Cross-Reference to Related Applications

This application claims priority to, and the benefit of, U.S. Provisional Application No. 63/347,769, filed on June 1, 2022, the content of which is incorporated by reference herein in its entirety.

Technical Field

The disclosure relates generally to energy storage, and, more particularly, to systems and methods for providing low temperature, long-duration thermal energy storage.

Background

Energy storage is the capture of energy produced at one time for use at a later time, so as to reduce imbalances between energy demand and energy production. Grid energy storage, for example, is a collection of methods used for energy storage on a large scale within an electrical power grid. Electrical power has largely been generated by burning fossil fuel. When less power is required, less fuel is burned and vice-a-versa. Due to concerns over air pollution, energy imports, global warming, a global-scale transition to renewable energy sources is currently underway.

Many renewable energy sources (most notably solar power and wind power) produce variable power. With widespread integration of renewable energy sources into the power grid comes challenges due to the inherent variability of power generation from such intermittent renewable energy sources. For example, intermittent renewable energy sources have relatively predictable and periodic daily and seasonal variations in output, in addition to relatively aperiodic variations. For example, wind power is uncontrolled and may be generating at a time when no additional power is needed and solar power varies with cloud cover and at best is only available during daylight hours, while demand often peaks after sunset.

On the utility-scale, variability on the demand-side is typically managed in real time by turning additional "peaker" power plants on during times of high demand, and off during times of low demand. Additionally, on the power generation side, the output power of conventional nonrenewable power plants is highly stable over time. However, such conventional solutions are not applicable to the inherently high variability power output from renewable energy sources. Tn particular, the high variability (from renewable energy sources, such as solar and wind power) requires either a significant overbuilding of capacity (in the event that turning off generation sources will be used to limit power input into the grid in times of low demand) or some form of variable storage or consumption of excess power to buffer the grid at times of high generation and low-demand.

Some technologies provide short-term energy storage. For example, short-term (daily to weekly) energy storage can largely be addressed by technologies such as rechargeable batteries, pumped-storage hydroelectricity, compressed air energy storage, and other well-established short-term energy storage systems. The relatively moderate energy storage requirements compared to longer duration systems limits the need for particularly high energy density to reduce land area usage.

In some instances, long-term (or long-duration) energy storage is desired (i.e., storage of energy on the timescale of months to years). However, long-term, seasonal energy storage is particularly difficult to achieve by the aforementioned technologies in their current embodiments. For example, long-duration energy storage fundamentally requires a low cost and low-loss energy storage medium. Additionally, the energy density should be high enough such that, if scaled to a size sufficient to buffer variable energy demands on a global scale, the land area required for energy storage would remain moderate (e.g., less than one percent of global land, and without direct competition for arable farmland or other critical resources).

In light of the noted restrictions on land area usage, as a result of the energy density of the storage medium, existing energy storage systems, including compressed air energy storage or pumped-storage hydroelectricity, are simply not suitable for providing long-term storage. For example, if the global buffer required for seasonal energy storage is on the scale of 10% of global annual energy usage, then the global energy buffer required is on the order of 2,700 Terawatt-hour (TWh). In light of such a requirement, neither pumped-storage hydroelectricity nor compressed air energy storage technologies would be sufficient or practical.

Pumped-storage hydroelectricity, with a lift of 200 meters and 70% round trip efficiency, would require 7*10 ¹⁵ liters of water. If stored in reservoirs with an average depth of about 20 meters, such storage technology would require a land area approximately the size of Germany to meet the 2,700 TWh demand. With an annual net evaporation of 350 mm/year, losses due to evaporation would also require about 10 ¹⁴ liters of water for replacement each year - more than a quarter of the annual water usage of the United States. Compressed air energy storage is limited by the availability of suitable underground resources, with significant barriers to development related to identification of geologic resources. If all natural gas storage facilities in the United States, about 4 trillion cubic feet, could be converted to compressed air storage facilities at 300 PSI, the stored energy (by unit conversion) is about 50 TWh, including the real conversion losses of operational systems, about 50%, the potential for stored energy is about 25 TWh, about 0.5%- 1% of the global need.

Therefore, interest in long-term energy storage, particularly for storage of power from intermittent renewable energy sources, grows as the renewable energy industry begins to generate a larger fraction of overall energy consumption.

Summary

The present invention recognizes the drawbacks of current energy storage systems, notably the inability of current systems to effectively provide long-duration energy storage solutions. To address such drawbacks, the present invention provides a thermal energy storage and exchange system that utilizes subterranean reservoirs including a bulk storage medium for receiving and retaining thermal energy for long-term storage timeframes. In particular, the present invention recognizes the benefits of maintaining the reservoirs and associated storage medium at a certain temperature relative to the surrounding local subterranean environment. By maintaining an average temperature differential (i.e., a temperature difference between subterranean reservoirs, including the thermal energy stored therein, and surrounding local subterranean environment), the present invention greatly reduces the losses due to thermal conduction for a long-term timeframe (i.e., months), while still maintaining adequate energy density of the thermal energy for subsequent use.

Furthermore, the present invention allows for the storage of low temperature energy. Storage of this type of energy may permit efficient utilization of heat that otherwise would have been partially or entirely wasted. More specifically, the present invention allows for storage of energy from renewable energy sources (i.e., solar power and/or wind power). For example, the systems and methods described herein may utilize heat obtained from solar radiation from day to night or from summer to winter, as well as heat from central power plants, from hours of low to hours of high demand on both a diurnal and seasonal basis Yet still, the present invention allows for the storage of heat from industrial processes (i.e., industrial heat waste).

Accordingly, the system of the present invention provides a low temperature, long- duration thermal energy storage solution. The system provides for thermal energy storage having a sufficiently high energy density and the potential for sufficiently low energy loss at a storage timescale of months to allow grid-scale energy buffers of the size needed to manage seasonal energy supply and demand mismatches inherent with widely available renewable energy sources (primarily wind and solar). Additionally, the minimal constraints on the bulk energy storage medium afforded by the storage of energy as sensible heat is necessary for low- cost global-scale implementation, in contrast with the limited availability of reservoirs for pumped hydroelectric storage, or suitable geologic locations for compressed air energy storage. Furthermore, the effective cost of energy stored and delivered from geothermal battery systems can be reduced beyond alternative methods by the incorporation of low-cost industrial waste heat as a system input, in addition to higher cost electrical energy.

One aspect of the present invention includes an energy storage and exchange system. The system includes one or more subterranean thermal reservoirs comprising thermal storage medium configured to receive and retain thermal energy. An average temperature differential between the one or more subterranean reservoirs, including the thermal energy stored therein, and a surrounding local subterranean environment is maintained to thereby achieve low energy loss during a duration of storage of the thermal energy. For example, in one embodiment, the average temperature differential is 300 kelvin (K) or less. The low energy loss may include energy loss of no greater than 10% over a storage duration of 100 days.

The thermal storage medium may include at least one of a solid medium and a liquid medium. The thermal storage medium may include, but is not limited to, soil, sand, rock, composite material comprising fine and/or coarse aggregate and a binder, and an aqueous solution. For example, in one embodiment, the thermal storage medium may include concrete. Additionally, or alternatively, the thermal storage medium may include water-backfilled crushed rock.

The one or more subterranean thermal reservoirs may have a combined volume greater than 1,000 cubic meters. In some embodiments, the one or more subterranean thermal reservoirs may include an insulating region comprising a medium for minimizing heat loss by way of convection and/or conduction.

In some embodiments, the system may further include one or more heat pumps operably associated with the one or more subterranean thermal reservoirs. The one or more heat pumps are configured to convert input energy in the form of at least one of electrical energy, mechanical work, and industrial waste heat into thermal energy to be stored. In some embodiments, operation of the one or more heat pumps may be used to maintain the average temperature differential between the one or more subterranean reservoirs, including the thermal energy stored therein, and the surrounding local subterranean environment. More specifically, the one or more heat pumps may be configured to adjust a temperature of the one or more subterranean thermal reservoirs and/or the thermal energy stored therein relative to an ambient temperature of the surrounding local subterranean environment. For example, operation of the one or more heat pumps may be used to heat or cool the one or more subterranean thermal reservoirs and/or the thermal energy stored therein.

In some embodiments, at least a first subterranean thermal reservoir is maintained at a temperature greater than an ambient temperature of the surrounding local subterranean environment and at least a second subterranean thermal reservoir is maintained at a temperature less than an ambient temperature of the surrounding local subterranean environment.

The one or more heat pumps may be configured to operate in accordance with a thermodynamic cycle including at least one of vapor compression cycle and vapor absorption cycle to heat or cool the one or more subterranean thermal reservoirs and/or the thermal energy stored therein. Alternatively, in some embodiments, operation of the one or more heat pumps provide for a chemical reaction to heat or cool the one or more subterranean thermal reservoirs and/or the thermal energy stored therein. For example, in the event that industrial waste heat is used as input energy, rather than electrical energy, the heat pump(s) may be augmented or replaced with a reversible chemical reaction to increase the temperature of the waste heat, such as the conversion of phosphoric acid to diphosphoric acid and water.

In some embodiments, the system may further include one or more heat engines operably associated with the one or more subterranean thermal reservoirs, wherein the one or more heat engines are configured to convert stored thermal energy into at least one of electrical energy and mechanical work. For example, the one or more heat engines may be configured to operate in accordance with a thermodynamic cycle selected from the group consisting of an organic Rankine cycle, Stirling cycle, and Brayton cycle.

In some embodiments, the system may further include one or more primary heat exchangers associated with a respective one of the one or more subterranean thermal reservoirs, wherein each primary heat exchanger simultaneously couples the one or more heat pumps and the one or more heat engines to stored thermal energy via heat exchange fluid. Each primary heat exchanger may include a grid of boreholes through which heat exchange fluid is in contact with thermal storage medium storing the thermal energy.

In such a configuration, the one or more heat pumps and the one or more heat engines may be configured to utilize heat exchange fluid for effectuating heat exchange with the one or more subterranean thermal reservoirs.

Another aspect of the present invention includes a method for energy storage and exchange. The method includes the steps of receiving and storing thermal energy in one or more subterranean thermal reservoirs and maintaining an average temperature differential between the one or more subterranean reservoirs, including the thermal energy stored therein, and a surrounding local subterranean environment to thereby achieve low energy loss during a duration of storage of the thermal energy. For example, in one embodiment, the average temperature differential is 300 kelvin (K) or less. The low energy loss may include energy loss of no greater than 10% over a storage duration of 100 days.

The step of maintaining an average temperature differential comprises adjusting a temperature of the one or more subterranean thermal reservoirs and/or the thermal energy stored therein relative to an ambient temperature of the surrounding local subterranean environment. For example, adjusting a temperature of the one or more subterranean thermal reservoirs and/or the thermal energy stored therein may include heating or cooling the one or more subterranean thermal reservoirs and/or the thermal energy stored therein. In some embodiments, at least a first subterranean thermal reservoir is maintained at a temperature greater than an ambient temperature of the surrounding local subterranean environment and at least a second subterranean thermal reservoir is maintained at a temperature less than an ambient temperature of the surrounding local subterranean environment.

The thermal energy is stored in a thermal storage medium associated with the one or more subterranean thermal reservoirs. The thermal storage medium may include, but is not limited to, at least one of a solid medium and a liquid medium For example, the thermal storage medium may include, but is not limited to, soil, sand, rock, composite material comprising fine and/or coarse aggregate and a binder, and an aqueous solution. For example, in one embodiment, the thermal storage medium may include concrete. Additionally, or alternatively, the thermal storage medium may include water-backfilled crushed rock.

The one or more subterranean thermal reservoirs may have a combined volume greater than 1,000 cubic meters. In some embodiments, the one or more subterranean thermal reservoirs may include an insulating region comprising a medium for minimizing heat loss by way of convection and/or conduction.

The thermal energy may generally be provided to the one or more subterranean thermal reservoirs via one or more heat pumps operably associated therewith, wherein the one or more heat pumps are configured to convert input energy in the form of at least one of electrical energy, mechanical work, and industrial heat waste into thermal energy to be stored. Accordingly, maintaining an average temperature differential between the one or more subterranean reservoirs, including the thermal energy stored therein, and a surrounding local subterranean environment may be based, at least in part, on operation of the one or more heat pumps.

The one or more heat pumps may operate in accordance with a thermodynamic cycle including at least one of vapor compression cycle and vapor absorption cycle to heat or cool the one or more subterranean thermal reservoirs and/or the thermal energy stored therein. Alternatively, in some embodiments, operation of the one or more heat pumps provide for a chemical reaction to heat or cool the one or more subterranean thermal reservoirs and/or the thermal energy stored therein. For example, in the event that industrial waste heat is used as input energy, rather than electrical energy, the heat pump(s) may be augmented or replaced with a reversible chemical reaction to increase the temperature of the waste heat, such as the conversion of phosphoric acid to diphosphoric acid and water.

The method may further include converting stored thermal energy into at least one of electrical energy and mechanical work via one or more heat engines operably associated with the one or more subterranean thermal reservoirs. For example, the one or more heat engines may be configured to operate in accordance with a thermodynamic cycle selected from the group consisting of an organic Rankine cycle, Stirling cycle, and Brayton cycle. The one or more heat pumps and the one or more heat engines may be configured to utilize heat exchange fluid for effectuating heat exchange with the one or more subterranean thermal reservoirs. For example, in some embodiments, each of the one or more subterranean thermal reservoirs comprises a primary heat exchanger simultaneously coupling the one or more heat pumps and the one or more heat engines to the thermal energy via a heat exchange fluid. Each primary heat exchanger may include a grid of boreholes through which heat exchange fluid is in contact with thermal storage medium storing the thermal energy.

Brief Description of the Drawings

FIG. l is a diagrammatic illustration of a low temperature thermal energy storage system consistent with the present disclosure.

FIG. 2 is a line graph showing a minimum amount of energy stored in subterranean reservoirs (having a 1000 ft radius) of a system consistent with the present disclosure for a given duration to achieve conduction loses below 1%, 5%, and 10% at a 100 K temperature difference.

FIG. 3 is a line graph showing a minimum amount of energy stored in subterranean reservoirs (having a 100 ft radius) of a system consistent with the present disclosure for a given duration to achieve conduction loses below 1%, 5%, and 10% at a 100 K temperature difference.

Detailed Description

By way of overview, the present invention is directed to systems and methods for providing low temperature, long-duration thermal energy storage. In particular, the systems and methods described herein utilize subterranean reservoirs for receiving and retaining low temperature thermal energy for long-term storage (i.e., months to years). The thermal energy is stored within a storage medium, such as a solid or fluid, within the reservoirs. The reservoirs and associated storage medium are maintained at a certain temperature relative to the surrounding local subterranean environment (i.e., maintained at an average temperature differential), greatly reduces the losses due to thermal conduction for a long duration (i.e., months), while still maintaining adequate energy density of the thermal energy for subsequent use. Furthermore, by permitting the storage of low temperature energy (i.e., energy obtained via renewable energy sources and the like), the systems and methods of the present invention provide efficient utilization of heat that otherwise would have been partially or entirely wasted. Accordingly, the present invention provides a low temperature, long-duration thermal energy storage solution. The systems and methods described herein provide for thermal energy storage having a sufficiently high energy density and the potential for sufficiently low energy loss at a storage timescale of months, thereby allowing grid-scale energy buffers of the size needed to manage seasonal energy supply and demand mismatches inherent with widely available renewable energy sources (primarily wind and solar). Additionally, the minimal constraints on the bulk energy storage medium afforded by the storage of energy as sensible heat is necessary for low-cost global-scale implementation, in contrast with the limited availability of reservoirs for pumped hydroelectric storage, or suitable geologic locations for compressed air energy storage. Furthermore, the effective cost of energy stored and delivered from geothermal battery systems can be reduced beyond alternative methods by the incorporation of low-cost industrial waste heat as a system input, in addition to higher cost electrical energy.

FIG. l is a diagrammatic illustration of a low temperature thermal energy storage system consistent with the present disclosure. As shown, the system includes one or more subterranean reservoirs la, lb, for storage of thermal energy. The reservoirs may generally include a thermal storage medium, such as a solid medium and/or a liquid medium for receiving and retaining the thermal energy. For example, the storage medium may include, buy is not limited to, soil, sand, rock, a composite material comprising fine and/or coarse aggregate and a binder, and an aqueous solution. In one embodiment, the thermal storage medium may include concrete. Additionally, or alternatively, the thermal storage medium may include water-backfilled crushed rock. In some embodiments, the one or more subterranean thermal reservoirs may further include an insulating region comprising a medium for minimizing heat loss by way of convection and/or conduction. For example, the insulating region may include a similar material as the thermal storage medium (i.e., soil, sand, rock, concrete, aqueous solution, combination thereof, and the like) which may minimize heat loss by convection. The insulating region may have a sufficient thickness so as to minimize heat loss by conduction. The one or more subterranean thermal reservoirs may have a combined volume greater than 1,000 cubic meters.

The one or more reservoirs may be heated or cooled so as to maintain an average temperature differential between the one or more subterranean reservoirs, including the thermal energy stored therein, and a surrounding local subterranean environment to thereby achieve low energy loss during a duration of storage of the thermal energy. For example, in one embodiment, the average temperature differential maintained is 300 kelvin (K) or less. The low energy loss may include energy loss of no greater than 10% over a storage duration of 100 days.

The system further includes one or more heat pumps 2 operably associated with the one or more subterranean thermal reservoirs la, lb. The one or more heat pumps 2 are configured to convert input energy in the form of at least one of electrical energy, mechanical work, and industrial waste heat into thermal energy to be stored within the reservoirs. Accordingly, operation of the one or more heat pumps 2 may be used to maintain the average temperature differential between the one or more subterranean reservoirs la, lb, including the thermal energy stored therein, and the surrounding local subterranean environment. More specifically, the one or more heat pumps 2 may be configured to adjust a temperature of the one or more subterranean thermal reservoirs la, lb and/or the thermal energy stored therein relative to an ambient temperature of the surrounding local subterranean environment.

Operation of the one or more heat pumps may be used to heat or cool the one or more subterranean thermal reservoirs and/or the thermal energy stored therein relative to the surrounding subterranean environment. For example, as shown, at least a first subterranean thermal reservoir la is maintained at a temperature greater than an ambient temperature of the surrounding local subterranean environment (i.e., hot thermal reservoir la) and at least a second subterranean thermal reservoir is maintained at a temperature less than an ambient temperature of the surrounding local subterranean environment (i.e., cold thermal reservoir lb).

The one or more heat pumps 2 may be configured to operate in accordance with a thermodynamic cycle including at least one of vapor compression cycle and vapor absorption cycle to heat or cool the one or more subterranean thermal reservoirs and/or the thermal energy stored therein. Alternatively, in some embodiments, operation of the one or more heat pumps 2 provide for a chemical reaction to heat or cool the one or more subterranean thermal reservoirs and/or the thermal energy stored therein. For example, in the event that industrial waste heat is used as input energy, rather than electrical energy, the heat pump(s) may be augmented or replaced with a reversible chemical reaction to increase the temperature of the waste heat, such as the conversion of phosphoric acid to diphosphoric acid and water.

The system further includes one or more heat engines 3 operably associated with the one or more subterranean thermal reservoirs la, lb. The one or more heat engines 3 are configured to convert stored thermal energy into at least one of electrical energy and mechanical work. For example, the one or more heat engines 3 may be configured to operate in accordance with a thermodynamic cycle selected from the group consisting of an organic Rankine cycle, Stirling cycle, and Brayton cycle.

The working fluids used by the one or more heat engines 3 may include a solution of two or more component fluids which can be adjusted in concentration to control the boiling point, critical point, and other physical properties of the fluid allow high efficiency for a range of intermediate operating temperatures below the maximum temperature of the one or more reservoirs la, lb. For example, the solution may include a mixture of ammonia and water. Additional additives may be used to increase boiling point, such as sodium or potassium acetate, and/or to reduce viscosity, such as solvents or alcohols, as well as pH increasing or buffering agents such as Sodium or Potassium Hydroxide, and passivation or lubricating agents such as molybdenite or graphite. The one or more heat engines 3 are configured to use working fluids with a boiling point below 500°C at working pressures.

The system further includes one or more primary heat exchangers 4a, 4b associated with a respective one of the one or more subterranean thermal reservoirs la, lb. Each primary heat exchanger 4a, 4b simultaneously couples the one or more heat pumps 2 and the one or more heat engines 3 to stored thermal energy via heat exchange fluid. For example, the heat exchangers 4a, 4b may generally include an input and an output heat exchange for both the heat pump 2 and the heat engine 3. The primary heat exchangers 4a, 4b include a grid of boreholes through which heat exchange fluid is in contact with thermal storage medium storing the thermal energy. As shown, a single set of primary heat exchangers 4a, 4b and associated heat exchange fluid may be shared by both the heat pump 2 and the heat engine 3. In such a configuration, the one or more heat pumps and the one or more heat engines may be configured to utilize heat exchange fluid for effectuating heat exchange with the one or more subterranean thermal reservoirs.

This shared configuration increases the area available for heat exchange for the heat pump or heat engine relative to the use of separate heat exchangers. Additionally, such a configuration reduces losses in heat exchange from input to output due to the elimination of thermal resistances associated with the transition from input heat exchanger - to storage medium - to output heat exchanger. Such a configuration further results in elimination of heat leaks to the surface of the a given reservoir associated with an increased number of boreholes that would be required for an equivalent heat exchange surface area in a system with separate heat exchangers. It should be noted that the reservoirs 1 a, lb may be sealed or unsealed, and, as such, a region of elevated or depressed temperature may extend well beyond adjacent local environment of the heat exchangers 4a, 4b.

In some embodiments, the system may include secondary heat exchangers separately from the primary heat exchangers 4a, 4b. The secondary heat exchangers may be used to incorporate heat from an external process as an input to the system (i.e., to be converted into stored thermal energy). The heat from an external process may include, for example, waste heat from a power plant or industrial process. Additionally, or alternatively, the secondary heat exchangers may be used to provide space or process heat or cooling as system outputs.

Given a moderate 100 Kelvin temperature increase over ambient, the energy density of thermal energy storage as specific heat is about 30 kWh/m ³ for a thermal material similar to concrete, which is much greater than pumped hydroelectric or compressed air alternatives. For example, a compressed gas stored at a pressure of 300 PSI contains about 0.5 kWh/m ³ of energy, by simple unit conversion. Similarly, 1 m ³ of water raised 200 meters also contains about 0.5 kWh/m ³ of stored potential energy. For small quantities of stored energy, associated thermal losses are high. However, when scaled from systems storing gigawatt-hour (GWh) to TWh or larger energy storage capacities, the ratio of energy stored to energy lost due to surface losses is favorable, since it scales as the size of the system radius squared. The benefit of this scaling is that large systems are inherently much more efficient than small systems due to fundamental physical constraints.

FIG. 2 shows the minimum amount of energy stored for a given storage duration in order to achieve system losses due to conduction below 1%, 5%, and 10%, given a storage volume with a radius of 1000 ft, thermal properties similar to concrete, and a temperature increase of 100K. A thermal insulation of surrounding material equal in thickness to the radius of the storage medium is assumed. Losses due to thermal conduction are below 1% if energy is stored for 100 days given system capacities on the scale of several tens of GWh. FIG. 2 illustrates one of the primary benefits of low temperature thermal energy storage with the systems and methods of the present invention, including use of any natural subsurface storage medium (e.g., rock, soil, high or low moisture content, etc.) as a low-loss storage medium given sufficient system scale (with the characteristic minimum scale illustrated by FIG. 2). Smaller or larger systems have a minimum energy storage for a given duration that scaled linearly with system radius. However, for systems that include a storage volume smaller than about 100 ft in radius, the heat capacity of the material will significantly limit the energy that can be stored within the system volume in practice, thereby requiring all but the smallest systems to move to a higher temperature difference, and higher associated losses. The minimum stored energy for a given duration to achieve various storage efficiencies for a system with 100 ft radius is shown in FIG. 3. It should be noted that stored energies larger than about 3.5 GWh are inaccessible with a 100 K temperature difference for this volume, unless the heat capacity of the storage medium can be increased beyond the 1 J/gram-K assumed. FIG. 3 shows that systems with stored energy as small as tens of MWh can maintain low losses for durations on the order of one or several days.

As illustrated in FIG. 3, while small scale systems remain energetically viable, this niche has significant competition from conventional batteries with high round-trip efficiency and high energy density. Accordingly, thermal batteries are unlikely to be competitive in all but potentially the lowest-cost applications with relatively few size and weight constraints. Residential or small-scale battery backup systems, or hybrid battery backup systems that act as combined heat and power generators may be a viable small-scale use case (i.e., using the energy storage heat pump to store and/or remove heat from the thermal reservoir for space heating or air conditioning as well as for electrical backup purposes.

Accordingly, the primary use for the present invention is long-duration energy storage, an application for which no clear alternative exists. The systems and methods described herein provide for thermal energy storage having a sufficiently high energy density and the potential for sufficiently low energy loss at a storage timescale of months, thereby allowing grid-scale energy buffers of the size needed to manage seasonal energy supply and demand mismatches inherent with widely available renewable energy sources (primarily wind and solar). Additionally, the minimal constraints on the bulk energy storage medium afforded by the storage of energy as sensible heat is necessary for low-cost global-scale implementation, in contrast with the limited availability of reservoirs for pumped hydroelectric storage, or suitable geologic locations for compressed air energy storage. Furthermore, the effective cost of energy stored and delivered from geothermal battery systems can be reduced beyond alternative methods by the incorporation of low-cost industrial waste heat as a system input, in addition to higher cost electrical energy.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described (or portions thereof), and it is recognized that various modifications are possible within the scope of the claims. Accordingly, the claims are intended to cover all such equivalents.

Incorporation by Reference

References and citations to other documents, such as patents, patent applications, patent publications, journals, books, papers, web contents, have been made throughout this disclosure. All such documents are hereby incorporated herein by reference in their entirety for all purposes.

Equivalents

Various modifications of the invention and many further embodiments thereof, in addition to those shown and described herein, will become apparent to those skilled in the art from the full contents of this document, including references to the scientific and patent literature cited herein. The subject matter herein contains important information, exemplification and guidance that can be adapted to the practice of this invention in its various embodiments and equivalents thereof.