GB2620464A - Thermal energy conversion system - Google Patents

Abstract

A thermal energy conversion system 200 is arranged to deliver electrical power to a first load 102. The system includes a hot storage media 206, a cold storage media 204, an array of Stirling engines 202 each having a hot side thermally coupled to the hot storage media and a cold side thermally coupled to the cold storage media. An array of generators 216 is operable to produce a total power output, each generator connected to one of the Stirling engines. The system also includes a second load 220 operable to receive a portion of the total power output, and a controller operable to selectively connect and disconnect via switch 208 each of the generators with the second load to control the quantity of the total power output delivered to the first load.

Description

THERMAL ENERGY CONVERSION SYSTEM

BACKGROUND

[0001] Many energy sources, and in particular green energy sources (e.g., wind and solar) are abundantly available at times when the power generated may not be needed. Rather than not generating the energy, it is desirable to generate and store the energy for use when demand is higher.

SUMMARY

[0002] In one aspect, a thermal energy conversion system is arranged to deliver electrical power to a first load. The system includes a hot storage media, a cold storage media, an array of Stirling engines each having a hot side thermally coupled to the hot storage media and a cold side thermally coupled to the cold storage media. An array of generators is operable to produce a total power output, each generator connected to one of the Stirling engines. The system also includes a second load operable to receive a portion of the total power output, and a controller operable to selectively connect and disconnect each of the generators with the second load to control the quantity of the total power output delivered to the first load.

[0003] In another aspect, a thermal energy conversion system is arranged to deliver electrical power to a first load. The system includes a source of excess electrical power, a thermal converter including one of a heating system operable to heat a hot storage media and a cooling system operable to cool a cold storage media in response to the receipt of the excess electrical power. The system also includes an array of Stirling engines each having a hot side thermally coupled to the hot storage media and a cold side thermally coupled to the cold storage media, an electrical generator coupled to each of the Stirling engines and operable to produce a total power output, and a controller operable to distribute a portion of the total power output to the thermal converter and the remainder of the total power output to the first load.

[0004] In another aspect, a method of storing excess electrical power includes directing the excess electrical power to a thermal converter that includes one of a heating system operable to heat a hot storage media and a cooling system operable to cool a cold storage media, connecting an array of Stirling engines to the hot storage media and the cold storage media, operating the array of Stirling engines to power an electrical generator to produce a total power output, and varying a variable switch to distribute a portion of the total power output to the thermal converter.

100051 The foregoing has broadly outlined some of the technical features of the present disclosure so that those skilled in the art may better understand the detailed description that follows. Additional features and advantages of the disclosure will be described hereinafter that form the subject of the claims. Those skilled in the art will appreciate that they may readily use the conception and the specific embodiments disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure in its broadest form.

[0006] Also, before undertaking the Detailed Description below, it should be understood that various definitions for certain words and phrases are provided throughout this patent document, and those of ordinary skill in the art will understand that such definitions apply in many, if not most, instances to prior as well as future uses of such defined words and phrases. While some terms may include a wide variety of embodiments, the appended claims may expressly limit these terms to specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

100081 FIG. 1 s a schematic illustration of an arrangement of a microarid.

[0009] FIG. 2 is a schematic illustration of a thermal energy conversion system.

DETAILED DESCRIPTION

[0010] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in this description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

100111 Various technologies that pertain to systems and methods will now be described with reference to the drawings, where like reference numerals represent like elements throughout. The drawings discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged apparatus. It is to be understood that functionality that is described as being carried out by certain system elements may be performed by multiple elements. Similarly, for instance, an element may be configured to perform functionality that is described as being carried out by multiple elements. The numerous innovative teachings of the present application will be described with reference to exemplary non-limiting embodiments.

[0012] Also, it should be understood that the words or phrases used herein should be construed broadly, unless expressly limited in some examples. For example, the terms "including," "having," and "comprising," as well as derivatives thereof, mean inclusion without limitation. The singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Further, the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. The term "or" is inclusive, meaning and/or, unless the context clearly indicates otherwise. The phrases "associated with" and "associated therewith," as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like Furthermore, while multiple embodiments or constructions may be described herein, any features, methods, steps, components, etc. described with regard to one embodiment are equally applicable to other embodiments absent a specific statement to the contrary.

[0013] Also, although the terms "first", "second", "third" and so forth may be used herein to refer to various elements, information, functions, or acts, these elements, information, functions, or acts should not be limited by these terms. Rather these numeral adjectives are used to distinguish different elements, information, functions or acts from each other. For example, a first element, information, function, or act could be termed a second element, information, function, or act, and, similarly, a second element, information, function, or act could be termed a first element, information, function, or act, without departing from the scope of the present disclosure.

[0014] In addition, the term "adjacent to" may mean that an element is relatively near to but not in contact with a further element or that the element is in contact with the further portion unless the context clearly indicates otherwise Further, the phrase "based on" is intended to mean "based, at least in part, on" unless explicitly stated otherwise. Terms "about" or "substantially" or like terms are intended to cover variations in a value that are within normal industry manufacturing tolerances for that dimension. If no industry standard is available, a variation of twenty percent would fall within the meaning of these terms unless otherwise stated.

[0015] FIG. 1 illustrates one possible arrangement of a microgrid 100. Before proceeding, it should be noted that the microgrid 100 illustrated in FIG. 1 includes a number of features that may be omitted in other microgrid arrangements. In addition, other microgrids may include additional features not illustrated in FTG. I or described herein. Additional components could include components such as transformers, switches, electrical conditioning components, sensors, controllers, and other components that may add to the operation and functionality of the system. As such, microgrids should not be limited to the arrangement of the microgrid 100 of FIG. 1. In addition, the term "microgrid" is not meant to imply any size. Rather, it is simply a system that may include power generation, power storage, loads, and the ability to connect or disconnect from another grid or system.

[0016] With reference to FIG. 1, the microgrid 100 includes an AC bus 108 (alternating current bus), a DC bus 110 (direct current bus), a microgrid controller 138, and a grid connector 106 that operates to selectively connect or disconnect the microgrid 100 from a transformer 104 that ultimately connects to a local energy grid 102, such as a utility grid.

[0017] The AC bus 108 provides a common connection point for the collection and distribution of alternating current (AC) electrical power. The AC bus 108 also connects to the local energy grid 102 when the grid connector 106 is in a closed position to either deliver electrical power to the local energy grid 102 or to draw electrical power from the local energy grid 102 as may be required. The DC bus 110 is similar to the AC bus 108 and provides a common connection point for the collection and distribution of direct current (DC) electrical power. It should be noted that either the AC bus 108 or the DC bus 110 could be omitted in other microgrid systems.

[0018] An AC/DC converter 112 is provided to facilitate the transfer of power between the AC bus 108 and the DC bus 110. The AC/DC converter 112 may include one or more inverters that operate to convert DC power to suitable AC power for addition to the AC bus 108. One or more rectifiers may also be included to convert AC power from the AC bus 108 to DC power for delivery to the DC bus 110. In systems that do not include both the AC bus 108 and the DC bus 110, one or more AC/DC converters 112 could be included to allow the connection of both AC systems and DC systems to the microgrid 100.

[0019] Any number of systems and components can be connected to the AC bus 108 to either deliver power to the AC bus 108 (power generators or producers) or to extract power from the AC bus 108 (loads). The microgrid 100 of FIG. 1 includes a wind turbine 114, a concentrated solar generator 116, and a combustion turbine 118 connected to the AC bus 108, with each operable to deliver power to the AC bus 108.

[0020] The wind turbine 114 includes one or more separate turbines that operate to generate AC power in response to the wind. The power generated by each wind turbine 114 may be AC power or DC power but that power is ultimately delivered to the AC bus 108 as AC power. As is well-known in the art, power generated by wind turbines 114 can be classified as both a green energy source as well as a variable energy source as it relies on proper wind conditions to be capable of generating energy, and the amount generated varies with the wind conditions.

[0021] The concentrated solar generator 116 includes one or more plants that operate to concentrate solar energy to generate steam. The steam in turn powers a conventional steam turbine to generate AC power that can be delivered directly to the AC bus 108. Like the power delivered by the wind turbine 114, the power delivered by the concentrated solar generator 116 can be classified as both a green energy source as well as a variable energy source as it relies on access to sunshine to be capable of generating energy and the amount generated varies with the level of sunshine.

[0022] The combustion turbine 118 may include one or more combustion turbines 118 that combust a fuel to produce AC power that can be delivered directly to the AC bus 108. Power delivered by the combustion turbines 118 can be classified as green or not green depending upon the fuel combusted. For example, a combustion turbine 118 that combusts hydrogen or methane from biomass would generally be considered green so long as the source of hydrogen or biomass is green. In addition, other sources of methane can be considered green such that combustion turbines 118 that combust green methane could be considered green. Unlike the wind turbine 114 and the concentrated solar generator 116, the combustion turbines 118 are not considered variable energy sources as they are capable of delivering full power regardless of external conditions, so long as they have a fuel supply.

[0023] The wind turbine 114, the concentrated solar generator 116, and the combustion turbine 118 are examples of power sources suitable for use in the microgrid 100. However, other AC electrical generators 120 are also suitable for use with the microgrid 100 and in particular for connection with the AC bus 108. The additional AC electrical generators 120 may be variable and may be green. For example, additional AC electrical generators 120 could include generators powered by hydro, geothermal, nuclear, fossil fuels, tidal, and the like. It is also important to note that many of these power sources are capable of controlling the frequency and voltage of the AC power delivered to the AC bus 108, thereby adding to the stability of the microgrid 100 and potentially to the local energy grid 102 when the microgrid 100 is connected thereto.

[0024] In addition to power sources, AC energy storage systems 122 or power conditioning systems may also be connected to the AC bus 108. AC energy storage systems 122 include systems that use AC power to store energy, typically in another form, when that energy is abundant and then use that stored energy to generate AC power when additional AC power is required by the AC bus 108 or the local energy grid 102 when connected thereto. One example of AC energy storage system 122 is pumped storage hydro in which water is pumped to a higher elevation when excess energy is available, and the water is passed through a hydro turbine when AC power is required. Another AC energy storage system 122 includes a compressed gas storage system that operates to compress a gas with excess energy and then power a turbine or other device using that compressed gas to generate AC power when energy is needed. Other systems may store the energy thermally by heating and storing a hot fluid or solid or by cooling a fluid or solid. Power conditioning systems could include synchronous condensers or flywheels that operate to control reactive power and fast frequency response in some cases (e.g., spinning reserve).

100251 Another energy storage system could include a production facility that uses excess energy to produce hydrogen, methane, gasoline, or other compounds that efficiently store energy. With a hydrogen facility, excess electricity is used in an electrolysis process to produce hydrogen. The hydrogen is then pressurized and stored. When additional AC power required, the stored hydrogen is used as fuel in the combustion turbine 118. Many other AC energy storage systems 122 are suitable for use with the AC bus 108. As such, the microgrid 100 should not be limited to those examples discussed herein.

[0026] Also attached to the AC bus 108 are one or more AC loads 124. AC loads 124 are loads that do not provide power to the AC bus 108 but rather only draw AC power. AC loads 124 can include factories, homes, data storage systems, production facilities, and the like.

[0027] Like the AC bus 108, any number of systems and components can be connected to the DC bus 110 to either deliver power to the DC bus 110 or to extract power from the DC bus 110. For example, the microgrid 100 of FIG. I includes a PV solar generator 126 connected to the DC bus 110 to deliver DC power to the DC bus 110. Power delivered by the PV solar generator 126 can be classified as both a green energy source as well as a variable energy source as it relies on access to sunshine to be capable of generating energy and the amount generated varies with the level of sunshine.

[0028] Other DC electrical generators 134 may also be connected to the DC bus 110 to deliver DC power to the DC bus 110. For example, fuel cells could be connected to the DC bus 110 to deliver power to the DC bus 110. Many other DC power sources could also be employed such as but not limited to DC generators, alternators, and other variable frequency sources that include a rectifier.

[0029] The DC bus 110 is well-suited to supporting many energy storage devices including batteries 128, ultracapacitors 130, and other DC energy storage systems 132. Batteries 128 and ultracapacitors 130 are well-known energy storage devices with virtually any type and arrangement being suitable for use with the microgrid 100 of FIG. 1. Other DC energy storage systems 132 could include flywheels, electrochemical capacitors, thermal storage, and the like.

[0030] One or more DC loads 136 may be connected to the DC bus 110 to draw DC power therefrom. Unlike energy storage devices that can transfer power to and from the DC bus 110, the DC loads 136 only draw power from the DC bus 110. DC loads 136 could include heating systems, data centers, computers, or any other system or component that operates on or consumes DC power.

[0031] It should be noted that any AC system including loads, power-producing systems, and storage systems could be converted to DC systems using one or more rectifiers. Similarly, any DC system could be converted to AC with one or more inverters. As such, the examples provided herein should not be limited to connection to the AC bus 108 or the DC bus 110 as described herein.

[0032] The microgrid controller 138 is typically a microprocessor-based controller that includes a microprocessor, memory, a memory storage device, input devices, and some form of output such as a display that allows for user interaction. Of course, other controllers or arrangements of controllers could be employed. It is also important to note that while FIG. 1 illustrates a single microgrid controller 138, multiple components or systems could be distributed throughout the microgrid 100 and could cooperate with one another to perform the functions of the microgrid controller 138.

[0033] The microgrid controller 138 communicates with the various components of the microgrid 100 to monitor and/or control their operation. The microgrid controller 138 may include sensors that monitor temperatures, pressures, power flow, valve positions, switch and relay positions, voltage, frequency, and the like to operate the microgrid 100. The microgrid controller 138 also communicates with the AC/DC converter 112 and can operate to control the quantity of power flow and the direction of power flow between the AC bus 108 and the DC bus 110.

[0034] The microgrid controller 138 may also operate to control the dispatching of power to select the desired power sources to achieve a goal. For example, the microgrid controller 138 could operate to maximize the use of power from green energy sources when it is available to power the AC loads 124 and the DC loads 136 while also storing any excess power. When the green power is not available, the microgrid controller 138 could operate to use stored energy before initiating operation of non-green power sources. The microgrid controller 138 also operates to control the grid connector 106 to connect or disconnect the local energy grid 102 and the microgrid 100.

100351 In operation, the microgrid controller 138 determines the total load required by the AC loads 124 and the DC loads 136 and selects the power generation sources to provide at least that load. Specifically, the microgrid controller 138 may operate to first dispatch the green power sources, whether AC or DC to provide the necessary power to the AC loads 124 and the DC loads 136. If there is excess green power available, the microgrid controller 138 may initiate operation of one or more of the various energy storage systems to store that power. If the green power is not sufficient to support the AC loads 124 and the DC loads 136 the microgrid controller 138 determines which power source or sources to use to deliver the additional power. The microgrid controller 138 may initiate additional non-green power generators such as the combustion turbines 118, may utilize energy stored in one of the AC energy storage systems 122, the batteries 128, the ultracapacitors 130, and/or the DC energy storage systems 132, and/or may close the grid connector 106 to draw power from the local energy grid 102. In some cases, if it is not desirable, or possible to connect to the local energy grid 102, the microgrid controller 138 may operate to selectively reduce one or more of the AC loads 124 and the DC loads 136.

[0036] Under some conditions, the power generation capacity of the microgrid 100 may exceed the AC loads 124, the DC loads 136, and the energy storage capacity of the microgrid 100. In these situations, energy production can be reduced or the grid connector 106 can be closed to deliver power to the local energy grid 102.

[0037] Before proceeding, it should be noted that terms such as systems, loads, subsystems, and the like are interchangeable. Typically, a subsystem is part of a system or a load, however, subsystems can themselves be loads or systems as well. As used herein, terms such as "power source" can refer to any component, device, or system that is operable to deliver power to the microgrid 100 or to another load. Similarly, the term "load" could refer to any component, device, or system that draws power from the microgrid 100 or another source.

[0038] FIG. 2 illustrates a thermal energy conversion system 200 that could be used as part of the AC energy storage system 122 or the DC energy storage system 132 of FIG. 1 depending on the type of electrical power generated (e.g., AC, DC, variable-frequency AC, etc.). The thermal energy conversion system 200 includes an array of Stirling engines 202 that operates using at least one of a hot fluid stored in hot fluid storage 206 and a cold fluid in a cold fluid storage 204. The hot fluid storage 206 contains a hot fluid or hot storage media that could include any substance capable of holding heat energy. For example, one arrangement could include heated water or steam. Other systems may use a molten salt (e.g., KNO3, NaNO2, NaNO3, and/or one or more other salts), or another liquid (e.g., ethylene glycol, etc.) that is capable of being stored at high temperatures (e.g., greater than 500 degrees C and more preferably in excess of 800 degrees C). Still other systems could heat a solid material (e.g., aluminum, bricks, cast iron, concrete, granite, lava rocks, fireclay, sodium, or any other suitable material) that stores the energy as heat. A fluid may then be required to extract and move that heat from the solid material for use in the thermal energy conversion system 200. A primary heating system 222 may be provided to heat the hot storage media within the hot fluid storage 206. In preferred arrangements, excess power from sources such as wind, solar, nuclear, and the like may be used to power the primary heating system 222 and heat the hot storage media to store that excess energy.

100391 The cold fluid storage 204 includes a stored cold fluid or cold storage media that could include any substance capable of being cooled and maintained at a cooled temperature. For example, one arrangement uses air that is compressed and cooled. In still other constructions, the air is cooled to a cryogenic liquid (e.g., less than -196 degrees C) for more compact storage. Still other arrangements may use other fluids such as nitrogen, oxygen, carbon dioxide, ammonia, ethylene glycol, or refrigerants, with many other fluids being possible. A primary cooling system 224 may be provided to cool the cold storage media within the cold fluid storage 204. Like the primary heating system 222, the primary cooling system 224 is preferably powered using excess power from sources such as wind, solar, nuclear, and the like. It should also be noted that the compression process, and even the cooling process produces waste heat that could be captured and used to heat the hot fluid at various points within the I0 cycle. Additionally, other components (e.g., generators, pumps, compressors, etc.) may produce heat that could be captured and used to heat the hot fluid as desired. Any recapture of waste heat serves to improve the efficiency of the system.

[0040] The array of Stirling engines 202 may include any number of Stirling engines 210 with at least 10 being preferred. "Stirling engine" refers to a heat engine that is operated by the cyclic compression and expansion of air or other gas (the working fluid) between different temperatures, resulting in a net conversion of heat energy to mechanical work.

100411 More specifically, the Stirling engine is a closed-cycle regenerative heat engine with a permanent gaseous working fluid. "Closed-cycle", in this context, means a thermodynamic system in which the working fluid is permanently contained within the system, and "regenerative" describes the use of a specific type of internal heat exchanger and thermal store, known as the regenerator.

[0042] In the Stirling engine, a gas is heated and expanded by energy supplied from outside the engine's interior space (cylinder). The gas is then shunted to a different location within the engine where it is cooled and compressed. A piston or pistons move the gas to the correct places within the engine at the correct time in the cycle and extract mechanical power therefrom. The gas oscillates between these heating and cooling spaces, changing temperature and pressure as it goes.

[0043] The heat is supplied from the outside, so the hot area of the engine can be warmed with any external heat source. Similarly, the cooler part of the engine can be cooled by an external heat sink. The gas, in an ideal engine is permanently retained in the engine allowing for the use of a gas with the most suitable properties, such as helium or hydrogen. There are no intake or exhaust gas flows, so the engine is practically silent.

100441 In the construction of FIG. 2, each Stirling engine 210 includes a hot side 212, a cold side 214, and a generator 216. The hot side 212 is exposed to the hot storage media stored in the hot fluid storage 206 and the cold side 214 is exposed to the cold storage media stored in the cold fluid storage 204. It should be noted that both cold fluid storage 204 and hot fluid storage 206 are not required to operate the Stirling engines 210. All that is required is a large temperature difference. Therefore, some systems may use only the hot storage media and hot fluid storage 206 with ambient air or a cooling source such as water acting as the cold storage media. Alternatively, cold storage media stored in the cold fluid storage 204 could be used with atmospheric air acting as the hot storage media. Each of these offers enough temperature difference to operate the Stirling engines 210. However, efficiency and cost effectiveness each increase with larger temperature differentials such that the use of both cold fluid storage 204 and hot fluid storage 206 is preferred.

[0045] While not illustrated in FIG. 2, a preferred arrangement would deliver hot storage media and cold storage media to the respective hot sides 212 and cold sides 214 via manifolds such that each Stirling engine 210 receives hot storage media at its highest temperature and cold storage media at its lowest temperature to enhance the efficiency of each Stirling engine 210.

[0046] As illustrated in FIG. 2, each Stirling engine 210 drives a generator 216 to generate electrical power. Any suitable generator could be employed as the generator 216 including but not limited to linear generators, AC generators, DC generators, high-frequency generators, and the like. It should also be noted that while each Stirling engine 210 is illustrated as driving a separate generator 216, other arrangements could use fewer generators or even a single generator driven by each of the Stirling engines 210.

[0047] The electrical power generated by the generator 216 or generators 216 is delivered to a bus 218. The power is then directed to a variable switch 208 that can distribute the power to the local energy grid 102 or to a thermal converter 220. The illustrated thermal converter 220 includes a resistive heating system that uses some of the electrical power to heat the hot storage media within the hot fluid storage 206. In alternative arrangements, the thermal convertor includes a cooling system that operates to cool the cold storage media in place of or in conjunction with the resistive heating system.

[0048] The use of the switch 208 overcomes one of the weaknesses of Stirling engines 210. Specifically, Stirling engines 210 do not change load quickly or easily and are best operated at a full load condition. To allow for quick and efficient load changes, the switch 208 diverts some of the generated power to the thermal converter 220 to lower the power delivered to the local energy grid 102 or other loads. The use of the array of Stirling engines 202 further allows for single engines to be shut down when the demand drops to a level where the engine is not needed. Thus, the engines can be operated at full load, to ensure maximum efficiency.

[0049] It should be noted that other constructions may employ multiple switches 208 and/or multiple resistive heaters. For example, one construction may include a switch 208 for each individual Stirling engine 210 such that each switch 208 operates with only one of the Stirling engines 210.

[0050] In operation, the microgrid 100 operates to generate electrical power for use by various sources. Under some operating conditions, excess electrical power may be available. For example, during the day, excess solar or wind power may be available but may be unused. The thermal energy conversion system 200 of FIG. 2 uses the excess electrical power to heat the hot storage media within the hot fluid storage 206 and/or to cool and compress the cold storage media stored in the cold fluid storage 204 [0051] When additional energy is needed, the Stirling engines 210 of the array of Stirling engines 202 are started, either as a unit or individually. Each Stirling engine 210 operates based on the temperature difference between the hot storage media and the cold storage media to power a generator and generate electrical power. In the construction described with regard to FIG. 2, the hot storage media is a molten salt stored at a temperature of 800 degrees C or hotter. The cold storage media is stored at a temperature at or below -196 degrees C to establish a temperature difference of about 1000 degrees C. [0052] In one construction, each Stirling engine 210 has a maximum electrical power output between 0.2 MWs and 2 MWs with the array of Stirling engines 202 being capable of any desired total power output. For example, a 50 MVV system could include twenty-five 2 MW Stirling engines 210.

[0053] As noted above, Stirling engines 210 operate best at full load and are typically not capable of easily or quickly changing loads. By utilizing an array of Stirling engines 202, individual engines can be disconnected or reconnected to quickly vary the total power output of the array of Stirling engines 202. In the illustrated construction, a variable switch 208 is provided that can quickly and accurately distribute power between the local energy grid 102, or another point of use, and a thermal converter 220 that can be used to heat the hot storage media and/or to cool and compress the cold storage media.

[0054] The use of the switch 208 allows the load being provided to the local energy grid 102 to be quickly and accurately controlled without wasting the excess energy being generated by the array of Stirling engines 202. If the excess power generated by the array of Stirling engines 202 exceeds the power generated by individual Stirling engines 210, individual Stirling engines 210 can be shutdown. Thus, the use of an array of Stirling engines 202 along with the switch 208 provides the ability to quickly and accurately control the power output of the array of Stirling engines 202 without having to quickly vary the output of any individual Stirling engine 210 or to operate any engines at less than full capacity.

100551 Although an exemplary embodiment of the present disclosure has been described in detail, those skilled in the art will understand that various changes, substitutions, variations, and improvements disclosed herein may be made without departing from the spirit and scope of the disclosure in its broadest form.

[0056] None of the description in the present application should be read as implying that any particular element, step, act, or function is an essential element, which must be included in the claim scope: the scope of patented subject matter is defined only by the allowed claims. Moreover, none of these claims are intended to invoke a means plus function claim construction unless the exact words "means for" are followed by a participle.

Claims (21)

1. CLAIMSWhat is claimed is: I. A thermal energy conversion system arranged to deliver electrical power to a first load, the system comprising: a hot storage media, a cold storage media; an array of Stirling engines each having a hot side thermally coupled to the hot storage media and a cold side thermally coupled to the cold storage media; an array of generators operable to produce a total power output, each generator connected to one of the Stirling engines; a second load operable to receive a portion of the total power output; and a controller operable to selectively connect and disconnect each of the generators with the second load to control the quantity of the total power output delivered to the first load.
2. 2. The system of claim 1, wherein the hot storage media includes one of a molten salt, a heated solid, and ambient air.
3. 3. The system of claim 1, wherein the cold storage media includes one of ambient air, a chilled fluid, and a cryogenic fluid.
4. 4. The system of claim I, wherein there is a one-to-one correspondence between the Stirling engines and the generators, and wherein each generator is operable to produce between 0.2 MW and 2 MW.
5. 5. The system of claim 1, wherein the second load includes a resistive heating system arranged to heat the hot storage media.
6. 6. The system of claim 5, wherein the resistive heating system includes an array of variable switches, each variable switch positioned between one of the generators and the resistive heating system, and wherein the controller is operable to vary each of the variable switches to control the distribution of a generator power generated by each generator.IS
7. 7. The system of claim 5, wherein the array of generators delivers the total power output to a bus, and wherein a variable switch is coupled to the bus and is operable deliver a portion of the total power output to the second load and the remainder of the total power output to the first load.
8. 8. A thermal energy conversion system arranged to deliver electrical power to a first load, the system comprising: a source of excess electrical power; a thermal converter including one of a heating system operable to heat a hot storage media and a cooling system operable to cool a cold storage media, the thermal converter operable in response to the receipt of the excess electrical power; an array of Stirling engines each having a hot side thermally coupled to the hot storage media and a cold side thermally coupled to the cold storage media; an electrical generator coupled to each of the Stirling engines and operable to produce a total power output; a controller operable to distribute a portion of the total power output to the thermal converter and the remainder of the total power output to the first load.
9. 9. The system of claim 8, wherein the hot storage media includes one of a molten salt, a heated solid, and ambient air.
10. 10. The system of claim 8, wherein the cold storage media includes one of ambient air, a chilled fluid, and a cryogenic fluid.
11. I I. The system of claim 8, wherein the electrical generator includes an array of generators.
12. 12. The system of claim 11, wherein there is a one-to-one correspondence between the Stirling engines and the generators, and wherein each generator is operable to produce between 0.2 MW and 2 MW.
13. 13. The system of claim 12, wherein the heating system includes an array of variable switches and a resistive heater, each variable switch positioned between one of the generators and the resistive heater, and wherein the controller is operable to vary each of the variable switches to control the portion of the total power output delivered to the heating system.
14. 14. The system of claim 8, wherein the thermal converter includes a resistive heating system arranged to heat the hot storage media.
15. 15. The system of claim 8, wherein the thermal converter includes a cryogenic system operable to compress and cool air for storage as a cryogenic fluid.
16. 16. The system of claim 8, further comprising a variable switch coupled to the electrical generator and operable deliver a portion of the total power output to the thermal converter and the remainder of the total power output to the first load.
17. 17. A method of storing excess electrical power, the method comprising: directing the excess electrical power to a thermal converter that includes one of a heating system operable to heat a hot storage media and a cooling system operable to cool a cold storage media; connecting an array of Stirling engines to the hot storage media and the cold storage media operating the array of Stirling engines to power an electrical generator to produce a total power output; and varying a variable switch to distribute a portion of the total power output to the thermal converter.
18. 18. The method of claim 17, further comprising shutting down operation of a portion of the Stirling engines of the array of Stirling engines to reduce the total power output.
19. 19. The method of claim 17, wherein the thermal converter includes a resistive heater operable to heat the hot storage media.
20. 20. The method of claim 17, further comprising providing at least ten Stirling engines in the array of Stirling engines, each Stirling engine sized to produce between 0.2 MV^T and 2 MW.
21. 21. The method of claim 19, further comprising operating a primary heating system to heat a molten salt in response to the receipt of electrical power.