CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims benefit of and priority to U.S. Patent Application No. 63/284,110, filed November 30, 2021, U.S. Patent Application No. 63/284,020, filed November 30, 2021, and U.S. Patent Application No. 63/166,468, filed March 26, 2021, each of which is hereby incorporated by reference in its entirety.

FIELD

[0002] The present disclosure relates to thermal energy storage, recovery, and production.

BACKGROUND

[0003] There has been a long-standing need to provide energy generation from renewable sources on a flexible, dispatchable basis. Various renewable energy sources and approaches have been pursued, such as solar photovoltaic panels, wind, geothermal, and biomass or biofuels, as well as others.

[0004] In recent years, the so-called “duck curve,” in which excess solar photovoltaic electric energy is put onto various power grids, has caused increasing strain on legacy systems. In addition to the duck curve, which represents a diurnal imbalance between renewable energy availability and demand, there is a growing recognition that a second, seasonal imbalance exists between renewable energy availability during summer months and renewable energy availability during winter months. This has led to an emerging focus on long-term energy storage to mitigate these imbalances.

[0005] Various approaches have been taken to store energy. Batteries of various chemistries, pumped hydropower storage, flywheels, and other technologies have been tried. Although pumped hydropower is low cost, it is limited in terms of what sites are compatible and can have significant environmental consequences. Batteries, flywheels, and other technologies are very expensive. Thermal energy storage uses a thermal medium to store energy and is currently among the low- cost leaders for short-term energy storage. Additionally, geological formations represent a massive amount of thermal media that are capable of absorbing and later releasing massive amounts of energy, making them suitable for the task of storing large surpluses of energy in summer months for later use during winter months.

[0006] Thermal Energy Storage (TES) has been employed at concentrated solar power (CSP) plants in the past. Although lower cost than batteries and other approaches, TES systems are still costly enough to preclude storage of much more than eight hours, or about the equivalent of one day’s worth of solar energy. This makes seasonal storage of renewable energy through TES infeasible at present.

[0007] A CSP plant is different than a PV plant or field in that it can take advantage of cheap thermal storage technologies to change its power production profile instead of batteries or other storage media that can store the electricity generated by PV. Generally, the sun is used to heat either thermal oil or molten salt, though other heat transfer fluids are possible. These fluids can then either be used to heat a working fluid, generally water/steam or an organic, high-molecular- mass fluid, or can be stored in insulated tanks for later use. These tanks are vastly cheaper than an equivalent amount of battery storage.

[0008] Standalone CSP plants are therefore a solution to the dispatchability issue. They are not widely implemented, however, because of their extremely high capital costs. Even with the additional value of generating power only when power is needed, traditional CSP technologies are too expensive to see widespread deployment without significant advances in the field. Combining CSP and geothermal can therefore solve two issues: the dispatchability of the geothermal plant and the cost of the CSP plant.

[0009] While both CSP and geothermal systems are used to generate the same product using the same fundamental process, renewable electricity generated by a heat engine, they do so in different ways. CSP necessarily has a varying power generating capacity. CSP systems concentrate sunlight to heat a working fluid. This fluid is then run through a heat exchanger to produce electricity. The amount of sunlight available to be concentrated varies throughout the day and throughout the year, and the output of a CSP system is very nearly linearly correlated to the sunlight incident on the collector field. Even if thermal storage media is added to a system, variability will still be unavoidable due to multi-day cloud events and seasonal variation in available sunlight.

[0010] Geothermal power, on the other hand, necessarily has a constant power generating capacity. Geothermal power is produced by pumping cool water down into a geothermal resource and extracting hot water at a different point within that resource. This hot water can be flashed to steam and run through a heat engine directly or be used to heat a working fluid that is passed through the heat engine. While the system output can decline throughout its lifetime due to heat loss of the geothermal source, day-to-day and month-to-month production of a geothermal plant is largely constant.

[0011] Geothermal power plants typically run around the clock, every day of the year. However, in view of a push for flexible and dispatchable renewable energy systems in recent years, this need for baseload output is actually a disadvantage. Further, geothermal power plants are limited to locations where there is a pre-existing source of underground heat sufficient to economically run a heat engine.

[0012] While not a fundamental requirement of geothermal, it is a commonly accepted best practice to operate the system in a baseload (constant power generating) capacity to avoid harming the geothermal resource. Specifically, increasing the power output of a geothermal plant requires pumping more hot water out from the ground. If this is not well balanced, the pressure of the superheated water in the underground reservoir can go below the saturation pressure, and the entire reservoir can boil. This effectively destroys the resource and, correspondingly, renders the geothermal power plant inoperable.

[0013] At first glance, this baseload generating ability would seem to be a benefit, as power consumption, while not constant, is always of the same order of magnitude. The issue arises when additional renewable energy sources are added to the grid, specifically PV panels without battery storage. These panels, while very inexpensive, only generate electricity when the sun is up. This makes them a highly variable power source. There is now enough PV-generated electricity on the grid in some markets that a new problem has emerged.

[0014] Electricity generation from geothermal, nuclear, and coal is approximately constant throughout the day. This not only leads to an over supply of power during peak sunlight from the many PV panels connected to the grid, but also an undersupply of power during the afternoon as those panels begin to decrease their output with the setting sun. This shortfall is currently solved by natural gas peaker plants that only operate during these times of rapidly changing power demand and supply. There is, therefore, a significant need for a renewable energy source that can be turned on and off as needed to alleviate the issues caused by PV. This is known as dispatchable power generation. A method of generating dispatchable renewable energy by combining renewable generating capacity with energy storage technologies is needed to increase the percentage of global energy that is renewably produced.

[0015] Disclosed embodiments take advantage of a massive existing energy storage resource that is currently unused: underground oil reservoirs and other similar geologic features. In California, as in many other places, much of the oil that is extracted is extremely viscous in its natural state. To increase the production of the state’ s oil wells, many of them use a process known as Enhanced Oil Recovery (EOR) to help get the oil out of the ground. While there are several different methods of EOR, the relevant type to the process outlined herein uses natural gas to boil water and pushes the steam down into the oil reservoir. The steam heats the oil underground, reducing its viscosity and allowing it to be easily pumped to the surface. When the majority of the oil has been extracted from the reservoir, the wells are capped to prevent any further environmental issues.

[0016] These oil wells present a substantial opportunity for energy storage. Not only are the underground reservoirs massive, on the order of cubic miles in size, they have already been shown to be relatively isolated from the surrounding rock. This is why oil pools there. Furthermore, there are now multiple decades of data showing that these reservoirs are relatively thermally isolated as well. If they weren’t then the heat from the steam injected into the reservoir would dissipate into the surrounding rock before the viscosity of the oil was affected. Additionally, due to the widespread consumption of fossil fuels during the last century, the number of existing wells to access these reservoirs is enormous. California alone has tens of thousands of existing wells that can serve as passages to and from these reservoirs. This document outlines a method of transforming these oil reservoirs to generate dispatchable renewable energy and providing a supplementary heating system to ensure that the production from the plant is entirely predictable. [0017] Accordingly, there is a need for a system and method of storing renewable energy seasonally to provide for flexible, dispatchable renewable energy. There is a need for systems and methods of thermal energy storage and recovery that can utilize geothermal power systems and other geological formations. There is also a need for a multi-modal thermal energy storage system. SUMMARY

[0018] Embodiments of the present disclosure alleviate to a great extent the disadvantages of known thermal energy storage and recovery systems by providing a thermal energy storage (TES) system that has two subsystems operating within two different temperature ranges and two different time scales. One of the subsystems may be a geological formation. A concentrated solar power plant can supply heat energy to the system. The higher temperatures provided by CSP advantageously provide much higher efficiency of conversion and better overall plant economics. [0019] Disclosed embodiments further provide methods of creating a dispatchable renewable energy plant by combining above ground CSP with below ground thermal storage. In general terms, the present disclosure provides a method of combining CSP and geothermal power production to create a dispatchable renewable energy plant. This method can be used to create new power plants, but, crucially, it can also be used to improve the viability of existing geothermal power.

[0020] In exemplary embodiments, the thermal storage will take place in an underground geological formation. This will generally be an oil reservoir due to the existing oil wells that can be used to access it, but other formations may be suitable as well. This plant can be, but is not required to be, located such that a geothermal energy resource can be used to supplement the energy provided by the CSP system. Additionally, this plant can have a supplementary heating system to further augment the CSP system when necessary, such as during periods of prolonged cloudiness.

[0021] By combining CSP and geothermal, it is possible to have a geothermal power plant that provides baseload power and a solar plant with thermal storage that can provide dispatchable power. As described in the present disclosure, combining these two technologies at one power plant can have significant benefits over simply building a geothermal power plant and a separate CSP plant.

[0022] In a geothermal power plant, hot water is pumped up from a geothermal resource and either flashed (wholly or partially) into steam to be used as a working fluid or run through a heat exchanger to heat a working fluid. Both options are common in geothermal power plants depending on the specific site requirements. The working fluid is run through a heat engine and then cooled and condensed before being reinjected into the geothermal resource, if the geothermal brine is the working fluid, or reheated in a heat exchanger, if the brine is not. [0023] Advantageously, CSP increases the efficiency of the process. CSP can be used to raise the temperature of the working fluid much higher than it otherwise would be. Hot geothermal brine can be partially or fully flashed to steam (or used to do the same to a working fluid) before being superheated in a heat exchanger with the heat transfer fluid from a CSP system. This fluid can then be run through a heat engine at significantly higher efficiency than the geothermal turbines. The low temperature geothermal source is used to boil the working fluid, which requires a significant energy input, while the CSP can superheat the fluid. Crucially, while the low temperature source is used to perform the low temperature process (boiling) and the high temperature source is used to perform the high temperature process (superheating), both energy sources take advantage of the increased efficiency in the high temperature turbine. That is the fundamental idea behind combining geothermal and CSP.

[0024] An exemplary multi-modal thermal energy storage and recovery system comprises a first thermal energy storage subsystem and a second thermal energy storage subsystem operatively connected to the first thermal energy storage subsystem. The first thermal energy storage system operates within a first temperature range and contains a first thermal energy storage medium having a temperature within the first temperature range. The second thermal energy storage subsystem operates within a second temperature range higher than the first temperature range and contains a second thermal energy storage medium having a temperature within the second temperature range. The first thermal energy storage medium heats a working fluid, and the second thermal energy storage medium further heats the working fluid. A heater may be operatively connected to the first thermal energy storage subsystem and the second thermal energy storage subsystem. When the working fluid needs supplemental heat or energy the heater provides supplemental heat and/or supplemental energy to the working fluid.

[0025] In exemplary embodiments, the heater is a combustion-based heating system. The heater may bum gasoline, renewable gasoline, diesel, renewable diesel, natural gas, renewable natural gas, hydrogen, renewable hydrogen, and/or any other fuel derived from crude oil. The combustion-based heating system may be a once-through steam generator. The heater could also be an electric resistance heater, a mechanical resistance heater, a heat pump, a concentrated solar power plant, and/or waste heat from an industrial process.

[0026] In exemplary embodiments, the first thermal energy storage medium vaporizes the working fluid, and the second thermal energy storage medium superheats the working fluid. The first thermal energy storage medium may vaporize and superheat the working fluid, and the second thermal energy storage medium may further heat the working fluid. In exemplary embodiments, the first thermal energy storage medium preheats the working fluid, and the second thermal energy storage medium vaporizes or superheats the working fluid. The working fluid may be water or a high molecular mass organic compound, or the first thermal energy storage medium may act as the working fluid.

[0027] The multi-modal thermal energy storage and recovery system may further comprise a heat engine in fluid communication with the first thermal energy storage subsystem and the second thermal energy storage subsystem. In exemplary embodiments, the working fluid flows through the heat engine and the heater heats the working fluid flowing through it. The second thermal energy storage medium may vaporize or superheat the working fluid. In some embodiments, the first thermal energy storage medium preheats or vaporizes the working fluid, the second thermal energy storage medium vaporizes or superheats the working fluid, the working fluid is run through a heat engine, and then the working fluid is reheated by either the second thermal energy storage medium or both the first and second thermal energy storage media and is then run through a heat engine again.

[0028] In exemplary embodiments, the first thermal energy storage subsystem is a geological formation. The first thermal energy storage subsystem and/or the second thermal energy storage subsystem may be an enhanced oil recovery field. In exemplary embodiments, the first thermal energy storage subsystem comprises a hot zone and a cold zone, and the second thermal energy storage subsystem comprises a hot tank and a cold tank. The first thermal energy storage medium and/or the second thermal energy storage medium may comprise thermal oil or a similar heat transfer fluid, water, molten salt, rock, concrete, and/or a phase-change material. In exemplary embodiments, heat energy is supplied to the first thermal energy storage subsystem and/or the second thermal energy storage subsystem by concentrated solar power, an electric resistance heater, a heat pump, waste heat, and/or a geothermal resource.

[0029] An exemplary method of storing energy comprises directing a working fluid through a first thermal energy storage subsystem containing a first thermal energy storage medium and directing the working fluid through a second thermal energy storage subsystem operatively connected to the first thermal energy storage subsystem. The second thermal energy storage subsystem contains a second thermal energy storage medium. The first thermal energy storage medium has a lower temperature than the second thermal energy storage medium. The first thermal energy storage medium heats the working fluid, and the second thermal energy storage medium further heats the working fluid.

[0030] An exemplary embodiment of a multi-modal thermal energy system comprises a first energy subsystem comprised of a geothermal power plant and a second energy subsystem comprised of a concentrated solar power plant operatively connected to the first energy subsystem. The first energy subsystem operates within a first temperature range, and the second energy subsystem operates within a second temperature range higher than the first temperature range. A working fluid flows through the first energy subsystem and the second energy subsystem, and both subsystems heat the working fluid.

[0031] Exemplary embodiments further comprise a heat engine in fluid communication with the first energy subsystem and the second energy subsystem. The working fluid flows through the heat engine such that the heat engine generates electricity. In exemplary embodiments, the geothermal power plant and/or the concentrated solar power plant preheats the working fluid. [0032] Accordingly, it is seen that systems and methods of thermal energy storage and recovery and multi-modal thermal energy systems are provided. These and other features and advantages will be appreciated from review of the following detailed description, along with the accompanying figures in which like reference numbers refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The foregoing and other objects of the disclosure will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which:

[0034] FIG. 1 is a schematic of an exemplary embodiment of a multi-modal thermal energy system, storage and recovery system, and method in accordance with the present disclosure; [0035] FIG. 2 is a schematic of an exemplary embodiment of a multi-modal thermal energy system, storage and recovery system, and method in accordance with the present disclosure; [0036] FIG. 3 is a schematic of an exemplary embodiment of a multi-modal thermal energy system, storage and recovery system, and method in accordance with the present disclosure; and [0037] FIG. 4 is a schematic of an exemplary embodiment of a multi-modal thermal energy system, storage and recovery system, method in accordance with the present disclosure.

DETAILED DESCRIPTION

[0038] In the following paragraphs, embodiments will be described in detail by way of example with reference to the accompanying drawings, which are not drawn to scale, and the illustrated components are not necessarily drawn proportionately to one another. Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than as limitations of the present disclosure. As used herein, the “present disclosure” refers to any one of the embodiments described herein, and any equivalents. Furthermore, reference to various aspects of the disclosure throughout this document does not mean that all claimed embodiments or methods must include the referenced aspects.

[0039] Referring to FIGS. 1-4, exemplary embodiments of a multi-modal thermal energy storage system 1 have at least two different TES subsystems 10, 12 in fluid connection with each other. The subsystems 10, 12 would typically be of vastly different scales and operate at different temperature ranges. More particularly, a first TES subsystem 10 operates within a first temperature range, which may be a medium range, and a second TES subsystem 12 operates within a second, higher, temperature range. It should be noted that systems could employ more than one lower temperature TES subsystem 10 and/or more than one higher temperature TES subsystem 12. At least one of the subsystems which is not the highest temperature subsystem may be used to store at least double the energy of at least one of the other subsystems.

[0040] The different temperatures are such that, when used in concert, they heat, vaporize, and superheat a working fluid 22 for conversion into electricity by a heat engine 27 such as a turbine. The lower temperature storage medium is used to raise the working fluid 22 to a first temperature and the higher temperature storage medium is used to raise the working fluid 22 to a second, higher temperature. In some embodiments, the storage medium for the lower temperature TES subsystem 10 is the working fluid 22 that is heated and/or vaporized and/or superheated by one or several higher temperature TES subsystems 12. The working fluid 22 may be water, a high molecular mass organic compound, or any other working fluid.

[0041] In exemplary embodiments, the first, medium temperature subsystem 10 is a geological formation 14, such as a sedimentary rock formation that is injected with hot water and/or steam. Such wells can be purpose drilled or converted from other uses, and the geothermal resources from the geological formation 14 can be used to supply heat energy to one or more of the TES subsystems 10, 12. In addition, or alternatively, one of the thermal energy storage systems is or once was an enhanced oil recovery (either steam, water or C02 injection) field that is injected with hot water and/or steam.

[0042] Each subsystem 10, 12 contains an energy storage medium 16a, 16b, which could be the same or different material for each subsystem. Embodiments of the TES system 1 can use water, thermal oil, molten salt, concrete, rocks, phase change material, or other material as thermal energy storage media as well as geological formations of various composition as thermal energy storage media. As described in more detail herein, the first thermal energy storage medium 16a in the first TES subsystem 10 heats a working fluid 22, and the second thermal energy storage medium 16b in the second TES subsystem 12 further heats the working fluid 22. In exemplary embodiments, the first thermal energy storage medium 16a has a lower temperature than the second thermal energy storage medium 16b.

[0043] Heat energy can be supplied to one or both of the TES subsystems 10, 12 by a heater 23, which is used to supplement the heat provided by the thermal energy storage subsystems when they are insufficient to reach an operating parameter. It can heat the working fluid 22 at various stages of the cycle. For example, heater 23 can heat the working fluid 22 that is pumped up from the low-temperature storage reservoir 10; it can heat the working fluid 22 that is run through the heat engine 27; it can be used to heat a heat transfer fluid that transfers the heat to the working fluid 22 that is pumped up from the low-temperature storage reservoir.

[0044] More particularly, the heater 23 can augment the heat provided by the thermal energy storage subsystems 10, 12 to reach an operating parameter. Thus, by using a heater, exemplary embodiments provide the working fluid 22 more energy than just using the storage subsystems. This can be done in the event that the energy imparted from the storage subsystems 10, 12 to the working fluid 22 is not sufficient to raise the working fluid to its final conditions, i.e., its set of operating conditions (whatever conditions it is raised to after being heated by both the storage and heater). The heater’s time of use could be determined by an algorithm based on market data. [0045] Advantageously, many different sources and technologies could serve as the heater 23. For example, the heater could be an electric resistance heater, a mechanical resistance heater, a heat pump, a concentrated solar power plant, and/or waste heat from an industrial process. The electric resistance heater or heat pump may be powered by excess electricity on the electrical grid, allowing it to be stored. Alternatively, the heater could be a combustion-based heating system that bums gasoline, renewable gasoline, diesel, renewable diesel, natural gas, renewable natural gas, hydrogen, renewable hydrogen, and/or any other fuel derived from crude oil. In exemplary embodiments, the heater is a once-through steam generator.

[0046] In exemplary embodiments of the disclosed TES system 1, the higher temperature TES subsystem 12 is comprised of a hot tank 17 and a cold tank 19. The lower temperature TES subsystem 10 may include a hot zone(s) 18 and cold zone(s) 20, and the hot tank 17 and a cold tank 19 of higher temperature TES subsystem 12 contain a hot zone 18 and cold zone 20, respectively. In some embodiments, the medium temperature geological formation 14 has a hot zone 18 and cold zone 20. The gradient illustrating the change in temperature between the hot zone 18 and cold zone 20 of the lower temperature TES subsystem 10 can be seen in FIG. 4. The gradient is reversed for energy discharge when the hot working fluid is being pumped up.

[0047] The TES system 1 may also include a heat engine 27 in fluid communication with the two TES subsystems 10, 12. When charging either subsystem 10, 12, fluid from the cold section 20 is withdrawn, heated, and sent to the hot zone 18. When discharging either subsystem 10, 12, fluid is withdrawn from the hot zone 18, used to add heat to the working fluid of a heat engine (or itself become the working fluid of a heat engine), then routed to the cold section of the respective sub system.

[0048] Referring to FIGS. 3 and 4, additional components of an exemplary thermal energy storage and recovery system 1 can be seen. FIG. 3 illustrates a cycle in which the fluid is pumped up from the first TES subsystem 10, flashed, then pumped back down. FIG. 4 shows the fluid being pumped up, run through a heat exchanger, and then pumped back down. In exemplary embodiments, a flash tank 24 may be located between the two TES subsystems 10, 12 so the working fluid 22 from the first TES subsystem 10 passes through the flash tank. Flash tank 24 allows the brine pumped from low temperature TES subsystem 10 to boil and become the working fluid 22 that is subsequently passed through the heat engine 27. From flash tank 24, the working fluid 22 runs through a heat exchanger 25 that transfers heat from the low temperature TES subsystem 10 to the working fluid 22 that is run through the heat engine 27, generally vaporizing it. In exemplary embodiments, the working fluid 22 then runs through a condenser 28 and condensate pump 29. [0049] Alternatively, as shown in FIG. 4, the brine pumped from low temperature TES subsystem 10 runs through heat exchanger 25 that transfers heat from the low temperature TES subsystem 10 to the working fluid 22. Then working fluid 22 runs through supplemental heat exchanger 26 that transfers heat from the high temperature TES subsystem 12 to the working fluid

22 that is run through the heat engine 27, generally superheating it.

[0050] Exemplary embodiments provide a multi-modal thermal energy system, more particularly, a geothermal power and concentrated solar power plant. In the multi-modal energy system, the energy from the geothermal plant and the energy from a concentrated solar power plant

23 are both used to heat the same working fluid 22. The working fluid 22 is then run through a heat engine to generate electricity.

[0051] In exemplary systems, the geothermal power and/or the concentrated solar power are used in various ways to enhance operations, including to heat the working fluid 22. For example, geothermal power and/or concentrated solar power could be used to preheat, boil, and/or superheat the working fluid 22. In the case of preheating, boiling, and/or superheating, the steam from the geothermal brine is run through a heat engine 27. Concentrated solar power and/or geothermal power could be used to reheat the working fluid 22 after it passes through the high temperature heat engine 27. The concentrated solar power plant 23 may use thermal storage media 16a, 16b to change the time of day at which the working fluid is run through the higher temperature heat engine. The concentrated solar power plant 23 could also use the thermal storage media 16a, 16b to increase the percent of time that the working fluid 22 is run through the higher temperature heat engine 27. In exemplary embodiments, resistance heaters, heat pumps, and/or waste heat are used to reheat the working fluid 22 after it passes through the high temperature heat engine 27.

[0052] In operation, a working fluid 22 is pumped through the first TES subsystem 10 and is heated by the first thermal energy storage medium 16a. The working fluid 22 then flows through the second TES subsystem 12 and is further heated by the second, higher temperature, thermal energy storage medium 16b. Advantageously, exemplary embodiments have the versatility to heat the working fluid 22 to different temperatures to achieve different results depending on the application and the need of the user. In exemplary embodiments, the working fluid 22 is stored for some time in the first TES subsystem 10. That time period could be 1-12 hours, 12-24 hours, or greater than 24 hours. [0053] The lower temperature storage medium 16a may be used to vaporize the working fluid 22, and the higher temperature storage medium 16b may be used to superheat the working fluid 22. Alternatively, the lower temperature storage medium 16a may be used to both vaporize and superheat the working fluid 22, and the higher temperature storage medium 16b used to further raise the temperature of the working fluid 22. In exemplary embodiments, the lower temperature storage medium 16a is used to preheat the working fluid 22, and the higher temperature storage medium 16b is used to vaporize and/or superheat the working fluid 22. In exemplary embodiments, the working fluid 22 is divided so that only some is preheated and/or vaporized and/or superheated by more than one storage medium 16a or 16b while some is preheated and/or vaporized and/or superheated by only one storage medium.

[0054] In embodiments utilizing a heat engine 27, the working fluid 22 would either be pumped up from the lower temperature storage medium 16a, flashed, and then pumped back down (FIG. 3) or pumped up, run through a heat exchanger, and pumped back down (FIG. 4). The lower temperature storage media 16a may be used to vaporize and/or superheat the working fluid 22 that is run through the heat engine 27, and the higher temperature storage medium 16b may be used to reheat the effluent from the heat engine 27 so that it can once again be passed through the heat engine.

[0055] Conversely, the higher temperature storage media 16b may be used to vaporize and/or superheat the working fluid 22 that is run through the heat engine 27, and the lower temperature storage medium 16a may be used to reheat the effluent from that heat engine 27 so that it can once again be passed through the heat engine. In some embodiments, the lower temperature storage medium 16a and the higher temperature storage medium 16b heat the working fluid 22, which is run through the heat engine 27. Then the higher temperature storage medium 16b can reheat the working fluid 22 to be run through another heat engine.

[0056] Using liquid water, steam, or both as the heat transfer fluid, heat that would in general be at a temperature between (but without limitation) about 100° C and 250° C is injected into geological formations 14, typically, sedimentary formations with dense rock both above and below, through wells. Later, presumably during a different time of year, heat is withdrawn from the geological formation 14 through wells in the form of hot water, or steam, or both. It would in general not be feasible to store heat far above typical geothermal power plant operating ranges, simply because the technologies to do so present significant cost and practical obstacles. This would limit the upper range of efficiencies of this approach to that of geothermal power plants, in general, for a flash plant, not far above 25% at most, and would negatively affect the economics of the system.

[0057] Advantageously, a CSP field 23 is used in operation of disclosed systems and methods as a source of renewable energy because it is practically capable of much hotter temperatures, such as 400° C in the case of thermal oil, or 550° C in the case of molten salt. These higher temperatures advantageously allow much higher efficiency of conversion (30% and above for example) and allow better overall plant economics. To capture these improved economics, as discussed above, disclosed embodiments employ a second TES subsystem 12 operated at a higher temperature range.

[0058] In exemplary embodiments, the benefit of the increased temperature TES subsystem 12 is realized by the addition of a superheater section for the steam flow into a steam turbine. Generally, but not necessarily, the vaporization of fluid for the power plant is accomplished with the stored heat from the geological reservoir, then the vapor is passed through the superheater section and be superheated with the high temperature TES subsystem 12. The high temperature TES subsystem 12 would have to be charged daily while the geological reservoir would not. This means that the high temp TES subsystem 12, which would be much more costly per unit of storage than the geological formation, would not have to be as big to realize increased efficiencies throughout the year.

[0059] This approach also lends itself to storage of solar PV, wind, and other renewable electricity. Either the medium temperature TES subsystem 10 or the high temperature TES subsystem 12 could be configured with an electrical resistance heater or a heat pump, and heat could be added from the electrical grid. A computer connected to a grid operator, utility company, or other market actor could then be used to identify periods when there is surplus renewable energy available and activate the resistance heater or heat pump to store it. The same system could also be used to store renewable energy that is not considered surplus. In this way, other forms of renewable energy besides concentrated solar power could be stored seasonally or diurnally.

[0060] Exemplary dispatchable multimodal energy systems 1 function as follows. During the daytime, generally but not exclusively during the summer when solar energy generation is greatest, the thermal energy from a CSP system 23 is used to heat a heat transfer fluid (HTF) that conveys the heat down into the underground reservoir or geological formation 14. An exemplary embodiment of this system would have a CSP system 23 heat a thermal oil that is then run through a heat exchanger 25 to boil water. That steam would then be injected into the underground reservoir 14. The CSP system 23 may also use a different heat transfer agent, such as molten salt or even solid particles, or it may boil the injected fluid directly. The injected fluid may be water or any suitable alternative fluid.

[0061] The CSP system 23 gradually heats up the underground reservoir 14 until it has reached an equilibrium temperature, after which the energy from the CSP system 23 may be used only to maintain that temperature. This temperature will likely be similar to the existing reservoir temperatures of EOR reservoirs, approximately 260F, but may be higher or lower depending on the site specifics.

[0062] Once the system has reached equilibrium, the power generated by the CSP system 23 is then split into two streams. The first serves to maintain the temperature of the underground reservoir 14. The second is used to create a high temperature energy storage subsystem 12 that is much, much smaller than the underground reservoir. When power is needed, water or some other heat transfer fluid is pumped up from the underground reservoir at the equilibrium temperature, in this example 260F. It is then heated further by the above ground high temperature storage subsystem 12, or the supplementary heating source if the high temperature storage is insufficient, before being run through a heat engine. This temperature boost serves to increase the efficiency of the power cycle.

[0063] The value of this approach is due to the size of the underground formations. Depending on the size of the formation 14 and the size of the CSP system 23, it may take months to raise the reservoir to the equilibrium temperature. This is because the thermal capacity of the reservoir is enormous, and means that once that temperature is reached, the reservoir can be used as a thermal battery with months or potentially years of thermal storage without significant thermal losses. Water, or some other HTF, can be pumped up from the underground storage system at any time of the day, summer, or winter. This means that the high temperature thermal storage of the CSP system 23 does not need to be very large to still allow for dispatchable energy generation whenever it is needed. The high temperature storage subsystem 12 can be discharged and recharged daily, while the low temperature storage subsystem 10 would be held at a near-constant temperature at all times due to its immense thermal mass. [0064] This approach can be combined with geothermal resources to supplement, or even replace, the portion of the CSP that is used to heat and maintain the temperature of the large underground reservoir. The CSP can still be used to boost the temperature of the working fluid 22 prior to running it through a heat engine.

[0065] Advantageously, an additional component may be provided to improve reliability of the system, i.e., a backup heating system not power by solar energy. On cloudy days when very little solar energy can be produced, this system can still generate electricity, unlike existing solar plants. However, the efficiency of the plant would be greatly reduced by not having access to a high temperature source from the CSP system. A natural gas boiler or other heat source may be added so that, in the absence of high temperature storage material, it can heat the working fluid 22 up to the same high temperature. This heater generally would be used when the CSP system is unable to charge the high temperature storage system, such as during cloudy periods or if maintenance is needed.

[0066] Exemplary embodiments could be employed at new sites or at existing oil production sites. In particular, enhanced oil recovery sites using either steam flood or water flood techniques could convert operations to this approach and operate in a renewable cogeneration configuration or, at the end of life of the oil operation, could convert entirely to renewable power generation. C02 flood oil operations could also be converted to operate in this manner. The advantage of this approach is that wells have already been drilled to support oil extraction, and this is an emissions- free way to continue to extract economic value from these assets at what might otherwise be their end of life.

[0067] Thus, it is seen that systems and methods of thermal energy storage, recovery, and dispatchable production are provided. It should be understood that any of the foregoing configurations and specialized components may be interchangeably used with any of the apparatus or systems of the preceding embodiments. Although illustrative embodiments are described hereinabove, it will be evident to one skilled in the art that various changes and modifications may be made therein without departing from the scope of the disclosure. It is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the disclosure.