Submerged water energy storage system

Abstract

An underwater energy storage system includes a submerged storage reservoir configured to receive and store a lower-density fluid while operating in a first operating mode and, while in a second operating mode, passively supply the stored lower-density fluid to a downstream application. The underwater energy storage system also includes an energy storage control system coupled to the submerged storage reservoir configured to alternate the submerged storage reservoir between the first and the second operating modes based on a qualifying event.

Description

Submerged Water Energy Storage SystemCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application Serial Nos. 63 / 549,315 and 63 / 564,459, filed February 2, 2024, and March 12, 2024, respectively, entitled “DEEP-SEA FRESHWATER STORAGE AND DELIVERY” and “SUBMERGED WATER ENERGY STORAGE SYSTEM”, the disclosures of which are incorporated herein by reference.TECHNICAL FIELD

[0002] This invention relates to a system and method for storing energy. In some embodiments, this invention relates to an underwater energy storage system and method for storing and passively supplying a pressurized fluid to a downstream application.BACKGROUND

[0003] In the United States, there are more than 20 billion acre-feet of freshwater (reservoirs, lakes, and rivers) and virtually unlimited supplies of seawater (oceans) that can provide the nation with generally reliable supplies of water for drinking, agriculture, cooling, energy production, manufacturing, and other water-intensive processes. Generally, coastal facilities intake over 430 million acre-feet from natural water bodies to suit their production needs. A subset of these facilities, desalination plants, generally take in and desalinate seawater to produce freshwater. However, when electricity rates are high, production of freshwater may be inefficient. For example, throughout the course of a day, electricity rates often fluctuate based on an amount of electricity being consumed. At night, for instance, rates may be lower as most individuals are resting. Alternatively, during the day, rates may increase as individuals go to work and utilize devices that consume large amounts of electrical energy. Rates may further fluctuate based on the use of renewable energy generators, such as solar panels, wind turbines, or other renewable energy systems whose power supplies fluctuate with natural renewable processes such as when the sun is shining or the wind is blowing. As rates increase, the costs associated with the production of freshwater also increase. In turn, this may lead to increased costs being passed on to consumers. Therefore, what is needed is a desalinationstorage and delivery system with electrical rate awareness for actively producing freshwater during periods of low rates and passively producing freshwater during periods of high rates. This may ensure freshwater is produced in a more cost-effective and efficient manner.

[0004] Further, during power outages and equipment malfunctions, freshwater production may become halted or otherwise slowed. In turn, this may negatively impact any number of downstream activities that depend on the production of freshwater such as irrigation, mining, energy production, and residential operations. Depending on the severity of the shutdown, this may pose problematic to any number of industries. Therefore, what is needed is a desalination storage and delivery system capable of effectively and efficiently providing freshwater during such power interruptions and equipment failures. This may protect any number of consumers and industries that utilize and depend on freshwater.SUMMARY

[0005] In one embodiment, an underwater energy storage system is disclosed. The system includes a submerged storage reservoir configured to receive and store a lower-density fluid while operating in a first operating mode and, while in a second operating mode, passively supply the stored lower-density fluid to a downstream application. The system also includes an energy storage control system coupled to the submerged storage reservoir configured to alternate the submerged storage reservoir between the first and the second operating modes based on a qualifying event.

[0006] In another embodiment, an underwater energy storage system includes a lower- density fluid supply configured to receive a flow of seawater to produce a flow of freshwater, and wherein, in a first operating mode, the flow of freshwater is produced at a first fluid flow rate and, in a second operating mode, at a second fluid flow rate. In this embodiment, the system also includes a submerged storage reservoir fluidically coupled to the lower-density fluid supply, the submerged storage reservoir configured to, while in the first operating mode, receive and store the flow of freshwater, and, while in the second operating mode, receive the flow of freshwater at the second flow rate and passively provide the stored freshwater to a downstream application. The system also includes an energy storage control system configured to switch between the first and second operating modes based on a qualifying event.

[0007] Additionally, a method of storing and producing a flow of lower-density fluid from a submerged storage reservoir is disclosed. In one embodiment, the method includes receiving a first flow of lower-density fluid at a first fluid flow rate from a lower-density fluid supply located proximate to a seafloor and storing the first flow of lower-density fluid within an expanding body of the submerged storage reservoir. The method also includes receiving a second flow of lower-density fluid at a second fluid flow rate from the lower-density fluid supply, and in response to receiving the second flow of lower-density fluid, passively supplying the stored lower-density fluid to a downstream application.

[0008] In another embodiment, an underwater energy storage system includes a compressible and expandable storage reservoir physically coupled to a seafloor configured to, in a first operating mode, receive a flow of lower-density fluid from a lower-density fluid supply fluidically coupled to the compressible and expandable storage reservoir, and, in a second operating mode, store the received flow of lower density fluid within a body of the compressible and expandable storage reservoir. In this embodiment, the system also includes an energy storage control system coupled to the compressible and expandable storage reservoir configured to switch operating modes based on a qualifying event.BRIEF DESCRIPTION OF THE DRAWING

[0009] Fig. 1 is an underwater energy storage system in accordance with embodiments of the present invention.

[0010] Fig. 2 is an energy storage control system in accordance with embodiments of the present invention.

[0011] Fig. 3 is a method of controlling an underwater energy storage system in accordance with a detected qualifying event in accordance with embodiments of the present invention.

[0012] Fig. 4 is another method of controlling an underwater energy storage control system in accordance with a detected qualifying event in accordance with embodiments of the present invention.

[0013] Fig. 5 is another underwater energy storage system in accordance with embodiments of the present invention.

[0014] Fig. 6 is another underwater energy storage system in accordance with embodiments of the present invention.

[0015] Fig. 7 is another embodiment of an underwater energy storage system in accordance with embodiments of the present invention.

[0016] Fig. 8 is a chart comparing a duration of freshwater supply versus an onshore delivery rate for different subsea freshwater storage capacities in accordance with the present invention.DETAILED DESCRIPTION

[0017] In an embodiment, an underwater energy storage system and method are disclosed for storing hydrostatic potential energy in the form of a pressurized lower-density fluid and passively supplying the lower-density fluid to a downstream application, e.g., turbine, coastal facilities, submerged processing plants, seawater mining operations, ocean thermal energy conversion facilities, ocean carbon capture facilities, offshore hydrogen facilities, ecosystem restoration facilities, etc. In the present disclosure, the term “passively” is meant to refer to the leveraging of a higher-density fluid, e.g., seawater, and a lower-density fluid, e.g., desalinated water, wastewater, surface water, oil, etc., to displace or otherwise deform parts, liquids, or materials. However, while an underwater energy storage system of the present disclosure may operate passively to supply a flow of lower-density fluid to a downstream application without the assistance of a pump, in some embodiments, the system may use one or more pumps to augment the passive supply of lower-density fluid to the downstream application. In the present disclosure, an underwater energy storage system may include a lower-density fluid supply device, a pipeline subsystem, a valving subsystem, a storage reservoir, and, in some examples, an electrical assembly and an energy storage control system for generating and providing pressurized fluid or electrical power to a downstream or electrical application.

[0018] While a plurality of operating modes of the present system will be discussed, it is to be understood that any number of operating modes may be used. Further, while the present disclosure will proceed with a lower-density fluid supply in the form of a freshwater supply device, e.g., OceanWell’s submerged reverse osmosis (SRO) desalination pod, it is to be understood that other forms of lower-density fluid supply devices may be used as well, e.g., on-shore desalination facilities and sea-level or submerged vessels storing one or more lower- density fluids in the form of desalinated water, wastewater, surface water, oil.

[0019] In some embodiments, in a first operating mode, the freshwater supply device receives a flow of seawater, filters out or desalinates unwanted particulates and minerals fromthe flow of seawater to produce freshwater, and provides the freshwater to a storage reservoir, e.g., one or more bladder(s), accumulators, displacement tanks with a piston or plunger assembly, etc., along a pipeline subsystem. As the flow of freshwater is received, the storage reservoir may expand or otherwise deform. In some embodiments, as the freshwater is being stored, freshwater may also be simultaneously supplied to a downstream application along a pipeline. In a second operating mode, the freshwater supply device may operate at a reduced level to allow the storage reservoir to function as a passive displacement pump leveraging the density ratio between a surrounding body of water, e.g., seawater (SW) ( -1025 kg / m3), and a lower-density fluid, e.g., freshwater (FW) (-1000 kg / m3), to pressurize and thereby displace or deform some or all the reservoir’s parts or materials to passively deliver the stored freshwater to a downstream application, e.g., an electrical assembly, on-shore or offshore freshwater operation, etc. This may occur as the freshwater supply device supplies a reduced or in some instances a terminated stream of fresh water to the storage reservoir.

[0020] An underwater energy storage control system may switch operating modes between first and second operating modes based on a detected or undetected qualifying event. Qualifying events may include a variety of downstream pressurized fluid or electrical operations or conditions, including elevated electrical pricing, a remote operated vehicle operation, automated vehicle operation(s), pressure surges, usage surges, equipment malfunctions, increased demand, reduced electrical supply, energy supplier requests, rapid response, impending load-shedding requirements and other situations that may require additional energy or fluid during high demand or low supply periods. Such malfunctions may include detected or undetected power interruptions, equipment errors, particulate filter clogging, desalination membrane clogging or other failures, pump failures, pipeline leakages, and the like.

[0021] For example, advantageously, the disclosed system may operate during power outages to maintain a steady flow of freshwater to a downstream application when a pump of a lower-density fluid supply is rendered inoperative, or electricity is otherwise unavailable. Further, a storage reservoir of the present system may passively alleviate pressure surges or water hammering to protect against pipeline damage, and, during load shedding operations, may allow for a steady or consistent flow of freshwater to a downstream application during periods of variable supply into the system. Finally, in some examples, the disclosed system may act as an emergency storage supply for lower-density fluid during pipeline failures. Forexample, a storage reservoir of the present system may be unhinged, untethered, or otherwise released from the seafloor and allowed to passively float to the surface with the lower-density fluid.

[0022] In some examples, generated electricity from the present system may also increase operational revenue and value to an electrical grid. Representative qualifying events may be detected or otherwise determined through an energy storage control system as will be discussed below. However, it is also contemplated that pressurized fluid and electrical power may also be passively supplied without detecting a qualifying event. For example, as noted above, it may be desirable to generate a consistent supply of pressurized fluid or electricity as part of an onshore or off-shore supplier operation. Additionally, if a supply of freshwater to the storage reservoir is halted or otherwise slowed due to a power failure, such reservoir may automatically supply freshwater to a downstream application without having to detect a qualifying event. This may occur without requiring a powered pump due to a density differential between seawater and freshwater. In these examples, an energy storage control system may include a control signal generator configured to modify an operating position of one or more valve(s) positioned along a fluid pathway between a lower-density fluid supply, storage reservoir, and one or more downstream applications.

[0023] In some example, as compared to conventional pumped storage hydropower (PSH) systems, the disclosed underwater energy storage system may operate as a subsea reverse osmosis (SRO) enabled pumped storage hydropower (PSH) system that can store and release energy via load shedding by recharging a subsea reservoir with desalinated water and then generating electricity using natural hydrostatic pressure to passively push the desalinated water through a turbine-generator. This may allow for a continuous supply of pressurized fluid or renewable energy without the required physical infrastructure, initial capital costs, operation and management (O&M) costs, and deployment time of traditional PSH systems. For example, conventional PSH systems require elevated geographies with multiple reservoirs, liners, and onshore powerhouses. This is a costly and time-intensive endeavor that is largely limited to high-lying and rural areas. The underwater energy storage system of the present disclosure may be deployed, installed, and developed much more quickly to meet future demands more easily. Specifically, the present system may include modular, distributed storage reservoirs and portable supply devices capable of being deployed underwater at any number of locations. The system, once deployed, may be anchored to the seafloor and, through a buoyant design, readilymaintained and operated. Specifically, a density difference between stored lower-density fluid and the surrounding seawater may create a natural buoyancy that enables the system to store and provide energy. Its modular, subsea operation also relaxes many siting constraints, opening up new energy storage opportunities for coastal communities and offshore renewables, such as wind and wave power.

[0024] Additionally, the present system may also provide an environmentally friendly solution for supplying renewable energy. For example, once placed in seawater, a freshwater supply device of the present system may receive and desalinate the seawater to produce a steady flow of freshwater for a downstream storage reservoir and, in turn, an uninterrupted supply of freshwater for a downstream application for an extended period of time. During that period, repair or replacement of equipment or components may be carried out, power may resume, electrical rates may decrease, peak freshwater demand may subside, or other conditions may change to enable resumption of freshwater storage. Downstream applications may include any number or types of application, e.g., residential, commercial, water turbines, and the like. In an especially useful embodiment, such passive supply of freshwater may automatically operate during times of elevated electrical pricing. Doing so can reduce costs and energy requirements associated with producing freshwater, and, over time, provide significant commercial and environmental benefits.

[0025] This process may eliminate or reduce reliance on natural water resources, such as the Colorado River, while also mitigating environmental concerns stemming from land-based infrastructures, e.g., dams, powerhouses, etc. For example, the proposed system may operate without environmental and ecological barriers, e.g., dams, powerhouses, etc., which can be detrimental to fish, organisms, etc. Further, the disclosed system minimizes environmental impacts with its life-safe circulation system, eliminates climate risks because it is submerged, and solves operation / maintenance challenges with its buoyant design. Notable, the SRO- enabled PSH technology requires no land, and because it operates deep in the aphotic zone of the ocean where bioactivity is low and a threat to organisms is mitigated, it is naturally protected from surface-related risks such as fouling, algal blooms, sea level rise, droughts, floods, wildfires, and extreme weather.

[0026] The proposed technology leverages the density difference between freshwater ((-1000 kg / m3) and seawater (-1025 kg / m3) and the hydrostatic pressure of the ocean at about 400 m deep (-600 psi) to fill and drain a modular array of freshwater accumulatortanks / bl adders located underwater, anchored to the seafloor - i.e., the subsea reservoir, which stores energy in the form of pressurized freshwater. Due to the density difference, about 2.5 m of added pressure head is produced from every 100 m of ocean depth. During periods of high demand, stored freshwater is released from the subsea reservoir, where the weight of the seawater column above it acts as a passive displacement pump that pushes freshwater to a downstream application. During periods of low demand, the subsea reservoir is recharged with freshwater produced via SRO, which uses up to 50% less energy to desalinate seawater than conventional land-based systems. This ocean-based system will result in a reliable, scalable energy storage solution that is not restricted to landforms with favorable geotechnical features. Furthermore, the disclosed system and method avoid the depletion of vital freshwater resources for PSH applications because it also creates a new source of freshwater.

[0027] Moreover, the present system’s variable subsea location and size may allow for a greater degree of flexibility. For example, variable storage volumes and submersion depths may allow for differing amounts of power. Specifically, as noted above, conventional PSH systems typically require two land-based reservoirs, one near the top of a mountain and another near the base. The power required to pump water up the mountain, or similarly the electricity that may be generated down the mountain, can be expressed as:P = q Ap Q (Eqn. 1)

[0028] Where q is the process efficiency, Q = dV / dt and is the volumetric flow rate, and Ap = pgAH and is the differential pressure between the upper and lower reservoirs. With respect to Ap, p is the density of the working fluid (e.g., for fresh water, -1000 kg / m3), g is the acceleration due to gravity, and AH is the elevation difference between the two reservoirs. As a result, the stored capacity and available energy of conventional PSH is often limited by the natural topography of the system, i.e., the volume and elevation changes are fixed parameters that make siting, construction, and future expansions difficult, if not impractical.

[0029] For the present system, the power required to pump a lower-density fluid into a storage reservoir or the electricity generated as lower-density fluid passively rises to the surface can be expressed by Eqn. 1, above. However, in the present system, Ap = pgAH and is the pressure differential induced by the hydrostatic head:AH=D (psw / pfw -1) (Eqn. 2)

[0030] Here, D is the depth of the storage reservoir and psw / pfw is the density differential between ambient working fluids, e.g., seawater (psw) and freshwater (ptw). As shown in Eqns. 1 and 2, the underwater energy storage system is a more flexible energy storage solution — the storage capacity and available power can be increased by increasing a depth or volume of a storage reservoir of the system. By adding more subsea storage reservoir(s), e.g., bladders, or operating deeper in the ocean with increased pressure, the present system can scale to numerous downstream applications.

[0031] Fig. 1 illustratively shows an underwater energy storage system in accordance with embodiments of the present invention. As shown, system 100 operates at or close to seafloor 124 or sufficiently below sea level 116 to allow for a passive displacement of lower-density fluid from a storage reservoir 104. It is to be understood that system 100 may operate in any number of water sources such as ocean water, seas, gulfs, bays, estuaries, reservoirs, lake water, river water, or pond water. Nearly any suitably dense body of water, including brackish or saline water, may be used in accordance with the present invention. Moreover, while components of system 100 are shown on the seafloor, it is contemplated that such components may operate at sea-level, above sea-level, or in the aphotic zone or other zones as well, e.g., 50, 100, 200, 300, 400, 500, 600... 10,000 meters below sea level 116. In some embodiments, such components may be tethered or otherwise connected to seafloor 124 and operate at numerous depths. As noted above, this may allow for a more flexible system depending on a desired energy output.

[0032] System 100 illustratively includes an electrical assembly 106 for producing a flow of electricity, a lower-density fluid supply 102 for supplying a lower-density fluid, a pipeline subsystem 112 for transporting the lower-density fluid, a storage reservoir 104 for storing and passively supplying the lower-density fluid to electrical assembly 106, electrical wiring 114 for transporting electrical power, and an energy storage control system 110 for regulating between active and passive delivery of a lower-density fluid.

[0033] While system 100 illustratively includes electrical assembly 106 and electrical wiring 114, in some embodiments, system 100 may operate without electrical assembly 106 and wiring 114. For example, it may be desirable for system 100 to supply a lower-density pressurized fluid to a downstream application without generating electricity. In these embodiments, system 100 may include lower-density fluid supply 102, storage reservoir 104, and pipeline subsystem 112 for actively and passively transporting energy in the form ofpressurized fluid to downstream application 108. In these embodiments, a lower density fluid may be supplied to reservoir 104 in a first operating mode, and, in a second operating mode, passively supplied along pipeline 112 from reservoir 104 to downstream application 108 (not shown).

[0034] Similarly, in some embodiments, it may be desirable to produce electricity and pressurized lower-density fluid. In these embodiments, system 100 may include the components set forth in Fig. 1 along with additional pipeline between reservoir 104 or electrical assembly 106 and downstream application 108 for actively and passively transporting a pressurized lower-density fluid. In this manner, energy in the form of electricity and pressurized fluid may be simultaneously provided to a downstream application.

[0035] Further, while supply 102, storage reservoir 104, and assembly 106 are shown adjacent to each other near seafloor 124, in other embodiments, assembly 106 may be located at differing depths or even onshore. Specifically, in some embodiments, it may be desirable to have onshore power generation as reservoir 104 collapses and a pressure head thereof drives an onshore turbine of assembly 106. Whether assembly 106 is positioned on-shore or off-shore may be based on many factors including a distance to the surface and shore, relative cost of pipe and cables, projected maintenance requirements and frequency, and cost and availability of onshore real estate. Similarly, while downstream application 108 is illustratively shown onshore, it is contemplated that it, or components thereof, may also be included at or below sea level 116.

[0036] Lower-density fluid supply 102 may include a desalination pod with filters, motors, pumps, internal fluid passageways, and reverse osmosis membranes for producing freshwater. In these embodiments, supply 102 may receive a flow of seawater through an intake system of the device, filter out unwanted particulates from the seawater, and remove salt and other undesirable minerals to provide freshwater to reservoir 104. Alternatively, in other embodiments, fluid supply 102 may include a storage vessel or reservoir 104 with one or more types of stored lower-density fluid, e.g., desalinated water, wastewater, surface water, oil, etc. In these embodiments, supply 102 may include an enclosure with internal fluid passageways, pumps, and motors for supplying the stored lower-density fluid to storage reservoir 104.

[0037] In operation, fluid supply 102 may provide a flow of lower-density fluid to storage reservoir 104 at differing rates depending on the operating characteristics of fluid supply 102. For example, in a first operating mode, fluid supply 102 may provide a high rate of lower-density fluid to reservoir 104 so that reservoir 104 is able to expand its capacity and store the lower-density fluid. This may result as control system 110 drives one or more motors and pumps of supply 102 at heightened operating characteristics. In a second operating mode, fluid supply 102 may provide a diminished or negligible amount of lower-density fluid to reservoir 104 so that reservoir 104 passively supplies the stored lower-density fluid to electrical assembly 106. As the lower-density fluid is received, a turbine of assembly 106 may rotate to drive a generator coupled thereto and, in turn, produce electricity along electrical wiring 114 for downstream application 108. In some embodiments, the second flow rate may be selected to prevent “salt-up” or unwanted particulates from clogging or otherwise accruing on reverse osmosis membranes of liquid supply 102 while still allowing for the passive supply of a lower- density fluid.

[0038] Pipeline subsystem 112 may include entry and outgoing pipelines for fluidically coupling fluid supply 102, electrical assembly 106, storage reservoir 104, and, in some embodiments, downstream application 108. Through pipeline subsystem 112, fluid supply 102, storage reservoir 104, assembly 106, and downstream application 108 may be in fluid communication with each other. In operation, pipeline subsystem 112 may be filled with a lower-density fluid that is pressure-balanced with the external environment (ambient pressure seawater), such that there is a minimal pressure differential across the thickness of a pipeline wall. Depending on the desired lower-density fluid operation, subsystem 112 may include piping of differing lengths, types, sizes, and shapes. Further, any number of pipelines may be used in accordance with the present invention. Moreover, as shown in Fig. 7, it is also contemplated that pipeline subsystem 112 may include a valving system that regulates the flow of lower-density fluid through system 100. Such valve(s) may include one-way valves, multidirectional valves, etc.

[0039] Electrical wiring 114 may include entry and outgoing cables for electrically coupling a generator of electrical assembly 106 to downstream application 108, e.g., storage device 120 or electrical grid 112. For protection, such cables 114 may include a variety of sheaths and insulation to protect the conductive wiring enclosed therein. Depending on a desired deployment site, such sheaths and insulation may have varying thicknesses and include any number of layers.

[0040] As noted above, in a first operating mode, storage reservoir 104 receives and stores a lower-density fluid from fluid supply 102 and, in a second operating mode, passivelytransmits the stored fluid to electrical assembly 106 or, in some embodiments, downstream application 108. In this manner, reservoir 104 may act as both a storage vessel for a lower- density liquid and as a passive displacement pump for supplying the lower-density fluid to electrical assembly 106 or downstream application 108. To store and passively displace the lower-density liquid, reservoir 104 may leverage the density difference between seawater (SW) and the lower-density liquid (LDL) to pressurize and thereby displace or deform some or all the reservoir’s parts or materials during a first operating mode (increasing the stored volume ((storage)) or during a second operating mode (decreasing the stored volume (delivery)).

[0041] In some embodiments, reservoir 104 may include one or more deformable bladder(s), e.g., a tough flexible bag or balloon, enclosed within a protective housing directly exposed to surrounding seawater. Alternatively, reservoir 104 may include one or more cylindrical displacement tanks equipped with a piston / plunger assembly or other device to vary the cylinder volume. Depending on a desired power operation, overall storage requirements, and liquid production rates, reservoir 104 may be sized and shaped to hold any amount of lower-density fluid. Further, to prevent puncturing, reservoir 104 may be made of any material durable enough to avoid puncturing.

[0042] As illustratively shown, reservoir 104 includes an inlet and outlet 126 for receiving and passively supplying a flow of lower-density fluid. In a first operating mode, as indicated by arrow 130, a flow of lower-density fluid may be supplied from fluid supply 102 along pipeline subsystem 112 and into an expanding internal volume within reservoir 104. In a second operating mode, the internal volume of reservoir 104 may contract due to the greater density of the surrounding salt water compared to the lower density of the fluid within reservoir 104, thereby enabling reservoir 104 to serve as a passive displacement pump to supply a flow of stored fluid to electrical assembly 106 and, in some embodiments, back to lower-density fluid supply 102 or to downstream application 108. In turn, received fluid in supply 102 may be restored or passively released into the surrounding seawater. As the lower-density liquid is actively or passively received by electrical assembly 106, a turbine (not shown in Fig. 1) within a housing device of assembly 106 may convert the kinetic energy of the lower-density fluid into mechanical energy to drive a rotor of a generator (also not shown in Fig. 1). In turn, electricity may be provided to downstream application 108 along electrical wiring 114.

[0043] As noted above, electrical assembly 106 may include a turbine physically coupled to a generator within a housing device. Assembly 106 may be fluidically coupled to fluid supply102 and reservoir 104 along pipeline 112. In operation, a turbine of assembly 106 may include one or more angled blades to direct rotation for electrical production. Specifically, in either the first or second operating modes, assembly 106 may receive a flow of lower-density fluid from either fluid supply 102 or storage reservoir 104 and convert the kinetic energy of the liquid to mechanical energy to drive a generator coupled thereto. This may result in a consistent supply of electricity for downstream application 108.

[0044] However, in other embodiments, based on a configuration of pipeline 112 or assembly 106, pressurized fluid or electrical power may only be provided in a second operating mode to downstream application 108. Specifically, pipeline 112 may run directly into reservoir 104 without first passing through assembly 106. Alternatively, blades of turbine may be oriented to only allow for rotation in a second operating mode in which lower-density fluid is received from storage reservoir 104. In some embodiments, it may even be desirable to operate a generator as a motor and a turbine as a pump for facilitating movement of a stored lower- density fluid from reservoir 104 to fluid supply 102. This may be advantageous in embodiments where a lower-density fluid is provided in fixed amounts and needs to be recycled between fluid supply 102 and reservoir 104.

[0045] As discussed above, pressurized fluid and electricity may be continuously or intermittently supplied to one or more downstream applications 108. Downstream applications 108 may include an onshore or offshore pressurized fluid operation, seawater property sensor, electrical supplier, electrical storage device, power lines, etc. Any number of onshore or offshore delivery points may be used as generated pressurized fluid or electricity is wheeled across any number of locations. Further, it is to be understood that the pressurized fluid may be modified in numerous ways, e.g., using valves, flow restrictors, holding tanks, etc., and that the generated electricity may be modified in numerous ways as well, e.g., using transformers, inverters, rectifiers, etc.

[0046] Energy storage control system 110 may be used to switch between first, e.g., active, and second, e.g., passive, operating modes. For example, in a first operating mode, control system 110 may operate one or more (electro)mechanical subsystems, e.g., pumps, motors, etc., of fluid supply 102 to produce a flow of lower-density fluid at a first fluid flow rate. At this flow rate, reservoir 104 may store the received fluid within a body of reservoir 104. In turn, an internal volume of reservoir 104 may increase as more lower-density fluid is received. At the same time, reservoir 104 and electrical assembly 106 may actively supply one or moredownstream applications with pressurized fluid and electricity. Such production may be advantageous when electrical prices are low.

[0047] However, when electrical prices rise, it may be advantageous to have reservoir 104 passively supply pressurized fluid to downstream application 108 or lower-density liquid to electrical assembly 106 for cheaper electrical production. In this embodiment, control system 110 may generate one or more control signals to the (electro)mechanical subsystems of liquid supply 102 to reduce or diminish an operating capacity of fluid supply 102. As a result of the diminished fluid flow rate, a density differential between a lower-density fluid and seawater may act to displace the stored lower-density liquid to passively supply downstream application 108 or electrical assembly 106. When electrical pricing is again low, control system 110 may switch operations back to the first mode.

[0048] In addition to electrical pricing, it may also be desirable to produce electricity to assist in the prevention of load-shedding operations. For example, in periods of high demand, additional electrical sources may be needed to meet the elevated demand. In these examples, control system 110 may similarly switch operating modes to passively produce electricity using reservoir 104 without having to engage the (electro)mechanical subsystems of liquid supply 102. As a result, reservoir 102 may act as a subsea battery storing hydrostatic potential energy in the form of pressurized lower-density liquid to meet fluctuating electricity rates, blackouts, increased demand, etc.

[0049] Fig. 2 is an energy storage control system 200 in accordance with embodiments of the present invention. While one example of a control system is shown, as noted above, it is to be understood that a control system of the present invention may take a variety of different forms and include additional or fewer components. However, as shown, control system 200 illustratively includes an electrical pricing module 202, a load shedding module 222, an emergency supply module 296, a pressure surge module 209, ROV module 292, timing logic 240, volume logic 236, a control signal generator 216, controller(s) / processor(s) 218, I / O device(s) 234, communication system 238, data storage / memory 242, and other modules and logic 220. It is to be understood that system 200 and components thereof may be stored remotely on server(s) 276 via network 290, or locally within fluid supply 217, reservoir 219, electrical assembly 106, downstream application 108, etc.

[0050] While a singular server 276 is shown, it is to be understood that control system 200 may be located across multiple servers as well. Moreover, it is to be understood that any or allmodules and logic of system 200 may be stored as computer readable instructions on non- transitory data storage / memory 242 that, when executed by controller(s) / processor(s) 218, causes controller(s) / processor(s) 218 to perform the computer-implemented steps described in the present application. System 200 may take the form of any software or hardware capable of carrying out the functions described herein. Moreover, any components of system 200 may be communicatively coupled via a bus. Other components may be included as well such as any number of drivers, operating systems, network settings, location systems, power supplies, etc.

[0051] Communication system 238 may include any type of wired or wireless components that allow system 200 to communicate with server 276, reservoir 219, electrical assembly 106, fluid supply 217, and components thereof. Such communications protocols and corresponding components, e.g., transceivers, antennas, etc., will be familiar to those of ordinary skill in the art. I / O device(s) 234 may include display devices, buttons, etc. for receiving user inputs and displaying information.

[0052] In operation, control system 200 may switch operating modes of an underwater energy storage system, e.g., system 100, through the generation of one or more control signals using control signal generator 216. For example, module(s) 202 and 222 or timing logic 240 may detect a qualifying event or an exceeded threshold period of time and direct control signal generator 216 to generate one or more control signals to modify an operating parameter of (electro)mechanical subsystems 262, e.g., motor(s), pump(s), etc., of fluid supply 217. In so doing, fluid supply 217 may be operated in a diminished state to allow lower-density liquid to passively pass into electrical assembly 106 from reservoir 219 or to downstream application 108

[0053] Referring now to electrical pricing module 202, module 202 illustratively includes electrical pricing logic 204, predictive pricing logic 206, historical pricing logic 208, operating parameter logic 210, threshold logic 214, and other forms of logic 212 for determining or predicting electrical prices and a corresponding operating parameter thereof. For purposes of the present disclosure, electrical pricing information may be measured in price per kWh and correspond to electrical rates used to supply system 100, downstream application 108, or any other local rates or prices. Such information may be publicly available online from any number of private, public, or governmental agencies, e.g., Independent System Operators such as the California Independent System Operator (CAISO), Midcontinent Independent System Operator (MISO), ISO New England, etc.

[0054] In one embodiment, electrical pricing logic 204 may query or otherwise obtain electrical pricing information 280 from server 276 or local memory 242. As information is received, historical logic 208 may index or otherwise store such pricing information in memory 242. Once received, the pricing information may be provided to threshold logic 214. In turn, threshold logic 214 may compare the received electrical price to a stored threshold price, and based on the comparison, generate an output for operating parameter logic 210. Based on the received output, operating parameter logic 210 may determine an operating parameter for system 100. Corresponding parameters may be stored locally or remotely and take the form of a table setting forth a range of operating parameters for (electro)mechanical subsystems based on differences between the received price and the threshold price. However, in other examples, received pricing information from pricing logic 204 may be directly compared to stored operating parameters without being compared to a stored threshold price. In this example, a table may set forth a range of prices and corresponding operating parameters of (electro)mechanical subsystems of system 100.

[0055] Once one or more parameters are identified, operating parameter logic 210 may generate an output to control signal generator 216 indicative of the identified parameters. Once received, control signal generator 216 may generate one or more control signals for electromechanical or mechanical subsystems 262, e.g., motors, pumps, and the like, of supply device 217 to operate system 100 at the identified parameters. As noted above, this may switch system 100 from a first, active, to a second, passive, operating mode and vice versa.

[0056] In some embodiments, predictive pricing logic 206 may predict or otherwise forecast electrical pricing information based on stored pricing information. For example, as historical logic 208 stores pricing information over time, predictive logic 206 may identify patterns or trends in the information to predict future electrical prices. Such calculations may use weighted averages or other forms of statistical analysis to predict such trends. Based on the predicted price, an output may be sent to control signal generator 216 to modify an operating parameter in advance of any actual changes in price.

[0057] Outside of electrical pricing information, control system 200 may also modify an operating parameter of system 100 to assist with, or otherwise prevent, a load shedding operation. For example, system 200 may include load shedding module 222 for detecting an impending load shedding operation and determining a desirable operating parameter of system 100. Module 222 illustratively includes electrical load detection logic 224 for monitoring anelectrical load across a grid, surge detection logic 226 for detecting rapid supply and demand changes, threshold logic 230 for comparing the received load and surge information to stored threshold values, and operating parameter logic 228 for determining corresponding operating parameters of system 100.

[0058] In operation, electrical load detection logic 224 may query or otherwise obtain electrical load information for a desired grid from server 276 or local memory 242. Electrical load information may indicate the demand, or load, on an electrical grid at any given time. Information may be retrieved online from any number of private, public, or governmental websites or other datastores. As information is received, such information may be indexed or otherwise stored within memory 242. Once received, the load information may be provided to threshold logic 230 for comparing to threshold load values. Such comparison may indicate that demand is currently, or about to, exceed an available electrical supply. Alternatively, such comparison may indicate that the demand is well within the electrical power supply.

[0059] Based on the comparison, threshold logic 230 may generate an output for operating parameter logic 228 indicative of the comparison. From the comparison, operating parameter logic 228 may determine one or more corresponding operating parameters of system 100, e.g., fluid supply device 217, reservoir 219, electrical assembly 221, etc. Corresponding parameters may be stored locally or remotely and take the form of a table setting forth a range of operating parameters for (electro)mechanical subsystems based on the threshold comparison.

[0060] In turn, operating parameter logic 228 may generate an output to control signal generator 216 indicative of the identified parameters. Once received, control signal generator 216 may generate one or more control signals to (electro)mechanical system 262 to operate system 100 at the identified parameters. As noted above, this may switch system 100 from a first, active, to a second, passive, operating mode, and vice versa.

[0061] Additionally, in some embodiments, surge detection logic 226 may receive and track the load information over time to predict sudden surges in supply and demand. For example, using statistical analysis on stored load information within data storage 242, surge detection logic 226 may detect sudden jumps or increases, e.g., sudden deviations from an average load increase or decrease, and preemptively detect an impending load shedding operation. Such increases may include abnormal load increases that fall outside of daily load fluctuations. As a result, in some embodiments, surge detection logic 226 may preemptively send an output to operating parameter logic 228 in advance of a load shedding operations.

[0062] Outside of electrical pricing information, control system 200 may also modify an operating parameter of system 100 based on a qualifying event in the form of a malfunctioning part, power outage, or leakage. For example, control system 200 may include emergency supply module 296 for detecting a malfunctioning part, power outage, or leakage. Based on such event, module 296 may modify an operating parameter of system 100 to allow for an active or passive delivery of freshwater or electricity. Specifically, based on received sensor signals, e.g., from sensor(s) 258, 256, and 244, module 296 may identify a malfunctioning part, power interruption, or leakage and instruct control signal generator 216 to modify an operating parameter of device 217 to switch from active to passive delivery of freshwater or vice versa. In one embodiment, modifying an operating parameter may include placing supply device 217 in an idle or standby mode while freshwater is passively supplied from reservoir 219. Once resolved, module 296 may place device 217 in a default or active operating mode in which freshwater is stored within reservoir 219. Sensor(s) 258, 256, and 244 may include optical sensors, e.g., cameras, infrared, etc., flow rate sensors, pressure sensors, acoustic sensors, or any other type of sensor capable of detecting a malfunction, leakage, pressure surge, power interruption, etc.

[0063] Emergency supply module 296 may in some embodiments include supply device error logic 298, power outage detection logic 201, pipeline interruption logic 203, operating parameter logic 205, and other logic 207 for identifying a qualifying event in the form of a malfunctioning part, leakage, or power outage. In operation, supply device logic 298 may receive one or more signals from sensors, e.g., sensors 246, identify a malfunctioning component of device 217, and generate an output for operating parameter logic 205. Operating parameter logic 205 may then determine one or more operating parameters of device 217 based on the identified malfunctioning part and generate an output for control signal generator 216 to modify an operating parameter of one or more subsystems 262. This may place device 217 in an active or passive state.

[0064] In addition to detecting malfunctioning parts, power outage detection logic 201 and pipeline interruption logic 203 may receive sensor signals and detect a power interruption and pipeline leakage, respectively. Based on an identified interruption or leakage, operating parameter logic 205 may identify operating parameters for one or more subsystems 262 and generate an output for control signal generator 216 to modify parameters of subsystems 262. For pipeline leakage, system 100 may be placed in a reduced operating state so as to conservepower and not continuously supply freshwater to surrounding seawater. Once remedied, system 100 may return to a normal operating state.

[0065] In some embodiments, a qualifying event may also include a pressure surge. As illustratively shown in Fig. 2, control system 200 includes pressure surge detection module 209 for detecting such a surge and identifying corresponding operating parameters of device 217. Specifically, surge detection logic 211 may receive signals from one or more sensors, e.g., sensor(s) 246, identify an existing pressure surge, and provide an output for operating parameter logic 213 to identify corresponding operating parameters of subsystems 262. Once identified, outputs may be provided to control signal generator 216 to modify such subsystems accordingly.

[0066] Further, as shown in Fig. 2, control system 200 includes ROV module 292 for identifying a ROV operation and modifying an operating parameter of one or more subsystems 262 based on the operation. For example, prior to an ROV operation, it may be desirable to ensure reservoir 219 is filled with freshwater prior to engaging with an ROV. As such, module 209 may identify such operation through one or more received sensor signals from sensor(s) 244 and ensure that reservoir 219 is full prior to engaging with a ROV. Necessary inputs may be received remotely from a remote source through communication system 228.

[0067] Moreover, outside of detected qualifying events, in some embodiments, control system 200 may modify an operating parameter of system 100 based on a passage of time. For example, timing logic 240 may receive one or more sensor signals from a clock, timer, or sensor(s), e.g., sensors 244, 256, or 258, and detect how long system 100 has been operating under a particular parameter. Using stored threshold times within data storage 242, timing logic 240 may automatically provide an output for control signal generator 216 to modify such parameters if a threshold time period is reached or exceeded. Sensor(s) 244, 256, and 258 may include any number or type of sensors, e.g., imaging sensors, pressure sensors, flow rate sensors, etc. capable of detecting operating parameters of system 100.

[0068] Finally, in some embodiments, it may be desirable to modify an operating parameter of system 100 based on an amount of stored lower-density fluid within reservoir 219 or a positioning of a piston and plunger assembly associated thereon (shown in Fig. 7). This may serve to ensure that reservoir 219 or a piston and plunger assembly is not over or under expanded or extended. In operation, volume logic 236 of system 200 may receive one or more sensor signals from sensor(s) 244 indicative of a stored volume of lower-density fluid,determine an amount of stored fluid based on such signals, and generate a corresponding output for control signal generator 216. Such determination may for example indicate a reservoir 219 capacity of >50%, >60%, >70%, >80%, >90% or >99%. Sensor(s) 244 may be internally or externally fixed to a body of reservoir 219, a piston or plunger assembly, or other components and include strain gauges or any other form of sensor capable of detecting a volume of freshwater or a positioning of a piston and plunger assembly located thereon.

[0069] While control system 200 is illustratively shown with different types of modules and logic for detecting electrical pricing, equipment malfunctions, pressure surges, operating volumes or positions, and ROV operations, it is contemplated that additional qualifying events may be detected as well through other modules and logic 220.

[0070] Fig. 3 is a method of controlling an underwater energy storage system in accordance with a detected qualifying event in accordance with embodiments of the present invention. As shown, method 300 begins at block 302 where a control system, e.g., system 200, detects a current operating mode of an underwater energy storage system, e.g., system 100, based on one or more received sensor signals. Such signals may be provided from any or all types of different sensors, e.g., sensor(s) 244, 256, and 258, and indicate a current operating parameter of the underwater energy storage system, e.g., whether the system is operating in a first, active mode 304 or second, passive mode 306. However, other information 308 may be provided as well. Next, the disclosed method proceeds to block 310 where electrical pricing logic, e.g., logic 204 of control system 200, obtains electrical pricing information for a desired location. Such electrical pricing may be for a downstream application, e.g., applications 108, an underwater energy storage system, or any other desired location. Pricing information may be obtained every second 312, minute 314, or other interval 316, online or privately from any public, private, or governmental agency.

[0071] Once received, method 300 proceeds to block 318 where threshold logic, e.g., logic 214, compares the received electrical price to a threshold price. Threshold price(s) may be stored within a control system database and indicate desirable prices at different times or locations. For example, when electrical rates are low, a desired threshold price at a given time or location may be a Locational Marginal Price (LMP) of $16.33 per megawatt hour (MWH). If the received price is $16.28, threshold logic may compare and indicate a difference of $0.05 below LMP.

[0072] After comparing, method 300 proceeds to block 320 where operating parameter logic, e.g., logic 210 of control system 200, determines an underwater energy storage system, e.g., system 100, operating parameter based on the received input from threshold logic, e.g., logic 214. In this example, a received input of minus $0.05 may indicate that electrical rates are favorable and, as such, the energy storage system should operate in a first, active operating mode 322. Alternatively, if rates were higher than a desired price, such input may indicate the system should operate in a second, passive operating mode 324. However, other operating modes 326 are contemplated as well.

[0073] Once a corresponding operating parameter is determined, method 300 proceeds to block 328 where a control system generator, e.g., generator 216, receives the desired operating parameters and determines if an underwater energy storage system is currently operating under the desired parameters based on the information received in block 302. If yes, method 300 reverts back to block 310 where updated electrical pricing information is received. If no, method 300 proceeds to block 330 where a control signal generator generates one or more control signals to modify an operating parameter of the underwater energy storage system. Such signals may be provided to one or more (electro)mechanical systems, e.g., pumps, motors, etc., to switch operating modes of the underwater energy storage system. After which, method 300 reverts to block 302 where an updated operating mode of the underwater energy storage system is determined.

[0074] While the present method compares a received electrical price to a desired threshold price, in other embodiments, system 100 may operate without a threshold price in which a received electrical price is directly matched to a desired operating parameter via operating parameter logic 210. In these embodiments, received pricing information may be directly matched to an operating parameter without having to first compare the value to a stored threshold value.

[0075] Fig. 4 is another method of controlling an underwater energy storage control system in accordance with a detected qualifying event in accordance with embodiments of the present invention. As shown, method 400 is similar to method 300 except for the obtained and compared information. Specifically, rather than obtaining an electrical price, method 400 receives and compares electrical load information and compares the received information to a desired threshold load. Based on the comparison, one or more desired operating parameters of an underwater energy storage system may be determined and carried out. Similarly, whilethreshold values are compared and used to select a desired operating parameter, in other embodiments, received electrical load information may directly correspond to one or more operating parameters as well.

[0076] Fig. 5 is another embodiment of an underwater energy storage system in accordance with embodiments of the present invention. As illustratively shown, system 500 includes a first storage reservoir 502 on a platform 526, e.g., an oil or refinery platform, a second subsea reservoir 518, a drive mechanism 520, and electrical assembly 534 in a closed-loop system for recycling a lower-density fluid 528 to generate electricity. While system 500 includes electrical assembly 534, it is to be understood that, in one example, system 500 may operate to recycle fluid 528 between reservoirs 502 and 518 without assembly 534. In this example, fluid 528 may be transported and used as an energy source in any number of different applications. However, in a first operating mode, as shown, drive mechanism 520, e.g., a windmill, etc., may utilize wind energy 522 to drive a motor 530 and a pump 532 coupled thereto to displace a lower-density fluid from reservoir 502 to reservoir 518. As lower-density fluid, e.g., oil, freshwater, etc., travels along fluid path 504 to reservoir 518, such fluid 528 may be provided to electrical assembly 534 and drive a turbine and generator thereof to generate electricity along wiring 508 for a downstream application 512, e.g., battery, grid, etc.

[0077] As lower-density fluid 528 is received, reservoir 518 may expand and store fluid 528 within a body of reservoir 518. Alternatively, when wind energy is unavailable or reduced, reservoir 502 may act in a second diminished operating mode and supply a reduced amount of fluid 528 to reservoir 518. In these situations, as noted above, reservoir 518 may act as a passive displacement pump to provide the stored lower-density fluid 528 to electrical assembly 534 and back to storage reservoir 502. As such, system 500 may operate in a closed loop manner and recycle a lower-density fluid based on available wind energy.

[0078] Fig. 6 is another embodiment of an underwater energy storage system in accordance with embodiments of the present invention. As illustratively shown, system 600 includes an on-shore lower-density fluid supply 602, e.g., desalination plant 604 or other plant 606, for supplying a lower-density fluid to reservoir 618. In this embodiment, in a first, active operating mode, a lower-density fluid may be provided and stored within expanding reservoir 618. In some embodiments, while fluid is actively supplied to reservoir 618, fluid may also drive a turbine and generator of assembly 612 along a pipeline 614. This may be advantageous when electrical rates are low. Alternatively, when rates are high, supply 602 may operate in a second,reduced rate supplying a diminished amount of lower-density fluid to reservoir 618. In turn, as noted above, reservoir 618 may act as a passive displacement pump to supply stored lower- density fluid to assembly 612 and back to supply 602 or components thereof 606, e.g., energy exchangers, etc.

[0079] Fig. 7 illustratively shows another embodiment of an underwater energy storage system in accordance with embodiments of the present invention. As shown, system 700 may operate at or close to seafloor 728 or sufficiently below sea level 716 to allow for a passive displacement of freshwater from a freshwater container to a downstream application. Similar to system 100, it is to be understood that system 700 may operate in any number of water sources such as ocean water, seas, gulfs, bays, estuaries, reservoirs, lake water, river water, or pond water. Nearly any suitably dense body of water, including brackish or saline water, may be used in accordance with the present invention.

[0080] System 700 illustratively includes a lower-density fluid supply 704 for producing freshwater, a pipeline subsystem 732 for transporting freshwater, a valving subsystem 734 for controlling a directional flow of freshwater, a storage reservoir 730 for storing and passively supplying freshwater 736 or another low-density liquid to a downstream application 708, and an energy storage control system 702 for regulating between active and passive delivery of freshwater or lower density fluid. However, while supply 704 and reservoir 730 are shown adjacent each other near seafloor 728, in other embodiments, supply 704 may be located at a different depth than reservoir 730 or even onshore.

[0081] Supply 704 may for example include a desalination pod with filters, motors, pumps, internal fluid passageways, and reverse osmosis membranes for producing freshwater. However, other freshwater supply systems may be used depending on the system environment. Exemplary such devices include ultrafiltration, evaporation, distillation and other devices that will be familiar to persons having ordinary skill in the art.

[0082] In operation, supply 704 may receive a flow of seawater through an intake system of the device, filter out suspended or dissolved solids, and provide freshwater to storage reservoir 730. Supply 704 may filter out 60%, 70%, 80%, 90%, or 99% of suspended or dissolved solids from seawater. Freshwater may be provided to reservoir 730 at differing rates depending on the operating characteristics of supply 704. For example, in a first operating mode, supply 704 may supply a high rate of freshwater to reservoir 730 so that reservoir 730 is able to store the freshwater, and, in some examples, freshwater is simultaneously providedto downstream application 708. In a second operating mode, supply 704 may supply a diminished or negligible amount of freshwater to reservoir 730 so that reservoir 730 passively supplies the stored freshwater. The second flow rate may be selected to prevent “salt-up” or unwanted particulates from clogging or otherwise accruing on reverse osmosis membranes of supply 704 while still allowing for the passive supply of freshwater.

[0083] Pipeline subsystem 732 illustratively includes entry and outgoing pipeline(s) 724 and 710 for fluidically coupling supply 704, reservoir 730, and application 708. Through pipeline subsystem 732, supply 704 and reservoir 730 are in fluid communication with downstream application 708. In operation, pipeline subsystem 732 may be filled with freshwater that is pressure-balanced with the external environment (ambient pressure seawater), such that there is a minimal pressure differential across the thickness of the pipeline wall. Depending on the desired freshwater storage and production operation, pipeline subsystem 732 may include piping of differing lengths, types, sizes, and shapes. Further, any number of pipelines may be used in accordance with the present invention.

[0084] Valving subsystem 734 illustratively includes a valve 706 along pipeline 724 in fluid communication with reservoir 730 and supply 704. In operation, valve 706 may be a oneway valve that allows reservoir 730 to be filled with freshwater in a first mode of operation and, in a second mode of operation, prevents a backflow of freshwater upstream. While one valve, e.g., valve 706, is shown, it is to be understood that system 700 may include any number of valves. For instance, additional valves may be situated in pipeline 710, downstream from an outlet of reservoir 730, to further regulate a flow of freshwater to downstream application 708.

[0085] Storage reservoir 730 stores freshwater from supply 704 and passively conveys the stored freshwater to downstream application 708. In this manner, reservoir 730 may act as both a storage vessel for freshwater and as a passive displacement pump to provide freshwater to downstream application 708. To store and passively displace the freshwater, reservoir 130 can leverage the density difference between seawater (SW) and freshwater (FW) to pressurize and thereby displace or deform some or all the storage reservoir’s parts or materials during a first operating mode (increasing the stored volume (storage)) or during a second operating mode (decreasing the stored volume (delivery)).

[0086] While storage reservoir 730 is illustratively shown as a cylindrical displacement tank, it is to be understood that this is merely one illustrative embodiment. As shown, reservoir 730 includes a cylindrical displacement tank with an inlet 720 for receiving freshwater, anexpandable body 726 for storing freshwater, a piston or plunger assembly 722 for facilitating the storage and displacement of freshwater, and an outlet 718 for providing freshwater to downstream application 708. In other embodiments, reservoir 730 may be a deformable bladder, e.g., a tough flexible bag or balloon, that allows a stored volume of freshwater to increase during filling (viz., expanding the bladder’s volume) and decrease during draining (viz., contracting the bladder’s volume). Depending on desired flow rates, overall storage requirements and freshwater production rates, reservoir 730 may be sized and shaped to hold any required amount of freshwater. Further, to prevent puncturing, reservoir 730 may be made of any material durable enough to avoid puncture. Storage reservoir 730 may also be composed of an array of multiple redundant storage containers.

[0087] Piston or plunger assembly 722 includes an open top portion that interacts with seawater, a closed lower portion, and a piston or plunger. In operation, assembly 722 allows a stored volume of freshwater within body 726 to increase when filled (translating the piston or plunger outward) and decrease when drained (translating the piston or plunger inward).

[0088] In this embodiment, the pressure head and delivery flowrate provided by a simple quasistatic case of a displacement tank in the form of a cylindrical storage vessel with a linearly translating piston-style end cap can be shown by two equations. The first is:H (Eqn. 3)

[0089] where (H), reference numeral 714, is the elevation above sea level of an onshore delivery point and is the function of the depth of the seawater and freshwater interface (D), reference numeral 712, and the ratio of densities ( ) of seawater (SI / F) and freshwater (FVF). The second is:„ dV . dl .« = » = -4» <Etln 4>

[0090] where (Q) is the onshore freshwater delivery flowrate and is the function of the rate d I of change of the stored volume (dV) over time (dt). Further, (4) is the piston area and — is the piston velocity. Eqn. 4 may be used to calculate the duration (t) and capacity (F) of freshwater supplies available.

[0091] In some embodiments, a subsea depth of storage reservoir 730 may be located at or near a depth of a subsea freshwater supply, e.g., device 704, which may typically be located around (D) = 400-800 meters below sea level. In this embodiment, assuming the densities ofseawater and freshwater are psw= 1026 kg / m3and pPW= 1000 kg / m3, respectively, the elevation for the onshore freshwater delivery point is about H = 10-20 meters above sea level. Accordingly, suitably low-lying land at or near sea level may be passively provided with stored seawater without requiring powered submerged or onshore pumps. Deep sea storage beyond depths of 400-800 meters can allow for an emergency delivery of freshwater to even higher elevations. For example, subsea freshwater storage located at (D)=20,000 meters below sea level could provide passive onshore freshwater delivery at elevations of about (H)=500 meters above sea level. Therefore, it is contemplated that system 700 may be used in depths of at least about 200 meters, 300 meters, 400 meters, 500 meters, 600 meters, 700 meters, 800 meters, 900 meters, 1000 meters, or more below surface level.

[0092] In some embodiments, a barrier fluid, e.g., freshwater or any other fluid, may also be used to prevent intermixing of freshwater and seawater. For example, if a piston were to leak, freshwater within reservoir 730 may intermix with the surrounding seawater. Therefore, in some embodiments, it may be advantageous to include a barrier fluid as well. Barrier fluid may be included within a bladder or other storage vessel coupled to the piston. In this embodiment, hydrostatic pressure may act on the bladder or vessel to compress the barrier fluid and, in turn, drive the piston to displace the freshwater. If the piston were to leak, such barrier fluid may serve as a protective intermediary. However, in other embodiments, multiple bag arrangements may be used in which a bag of barrier fluid encapsulates a storage container or parts thereof. Other arrangements are contemplated herein.

[0093] Moreover, added mass or other forces to the seawater and freshwater interface of the subsea storage reservoir 730 may increase the elevation of the freshwater delivery point, depending on a loading scenario. However, the added mass effect is minimal, requiring about 500 tons to increase the elevation of the onshore delivery point an additional 1-2 meters. Alternatively, an onshore booster pump, located near the onshore delivery point, may be used to elevate the freshwater supply above the onshore delivery point on land.

[0094] Additionally, the density difference between the stored freshwater and surrounding seawater may cause a natural buoyancy. As a result, when filled with freshwater, a net positive buoyancy may be achieved for reservoir 730. In some embodiments, reservoir 730 may be anchored or moored to seafloor 728 to minimize its seabed footprint and its impact on benthic ecosystems.

[0095] As discussed above, freshwater may be continuously or intermittently supplied to one or more downstream applications 708. Downstream applications 708 may include an onshore delivery point located near an elevation above sea level at which the equilibrium pressure of the seawater and freshwater interface of subsea reservoir 730 is balanced with the equilibrium pressure of the atmosphere and freshwater interface of the onshore delivery point.

[0096] Downstream applications 708 may include coastal facilities, submerged processing plants, and onshore or offshore facilities such as ocean thermal energy conversion, ocean carbon capture, offshore hydrogen, seawater mining, ecosystem restoration, and other current and future innovations within the growing ocean economy. Additionally, downstream applications 730 may include irrigation operations and water-intensive industrial processes, e.g., mining operations, oil and gas operations, semiconductor manufacturing, irrigation, or textile manufacturing. Further applications for filtered water may include supplying a cooling system for a power plant, data center, air conditioning system or civil infrastructure.

[0097] Additionally, in some embodiments, as noted above, downstream application 708 may include a water turbine that generates electricity from flowing freshwater as it comes onshore. Thus, in this embodiment, both freshwater and electricity may be passively supplied. In a related alternative embodiment, a turbine that generates electricity from flowing freshwater may be located subsea, subsea near reservoir 730, or onshore to generate electricity locally for subsea or offshore applications.

[0098] In additional embodiments, energy storage control system 702 may be used to switch between first, e.g., active, and second, e.g., passive, operating modes. In one example, energy storage control system 702 may include any or all of the logic, modules, and components as control system 200. In a first operating mode, control system 702 may operate one or more (electro)mechanical subsystems, e.g., pumps, motors, valves, and the like, of lower-density fluid supply 704 to produce a flow of freshwater at a first fluid flow rate. At this flow rate, reservoir 730 may store the received freshwater within body 726 of reservoir 730. In turn, an internal volume of reservoir 730 may increase as more freshwater is stored. At the same time, freshwater may be actively (e.g., using electrical power from supply 704) supplied to downstream application 708 from one or both of supply 704 and reservoir 730. Such operating mode may be advantageous when electrical prices are low.

[0099] However, when electrical prices rise, it may be advantageous to have reservoir 730 passively supply freshwater. In this embodiment, control system 702 may generate one or morecontrol signals to the (electro)mechanical subsystems, e.g., pumps, motors, valves, etc., of device 704 to reduce or dimmish a fluid flow rate. As a result of the diminished fluid flow rate, a density differential between freshwater and seawater may act to displace the freshwater to passively supply freshwater to downstream application 708. When electrical pricing is again low, control system 702 may switch operations back to the first mode.

[0100] In addition to electrical pricing, there are numerous other instances where it may prove advantageous to passively supply freshwater. Such qualifying events may include power interruptions, pressure surges, equipment malfunctions, leaks, remote operated vehicle operations, autonomous vehicle operations, passage of time, and the like. In one embodiment, one or more sensors may be affixed along system 700 to detect such qualifying events and generate signals for control system 702. Sensors may include any number or type of sensors capable of detecting such events, e.g., imaging sensors, pressure sensors, flow rate sensors, and the like. Based on the received sensor signals, control system 702 may modify one or more operating parameters of supply 704 or system 700. However, while control system 702 may actively detect such qualifying events, in other embodiments, reservoir 730 may serve to passively supply freshwater without system 702 ever detecting such event. For example, during a power outage, limited or no freshwater may be provided to reservoir 730, and, as a result, freshwater may be passively supplied without ever detecting such an event.

[0101] In the case of upstream system failures or power interruption or shedding that stops or slows a supply of freshwater to reservoir 730, a hydrostatic potential energy of the stored volume of freshwater may allow for its passive deliverance from reservoir 730 to downstream application 708 via pipeline 710. This may prove beneficial during interventions or upstream equipment servicing events when freshwater supplies to reservoir 730 may be temporarily interrupted.

[0102] In additional embodiments, stored freshwater within reservoir 730 may serve as an emergency batch supply of freshwater. For example, in the case of downstream system failure or pipeline interruptions or leaks that stop or slow the supply of freshwater to land, so long as reservoir 730 has a gravitational potential energy and net-positive buoyancy from the stored freshwater, it may be released from the seabed and passively floated to sea surface 716. Reservoir 730 may then be retrieved and towed to shore via an offshore vessel. This may also prove useful if a continuous supply to shore is infeasible due to various risk factors, such as high costs, long offshore distances, unfavorable bathymetries, and the like.

[0103] As noted above, reservoir 730 with freshwater may also be used as an energy storage or load shedding device. Reservoir 730 with freshwater may act as a subsea battery storing hydrostatic potential energy in the form of pressurized freshwater, allowing the upstream production of freshwater to be modulated in response to fluctuating electricity rates, power demand, blackouts, rationing, and the like.

[0104] In additional embodiments, reservoir 730 may serve as a pulsation damping or accumulator tank. In these embodiments, reservoir 730 may serve as an expansion tank that modulates pressure surges often caused by rapid changes in hydraulic pressure, such as water hammer and pump cycling, reducing wear and tear, improving energy efficiency, and protecting upstream and downstream systems from pressure-related damage.

[0105] Reservoirs 730 may also be used to store freshwater for remote operated vehicle (ROV) operations. For example, an ROV may connect to reservoir 730 and receive a stored volume of freshwater to carry out a variety of maintenance tasks, such as pressure washing or actuating hydraulic valves or connectors. This may avoid the need for freshwater to be carried onboard the ROV or be supplied from an energized topside source via a subsea hose, which, in turn, may reduce the cost and complexity of subsea ROV operations involving the use of freshwater or hydraulic energy.

[0106] Fig. 8 illustratively shows a chart comparing a duration of freshwater supply versus an onshore delivery rate for different subsea freshwater storage capacities in accordance with the present invention. Specifically, using Eqn. 4, provided above, Fig. 8 shows a duration of freshwater supply versus onshore delivery rate for different subsea freshwater storage capacities from 4,000 m3to 20,000 m3.

Claims

We claim:

1. An underwater energy storage system, comprising: a submerged storage reservoir configured to receive and store a lower-density fluid while operating in a first operating mode and, while in a second operating mode, to passively supply the lower-density fluid to a downstream application; and an energy storage control system coupled to the submerged storage reservoir configured to alternate the submerged storage reservoir between the first and the second operating modes based on a qualifying event.

2. The underwater energy storage system of claim 1, wherein the qualifying event comprises electrical pricing rates, a system failure, pressure surges, demand surges, an exceeded storage capacity of the storage reservoir, a passage of time, a remote operated vehicle (ROV) operation, or an autonomous vehicle operation.

3. The underwater energy storage system of claim 2, wherein the system failure comprises a lower-density fluid supply operating error or a power outage.

4. The underwater energy storage system of claim 1, wherein the submerged storage reservoir passively supplies the stored lower-density fluid to the downstream application based on a density difference between the stored lower-density fluid and surrounding seawater.

5. The underwater energy storage system of claim 1 or claim 4, wherein the submerged storage reservoir comprises a displacement tank with a piston configured to, while in the first operating mode, extend outward to allow a stored volume of lower-density fluid to increase within a body of the displacement tank, and, while in the second operating mode, retract inward to displace the stored lower-density fluid from the body of the displacement tank.

6. The underwater energy storage system of claim 1 or claim 4, wherein the submerged storage reservoir comprises a deformable bladder configured to, while in the first operatingmode, expand outward while the lower-density fluid is being supplied to a body of the submerged storage reservoir and, while in the second operating mode, collapse inward as the stored lower-density fluid is being supplied to the downstream application.

7. The underwater energy storage system of any one of the preceding claims, further comprising a barrier fluid positioned between the submerged storage reservoir and surrounding seawater.

8. The underwater energy storage system of any one of the preceding claims, wherein the downstream application comprises industrial, military, civil, residential or commercial water usage.

9. The underwater energy storage system of claim 1, wherein the downstream application comprises an onshore or offshore turbine configured to generate electricity from the passive supply of lower-density fluid.

10. The underwater energy storage system of claim 9, wherein the onshore or offshore turbine comprises a subsea turbine configured to generate electricity from the received lower- density fluid.

11. The underwater energy storage system of claim 1, wherein the downstream application comprises a second submerged storage reservoir configured to receive and store the lower-density fluid from the submerged storage reservoir and passively supply the lower- density fluid to a second downstream application.

12. The underwater energy storage system of claim 1, further comprising: a lower-density fluid supply configured to supply the lower-density fluid to the storage reservoir, wherein the lower-density fluid is selected from the group consisting of desalinated water, wastewater, surface water, and oil.

13. The underwater energy storage system of claim 1, further comprising:a lower-density fluid supply configured to, while in the first operating mode, receive a flow of unfiltered deep-sea water, filter out unwanted suspended and dissolved solids from the flow of unfiltered deep-sea water to produce the lower-density fluid, and provide the flow of lower-density fluid to the submerged storage reservoir at a first fluid flow rate, and, while in the second operating mode, provide the flow of lower-density fluid to the submerged storage reservoir at a second fluid flow rate.

14. The underwater energy storage system of claim 13, wherein the lower-density fluid supply comprises one or more reverse osmosis membranes for filtering out the unwanted suspended and dissolved solids from the flow of unfiltered deep-sea water.

15. The underwater energy storage system of claim 14, wherein the lower-density fluid supply is submerged.

16. The underwater energy storage system of claim 15, wherein the lower-density fluid supply is configured to, while in the first operating mode, simultaneously provide the flow of lower-density fluid to a plurality of submerged storage reservoirs.

17. The underwater energy storage system of claim 13, wherein the energy storage control system comprises: an electrical pricing module configured to receive a pricing input indicative of a local electrical price, determine a corresponding operating parameter of the lower- density fluid supply or storage reservoir based on the received local price, and generate an operating output; and a control signal generator configured to receive the operating output and generate one or more control signals for the lower-density fluid supply to operate at the first or second operating mode.

18. The underwater energy storage system of claim 13, wherein the energy storage control system comprises:an emergency supply module configured to receive an input indicative of an operating malfunction of the lower-density fluid supply or the storage reservoir, determine a corresponding operating parameter of the lower-density fluid supply and the storage reservoir based on the received input, and generate an operating output; and a control signal generator configured to receive the operating output and generate one or more control signals for the lower-density fluid supply and storage reservoir to operate at the first or second operating mode.

19. The underwater energy storage system of claim 13, further comprising: a valve subsystem fluidically coupled to the storage reservoir and the lower-density fluid supply configured to, in the first operating mode, permit passage of the flow of lower-density fluid from the lower-density fluid supply to the storage reservoir and the downstream application, and, in the second operating mode, prevent a backflow of lower-density fluid.

20. An underwater energy storage system, comprising: a lower-density fluid supply configured to receive a flow of seawater and filter out suspended and dissolved solids from the flow of seawater to produce a flow of freshwater, and wherein, in a first operating mode, the flow of freshwater is produced at a first fluid flow rate and, in a second operating mode, at a second fluid flow rate; a submerged storage reservoir fluidically coupled to the lower-density fluid supply, the submerged storage reservoir configured to, while in the first operating mode, receive and store the flow of freshwater, and, while in the second operating mode, receive the flow of freshwater at the second flow rate and passively provide the stored freshwater to a downstream application; and an energy storage control system configured to switch between the first and second operating modes based on a qualifying event.

21. The underwater energy storage system of claim 20, wherein the lower-density fluid supply comprises a plurality of reverse osmosis membranes for filtering out the suspended and dissolved solids from the flow of seawater to produce the flow of freshwater.

22. The underwater energy storage system of claim 20, further comprising: an electrical assembly, fluidically coupled to the storage reservoir, configured to passively receive the flow of stored freshwater from the storage reservoir based on a density differential between a surrounding body of water and the stored freshwater within the storage reservoir, and, from the received passive flow of freshwater, generate electricity for an electrical application.

23. The underwater energy storage system of claim 22, wherein the electrical assembly comprises a turbine configured to passively receive the flow of stored freshwater from the storage reservoir and convert a kinetic energy of the passive flow of stored freshwater to mechanical energy to drive a generator physically coupled to the turbine.

24. The underwater energy storage system of claim 23, wherein the generated electricity from the generator is provided to an electrical device or an electrical grid along one or more cables.

25. The underwater energy storage system of claim 22, wherein the electrical assembly, the storage reservoir, and the lower-density fluid supply are submerged.

26. The underwater energy storage system of claim 24, wherein the electrical device is a sensor.

27. The underwater energy storage system of claim 20, wherein the storage reservoir comprises a plurality of deformable bladders configured to supply the passive flow of stored freshwater to the downstream application.

28. The underwater energy storage system of claim 27, wherein, in the first operating mode, the plurality of deformable bladders are configured to expand outward as the flow of freshwater is received from the lower-density fluid supply, and, in the second operating mode, collapse inward as the passive flow of freshwater is supplied to the downstream application.

29. The underwater energy storage system of claim 20, wherein the qualifying event comprises an electrical power outage, a pressure surge, or a passage of time.

30. The underwater energy storage system of claim 20, wherein switching the lower- density fluid supply between the first and second operating modes comprises generating one or more control signals to electromechanical systems of the underwater energy storage system.

31. The underwater energy storage system of claim 30, wherein generating one or more control signals results in the passive production of stored freshwater from the submerged storage reservoir to the downstream application.

32. A method of storing and producing a flow of lower-density fluid from a submerged storage reservoir, comprising: receiving a first flow of lower-density fluid at a first fluid flow rate from a lower- density fluid supply located proximate to a seafloor; storing the first flow of lower-density fluid within an expanding body of the submerged storage reservoir; receiving a second flow of lower-density fluid at a second fluid flow rate from the lower-density fluid supply in response to a qualifying event; and in response to receiving the second flow of lower-density fluid, passively supplying the stored lower-density fluid to a downstream application.

33. The method of claim 32, wherein the first fluid flow rate is greater than the second fluid flow rate to store the first flow of lower-density fluid in a first operating mode and passively supply the stored lower-density fluid in a second operating mode.

34. The method of claim 32, wherein the submerged storage reservoir comprises a displacement tank or a deformable bladder.

35. The method of any one of claims 32 to 34, wherein the lower-density fluid supply comprises a deep-sea desalination device configured to receive a flow of seawater, desalinate suspended and dissolved solids from the flow of seawater, and produce a flow of freshwater.

36. The method of any one of claims 32 to 35, further comprising: passively receiving the stored lower-density fluid and generating electricity from the passively received flow of lower-density fluid.

37. An underwater energy storage system, comprising: a compressible and expandable storage reservoir physically coupled to a seafloor configured to, in a first operating mode, receive a flow of lower-density fluid from a lower-density fluid supply fluidically coupled to the compressible and expandable storage reservoir, and, in a second operating mode, store the received flow of lower density fluid within a body of the compressible and expandable storage reservoir; and an energy storage control system coupled to compressible and expandable storage reservoir configured to switch operating modes based on a qualifying event.

38. The underwater energy storage system of claim 37, wherein, in the second operating mode, the compressible and expandable storage reservoir is configured to be detached from the seafloor and passively rise to a sea surface.

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