Storage system for hydrogen in groundwater

Abstract

Storage system for hydrogen in groundwater, comprising - electrolysis equipment (102) designed to electrolyze water using the energy of an energy source, having an oxygen-producing anode chamber (119) and a hydrogen-producing cathode chamber (118); - at least one ground probe containing — a side wall (201) closed at the bottom and defining an internal space filled with groundwater up to the groundwater level (203), the sidewall (201) is provided with a discharge opening below the groundwater level (203) near the groundwater level: and — a cartridge (202) having a closed end (214), an open end opposite the closed end (214) and a closed sidewall extending between the ends, where the ends and sidewall together form an internal space; — wherein the cartridge (202) is mounted below the groundwater level (203) in the interior of the side wall (201) in a position where the closed end (214) is positioned closer to the groundwater level (203) than the open end, and the side wall of the cartridge (202) is perforated (see 217) near the open end; — wherein the cartridge (202) is designed to retain tire hydrogen gas generated in the cathode chamber (118) during operation of tire electrolysis equipment (102) against the hydrostatic pressure of the groundwater.

Description

[0001] STORAGE SYSTEM FOR HYDROGEN IN GROUNDWATER

[0002] Technical field

[0003] The invention relates primarily to the storage of hydrogen in groundwater and its recovery therefrom. More specifically, the present invention discloses a soil probe for temporary storage of hydrogen, an energy storage assembly realized with such a soil probe, as well as a method of hydrogen storage / reuse, all of which use groundwater as energy storage option.

[0004] Background art

[0005] A major challenge for ‘green’ energy production is that peak production periods do not coincide with peak consumption periods. In addition, the ‘greener’ the energy production is, i.e. the higher the share of electricity generated from alternative energy sources such as solar, wind, geothermal, biomass, tidal, etc. in the electric power supply, the higher the peaks of overproduction. Short- or even long-term storage of ‘green’ energy produced is, thus, a huge challenge. Such storage of energy in the form of hydrogen is therefore becoming increasingly important.

[0006] Hydrogen is widely known as energy-carrying medium and currently several solutions for its storage exist. Storage plays a crucial role in the energetic use of hydrogen. The solutions used have to allow the energy stored as hydrogen to be recovered cheaply and efficiently, while minimizing maintenance and servicing costs of the pieces of equipment applied. In addition, recovery is typically needed at times when the source of stored energy is not available (e.g. at night or during periods of low wind).

[0007] During recovery, the hydrogen produced by alternative energy sources can particularly be used in so-called fuel cells, in which the chemical energy stored by the hydrogen is converted into electricity through an electrochemical reaction.

[0008] Japanese Published Patent Application No. 2005081803 discloses a solution for separating and recovering natural gas dissolved in groundwater in a well apt for pumping groundwater containing natural gas. The well is located in an underground layer where natural gas that is water-soluble in groundwater is naturally present and can thus be separated from groundwater. The well comprises an outer tube with an opening for the in-flow of groundwater containing the natural gas and an inner tube arranged within the outer tube, wherein the inner tube has a diameter smaller than that of the outer tube, and wherein the lower end of the inner tube is located above the lower end of the outer tube. Both the inner tube and the upper end of the outer tube at ground level are sealed with a gasket. The inner tube is further equipped with a device to reduce and adjust the pressure prevailing within the inner tube. The outer tube is further equipped with a pressure adjusting means to regulate and maintain the pressure prevailing within the outer pipe at normal pressure. As a result, the pressure due the water in the outer tube does not collapse the inner tube. By suitably reducing the pressure within the inner tube, natural gas in the inner tube can be released from groundwater, by means of e.g. vaporizing the groundwater, and then it accumulates at the upper end of the inner tube at ground level. From here, it is suitably discharged and used, for example, to generate electricity.

[0009] US Published Patent Application No. 2011 / 0274492 Al describes an underground gas, e.g. hydrogen gas, storage system, wherein the gas is stored in tubes inserted in wells formed by conventional well-drilling techniques. To store the gas, the gas to be stored is simply injected into the tubes by making use of a suitable pumping unit. The gas is stored in said tubes at a pressure higher than the atmospheric pressure prevailing outside, which facilitates the recovery of said gas.

[0010] US Published Patent Application No. 2020 / 0003365 Al describes a solution for underwater hydrogen storage. According to the solution, a storage device for storing hydrogen is attached to a sea or lake bottom at a selected depth, or is arranged in dead- water and maintained at a desired depth, such that the interior of the storage device is open to the space outside the storage device and thus water surrounding the storage device is free to flow into and out of the storage device. For storage purposes, the hydrogen to be stored in the storage device is preferably fed from the water surface into the storage device, wherein it gets continuously accumulated and displaces the water from the interior of the storage device. The fed hydrogen gas is then kept in equilibrium at all times with the hydrostatic pressure in the water at the given depth. Recovery of the stored hydrogen gas from the storage device is accomplished by means of a suitably arranged pipeline, as well as an appropriate system of valves and / or a pressure regulating unit arranged in said pipeline, where appropriate, in accordance with the actual requirements. Here, the hydrogen gas required to fill the storage device is supplied to the interior of the storage device in hydrogen storage drums, which are transported by a suitable conveying system, and then the content of said drums is simply vented. The separate transport system used to transfer hydrogen gas to be stored into the storage means is complex and requires the application of costly additional devices. These devices are permanently submerged in water and are thus subjected to corrosion and occasionally (e.g. during storms) to very strong water movements. To avoid said devices being damaged, constant monitoring is needed that increases the costs of hydrogen storage. Installing the transport system into greater water depths also leads to higher mechanical loads on the transport system itself, making the choice of materials for constructing said system critical.

[0011] US Published Patent Application No. 2014 / 0261132 Al describes an energy storage assembly arranged under water surface and using gas, preferably hydrogen gas, as working medium. The assembly comprises one or more thin-walled tanks anchored to the sea or lake bottom, open at the bottom and thus each defining an internal space that communicates with the external water space. The tanks are filled by hydrogen gas either supplied from the water surface through pipelines to said tanks or obtained by in situ chemical reactions between chemicals and water, possibly seawater, within the tanks; in the latter case, a continuous replenishment of the reactants is required. Filling of the tanks is carried out against the hydrostatic pressure at the site of each tank by the hydrogen being fed / generated continuously that displaces water within the tank interior through the open bottom of the tank until a desired gas level in the tank is achieved. Anchoring the tanks significantly increases the cost of this type of underwater gas storing method. The anchoring cables are subjected to continuous mechanical stresses and corrosion, which can be particularly significant in the case of subsea energy storage assemblies, and therefore require continuous monitoring. In addition, the anchoring cables have to also withstand the buoyancy forces acting on the tanks. As buoyancy is proportional to the volume of each tank, the buoyant force can be significant for larger tanks, requiring the use of cables with reinforced materials. This further increases the cost of energy storage. A further disadvantage of this solution is that the large water / gas contact surface in the tanks used, especially in the case of a tank with a large footing area, leads to high dissolution of stored gas into water, resulting in significant amounts of hydrogen gas dissolving into water, especially during long storage periods. This results in a loss in the amount of hydrogen that can be recovered from the tanks and reduces the efficiency of the storage / recovery process. The loss further increases if, in order to accelerate water displacement from the tanks during the filling process, each tank has an open bottom or relatively large openings in the bottom through which water flows in and out. Russian Patent No. 2,715,199 Cl describes a double-walled tank for deep-water hydrogen storage, which can be stabilized by a keel, said tank comprising an inner wall and an outer wall. Here, after having placed the tank below the water level at a desired depth and fixed it in position by the keel, the pressure of the gaseous hydrogen in the tank, supplied to the internal volume of the tank by means of a turbo compressor, is counterbalanced by controlling the pressure prevailing between the inner and outer walls by means of a valve.

[0012] An object of the invention is to eliminate, or at least alleviate, the disadvantages of the above-referred underwater energy storage solutions.

[0013] In particular, the invention aims at providing a cheap and economical solution for the temporary storage and recovery of energy in gas, preferably hydrogen, while minimizing the operation and maintenance costs, either in isolated domestic power plants or in large grid-connected power plants. The source of the energy to be stored can be either the surplus electricity temporarily generated in the electricity grid systems or the electricity generated from time to time by means of said alternative energy production processes but not used up.

[0014] The invention also aims at providing an energy storage system that is equally suitable for serving isolated domestic power plants or large grid-connected power plants, i.e. with a capacity that can be adapted to the needs of the producers and / or users, and which is relatively easy to be expanded in terms of storage capacity.

[0015] Brief description of the invention

[0016] Our investigations have led us to the finding that the storage and recovery of available energy in the form of a gaseous working medium at a given depth under water and under / against the hydrostatic pressure occurring at that depth can be achieved without the disadvantages of open water energy storage as described above, by making use of a well deepened into the ground to the desired depth and a specially designed storage device arranged in said well. From now on, the combination of the well and the special gas storage device arranged in the well will be referred to as a soil probe.

[0017] The wells to be used for energy storage are conventional wells, e.g. wells that can be drilled using conventional, e.g. residential (in the case of domestic geothermal systems) or industrial (e.g. in the field of oil industry) drilling techniques. In each case, the technology to be used will depend on the well diameter determined by the designed storage capacity and the subterranean conditions in the geographical area selected for storage.

[0018] By increasing the number of wells, and hence soil probes, to be constructed, storage capacity can be easily expanded in a modular way.

[0019] Energy storage according to the invention can be particularly advantageous in geographical areas where the necessary wells can be drilled in the ground using known well drilling technologies without significant costs, and where groundwater itself is easily accessible and abundant for the installation of the soil probes.

[0020] The energy storage in soil probes according to the present invention comprises converting available energy, primarily electrical energy, into an energy-carrying working medium in an energy conversion device, then introducing the thus obtained working medium into the soil probe under pressure conditions of the energy conversion device and storing said working medium in the gas phase in the soil probe under the hydrostatic pressure in the soil probe until the time of recovery. At the time of recovery, the energy-carrying working medium is simply expelled from the soil probe through a suitably designed pipeline by the hydrostatic pressure in the soil probe. The expelled working medium is then supplied into an energy recovery device, wherein the energy stored in the working medium is converted back into electricity which can then be used.

[0021] The energy conversion device is preferably an electrically powered electrolysis unit, wherein electricity is converted into the chemical energy of working media of hydrogen and oxygen, which are separated from each other in the electrolysis unit, preferably by a water splitting reaction, i.e. electrolysis. The resulting hydrogen is fed to the soil probe, preferably in the gas phase, by the pressure prevailing in the electrolysis unit, by means of suitable pipeline(s) and pressure regulating unit(s), as well as valve(s) in the pipelines. Due to the special design of soil probe used, gaseous hydrogen is trapped in the soil probe below the level of the groundwater that flows into the soil probe from the geological formation (soil) receiving (and - after its installation - thus embedding) said soil probe and gets stored therein at a given depth under the hydrostatic pressure exerted by the groundwater. Hydrogen gas thus injected into the soil probe during a filling / charging step can be stored in said soil probe for a longer or shorter period of time, depending on the demands, with no further energy input and with minimal solution losses due to the design and geometry of the soil probe. For reuse, in a discharging step, hydrogen stored in the soil probe can be recovered from the soil probe with no energy input, simply by the hydrostatic pressure of the groundwater in the soil probe, and after recovery it can be supplied into the energy recovery device, e.g. a fuel cell or gas engine, and converted into electricity. As the energy recovery device, any suitable combustion device can equally be used. In this case, the energy previously stored in hydrogen temporarily as chemical energy can be converted back by mixing the extracted hydrogen, in a desired proportion, with e.g. natural gas, and then burning the resulting gas mixture.

[0022] The above-referred charging and discharging steps can be repeated successively by means of the energy storage assembly at will without significantly reducing the capacity and lifetime of said energy storage assembly over time. Thus, the assembly in question can be operated over a long period of time and without interruption if proper maintenance is performed.

[0023] It should be here also noted that, in case of need, it is also possible to apply the same procedure for the storage of oxygen, the by-product of hydrogen production, i.e. to introduce and store gaseous oxygen in one or more further similar soil probes.

[0024] Brief description of the drawing

[0025] Figure 1 illustrates schematically a preferred exemplary embodiment of an energy storage assembly using a soil probe according to the invention, wherein the energy to be stored is electricity obtained specifically from solar energy and the energy conversion device is an electrolysis unit based on PEM (Proton Exchange Membrane) technology for water splitting.

[0026] Figure 2 depicts schematically an soil probe element of a modularly deployable system of soil probes for the temporary storage of converted energy, including at least one soil probe as part of the energy storage assembly shown in Figure 1.

[0027] Figure 2A is an enlarged schematic view of a head section of the soil probe presented in Figure 2.

[0028] Detailed description of the invention

[0029] The energy storage assembly according to the invention comprises: an energy source providing the energy to be stored temporarily; an energy conversion device producing at least one gaseous energy-carrying working medium by making use of the energy to be stored temporarily, the energy conversion device being connected to the energy source; a system of soil probes comprising at least one soil probe that stores at least one of the one or more gaseous energy-carrying working media produced, against hydrostatic pressure exerted by groundwater in the soil probe; a supply unit connected between the energy conversion device and the system of soil probes for transferring at least one of the one or more gaseous energy-carrying working media produced by the energy conversion device from said energy conversion device to the system of soil probes; and an energy recovery device for recovering, from the system of soil probes, at least one gaseous energycarrying working medium temporarily stored in one of the soil probes and for converting the energy of said energy-carrying working medium to a usable energy on demand, the energy recovery device being connected to the system of soil probes.

[0030] Figure 1 illustrates schematically a preferred exemplary embodiment of an energy storage assembly according to the invention. Said embodiment specifically realizes the storage of electricity generated from solar energy in the form of gaseous hydrogen as an energycarrying working medium and its recovery from said hydrogen as follows.

[0031] In case of the embodiment shown in Figure 1, an energy source 101 of the assembly according to the invention comprises one or more solar panels, or in other cases a wind turbine or a connection to an electrical grid, the latter is configured to receive energy from the electrical grid itself. The energy source 101 can also be provided as a combination of the energy sources mentioned or any other alternative ‘green’ energy source. If the energy source 101 is not a stand-alone energy generating unit, it may be installed in the energy storage assembly as a stand-alone electrical consumer. It then converts and thus stores the excess electricity generated at other points in the electrical grid.

[0032] If the energy source 101 is in the form of solar panel(s), an inverter or converter 16 is installed in the electrical connection between the energy source 101 and the energy conversion device 102 to control the direct current supplied from the energy source 101 to the energy conversion device 102. Said control provides for the operation of the solar panel(s) at the working point.

[0033] The energy conversion device 102 of the assembly according to the invention, in the embodiment shown in Figure 1, is a PEM membrane technology electrolysis unit, known in literature. Said electrolysis unit is built up of modularly expandable sections. In each section, stainless steel plates 104 are configured such that said plates 104 are positioned as close to each other as possible when the electrolysis unit is assembled. The plates 104 are all perforated as densely as possible, since during electrolysis, more gas is formed on plate edges than on plate surfaces. The plates 104 are insulated from each other against fluid flow and electrically as well, the individual insulations being provided by prefabricated seals 105 disposed between the plates 104; said seals 105 are preferably insulations made of klingerite. Negative and positive side plate assemblies of the electrolysis unit are separated by a particular PEM membrane 121. Said PEM membrane 121 allows the electrons to pass through the membrane but does not allow hydrogen and oxygen generated during electrolysis to pass through it; thus, hydrogen and oxygen are generated and present in the electrolysis unit on opposite sides of the PEM membrane 121, being separated from each other. Consequently, when the energy storage assembly operates, the PEM membrane 121 keeps the hydrogen and oxygen bubbles that form during the electrolysis taking place in the electrolyte fluid of the electrolyser unit separated.

[0034] In the embodiment shown in Figure 1, the supply unit of the assembly according to the invention comprises a gas collection and pressure regulating unit 103. The energy conversion device 102 forms a single fluid circuit with the gas collection and pressure regulating unit 103. The gas collection and pressure regulating unit 103 comprises three tanks 106, 107, 108 which are in fluid communication with each other through a common reservoir arranged at the bottom of each of said tanks. The gas collection and pressure regulating unit 103 is preferably made of a non-corroding material, such as stainless steel, and is capable of withstanding at least a working pressure of 30 bar. In this embodiment of the energy conversion device 102, the tank 107 is filled with an electrolyte fluid, preferably water or KOH electrolyte solution of the electrolysis unit up to a level 120 . In the lower connecting tank of said gas collection and pressure regulating unit 103, a closed-circuit heat exchanger 109 is installed, which forms part of a liquid circuit separated from the electrolyte fluid. Here, the heat exchanger 109 functions to increase the operating temperature of the electrolyte fluid by absorbing heat from a cooling medium to be applied to cool the surfaces of the one or more solar panels that form the energy source 101 of the energy storage assembly if, for optimal operation, the solar panel(s) are adapted to be cooled by the cooling medium. The use of a higher temperature electrolyte fluid in the electrolysis unit improves the operating efficiency of the electrolysis unit. Circulation in said liquid circuit is performed / maintained by a pump 110. A periodic circulation of the electrolyte fluid to the electrolysis unit is provided by a separated circulating pump 117, the operation of which is controlled by control electronics, not shown in the drawings, which form part of the energy storage assembly.

[0035] The tank 106 is in fluid communication with a negative side outlet 111 of the electrolysis unit, while the tank 108 is in fluid communication with a positive side outlet 112 of the electrolysis unit. A high-pressure vent valve 113 is installed in the upper part of each of the tanks 106 and 108. The vent valves 113 function to prevent the liquids discharged from the electrolysis unit through the outlets 111 and 112 into the tanks 106 and 108 and being collected in said tanks 106 and 108, respectively, from exiting from the tanks 106 and 108 together with gaseous hydrogen and oxygen, respectively, accumulating in the upper parts of the tanks 106 and 108. Thus, the electrolyte fluid can only flow to the electrolysis unit.

[0036] To control the operating pressure of the energy storage assembly, an actuated pressure regulating valve 114 is used on the oxygen side of the electrolysis unit to back-pressurize the oxygen gas accumulating in the tank 108. This control ensures that the pressure of the hydrogen gas accumulating in the tank 106 and exiting the tank 106 through a solenoid valve 115 is always just the pressure required for an instant operation of the energy storage assembly. The value of this pressure is determined by the amount of hydrogen stored in one or more of the soil probe(s) of the system of soil probes, i.e. the charge level of the system of soil probes, or putting this another way, the level of hydrostatic backpressure that the energy conversion device 102 must overcome to supply / charge hydrogen into the system of soil probes. The operation of the pressure regulating valve 114 is also controlled by the control electronics of the energy storage assembly.

[0037] Hydrogen gas accumulated in the upper part of the tank 106 is discharged into one or more soil probe(s) 202 of the system of soil probes through a 116 valve, the outlet side of which is connected to a common hydrogen inlet tube 224 (see Figure 2) of the one or more soil probe(s) 202 of the system of soil probes.

[0038] Onto the top of the tank 107, a pressure sensor 122 is mounted, which measures the instant pressure of the electrolyte fluid therein and transmit the measured value to the control software that controls the operation of the energy storage assembly. Said control software is preferably stored in a processor / memory which is part of the control electronics.

[0039] The well-known energy recovery device of the assembly according to the invention is not depicted in Figure 1. In the upper part of tank 108, oxygen gas (O2) accumulates, which can be processed in a known way when transferred to other technologies or can be stored or simply released into the open air / atmosphere.

[0040] The energy stored in hydrogen collected in said soil probes 202 can be recovered in several ways. After having charged the soil probes 202 installed modularly, when stored energy is to be recovered, a controlled amount of hydrogen must be directed through a pipe 219 in Figure 2 to the appropriate energy recovery device in order to obtain electrical or thermal energy.

[0041] Reuse of the energy stored in hydrogen can be performed by several known methods.

[0042] 1. By means of a properly designed fuel cell, it is possible to produce electricity. In such a case, the complete energy storage assembly according to the invention can be operated as a system of electricity input / electricity output.

[0043] 2. A generator equipped with a suitably designed hydrogen gas engine can be operated with a controlled amount of hydrogen through the pipe 219 illustrated in Figure 2, similarly to the procedure of item 1 above.

[0044] 3. Energy can also be extracted from the energy storage assembly according to the invention by connecting it to a natural gas combusting system arranged above the ground level. In such a case, the controlled amount of hydrogen is supplied from the pipe 219 illustrated in Figure 2 through a mixing valve to natural gas. Thus, electricity input and a mixture of e.g. 18% hydrogen and 82% natural gas as output is obtainable to produce thermal energy.

[0045] It is, however, obvious to a person skilled in the art that the exemplary embodiment of the energy storage assembly shown in Figure 1 can be readily changed, without going beyond the inventive concept, to a storage assembly of electricity obtainable from other alternative energy sources or even electricity extracted from the electrical grid by way of hydrogen gas by replacing the unit that converts the energy coming from an alternative energy source into electricity, here, by replacing the one or more solar panels.

[0046] Moreover, to produce hydrogen, further pieces of hydrogen production equipment known to a person skilled in the art can also be used instead of the present electrolysis-based energy conversion equipment used in the exemplary embodiment of the energy storage assembly shown in Figure 1. Figure 2 illustrates schematically a modularly deployable system of soil probes with two soil probes as an example. From now on, thus, the terms ‘system of soil probes’ or ‘soil probe system’ equally refer to a series of artificial objects, specifically drilled wells, with an internal gas storage cartridge inserted in each of said objects / wells which are constructed in an installation area as close as possible to each other, enabled by the geological conditions of said area; the gaseous energy-carrying working medium is stored within an internal cartridge space of the gas storage cartridge against water filling the cartridge space up to a given level, preferably against groundwater available in the area.

[0047] The soil probe of the energy storage assembly is used for short- and long-term storage of hydrogen produced by an electrolyser. Its construction must take into account the location of the groundwater layers in the soil. The soil probe is a well tubing of 160 mm in diameter, drilled essentially vertically to 150-300 m deep, sealed at the bottom and perforated with a filter towards the first, uppermost aquifer. When installing the well tubing, care must be taken to isolate the aquifers between the water barrier layers. The material of the tubing to be installed in the drilled borehole should preferably be a 160 mm cased PVC well lining tube, in harmony with DIN 4925. When designing the energy storage assembly, the depth dimensions, the diameter of the soil probes can be varied to take into account the local particular soil mechanics characteristics of the installation area. By varying these constructional parameters, the capacity of the energy storage assembly will change. The scope of protection defined by the appended set of claims also includes those installations which are constructed with different sizing required due to local geological conditions. Diameter of the well / well tubing may be varied to also take account of economic considerations.

[0048] The soil probes are installed in a modular manner with a suitable spacing of 3-6 m from one another, preferably side by side. The bottom of each soil probe is sealed with a bottom plug 204 manufactured for the well tubing 201 and installed vertically in a borehole of 200 mm in diameter drilled below a ground level 203 to a depth of 300 m, so that a filtering surface 205 forms at the height of the uppermost aquifer 207. The volume between the borehole of 200 mm in diameter and the well tubing of 160 mm in diameter is filled with concrete 206 used for drilling wells, thus excluding the possibility of different water layers flowing together and cross-contaminating each other.

[0049] The deployed well tubings 201 will be fitted with internal cartridges 202, preferably made of Soul Force H2T tubing (or any equivalent tubing designed for hydrogen), preferably of 125 mm in diameter. The material and construction of this tubing is such that the hydrogen collected in the inner cartridge 202 cannot diffuse towards the groundwater. Stainless steel centering plates 208 are used to center the inner cartridge 202. The upper centering plate 208 is fitted with two stainless steel drawn rods 210 of 12 mm each in diameter with threaded ends. On the ground surface, around each soil probe, a prefabricated reinforced concrete plate 213 of about 15 cm in thickness is arranged, which acts as counterweight on the inner cartridge 202 when said cartridge 202 is filled with hydrogen. A closure plate 211 is affixed by a bonding technique to the reinforced concrete plate 213 by means of foot bolts 212; said closure plate 211 functions to transfer the buoyancy force from the inner cartridge 202 to the reinforced concrete plate 213. This force acts when the inner cartridge 202 stores separated hydrogen.

[0050] Figure 2A, which is an enlarged representation of detail A of Figure 2, shows a schematic of the internal cartridge header design. The shape of this structure is very important for the operation of the energy storage assembly. When installing it, care must be taken to ensure that the head structure of the inner cartridge 202214 is below the installation depth of the well screen 205.

[0051] This is important to ensure that during operation the inner probe is always operating below the water level entering the well from the top 215 aquifer, so that the hydrogen in the inner cartridge can never come into contact with the surface air.

[0052] The head portion of the internal 202 cartridge 214 should be tapered in order to separate hydrogen bubbles from the water during filling due to the sudden increase in volume of the water coming through the filling tube 216. The design of the loading tube 218 entering the head portion of the inner cartridge is a 90 degree stainless elbow turned towards the inner wall of the inner cartridge, with the end cut off at 45 degrees. Its function is to ensure that the water between the hydrogen bubbles entering the inner cartridge during filling does not fall to the bottom of the cartridge, but flows down the inner cartridge, inner sidewall. The bottom of the inner cartridge 217 is perforated and open towards the wellbore. The perforated holes 217 allow water to flow out of the inner cartridge into the outer wellbore, and from there the water exits through the wellbore filter 205 towards the top water table 207.

[0053] The internal cartridge head is fitted with outlet pipes 219, which discharge the hydrogen from the internal cartridge, regulated by 220 solenoid valves.

[0054] The deployed soil probes are connected to a common 221 water pipe system. This water system includes a properly designed 222 circulating pump, a 223 check valve. The role of the interconnected water system is to ensure that the modularly deployed soil probes form a closed water system prior to hydrogen recharge.

[0055] The hydrogen feed tube 224, which is connected to the hydrogen discharge 116 tube of the energy conversion device 102 shown in Figure 1. This pipe system shall be designed for the energy converter design of the energy storage assembly. It is preferably made of pressed stainless steel tubing. The 225 components are controlled hydrogen gas solenoid valves.

[0056] Component 226 is a hydrogen gas pressure and temperature transducer that transmits the internal pressure and temperature to the control system.

[0057] When sizing the equipment, the loading and unloading rates of the energy stored in the soil probes must be taken into account. In addition, the capacity of the soil probes should preferably be larger than the maximum daily hydrogen production of the 102 energy conversion units.

[0058] As will be apparent to the person skilled in the art, the numerical diameter figures given in the description of soil probes above are merely preferred example embodiments, and soil probes of other diameters can also be designed.

[0059] The following is a brief description of the operation of the energy storage assembly according to the invention.

[0060] When the solar panels are generating enough electricity, the 16 inverters supply the positive and negative points of the 118, 119 energy converters with electrical voltage. The circulating pump 117 installed in the electrolyte liquid circuit operates for a period of 20 seconds, controlled by the equipment's custom-developed software. During its operation, the electrolyte fluid circulates in the closed electrolyte system and any stray hydrogen and oxygen bubbles are collected in the corresponding 106 hydrogen side and 108 oxygen side tanks.

[0061] The direct current causes gas bubbles to form on the plates 104 of the energy conversion device 102 and on the perforation edges of the plates 104. On the positive side (anode chamber) oxygen, on the negative side (cathode chamber) hydrogen. At a certain size, the gas bubbles are detached from the stainless or other corrosion resistant (and electrochemically suitable) plate and, since the system is closed, move towards the container 106 or 108. Due to the incompressible nature of the electrolyte fluid, the pressure in the system rises steadily and an inertial circulation is established, at which point the pump 117 is stopped by the control and the electrolyte fluid can circulate by gravity without circulating energy.

[0062] Due to the increasing gas volume, no additional pump energy is needed to circulate the electrolyte fluid, because the increase in pressure causes the fluid in the tanks to flow towards the energy conversion equipment, ensuring a continuous electrolyte fluid replenishment. The separation of oxygen and hydrogen is made possible by the integrated 120 PEM membrane.

[0063] The continuous direct current causes hydrogen and oxygen to flow continuously into the corresponding tanks, and as the gases produced cannot compress the electrolyte fluid, the pressure in the entire energy conversion system rises.

[0064] Solenoid 115 of the energy converter unit is connected to the pipe marked 216, which is the charging pipe of the soil probe.

[0065] The oxygen outlet valve 114 of the gas collection unit 103 of the energy conversion device 103 is controlled to be at a value greater than the hydrostatic back pressure in the soil probes. The component 226 is a hydrogen gas pressure transducer that measures the pressure in the filling tube of the internal cartridges of the soil probes.

[0066] In this operating state, the fluid and gas motions generated result in a continuous flow of hydrogen phases in the inner cartridges of the soil probes202, separating and displacing volume from the inner cartridges. The control allows one cartridge to be filled at a time, and can control the direction of the fills to the additional soil probes by controlling solenoid valves in the feed tube 225 of the inner cartridge.

[0067] The continuous flow of hydrogen from the inner cartridge 202 of the soil probe expels the groundwater out of the inner cartridge 202 into the water space 230 between the soil probe 202 and the well tubing 201 through the openings 217 in the bottom of the inner cartridge. This raises the level of groundwater in the well tubing 201, which flows through the filter surface 205 of the well tubing towards the soil and is absorbed by the soil. The charging phase can be stopped at any time using the control and restarted as required. The capacity of the soil probes used is not reduced by the cyclical nature of the charging / discharging process, provided that they are properly cleaned.

[0068] When the solar panels 101 are in operation, the harmful heat rise generated in the solar panels can be transferred to the electrolyte fluid by the cooling fluid flowing through the heat exchanger 109 and the rotation of the circulating pump 110. In this way, the temperature of the electrolyte fluid can be raised, if required. This supports better energy conversion efficiency and improves the efficiency of the solar panels.

[0069] Below is the energy recovery, energy storage assembly immersion.

[0070] The hydrogen stored in groundwater can be stored in the energy storage assembly for up to months with minimal loss due to the special geometry of the soil probes. The tube used for the internal 202 cartridges ensures that hydrogen loss is minimised. Separated hydrogen in contact with water results in minimal dissolution and loss.

[0071] To recover the energy, hydrogen content of the soil probes can be fed into a fuel cell or gas engine, under control. Since the internal cartridges of the soil probes 202 are pressurized by the entire groundwater column displaced, the pressure in the pipe 219 is always equal to the full height of the displaced groundwater column, which e.g. for soil probes of 300 m in length is about 30 bar.

[0072] If hydrogen from the soil probes is used by one of the energy recovery units, groundwater is forced from the soil through the filter 205 into the space between the well 201 and the internal cartridge of the soil probe 202, and the full hydrogen content can be recovered with no further energy input.

[0073] The minimum hydrogen pressure value is equal to the pressure at the water depth at the top of the inner cartridge202. This depth should be taken into account for the minimum hydrogen pressure requirements of energy recovery systems, in order to avoid the need for investing energy for hydrogen extraction.

Claims

CLAIMS1. A storage system for storing hydrogen in groundwater, the storage system comprises- an energy source;- an electrolysis unit for water electrolysis using energy of the energy source, said electrolysis unit having an anode chamber and a cathode chamber, wherein the anode chamber is configured to accommodate oxygen-producing oxidation reaction of water and equipped with a first inlet and a first outlet; the cathode chamber is configured to accommodate hydrogen-producing reduction reaction of water and equipped with a second inlet and a second outlet;- at least one soil probe constructed in a geologically suitable host formation, the soil probe comprises an object defining an interior space filled with groundwater up to a level of groundwater in the host formation, the object further comprising a sidewall closed at the bottom and an outlet in said sidewall formed below the level of groundwater in the vicinity of said level of groundwater, and a cartridge having a closed end, an open end opposite the closed end, and a closed sidewall extending between said ends, wherein the ends and the sidewall together form a cartridge space; the cartridge is mounted inside the object below the level of the groundwater in a position in which said closed end is closer to the level of groundwater than said open end, and the sidewall of the cartridge is perforated near the open end;- a circulating pump with a pump inlet and a pump outlet, wherein the pump inlet is in fluid communication with the interior of the object via a pipe that terminates below the level of groundwater, the pump outlet is in fluid communication with the second inlet of the cathode chamber via a pipe, and to form a closed circulation system, the second outlet of the cathode chamber is in communication with the cartridge space via a pipe passing through the closed end of the cartridge;wherein the cartridge is configured to retain gaseous hydrogen produced in the cathode chamber during the operation of said electrolysis unit against hydrostatical pressure of the groundwater.

2. The storage system according to claim 1, characterized in that the energy source is an alternative energy source selected from a group consisting of solar plants, geothermal plants, wind farms, biomass plants.

3. The storage system according to claim 1 or 2, characterized in that the closed end of the cartridge is constructed as a section with an internal cross-section that gradually increases towards the open end of said cartridge.

4. The storage system according to any one of claims 1 to 3, characterized in that an outlet of the pipe passing through the closed end of the cartridge is formed as an outlet facing substantially to the sidewall of the cartridge.

5. The storage system according to any one of claims 1 to 4, characterized in that the cartridge is further equipped with a discharge stub at the closed end thereof, said discharge stub is in communication with the cartridge space and is distinct from the pipe passing through the closed end of the cartridge.

6. The storage system according to any one of claims 1 to 5, characterized in that said soil probes of the storage system are arranged apart from each another by a set distance, the distance being determined by geological conditions of the host formation.

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