly 500 m, it provides stored energy density equal to or greater than lead-acid batteries while requiring only a pressure vessel. If the geologic structure is appropriate, the vessel may already exist naturally.

Because this process does not require compression of the gas(es), when the gas(es) is expanded it become quite cold and therefore extracts heat from the atmosphere. When combined with a sustainable energy source such as wind, solar, ocean or other similar source—the entire process is endothermic. The cold gas(es) can also be used to precipitate CO.sub.2 and condense CH.sub.4 directly from the atmosphere. This means the combination of these processes removes heat and carbon from the environment at the same time they provide large scale, lower cost grid energy storage.

Claims

1. A process for electrolyzing water, under (or augmented by) the high ambient pressure present in deep water aquifers or wells, into highly pressurized hydrogen and oxygen

2. A process using the highly pressurized hydrogen and/or oxygen (claim 1) for energy storage.

3. A process which expands the high pressure gas(es) produced (and/or stored) by electrolysis of water at great depth under ground (claims 1 & 2) adiabatically to produce cold or liquid hydrogen and/or oxygen.

4. A process which uses a heat engine, the environment as the heat source and the cold gas(es) and/or liquid(s) produced by adiabatic expansion (claim 3) as the cold sink to produce electricity or mechanical work endothermically.

Description

FIG. 1 STORAGE CAPACITY VS WATER DEPTH

[0048] FIG. 1 shows a graph of energy density vs depth for gas pressure (Eq 1), hydrogen (Eq 7) and the two combined. The energy of a typical, lead acid battery is included for reference. This graph clearly shows the efficiency benefits of this process.

[0049] The primary benefits of this process are: [0050] It has energy density as much as 20 times greater than lead-acid batteries. [0051] The process requires no rare materials such as lithium. [0052] It is sustainable. [0053] If the endothermic engine and carbon capture options are used, this system extracts carbon from the atmosphere and is carbon negative. [0054] It causes little to no displacement of the rock structure above the reservoir, resulting in little or no risk of damage to structures above the reservoir. [0055] When compared with gravity storage, it requires greatly reduced volumes of water. [0056] It has greatly reduced risk of subterranean water contamination. [0057] There is no risk of toxic leakage as there is with many batteries. [0058] Combined, these benefits make this one of the most effective methods for storing and buffering electrical energy.

[0059] Prior art and patents: [0060] U.S. Pat. No. 8,261,552 Advanced adiabatic compressed air energy storage system [0061] U.S. Pat. No. 4,808,029 System for subterranean storage of energy [0062] U.S. Pat. No. 4,182,128 Underground pumped liquid energy storage system and method [0063] U.S. Pat. No. 11,125,065 Hydraulic geofracture energy storage system with desalinization [0064] U.S. Pat. No. 10,669,471 Hydraulic geofracture energy storage system with desalinization [0065] U.S. Pat. No. 10,125,035 Hydraulic geofracture energy storage system with desalinization [0066] U.S. Pat. No. 9,481,519 Hydraulic geofracture energy storage system with desalinization

[0067] The Canadian company Hydrostor is using methods similar to those described in U.S. Pat. No. 8,261,552. They are either licensing this patent or hold a similar foreign patent.

[0068] The US company Quidnet is currently developing the geofracture storage approach. Dark Sky Innovative Solutions review of geofracture storage has raised some concerns. In public briefings it's claimed the energy is stored by compression. Since both water and rock are deemed ‘in-compressible’ in engineering texts, it is highly unlikely that they can store significant energy. This is expressed by the formulae

E=½kx.sup.2   Eq 8

and

F=kx   Eq 9

[0069] These can be solved for E as a function of F and k as

E=½F.sup.2/k   Eq 10

[0070] Equation 10 clearly shows that storing energy using force to compress a stiff material is very inefficient for energy storage. It is far more likely that the rock and water are lifted against gravity and act as a gravity battery.

[0071] In prior art, the working gas is taken from the atmosphere and pumped underground by force. The pumping step requires a great deal of energy and produces heat which must be recovered or released. This leads to the focus on an adiabatic (zero heat loss) process.

[0072] This process eliminates the compression step, replacing it with electrolysis of water into hydrogen and oxygen. This process stores much more energy per cubic meter, is endothermic and provides inherent carbon capture if desired.

[0073] These attributes make this process of far more commercial value and value to society and the welfare of the Earth's biosphere.

[0074] I, Robert R Tipton, declare that the material of this specification has not been changed.