Method for on-demand power generation using geothermal heat recovery

Abstract

Methods for providing power on demand to end users in various embodiments are disclosed. A closed loop heat recovery arrangement is disposed within a geologic formation having a predetermined potential heat output capacity. A power generation device is incorporated into the loop to recover energy. A working fluid is circulated within the loop at varying flow rates to oscillate the heat output about the predetermined potential heat output capacity to produce power on demand, wherein the average heat output can equal the predetermined potential heat output capacity. Integration with intermittent renewable energy sources is provided that optimizes performance and power distribution.

Description

TECHNICAL FIELD

[0001] The present invention relates to closed loop energy recovery from geologic formations with extractable heat, and more particularly, to a method of providing energy on demand using a closed loop production system. BACKGROUND

[0002] Prior activity in the geothermal / electric power production field has been well documented. One of the early examples is found in U.S. Patent Publication 20120174581 to Vaughan et al. published July 12, 2012.

[0003] Other examples include U.S. Patent Publication 2007024572 to Mickelson published April 21, 2004, U.S. Patent Publication 201100480 to McHargue published August 26, 2009, U.S. Patent No. 8,281,591 to Lakic published October 9, 2012, and most recently U.S. Patent No. 10,527,026 to Muir et al. published January 7, 2020.

[0004] These references represent the vanguard development in the art for heat recovery of power production bodies. Despite their usefulness, they are not instructive or authoritative in addressing the problem of power production needs and how these problems are mixed with intermittent renewable energy.

[0005] Intermittent renewable energy has recently become competitive with fossil fuel prices and now produces the majority (30-45%) of the power in some jurisdictions (California, Germany, etc.).

[0006] These carbon-free sources have the potential to greatly reduce greenhouse gas emissions. However, due to the inherent intermittency of energy production, the amount of solar / wind energy that can enter the grid is limited. These intermittent or variable sources of production are also referred to as non-dispatchable.

[0007] The high penetration of solar / wind energy in the grid has created problems for system integration, as it is difficult to replace the energy produced in the absence of sunlight and in the absence of wind. This is most concentrated in California, where there is a high penetration of solar energy and has created the colloquially known “duck curve”; https: / / en.wikipedia.org / wiki / Duck_ curve ).

[0008] Currently, in California, solar power plants cannot be built without some energy storage measure, typically 2-4 hours of lithium ion battery storage. However, true 8 hours or more of energy storage capability is very expensive.

[0009] By NREL “Generation Baseline Report” (https: / / www.nrel.gov / docs / fy17osti / 67645.pdf The comprehensive report written on power sources describes the problem of integrating non-dispatchable technologies. There is currently no viable solution to decarbonize the remaining approximately 50% of the grid.

[0010] Another problem with integrating intermittent renewable energy sources is that they tend to drop very rapidly, called rapid ramp-down. Therefore, an important and valuable feature expected in dispatchable power sources is the ability to ramp-up rapidly to offset the rapid drop in wind / solar power. Many technologies lack this ability to ramp-up rapidly (e.g., coal, nuclear, and some types of gas generation cannot ramp-up rapidly).

[0011] The challenge is to develop a cost-effective energy system to dispatch the evening and night loads when solar / wind energy is not available.

[0012] Conventional geothermal appears to be a natural choice to provide renewable dispatchable power. However, due to several fundamental problems, conventional geothermal systems operate in a base load manner, which hinders the ability to provide flexible / dispatchable power output.

[0013] Fluid from geothermal reservoirs cannot be accelerated without causing substantial parasitic pumping losses. This is due to Darcy flow regime and fracture flow regime within the rock reservoir; substantial energy is required to accelerate the flow rate above the normal base load operating point.

[0014] The reservoir can be pressurized, however, this can cause loss of reservoir seal, induce fracturing, and induce seismicity.

[0015] In addition to offsetting the parasitic losses of any total power increase during the ramping process, in conventional geothermal, there are many operational problems due to substantial up and down ramping of flow rates, sand production, liner failure, pump operating range, liquid / gas flow regime variability, geomechanical problems within the reservoir due to thermal expansion and cooling processes, injection well plugging, etc.

[0016] The US Department of Energy’s Request for Proposals (RFP) ( https: / / www.sbir.gov / sbirsearch / detail / 1523867Nordquist et al., GRC Transactions, Vol. 37, 2013). As described by the Ormat team, it is not easy to retrofit a base load power plant to full dispatchability. Power plants need to quickly adjust their power output to respond to the required ramp rates and maintain their frequency within tight tolerances of the grid power. This is a challenge for geothermal power plants because the heat source cannot naturally respond quickly to changes in demand. To address this challenge, Ormat decided to maintain the geothermal fluid flowing at a relatively steady rate while setting up bypasses around the power production equipment as needed. At partial loads, some geothermal fluid is pumped to the surface, bypasses the power production equipment, and is reinjected underground without extracting any useful enthalpy. This approach is robust, but it inevitably leads to high parasitic power consumption at partial loads due to the constant full flow pumping power requirement.

[0017] The geothermal reservoirs (underground systems) in the above examples are not producing at full capacity. The so-called dispatchability is in fact just running at a low capacity factor based on the geothermal underground capacity, or running the system at less than the potential heat output capacity of the geothermal system most of the time, and at equal to the potential heat output capacity at dispatch time.

[0018] Other researchers are focusing on using the underground as a storage medium for compressed air energy storage; in the article https: / / asmedigitalcollection.asme.org / memagazineselect / article / 137 / 12 / 36 / 380449 / Earth-BatteryCarbon-Dioxide-Sequestration-Utility medium for CO2, or pressurized water. These systems all face similar drawbacks. The key issue is that they are open systems (the volume of working fluid within the system is constantly changing) and therefore face the challenge of controlling and managing the flow in a porous medium and a large variable fracture network. Moreover, they are primarily energy storage systems, not energy production systems.

[0019] Still other researchers are working on using thermal energy storage (TES), i.e., systems that store the heat produced by geothermal systems on the surface, to optimize the daily energy output for end users. However, a key challenge is the temperature loss caused by sensible heat exchangers, and the resulting lower round trip efficiency. Moreover, the installation cost of large scale high temperature TES suitable for power generation is currently prohibitive.

[0020] A very different but still related field of prior art is low temperature underground thermal energy storage systems. These come in two types, Borehole Thermal Energy Storage (BTES) and Aquifer Thermal Energy Storage (ATES). ATES and BTES are essentially low temperature heat pump systems that store and extract seasonal energy from summer to winter and vice versa. BTES stores the heat of air conditioning waste heat in summer via heat conduction with the surrounding rock and then extracts this heat in winter. Neither ATES nor BTES are energy generating systems, nor even simple energy storage systems. Rather, they work with an energy driven heat pump and the entire system is an energy consumer, albeit more efficient than standard AC and space heating technologies.

[0021] Low temperature air storage is an attractive technology for storing excess power generated by renewable systems and discharging when needed. When used in conjunction with geothermal, the round trip efficiency of the storage technology increases. Some researchers have studied this type of integration, for example et al. in “Geothermal Energy Driven Low Temperature Energy Storage”, Vol. 77, Geothermics, 2018).

[0022] The academic paper above considers a geothermal system operating in a base load manner, rather than the dispatchable geothermal system disclosed here. The main challenge of this approach and other prior art is that the low temperature discharge occurs over several peak hours, whereas the geothermal output is base load (i.e. a smooth output over 24 hours).

[0023] What is needed to improve the current technology and base load limitations is a new paradigm that can provide power on demand to the end user at any time and supplement and optimize intermittent renewable energy sources when needed.

[0024] The present technology, which will be discussed further herein, solves all of the current problems in power generation, infrastructure, and power distribution without reliance on base load sources, non-dispatchable renewable energy, or batteries. SUMMARY

[0025] It is an object of one embodiment of the present invention to provide a method of producing dispatchable, scalable, and fast-ramping power using a closed loop engineered geologic heat retrieval system.

[0026] It is a further object of one embodiment of the present invention to provide a geothermal power output system that has a base load power distribution that is approximately equivalent to the oscillating discontinuous output period averaged over the power distribution period.

[0027] It is another object of one embodiment of the invention to provide a method for optimizing the characteristic potential thermal output capacity of a well system comprising a working fluid capable of being thermally charged from a geologic formation, the system having an inlet well and an outlet well and disposed within a geologic formation having a characteristic potential thermal output capacity, the method comprising: regulating circulation of the working fluid within the well system to oscillate thermal output from the thermally charged working fluid about the predetermined potential thermal output capacity, wherein the average oscillating thermal output is approximately equal to the predetermined potential thermal output capacity of the geologic formation.

[0028] In this embodiment, the thermal output is oscillating and cycles between a charging operation of thermally charging the working fluid by thermal conduction from the geologic formation and a discharging operation of processing the thermal energy.

[0029] The processing can comprise at least one of conversion to electrical energy, thermal energy, and combinations thereof.

[0030] In the regulation aspect, this can take many forms, including at least one of flow rate variation of the working fluid, residence time in the system, oscillation duration, thermal charging duration, thermal discharging, and combinations thereof.

[0031] Practice of the method allows for on-demand generation of energy for end users through interaction between the charged working fluid and a power generation device.

[0032] It is another object of one embodiment of the invention to provide a method for on-demand provision of electrical power to end users with a well system having an inlet well, an outlet well in a heat-producing geologic formation, the method comprising: forming a closed loop with a power generation device operably connecting the inlet and outlet; circulating a working fluid in the loop for a predetermined residence time to cyclically charge the working fluid with conductive heat from the formation; and regulating flow rate of the heat-charged working fluid within the loop for power generation based on user demand.

[0033] Depending on the specific parameters belonging to the geologic formation, the inlet well and the outlet well can be operably and fluidly connected with interconnecting segments disposed for conduction in the heat-producing geologic formation.

[0034] For enhanced heat recovery and networking of well systems, and many other advantages, the inlet well and the outlet well can be connected with a plurality of interconnecting segments in a predetermined pattern within the geologic formation. From the system design point of view, the patterning of well systems, interconnecting segments, networks of well systems is simplified and not limited due to the applicant's patented and published technology.

[0035] For power generation, output management and dispatchability, selective regulation of the work fluid circulation can be performed within predetermined sections of the plurality of interconnected sections of the well system to oscillate the thermal output from the hot charged work fluid about the predetermined potential thermal output capacity of the formation, with the average oscillating thermal output being approximately equal to the predetermined potential thermal output capacity of the formation.

[0036] In the case of a well system comprising a plurality of well systems having a plurality of interconnected sections, selective regulation of the work fluid can be implemented in each of the interconnected sections of the well system, in some or all of the interconnected sections, in a specific time and a specific order and in a user selected manner with adjacent well systems.

[0037] The method is based on the flexibility of deployment and, as such, any geologic formation having a temperature higher than 90°C can be exploited, regardless of the rock type, i.e. high permeability, low permeability, hot dry rock, geothermal formation, sedimentary formation, volcanic formation, variable permeability formation and combinations thereof. To increase flexibility, the method is not limited by rock formation incompatibility, i.e. naturally fractured, fractured or broken rock, synthetically fractured, fractured or broken rock and combinations thereof. The method can be applied to any scenario.

[0038] In terms of work fluid, the desired fluid can be water, which can include drag reducing additives, such as surfactants, polymeric compounds, suspensions, biological additives, stabilizers, anti-fouling agents, corrosion inhibitors, drag reducers, anti-freeze chemicals, biocides, hydrocarbons, alcohols, organic fluids and combinations thereof.

[0039] Other suitable fluids can contain supercritical carbon dioxide, lower alkanes, e.g. C1-C10, fluids containing phase change materials, refrigerants. There are many examples of these and they are easily derived from the prior art.

[0040] Additives that facilitate the maintenance of the well system are contemplated for use in the work fluid as compounds that enhance the thermodynamic efficiency of the work fluid.

[0041] Another object of one embodiment of the invention is to provide a method for providing energy on demand to an end user using geothermal mechanisms, which include an inlet well, an outlet well and an interconnected section between them in a geologic formation, the method comprising: forming a closed geothermal loop with power generation equipment connecting the inlet and the outlet; circulating a work fluid in the loop with a predetermined residence time to load the circulating work fluid with conductive heat from the formation; and adapting the flow rate of the heat loaded work fluid within the loop based on user demand.

[0042] The geothermal well and the interconnected section can be newly formed or existing. If existing, the method herein can be readily adapted to retrofit the existing installation to increase efficiency.

[0043] Depending on the proposed end use, the energy can be electrical or thermal, and the residence time is sufficient to facilitate power generation for the duration of the user's demand.

[0044] The interaction between the loop-internal charging working fluid and the power generation device includes minimizing the residence time by increasing the flow rate of the charging working fluid.

[0045] To further increase efficiency, the thermal energy from the charging working fluid can be stored in a geothermal formation, and the working fluid can be supplemented with energy-charged working fluid from an adjacent well in the formation. The supplementation can take the form of rerouting the working fluid from the adjacent well to the well and the power generation device, depending on the user's demand.

[0046] Another object of one embodiment of the invention is to provide a method of delivering power on demand to an end user, comprising: providing an inlet well, an outlet well, and a well interconnect section between the inlet well and the outlet well and disposed within a geologic formation having a predetermined latent thermal capacity with a temperature of at least 90°C; effecting a closed loop arrangement within the formation by connecting the outlet well to a power generation device to recover energy from the well arrangement in a closed loop between the well and the power generation device, the closed loop arrangement having a predetermined energy output within the available latent thermal capacity; circulating a working fluid within the loop with a predetermined residence time at least within the interconnect section to maximize energy transfer from the formation to form an energy-charged working fluid; and generating power on demand for the end user by interaction between the charged working fluid and the power generation device.

[0047] In keeping with the flexibility that has been established with the present method, the interconnect section can be cased, uncased, lined, chemically treated to enhance electrical conductivity, chemically sealed, self-healing when sealed, thermally sealed, including a single pipe optionally perforated, a coaxial pipe optionally perforated, and combinations thereof in continuous or discontinuous configurations. The working fluid can be designed to maintain the integrity of the borehole by sealing fissures or generated permeability. If the borehole is at risk of sloughing or compressive failure, the fluid density can be increased to provide sufficient compressive strength on the formation. Conversely, if the formation is sufficiently cooled, it can be at risk of tensile failure, in which case a fluid with reduced density can be selected.

[0048] The working fluid can be circulated within the loop at varying flow rates to oscillate the thermal output about the predetermined energy output capacity to produce power on demand, wherein the average thermal output can equal the predetermined latent thermal output capacity.

[0049] In an alternative embodiment, a plurality of interconnect sections (multi-lateral) common to the inlet well and the outlet well are disposed in a configuration to maximize thermal recovery from the thermal gradient of the formation. If the footprint of the arrangement is an issue, the inlet well and the outlet well can be co-located.

[0050] In further alternative embodiments, to take advantage of the thermal gradient within the formation, the interconnection segments can be arranged symmetrically relative to adjacent interconnection segments, asymmetrically relative to adjacent interconnection segments, in a interdigitated relationship with adjacent interconnection segments, in a coplanar relationship with adjacent interconnection segments, in a parallel plane relationship with adjacent interconnection segments, in an independent or grouped network, and suitable combinations thereof.

[0051] To improve power distribution, which will be further elaborated upon below, multiple closed loops with outlet wells of adjacent loops can be selectively connected to inlet wells of additional wells in the form of a daisy chain configuration, which can be further fitted with valves for user selection.

[0052] It is a further object of one embodiment of the present invention to provide a method for optimizing power distribution on a pre-existing power grid, comprising: providing an intermittent power generation arrangement having a designed maximum power generation and a second effective power generation on a pre-existing power grid; positioning an energy recovery and production closed loop within a thermally conductive geological formation adjacent to the intermittent power generation arrangement, the loop comprising an inlet well, an outlet well, an interconnection segment between the inlet well and outlet well, the interconnection segment positioned in the formation to facilitate thermal recovery in the formation, the formation having an available potential thermal capacity; positioning the closed loop in a configuration within the formation to produce a predetermined energy output from the available potential thermal capacity; circulating a working fluid within the loop for a predetermined residence time to thermally charge the circulating working fluid by conduction from the formation; and selectively thermally discharging the working fluid by the intermittent power generation arrangement to increase power generation above the second effective power generation and below the designed maximum power generation, thereby optimizing total power generation using the pre-existing power grid.

[0053] The intermittent power generation arrangement and energy recovery and production closed loop can be located on a common geographic footprint to produce energy on demand.

[0054] The selective thermal discharging of the working fluid by the intermittent power generation arrangement is implemented during periods of significant user power demand, and transmitted using the transmission capacity and infrastructure of the pre-existing power grid of the intermittent power generation arrangement. Intermittent energy sources are well known wind, solar, and battery energy sources.

[0055] It is a further object of one embodiment of the invention to provide a method of generating electricity comprising: providing an electricity transmission grid for transmitting generated electricity to end users, the grid having an output capacity; providing a power generation arrangement on the grid having a designed maximum power generation capacity and a second effective power generation capacity; positioning an energy recovery and production closed loop within a heat bearing geological formation adjacent the intermittent power generation arrangement, the loop comprising an inlet well, an outlet well, an interconnecting section between the inlet and outlet wells, the interconnecting section being positioned in the formation to facilitate heat recovery from the formation, the formation having an available potential heat capacity; positioning the closed loop within the formation in a configuration to produce a predetermined energy output from the available potential heat capacity; circulating a working fluid within the loop for a predetermined residence time to thermally charge the circulating working fluid by conduction from the formation; and selectively thermally discharging the working fluid by the power generation arrangement to maintain the power generation capacity of the entire electricity transmission grid at the capacity.

[0056] The electricity transmission grid can comprise a plurality of separate electricity distribution zones for distributing electricity within a geographical area, at least some of the electricity distribution zones comprising an energy recovery and production closed loop.

[0057] It is therefore a further object of one embodiment of the invention to provide a power plant for providing a predetermined electricity distribution to users comprising: a thermal energy recovery device configured to regulate circulation of a working fluid in a heat producing formation whereby thermal energy is transferred into the working fluid, the device being for oscillating a discontinuous output cycle that is averaged over an electricity distribution cycle; and an electricity distribution device for distributing the average electricity output as the user predetermined electricity output.

[0058] The invention having thus been described generally, reference will now be made to the accompanying drawings.

[0059] Industrial Applicability

[0060] The technology herein can be applied to the field of energy recovery and power generation. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 is a schematic diagram of an energy recovery arrangement disposed in a heat bearing geological formation;

[0062] Figures 2A-2D is a schematic diagram of an alternative interconnecting section or polygonal section for use in the recovery arrangement;

[0063] Figure 3 is an alternative to the recovery arrangement;

[0064] Figure 4 is a graphical representation of a series of operating scenarios depicting temperature (thermal output) as a function of time for each scenario;

[0065] Figure 5 is similar to Figure 4a graph of the curve presenting data over several days;

[0066] Figure 6 is Figure 4 and Figure 5 a schematic of heat output over 30 years in the specific scenario cited in

[0067] Figure 7 is a schematic of a dispatchable geothermal system integrated with other non-dispatchable renewable energy sources;

[0068] Figure 8 is a schematic of multiple dispatchable geothermal loops in a network;

[0069] Figure 9 is a flow chart showing the process of planning, controlling and optimizing the integration of non-dispatchable renewable energy sources with dispatchable geothermal systems;

[0070] Figure 10 is a schematic of the combined power output capacity of a network of generators;

[0071] Figure 11 is a schematic of the use of intermittent power sources to mitigate grid saturation; and

[0072] Figure 12 is a schematic of an alternative embodiment of the invention.

[0073] The same numbers are used in the drawings to represent the same elements. DETAILED DESCRIPTION

[0074] Reference is now made to the drawings, in which Figure 1 An example of the overall arrangement for practicing embodiments of the methods described herein is shown. The number 10 refers generally to the overall arrangement. A geologic formation 12 having thermal energy is at least 90°C, and can typically be higher than 150°C, or even 600°C or more, the geologic formation 12 including a subsurface loop arrangement having an inlet well 14 and an outlet well 16, which can be co-located, interconnected with at least one interconnection section 18. In the example, several sections 18 are depicted. The thermal gradient will depend on the formation characteristics.

[0075] At the surface 20, the inlet 14 and outlet 16 are connected to a power generation device 22. The device 22 completes the loop arrangement of the closed loop, which for simplicity will be referred to as L. It is apparent that in order to recover thermal energy from the surrounding formation 12, the segments 18 are disposed within the geological formation. For clarity, the closed loop L and in particular the segments 18 can include fissures, openings, cracks, within which fluid can be transported, however, this does not depart from the gist of the closed loop concept; the flow pattern remains closed in the combination of inlet, interconnections, outlet, power generation device 22 elements, notwithstanding the fact that there can be local anomalous multidirectional flow, but this is not essential.

[0076] The geological formation can be any formation that provides temperature as described above. In this regard, examples include geothermal formations, low permeability formations, hot dry rock, sedimentary formations, volcanic formations, high temperature formations, variable permeability formations, and combinations thereof. These are examples only; any number of other formations are within the scope of the present invention.

[0077] Depending on its nature, the formation will have a predetermined potential thermal output capacity, which can be pre-analyzed by suitable techniques known to those skilled in the art. Of course, each formation will have a different output capacity.

[0078] With this in mind, each loop L will have a predetermined potential thermal output capacity, which reflects its design parameters, such as the number of segments 18, its geometric arrangement, depth, length, formation temperature, formation rock properties, etc. All these parameters are apparent to the skilled person.

[0079] For recovery, the working fluid is circulated through the loop L and out of the outlet well 16, through the power generation device 22, which converts thermal and / or kinetic energy into electrical power for end users, generally designated by the numeral 24, and / or for redistribution at 26 for alternative uses to be discussed hereinafter. Once circulated as shown, the working fluid is reintroduced into the inlet 14.

[0080] By circulating the working fluid through the closed loop L at a relatively low flow rate during the charging cycle, the working fluid is thermally "charged" or loaded. The residence time of the working fluid within the subsurface flow path is increased and thus the fluid is heated to a high temperature via thermal conduction with the surrounding formation 12.

[0081] By significantly increasing the flow rate and flushing out the volume of heated working fluid within the hot subsurface portion of the closed loop L, the system is "discharged".

[0082] The working fluid can include water, supercritical carbon dioxide, etc., and include drag-reducing additives such as surfactants, polymeric compounds, suspensions, biological additives, stabilizers, anti-fouling agents, corrosion inhibitors, drag reducers, freeze-prevention chemicals, biocides, hydrocarbons, alcohols, organic fluids, and combinations thereof. Those skilled in the art will appreciate other suitable examples. It is contemplated that the composition of the working fluid can be dynamically changed in the event of changing subsurface thermal properties.

[0083] Reference is now made to Figure 2A , Figure 2B , Figure 2C and Figure 2D showing schematic diagrams of possible configurations and combinations of interconnection segments 18. The diagrams generally show that adjacent interconnection segments can be symmetrical, asymmetrical with respect to adjacent interconnection segments, in an interdigitated relationship with adjacent interconnection segments, in a coplanar relationship with adjacent interconnection segments, in a parallel planar relationship with adjacent interconnection segments, in isolated or grouped networks, and combinations thereof. The specific geometric configuration will vary depending on the temperature gradient characteristics. The figures are merely exemplary; the designer will appreciate suitable variations.

[0084] Figure 3 An example is shown in which the loop L includes multiple interconnection segments 18, with the output 16 of one segment 18 serving as the input 14 of an adjacent segment 18, collectively collected at the power plant 22. In this way, the loop L is subdivided into a daisy chain configuration for the method operation.

[0085] The potential thermal output capacity is the maximum sustainable thermal energy output of the system. The thermal output can be temporarily varied with the methods disclosed herein, but the long-term average output (i.e. average over months or years) cannot exceed the potential thermal output capacity.

[0086] The overall geothermal efficiency of the system is equal to the average thermal output divided by the potential thermal output capacity, which is often referred to as the geothermal “capacity factor”. It is advantageous to have a high capacity factor, or high utilization of the available potential thermal output capacity. Conventionally, this is achieved with a constant thermal output at or near the potential thermal output capacity. Many geothermal systems operate in this way at capacity factors greater than 90%, sometimes referred to as “baseload” operation. The disclosed methods enable high geothermal capacity factors, while also providing flexible on-demand energy output, rather than constant output.

[0087] Figure 4 An example of transient thermodynamic modeling based on the closed loop multi-lateral system described in Applicant’s co-pending application No. PCT / CA2019000076, etc. is shown. The inputs to the thermodynamic model are seen in the table below.

[0088] Figure 4 Example data

[0089]

[0090]

[0091] This figure illustrates three operating scenarios for the same geothermal loop: operating in base load mode at a constant flow rate (base case), in which the thermal output equals the potential thermal output capacity; operating at 33 kg / s for 16 hours and then at 130 kg / s for 8 hours; and operating at 30 kg / s for 12 hours and then at 100 kg / s for 12 hours.

[0092] Typically, the charging period will be performed when energy prices are low or there is an excess of variable renewable energy supply. This allows the interconnection section 18 mentioned previously herein to recover thermal energy from the formation.

[0093] Figure 5 Key details are shown over a 3-day time frame. If the system is operated in base load mode, the average flow rate over the combined charging / discharging cycle is approximately equal to the optimum fixed flow rate. In this example, if operated in base load mode, the same subterranean well arrangement shown in the previous figure at a flow rate equal to 60 L / s will always equal the potential thermal output capacity. In layman's terms, the system will operate at full subterranean geothermal capacity. This is a key difference from some prior art (Ormat by Puna), in which the average geothermal output of the combined "charging" and "discharging" cycles is significantly lower than the long-term capacity.

[0094] The charging cycle establishes a strong thermal siphon, driven by the density difference of the cold fluid in the inlet well 14 relative to the hot fluid in the outlet well 16. During the charging cycle, the thermal siphon pressure drives above the pressure required to maintain the required flow rate. The flow rate is therefore controlled by applying a pressure drop using a flow control valve or other means (not shown) to suppress flow downstream of the outlet well 16. The flow control valve is automatic and can be controlled with software that uses a thermodynamic model to calculate the required position of the valve. The control valve also helps to manage the pressure in the subterranean loop to keep it within desired limits based on the density of the working fluid and the pump discharge pressure.

[0095] When discharging, the flow rate can be increased immediately by releasing the choke (opening the control valve). This near-instantaneous increase in flow rate enables fast ramping capability. The flow rate can be increased up to the point where the hydraulic losses through the closed loop equal the thermal siphon pressure drive.

[0096] Using a pump can increase the flow rate beyond this level, which will require a parasitic power load. However, as long as the majority of the pressure drive is generated by the thermal siphon effect, the parasitic load is in fact acceptable.

[0097] Using these methods, the flow rate can be controlled to match the power output to the end user's demand through the charge and discharge cycles and the residence time of the working fluid in the loop.

[0098] In prior art conventional open-loop geothermal systems or flow in porous media, the pumping pressure required to achieve high flow rates during discharge results in unacceptably high parasitic pump loads and significantly reduces or eliminates any gain in net power output. It has been found that the practical limit is reached when the ratio of pressure losses in the circuit to the thermosyphon pressure drive is about 1.5. The system must be designed with hydraulic losses less than 1.5 times the thermosyphon pressure drive. Ideally, the pressure losses are less than 1 times the thermosyphon drive and the entire flow is driven by the thermosyphon. Thus, there is no parasitic pump load.

[0099] Energy is stored in the working fluid itself. During the charge cycle, sufficient residence time is required to heat the working fluid to accommodate the discharge cycle. For example, if the discharge cycle is typically 8 hours long, the fluid circuit transit time must be at least 8 hours (the average of the discharge and charge cycles).

[0100] During the charge cycle, energy can also be temporarily stored in the rock near the subsurface flow path and the outlet well 16. At low flow rates, heat is conducted from the hotter rock in the formation 12 into the working fluid, and as the fluid progresses through the system, it encounters cooler rock (typically shallower, such as in the outlet well 16), where energy is transferred from the fluid to the cooler rock and temporarily stored. During the discharge cycle, the average fluid temperature drops, and the stored heat is transferred back into the working fluid.

[0101] The closed loop avoids the operational problems of conventional geothermal systems, which, as discussed herein, are exacerbated when the flow rate changes dramatically. For example, common operational problems are caused by brine, solids, scaling, clogging, and dissolved gases.

[0102] The dispatchability disclosed herein integrates well with low temperature air storage (CES), hydrogen production, or other systems that use stored electrical energy. An example of a process flow is shown below. The CES charge cycle can use cheap excess power from the grid or co-located renewable energy (e.g., solar power during daytime peak hours). The CES can also use produced geothermal energy to charge, but this is not required. In one embodiment, the geothermal system will produce a fixed amount of power throughout the charge and discharge cycles. The increase in thermal energy produced during the discharge cycle is used to heat the air stream from the CES process before expansion in the turbine.

[0103] There are several advantages to using CES with dispatchable geothermal:

[0104] The size of the heat engine, which converts thermal energy to electricity, is only sized for the peak output of the charging period, not the discharging period, greatly reducing equipment and asset costs.

[0105] Less additional infrastructure is required to supply heat to the CES facility.

[0106] The CES discharges only during a few peak hours of the day. The dispatchable geothermal system discharge period can match the CES discharge period.

[0107] Figure 6 The 30-year thermal output is shown for the "base case" and "8-hour dispatchable case" mentioned in the previous figures. The base case operates in a base load manner and is equal to the available thermal output capacity, while the "8-hour dispatchable case" achieves an effective capacity factor of approximately 97% despite operating in a dispatchable output, and thus is roughly equal to the predetermined potential thermal output capacity of the formation.

[0108] This illustrates the main invention, that the output can be dispatchable while still maintaining a high geothermal capacity factor, typically over 80% and close to 100%.

[0109] The transient thermal simulations described above were tested in a prototype geothermal system in central Alberta, Canada. The system included a 2.4 km deep multi-leg U-tube heat exchanger, and was 2.5 km from the surface site to site. The results validated the modeling and confirmed that dispatchability can be predicted and controlled by regulating the flow rate using an automated control valve at the outlet well in this example. The empirical results confirmed that the system is very fast-ramping, and when combined with a power generation system such as an Organic Rankine Cycle (ORC), can meet the fast-ramping requirements for integration with solar systems.

[0110] Figure 7 It is shown how the dispatchable geothermal system can be used when integrated with other non-dispatchable renewable energy sources. The system ramps down during solar peak hours and ramps up as solar decreases. The dispatchable geothermal fills the gap between the energy demand and the non-dispatchable renewable energy. This is merely an example, and the output can be modified to match any combination of charging / discharging periods, and the flow rate can be changed to meet any shape of output within the physical limitations.

[0111] Solar power generation is used as an example, however, the same dispatchable mechanism can be used for integration into direct heat utilization applications, such as district heating systems or district cooling systems.

[0112] Figure 8Multiple dispatchable geothermal loops in a network are shown. A charge / discharge cycle can be predetermined for each loop such that the total output meets a desired shaped output curve. An automated control system coupled with a thermodynamic model is used to control flow rates, thermosyphons, and temperatures in each loop. The charge / discharge cycle can be sequential or simultaneous depending on the situation and parameters of each loop.

[0113] Figure 9 is a process flow diagram to plan, control, and optimize the integration of non-dispatchable renewable energy with dispatchable geothermal. A grid system is provided with a demand curve over time, existing supply curves from different non-dispatchable renewable resources (such as PV, wind, base load nuclear, etc.), the control technique optimizes the network of dispatchable renewable geothermal generators to fill the gap between the existing non-dispatchable supply curves and the demand curve. The optimization parameter can be to meet the net demand, or it can be to maximize the price or revenue received (price times volume), or any other factor in combination. These can only form part of the optimization / scheduling algorithm.

[0114] In the network of dispatchable geothermal loops, a network of power generation modules (not shown) will be utilized that convert potential and thermal energy into electricity. These power generation systems can be ORC, flash equipment, pressure driven systems, direct turbines, or any other conversion component. The power generation modules can be arranged in series or parallel or a combination. A control system directs the flow from each geothermal loop to the appropriate conversion module based on proximity, dispatch, temperature, and other relevant factors.

[0115] Figure 10 The combined power output capacity of the generator network is shown, which is necessarily higher than the potential thermal output capacity of the geothermal loop network. The power generation capacity is designed to meet the peak output of the geothermal network at dispatch, which can be set to meet the peak demand from end users. This figure illustrates that while the subsurface system has a high geothermal capacity factor, over 80% and often over 90%, (where the denominator is the potential thermal output capacity), the surface power conversion modules have a relatively lower capacity factor to achieve dispatch.

[0116] Figure 11 An embodiment of the invention is shown that is designed to utilize an intermittent power source to mitigate grid saturation. In the example, a solar energy recovery arrangement 30 is operably connected to a loop L (loop arrangement or solution), and more particularly at 32 to the array 30. The power generation equipment 22 is in electrical communication with a grid (not shown) having a particular capacity. This is generally indicated by reference numeral 34.

[0117] For the following example, the loop arrangement or loop solution is intended to encompass the arrangements discussed previously herein, i.e. wells 14, 16 and interconnections 18 in a heat bearing geological formation which can include power generation equipment 22.

[0118] In the process of moving to newer, cleaner forms of energy, solar energy is in the lead. However, success has its own complications. Many power grids are now saturated with wind and solar energy to the point that it is difficult to absorb more intermittent energy. In this case, there is a need for scalable green dispatchable power. The technology herein can complement new or even existing solar power plants.

[0119] A typical 10 MW loop L unit combines a 5 MW subsurface base load solution with ORC and surface facilities scaled to 10 MW. This is to facilitate the inherent dispatchability of the energy produced by the loop L. This can then be further scaled by simply adding more loop arrangements L. By way of example, a 200 MW loop L arrangement has the following operating data.

[0120] Example - grid saturation mitigation

[0121]

[0122] Solar only solution

[0123] For a 200 MW solar power plant, due to its intermittency, on average only 40 MW of power can be produced. If it is desired to increase the average power production by a factor of 3.5 or an additional 100 MW on average, then an additional 500 MW solar power plant and an additional 500 MW of transmission capacity must be added. The reason for this is simple, the solar load factor will be between 10% and 25%. Unfortunately, this not only requires a 3.5 times increase in ground footprint, but also a 3.5 times upgrade of the transmission network (or, even less desirably, the building of new transmission lines to the new solar power plant). This situation is further exacerbated in that a large portion of the added capacity will be produced at times of the day that can achieve far less than the average price.

[0124] Loop solution

[0125] By contrast, the same result can be achieved by incorporating a 200 MW loop solution directly under the existing ground footprint of a current or planned solar power plant. Advantageously, no new land acquisition is required. Furthermore, since the loop arrangement will utilize its inherent dispatchability to produce power at around the 20% load factor of the solar power plant, no additional transmission capacity is required, saving time and money. Finally, while the loop does not have much transmission capacity to produce during the solar production peak period around midday, the midday production (which is usually of little value) can be turned into an attractive monetization, since a premium can be achieved for dispatchable power, as opposed to intermittent or base load power.

[0126] Solar + Battery solution

[0127] Of course, solar can be mimicked by adding enough battery to the loop solution, but at a considerable cost. The solar developer needs to add 500 MW of solar capacity, instead of just 200 MW of loop solution, which requires a massive expansion of surface footprint and 200 MW of 8-hour battery storage, inevitably increasing cost and delay.

[0128] As a variation of this example, Figure 11 An arrangement is depicted using windmills 36 as prime movers.

[0129] Referring now to Figure 12 , another variation of this example is shown. The numeral 40 represents a geographical area over which a power distribution center 42 is arranged to provide power delivery via 44 to a power transmission grid (not shown). As is well known, the grid has an output capacity. The center 42 contributes to a power generation system on the geographical area 40, which has a designed maximum power generation and a second effective or "actual" power generation on the grid.

[0130] Obviously, over the broad area 40 between the centers 42, "brownouts" or other delivery anomalies can occasionally occur due to various reasons known to those skilled in the art, such as peak demand of a large number of users or reallocation between the centers 42.

[0131] To mitigate the inconsistent delivery problem, a loop arrangement L can be integrated on the loop of the center 42, such as between adjacent electrical communication centers 42. As with the previous example and the explanation here, the closed loop configuration can be provided within the underlying geologic strata to produce a predetermined energy output from the available potential heat capacity of the strata.

[0132] The working fluid can then be circulated as already discussed and selectively thermally discharged through the power generation arrangement 22 to maintain power generation to the capacity of the entire power transmission grid. This correspondingly mitigates the above-mentioned anomalies or irregularities.

[0133] Depending on the geographic region and other factors, the main distribution center 46 containing multiple loop arrangements L can augment or replace some or all of the centers 42 and individually located loops L.

Claims

1. A method for controlling thermal output of a geothermal well system, the well system comprising an inlet wellbore, an outlet wellbore, an interconnecting wellbore connecting the inlet wellbore and the outlet wellbore within a geothermal formation, and a working fluid in the inlet wellbore, the outlet wellbore, and the interconnecting wellbore capable of being thermally charged from formation heat, the method comprising: circulating the working fluid within the well system; and adjusting the circulation of the working fluid within the well system to vary thermal output of the thermally charged working fluid over a characteristic potential thermal output capacity of the well system, wherein the characteristic potential thermal output capacity of the well system is the capacity of the working fluid to operate at a base load thermal output at a constant flow rate over a specified time period, and wherein adjusting the circulation comprises adjusting the circulation to produce an average thermal output over the specified time period equal to or less than the potential thermal output capacity.

2. The method of claim 1, wherein, the average thermal output exceeds 80% of the potential thermal output capacity.

3. The method of claim 1, wherein, the average thermal output exceeds 90% of the potential thermal output capacity.

4. The method of claim 1, wherein, the average thermal output is at least 97% of the potential thermal output capacity.

5. The method of claim 1, wherein, the specified time period is at least thirty days.

6. The method of claim 1, wherein, the adjusting the circulation comprises controlling a residence time of the working fluid in the geothermal formation.

7. The method of claim 1, wherein, wherein, the adjusting the circulation comprises adjusting the circulation between a charging cycle of the working fluid by thermal conduction with the formation heat and a discharging cycle of removing thermal energy from the working fluid, and the method further comprises: the adjusting the circulation further comprises conducting the charging cycle during a solar power generation peak period; and generating power from the removed thermal energy into an electrical grid during the discharging cycle.

8. The method of claim 1, wherein, the adjusting the circulation comprises adjusting the circulation between a charging cycle of the working fluid by thermal conduction with the formation heat and a discharging cycle of removing thermal energy from the working fluid, and wherein the discharging cycle is conducted during nighttime.

9. The method of claim 1, wherein, the adjusting the circulation comprises adjusting the circulation between a charging cycle of the working fluid by thermal conduction with the formation heat and a discharging cycle of removing thermal energy from the working fluid, and wherein the discharging cycle is scheduled based on a charging and discharging status of another geothermal well system.

10. The method of claim 9, wherein, the discharging cycle is sequenced relative to a discharging cycle of the another geothermal well system.

11. The method of claim 10, wherein, the discharging cycle is sequenced relative to a discharging cycle of the another geothermal well system based on a demand curve of a second specified time period.

12. The method of claim 9, wherein, the discharging cycle is synchronized with a discharging cycle of the another geothermal well system.

13. The method of claim 9, wherein, the method comprises generating power from the removed thermal energy into an electrical grid during the discharging cycle of the geothermal well system and the another geothermal well system.

14. The method of claim 1, wherein, the adjusting the circulation comprises adjusting the circulation between a charging cycle of the working fluid by thermal conduction with the formation heat and a discharging cycle of removing thermal energy from the working fluid; wherein the method comprises generating power from the removed thermal energy into an electrical grid during the discharging cycle; and wherein the adjusting the circulation comprises adjusting the circulation to generate power based on an electrical grid demand curve.

15. The method of claim 1, wherein, the geothermal well system comprises a multi-leg system comprising a plurality of interconnecting wellbores.

16. The method of claim 1, wherein, the geothermal formation is hot dry rock, and wherein the geothermal well system is part of a closed loop heat recovery system.

17. The method of claim 16, wherein, The interconnected wellbores are uncased.

18. The method of claim 17, wherein, The geothermal well system includes a multi-lateral system including a plurality of interconnected wellbores.

19. The method of claim 17, wherein, The method further includes sealing fractures and / or permeations in the formation with the working fluid.

20. The method of claim 16, including regulating circulation to produce an average heat output that exceeds 90% of the potential heat output capacity.

21. A method for controlling heat output of a geothermal well system, the well system including therein a working fluid capable of being thermally charged from a geologic formation, the method comprising: regulating circulation of the working fluid within the well system to vary heat output of the thermally charged working fluid over a characteristic potential heat output capacity of the well system, wherein the characteristic potential heat output capacity is a capacity of the working fluid to operate at a base load heat output at a constant flow rate over a specified time period, and wherein regulating circulation includes regulating circulation to produce an average heat output over the specified time period that is equal to or less than the characteristic potential heat output capacity.

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