Thermal energy storage system and method

Abstract

This invention relates to a module for a modular thermal energy storage system. The module has a thermal storage mass, an electrical integration channel, and a fluid channel. The electrical integration channel is for at least partly enclosing a portion of an electrical heating element extending through the module. The fluid channel is for fluidic communication with a fluid input and a fluid output of the modular thermal energy storage system. The electrical integration channel is separate and different from the fluid channel. The present invention also relates different types of modules for a modular thermal energy storage system, modular thermal energy storage systems themselves, and methods for heating the thermal energy storage mass of a thermal energy storage system.

Description

[0001] THERMAL ENERGY STORAGE SYSTEM AND METHOD

[0002] Field of the invention

[0003] The present invention relates to thermal energy storage systems, particularly thermal energy storage systems that operate at ultra-high temperatures greater than 873K (600°C), and methods of operating the same.

[0004] Background to the invention

[0005] Energy sourced from renewable sources such as the sun, wind, waves or tides has significant environmental benefits over that sourced from fossil fuels and the like. Unfortunately, the energy that can be extracted from renewables and the demand for it varies both in terms of time and geographical location. Therefore, energy storage is required to match generation with use. To date grid-scale energy storage has been limited by low energy densities, long-term performance degradation, low round-trip efficiencies or limited deployment locations. Thermal storage at ultra-high temperatures is made challenging due to thermal loss (resulting in low energy densities) and uneconomical electricity generation efficiency.

[0006] There is a need to provide thermal energy storage systems, which are operable at ultra-high temperatures, having improved performance and reduced cost. It is in this context that the present invention has been devised.

[0007] Summary of the invention

[0008] According to an aspect of the invention there is provided a module for a modular thermal energy storage system, the modular thermal energy storage system having a fluid input, a plurality of modules, an electrical heating element for heating at least a subset of the plurality of modules, and a network of channels for heat exchange between fluid introduced via the fluid input and the plurality of modules to generate heated fluid, and a fluid output for outputting the heated fluid, the module comprising: a thermal storage mass; an electrical integration channel for at least partly enclosing a portion of the electrical heating element extending through the module; a fluid channel for fluidic communication with the fluid input and fluid output; and wherein the electrical integration channel is separate and different from the fluid channel.

[0009] The module having an electrical integration channel and fluid channel as described herein is suitable for receiving thermal energy, storing the received thermal energy and facilitating heat exchange between a fluid and a thermal mass. That is, the modules provide several of the main functions of a thermal energy storage system in modular form, thereby limiting the number of separate parts needed to provide a thermal energy storage system. By reducing the number of separate parts, efficient thermal transfer is facilitated. In addition, since fewer different parts need to be manufactured, thermal energy storage systems can be provided cost effectively. In addition, these modules provide users more flexibility in how thermal storage mass system are designed, and facilitate straightforward and cost-effective repair of these systems.

[0010] Typically, the modular thermal energy storage system may comprise a plurality of modules having the features of the module described hereinbefore.

[0011] Typically, the portion of the electrical heating element is less than the whole of the electrical heating element.

[0012] It may be that the module has a first face associated with the electrical integration channel (e.g., having a portion shaped to form a channel for accommodating an electrical heating element). It may be that the electrical integration channel extends along the first face between a second face and a third face. It may be that the second face is opposite the third face. Further, it may be that the module has a fourth face associated with the fluid channel (e.g., having a portion shaped to form a channel for heated fluid to flow). It may be that the fluid channel extends along the fourth face between a fifth face and the first face. It may be that the first face is opposite the fifth face. It may be that the module has a sixth face associated with a further fluid channel. It may be that the further fluid channel extends along the sixth face between a fifth face and the first face. It may be that a further electrical integration channel extends along the fifth face between the second face and the third face. It may be that the second face is for transferring heat between the module and an adjacent module (e.g., when multiple modules are stacked together). It may be that the third face is for transferring heat between the module and another adjacent module. Thus, one or more electrical integration channels and one or more fluid channels are conveniently integrated within a single modular component (e.g., a brick-based module). It will be understood that each of the faces described hereinabove are faces of the module.

[0013] It may be that the module comprises a brick-based module (e.g., stackable modules).

[0014] Typically, a body of the module is defined by the thermal storage mass, wherein the thermal storage mass is shaped to define both the fluid channel and the electrical integration channel.

[0015] Typically, the thermal storage mass has a first length extending along a first direction, the first length defined between a first end of the thermal mass and a second end of the thermal mass, wherein the electrical integration channel is suitable for supporting an electrical heating element extending along the first length and beyond both the first end and the second end. That is, the electrical heating element extends in, through and out of the module so that portions of the electrical heating element extending beyond the module can be integrated with another module.

[0016] It may be that the fluid channel is a gas channel - i.e. , suitable for allowing the passage of gas (e.g., air) therethrough.

[0017] It may be that the electrical integration channel is shaped to accommodate (i.e., at least partly enclose) a portion of a flat electrical heating element. It may be that the electrical integration channel is shaped to at least partly enclose two parallel portions of the same electrical heating element. It may be that the electrical heating element is not fully enclosed by the electrical integration channel along any part of its length.

[0018] The module may be suitable for a modular thermal energy storage system operable at greater than 800K, greater than 873K, greater than 900K, greater than 1000K, greater than 1200K, greater than 1400K, greater than 1600K, greater than 1800K, or greater than 2000K. The module may be suitable for a modular thermal energy storage system operable at less than 4000K, less than 3600K, less than 3000K, or less than 2000K.

[0019] That is, it may be that the thermal storage mass is configured to reach temperatures greater than 800K, greater than 873K, greater than 900K, greater than 1000K, greater than 1200K, greater than 1400K, greater than 1600K, greater than 1800K, or greater than 2000K. It may be that the thermal storage mass is configured to reach temperatures less than 4000K, less than 3600K, less than 3000K, or less than 2000K.

[0020] The thermal storage mass may comprise metal or ceramic.

[0021] It will be understood that the fluid channel is separate from the electrical integration channel in that the fluid channel is at a different position from the electrical integration channel. Typically, in use, the fluid channel is not in fluidic communication with the electrical integration channel.

[0022] The fluid channel may be different from the electrical integration channel in that it is shaped differently. The fluid channel may be different from the electrical integration channel in that it is sized differently. The fluid channel may be different from the electrical integration channel in that it extends along a different direction.

[0023] It may be that the fluid channel is one of a plurality of fluid channels each configured to be in fluidic communication with the fluid input and fluid output when in use.

[0024] By providing a module having a plurality of fluid channels a greater area of the module is in thermal contact with the fluid, thereby more effective heat transfer between the thermal storage mass and the fluid is achieved (as compared to providing a single channel having the same fluid volume capacity as multiple channels). It may be that the electrical integration channel extends along a first direction and the or each fluid channel extends along a second direction, different from the first direction. It may be that the first direction is perpendicular to the second direction.

[0025] By providing an electrical integration channel which extends along a different direction relative to the fluid channel, electrical and fluidic connections can be made more conveniently (i.e., it is more straightforward to provide these connections in different regions of the thermal energy storage system).

[0026] It may be that the electrical integration channel extends along a first direction perpendicular to the direction along which the fluid channel extends. Advantageously, this reduces the risk of fluid entering the electrical integration channel and potentially affecting the electrical heating element.

[0027] It may be that the first direction is the horizontal direction. It may be that the second direction is the vertical direction.

[0028] It may be that, in use, the or each fluid channel is configured such that the thermal storage mass is in direct contact with the fluid. It may be that the electrical integration channel is configured such that the thermal storage mass is in direct contact with the electrical heating element.

[0029] It may be that the or each fluid channel is configured such that the thermal storage mass is in direct contact with the fluid. Advantageously, this allows more effective thermal energy exchange between the fluid and thermal storage mass.

[0030] It may be that the electrical integration channel is configured such that the thermal storage mass is in direct contact with the electrical heating element. Advantageously, this allows more effective thermal energy exchange between the electrical heating element and thermal storage mass.

[0031] It may be that the or each fluid channel is configured to partly define a fluid pipe enclosed along its length when the module is arranged adjacent to a further module having the same orientation, wherein the or each fluid pipe is defined in part by a fluid channel of the module and in part by a respective fluid channel of the further module, and / or wherein the electrical integration channel is arranged so that the electrical heating element can extend through the module and an additional module, having the same orientation, along a respective electrical integration channel.

[0032] It may be that the or each fluid channel is configured to partly define a fluid pipe enclosed along its length (i.e. , so that only a minority, and preferably only a negligible amount, of the fluid directed along the fluid pipe may escape where the fluid channels of adjacent storage masses join).

[0033] It may be that the or each fluid channel is configured to partly define a fluid pipe enclosed along its length when the module is arranged directly adjacent to a further module having the same orientation.

[0034] It will be understood that the additional module is a different module to the further module (although they may be of the same type).

[0035] It may be that the or each fluid channel comprises three sides of equal length or a curved side. Advantageous, these channel shapes facilitate a favourable balance between heat exchange area, pressure drop and manufacturability.

[0036] It may be that the module comprises a first end, wherein the electrical integration channel comprises an outlet arranged before the first end, and wherein the module further comprises a trench region for supporting a first portion of the electrical heating element extending between the outlet and the first end and for allowing access to the first portion of the electrical heating element.

[0037] By providing a module having the trench region described herein, it is easier to provide electrical connection between different portions of the same electrical heating element (or different heating elements) extending along different axes, thereby facilitating improved deposition of heat within the modular thermal energy storage system.

[0038] The trench may be configured to support a second portion of the electrical heating element extending in a direction different to the direction along which the first portion extends. Accordingly, it is possible to provide thermal energy storage systems with a wide range of electrical heating element arrangements. In particular, heating elements having complex shapes can be more easily integrated. It may be that the electrical integration channel extends along a first direction, wherein the module is further configured to support a portion of the electrical heating element extending along a further direction different from the first direction, wherein the further direction is angled relative to the vertical direction. It may be that the module is further configured to cooperate with a connector module configured to support a portion of the electrical heating extending element along a further direction different from the first direction, wherein the further direction is angled relative to the vertical direction.

[0039] By supporting a portion of the electrical heating element along a further direction angled relative to the vertical direction, electrical creep is minimised (e.g., because the weight of the electrical heating element is supported), thereby prolonging the life and performance of electrical heating elements.

[0040] It may be that the first direction is the horizontal direction.

[0041] It may be that the module further comprises a retaining portion configured to cooperate with a corresponding portion of a further module to engage the module with the further module. It may be that the retaining portion comprises a protrusion configured to engage with an indentation of the further module. It may be the protrusion is defined by a portion of the electrical integration channel.

[0042] By providing a module having the retaining portion as described herein, modules can be more conveniently and securely removably retained together. Since the modules can be removably retained together, it is still straightforward to replace / re-arrange modules, thereby making repair / reconfiguration of the thermal energy storage system more straightforward.

[0043] It may be that the module further comprises a corresponding portion configured to cooperate with a retaining portion of another module. The corresponding portion may be a slot (e.g., a slot configured to receive a portion of an electrical integration channel of another module).

[0044] It may be that the module comprises a groove for supporting a moveable seal. It may be that the module, the further module and the additional module described hereinbefore may each be referred to as thermal storage mass modules.

[0045] According to another aspect of the invention there is provided a module of a thermal energy storage system, the thermal energy storage system having a fluid input, a thermal energy storage mass, and a fluid output for outputting heated fluid generated through heat exchange between the thermal energy storage mass and fluid received through the fluid input; the module comprising: a thermal energy storage mass having an exposed portion in thermal contact with the surroundings; and insulation extending around the circumference of the thermal energy storage mass; wherein the module is attachable to at least one other module such that, in use, heat can be transferred between attached modules via the exposed portion.

[0046] In some embodiments the thermal energy storage mass comprises a network of fluid channels for fluidic communication with the fluid input and fluid output. It may be that, in use, the thermal energy storage mass is in direct contact with the fluid.

[0047] By providing a module of a thermal energy storage system as defined herein, it is possible to transport and assemble thermal energy storage systems more easily. For example, the modules can be transported separately (or in another convenient arrangement for transportation) and then later assembled on site. In addition, these modules provide users with more flexibility in how thermal energy storage systems are designed (e.g., the size of the system can be chosen / varied depending on the energy storage capacity required). It is also more straightforward and cost-effective to repair these systems - since modules can be replaced individually.

[0048] It may be that the module is removably attachable to the at least one other module.

[0049] It may be that the thermal energy storage mass comprises a plurality of thermal storage mass modules as described herein.

[0050] It may be that the thermal energy storage mass comprises an outer thermal mass extending around the circumference of an inner thermal mass. It may be that the inner thermal storage mass comprises a plurality of thermal storage mass modules as described herein.

[0051] By providing a module having an outer thermal storage mass extending around an inner storage mass stored thermal energy is better insulated from the surroundings when the assembled thermal energy storage system is in use.

[0052] It may be that the module further comprises inner insulation between the inner thermal storage mass and the outer thermal storage mass.

[0053] In some embodiments the inner insulation comprises a first insulation layer extending at least partly around the circumference of the inner thermal storage mass and a second insulation layer arranged between the first insulation layer and the outer thermal storage mass, wherein the first insulation layer comprises a first material and the second insulation layer comprises a second material different from the first material. It may be that the first material is more heat resistant than the second material (i.e., more resistant to degradation from the effects of heat).

[0054] The insulation may comprise ceramic material (e.g., ceramic fibres, or the composite hardened material as described herein).

[0055] In embodiments involving a plurality of layers of insulation, the module may comprise one or more fasteners for securing the plurality of layers together. The one or more fasteners may comprise a portion that extends through the plurality of layers of insulation. The one or more fasteners may comprise dowel pins. The one or more fasteners may comprise bolts (e.g., bolts for co-operation with dowel pins). The fasteners may comprise ceramic material (e.g., ceramic fibres). The fasteners may be removable - e.g., so that the insulation layers can be securely attached during transport (for example) but removed before use. The channels left by the removal of the fasteners may be filled with an insulating material.

[0056] In some embodiments, the module may further comprise a supporting structure extending over adjacent surfaces of the module. The supporting structure may comprise a web. The supporting structure may comprise ceramic material. It will be understood that other types of modules (e.g., the fluid input module and / or fluid turning module described hereinafter) may also have a plurality of layers of insulation and / or fasteners and / or supporting structures described hereinabove.

[0057] In some embodiments, the module further comprises a protective layer between the first insulation layer and the inner thermal storage mass to protect the inner insulation (e.g., from gas flows or disturbance during maintenance / transportation).

[0058] The protective layer may be solid, comprise an insulating material, comprise treated fibres and / or comprise a porous material.

[0059] In some embodiments, the module further comprises a seal for preventing fluid leaving from the inner thermal storage mass to the surroundings / outer storage mass between adjacent modules. The seal may be moveable (e.g., slidable) to allow relative movement between adjacent modules. The seal may comprise a compressible material.

[0060] By providing moveable seals, relative movement between modules is accommodated (e.g., due to different temperatures / thermal expansion) whilst still preventing fluid escaping to the surroundings.

[0061] The module may comprise the seal (e.g., a moveable and compressible seal) extending along a first side of the inner thermal storage mass and an insulation layer extending along a second side of the inner thermal storage mass. Thus, it is possible to prevent unwanted fluid escape from the inner thermal storage mass in a cost- effective manner.

[0062] It may be that the first side is the top side of the inner thermal storage mass.

[0063] It may be that a moveable and compressible seal extends along the top side of the inner thermal storage mass. It may be that the further insulation layers / panels are arranged along the other three sides of the inner thermal storage mass.

[0064] The module has a width defined between a first surface and a second surface. It may be that the second insulation layer extends across the width between the first surface and the second surface. It may be that the first insulation layer only extends partly across the width between the first surface and the second surface. That is, the first insulation layer may extend from the first surface and terminate before the second surface at a first insulation end. It may be that the seal is arranged between the first insulation end and the second surface.

[0065] It may be that the outer thermal storage mass comprises a plurality of outer storage mass modules, wherein each outer storage mass module comprises at least one fluid passage for fluidic communication with the fluid input and fluid output. It may be that the or each outer storage mass module is shaped to have a uniform cross-section. It may be that at least a subset of the outer storage mass modules are removable.

[0066] It may be that outer thermal storage mass module comprises thermal storage mass material, wherein the thermal storage mass material is shaped to define the fluid passage so that, in use, the thermal storage mass material is in direct contact with the fluid.

[0067] The inventors have realised that outer storage mass modules shaped to have a uniform cross-section are straightforward to manufacture - e.g., using a low-cost extrusion process.

[0068] By providing a module having at least a subset of outer storage mass modules which are removable, it is more straightforward to obtain access to the inner portions of the thermal energy storage system (e.g., for repair / replacement of parts).

[0069] In alternative embodiments, it may be that the outer thermal storage mass comprises granulated material. The module may further comprise a pipe (or network of pipes) for directing the flow of fluid through the outer thermal storage mass.

[0070] It may be that the module further comprises inner insulation between the inner thermal storage mass and the outer thermal storage mass, wherein the inner insulation and the outer thermal storage mass each comprise a movable portion for allowing access to the inner thermal storage mass.

[0071] By providing a module with inner insulation and the outer thermal storage mass each comprising a movable portion (e.g., removable) for allowing access to the inner thermal storage mass, it is more straightforward to repair / replace inner portions of the thermal energy storage system.

[0072] It may be that the inner insulation comprises at least a first insulation layer extending at least partly around the circumference of the inner thermal storage mass, and wherein the module further comprises a protective layer extending around the first insulation layer so that, in use, the first insulation layer is inaccessible whilst the inner storage mass is accessible.

[0073] It may be that the inner insulation further comprises a second insulation layer arranged between the first insulation layer and the outer thermal storage mass, wherein the protective layer is arranged so that the second insulation layer is also inaccessible whilst the inner storage mass is accessible.

[0074] The protective layer may be solid, comprise an insulating material, comprise treated fibres and / or comprise a porous material.

[0075] It may be that the module has a second module portion between a first module portion and a third module portion, wherein the second module portion is slidable relative to the first module portion and the third module portion, wherein the second module portion comprises a first portion of the thermal energy storage mass and at least part of the insulation.

[0076] By providing a module having a second module portion, having at least part of the thermal energy storage mass, slidable relative to a first module portion and a third module portion, movement due to the thermal expansion of the thermal energy storage mass is accommodated, thereby avoiding deformation / damage during heating.

[0077] The relative movement of the modules may be along the vertical direction.

[0078] The first module portion and the third module portion may both comprise at least part of the insulation.

[0079] It may be that the thermal energy storage mass comprises an outer thermal mass extending around the circumference of an inner thermal mass, wherein the first portion of the thermal energy storage mass is the inner thermal storage mass. It may be that the first portion of the thermal energy storage mass comprises a plurality of separate mass portions, wherein, in a first configuration, the plurality of separate mass portions are prevented from moving relative to one another, and optionally wherein, in the first configuration, the module comprises a retaining element in a retaining configuration for preventing relative movement between at least a subset of the plurality of separate mass portions, wherein the retaining element is configured to change away from the retaining configuration in response to heating of the first portion of the thermal energy storage mass to allow relative movement between the plurality of separate mass portions.

[0080] Typically, modules must be manufactured to include gaps between portions of the thermal energy storage mass to allow for thermal expansion. Damage / misalignment is possible during transport since the internal parts can move relative to each other.

[0081] By providing a module having the retaining element in combination with the slidable portion described herein, it is possible to temporarily reduce these gaps during transport, thereby avoiding damage / misalignment.

[0082] The retaining element is configured to change away from the retaining configuration. In some embodiments, the retaining element melts.

[0083] According to another aspect of the invention there is provided a modular thermal energy storage system having a plurality of modules as described herein, each module being attachable to at least one other module.

[0084] By providing a modular thermal energy storage system having any of the module describes herein, it is possible to provide an energy storage system having a flexible design (which can be adapted based on the application / required energy storage capacity), whilst also being cost-effective to manufacture and repair.

[0085] It may be that each module is removably attachable to the at least one other module.

[0086] Typically, the modular thermal energy storage system comprises a fluid input, a thermal energy storage mass, and a fluid output for outputting heated fluid generated through heat exchange between the thermal energy storage mass and fluid received through the fluid input. It may be that modular thermal energy storage system comprises at least one electrical heating element.

[0087] The heating element may comprise a first end and a second end, and be shaped so that the heating element intersects a first reference plane at least twice between the first end and the second end. The heating element may be U-shaped. Thus, two connections to the heating element may be provided at the same side of the modular thermal energy storage system (providing for more convenient electrical connection).

[0088] In embodiments involving an inner thermal mass and an outer thermal mass, the modular thermal energy storage system may comprise supports extending between the inner thermal mass and outer thermal mass. Thereby the weight of the thermal masses is better supported, and the stability of the system is improved. The supports may be rods or tubes. The supports may comprise an inner support structure defining a plurality of cells. The cells may have a hexagonal cross-section (i.e., the support comprises an internal honeycomb structure). The incorporation of an inner support structure provides an increased area for load distribution, increased stiffness of the support and facilitates lower thermal loss through the support (compared to supports without this inner support structure). The supports may extend through insulation between the inner thermal mass and outer thermal mass. The supports may comprise ceramic material.

[0089] It may be that the modular thermal energy storage system comprises a plate arranged beneath the inner thermal mass for supporting its weight. It may be that the supports extend between the plate and the outer thermal mass.

[0090] The modular thermal energy storage system may comprise a base portion for supporting the thermal storage mass. The base portion may accommodate granular material to provide a level surface for the thermal energy storage mass to be supported thereon. In some embodiments the base portion comprises a heat exchanger (e.g., including a thermal storage mass / module described herein) for recovering energy that may otherwise be lost.

[0091] It may be that the modular thermal energy storage system has a first module (having at least a thermal energy storage mass, insulation, and an exposed portion) and a second module (having at least a thermal energy storage mass, insulation, and an exposed portion) wherein the first module is connected to a fluid input module comprising the fluid input and the fluid output, and wherein the second module is connected to a fluid turning module having a chamber for directing fluid from the fluid input through the first module and the second module to the fluid output.

[0092] The fluid input module may comprise multiple fluid inputs. The fluid input module may comprise a chamber in fluidic communication with the fluid input and the fluid output.

[0093] It may be that the modular thermal energy storage system further comprises a third module (having at least a thermal energy storage mass, insulation, and an exposed portion) and a fourth module (having at least a thermal energy storage mass, insulation, and an exposed portion), wherein the third module is connected to a further fluid input module comprising a further fluid input and a further fluid output, and wherein the fourth module is connected to a further fluid turning module having a further chamber for directing fluid from the further fluid input through the third module and the second module to the further fluid output, wherein the fluid turning module and further fluid turning module are arranged adjacent to one another.

[0094] Advantageously, the arrangement of two fluid turning modules adjacent to each other reduces thermal losses, thereby providing greater efficiency (compared to standalone systems).

[0095] According to another aspect of the invention there is provided a method for heating the thermal energy storage mass of a thermal energy storage system comprising: providing a first electrical heating element in contact with the thermal storage mass; providing a second electrical heating element in contact with the thermal storage mass; regulating the temperature of the first electrical heating element and the second heating element by switching between a first regulation mode and a second regulation mode; wherein, in the first regulation mode, the first electrical heating element is operated at a first power level and the second electrical heating element is operated at a second power level; and in the second regulation mode, the first electrical heating element is operated at a third power level less than the first power level, and the second electrical heating element is operated at a fourth power level greater that the second power level. Thus it is possible to steadily deposit thermal energy into the storage mass without overheating either electrical heating element. The time during which either electrical heating element is held at its maximum temperature is limited, thereby increasing their respective service lifetimes.

[0096] In addition, thermal gradients through the thermal energy storage mass are reduced. Since heat dissipates from the region immediately surrounding an electrical heating element during the regulation mode during which it is operating at its lower power level, the maximum temperature reached by the electrical heating element can be limited.

[0097] It may be that the thermal energy storage system is any of the modular thermal energy storage systems described herein. It may be that the first electrical heating element is in contact with a first module (e.g., having at least a thermal energy storage mass, insulation, and an exposed portion as described hereinbefore) of the thermal energy storage system. It may be that the second electrical heating element is in contact with a second module (e.g., having at least a thermal energy storage mass, insulation, and an exposed portion as described hereinbefore) of the thermal energy storage system. It may be that the first electrical heating element is in contact with, of the first module and the second module, only the first module. It may be that the second electrical heating element is in contact with, of the first module and the second module, only the second module.

[0098] It may be that the thermal energy storage system is configured to swich between the first regulation mode and the second regulation mode based on a measured characteristic. It may be that the measured characteristic is indicative of the temperature of at least one of the modules. It may be that the measured characteristic is indicative of a difference in temperature between a first module and a second module. It may be that the first module and the second module are neighbouring modules (e.g. , adjacent to one another). For example, it may be that the thermal energy storage system is configured to switch between the first regulation mode and the second regulation mode based on the measured characteristic indicating that a temperature difference between the first module and the second module exceeds a predetermined temperature threshold difference. The predetermined temperature threshold difference may be greater than 1 degree Celsius, such as greater than 10 degrees Celsius, for example greater than 30 degrees Celsius. The predetermined temperature threshold difference may be less than 100 degrees Celsius, such as less than 70 degrees Celsius, for example less than 55 degrees Celsius.

[0099] It may be that the measured characteristic is based on at least one temperature measured using a temperature sensor (e.g., a thermocouple). It may be that the measured characteristic is based on at least one measured current of the first electrical heating element and / or the second electrical heating element.

[0100] Thus, it is possible to regulate the temperatures of the electrical heating elements based on measured characteristics of the thermal energy storage system, thereby preventing overheating of the electrical heating elements. In this way the relative thermal expansion of different modules can also be controlled. By limiting the difference in thermal expansion between different modules, relative movement between the modules can be reduced. Advantageous, this reduces degradation / damage of the modules over time and avoids potential fluid leakage.

[0101] It may be that the method involves repeatedly switching between the first regulation mode and the second regulation mode.

[0102] The method may involve operating the system in the first regulation mode for a first time period. The first time period may be greater than 20 seconds, greater than 30 seconds, greater than 45 seconds, greater than 55 seconds, greater than 1 minute, greater than 10 minutes, greater than 30 minutes, greater than 45 minutes, greater than 1 hour, greater than 12 hours, greater than 24 hours, or greater than 36 hours. The first time period may be less than 1 minute, less than 10 minutes, less than 30 minutes, less than 45 minutes, less than 1 hour, less than 12 hours, less than 24 hours, or less than 36 hours.

[0103] The method may involve operating the system in the second regulation mode for a second time period. The second time period may be greater than 20 seconds, greater than 30 seconds, greater than 45 seconds, greater than 55 seconds, greater than 1 minute, greater than 10 minutes, greater than 30 minutes, greater than 45 minutes, greater than 1 hour, greater than 12 hours, greater than 24 hours, or greater than 36 hours. The second time period may be less than 1 minute, less than 10 minutes, less than 30 minutes, less than 45 minutes, less than 1 hour, less than 12 hours, less than 24 hours, or less than 36 hours. The method may involve switching between the first regulation mode and the second mode at a first frequency. The first frequency may be less than 2 Hz, less than 1 Hz, less than 1 / 40 Hz, less than 1 / 60 Hz, less than 1 / 90 Hz, less than 1 / 110 Hz, less than 1 / 120 Hz, less than 1 / 1200 Hz, less than 1 / 3600 Hz, less than 1 / 5400 Hz, less than 1 / 7200 Hz, less than 1 / 86400 Hz, less than 1 / 172800 Hz, or less than 1 / 259200 Hz. The first frequency may be greater than 1 / 120 Hz, greater than 1 / 1200 Hz, greater than 1 / 3600 Hz, greater than 1 / 5400 Hz, greater than 1 / 7200 Hz, greater than 1 / 86400 Hz, greater than 1 / 172800 Hz, or greater than 1 / 259200 Hz.

[0104] It may be that the second power level is less than the first power level, and the third power level is less than the fourth power level.

[0105] Thereby potential overheating of one heating element due to the other heating element is avoided.

[0106] It may be that the first power level corresponds to the same target power as the fourth power level, and / or wherein the third power level corresponds to same target power as the second power level.

[0107] It may be that the third power level corresponds to the first electrical heating element being switched off and / or wherein the second power level corresponds to the second electrical heating element being switched off.

[0108] Reducing the third and / or second power level to 0 W facilitates improved cooling of the respective heating elements.

[0109] According to an aspect of the invention there is provided a controller configured to carry out any of the methods for heating the thermal energy storage mass of a thermal energy storage system described herein.

[0110] The controller may comprise one or more processors and a memory configured to store instructions which when executed by the one or more processors cause the thermal energy storage system to carry out the functions of the controller described herein. The memory may be non-transitory, computer readable memory. The memory may have the instructions stored thereon. The present invention extends to a non- transitory computer-readable medium (e.g. memory) having the instructions stored thereon to control the apparatus as described herein. The memory may be solid-state memory. The controller may be provided in a single device. In other example, the controller may be distributed, having a plurality of processors. A first processor may be separated from a second processor in a distributed manner.

[0111] According to an aspect of the invention there is provided a computer program product comprising instructions which, when the program is executed on a computer processing means, causes the computer processing means to carry out any of the methods for heating the thermal energy storage mass of a thermal energy storage system described herein.

[0112] According to an aspect of the invention there is provided an electrical heating element suitable for integration with any of the modules, modular thermal energy storage systems or use with any of the methods described herein.

[0113] According to another aspect of the invention there is provided a pipe for a thermal energy storage system, the thermal energy storage system being configured to output heated fluid via a fluid output. The pipe has an inner channel and an outer channel surrounding the inner channel, wherein the inner channel is in fluidic communication with the fluid output of the thermal energy storage system. The outer channel is in fluidic communication with a fluid source. In use, fluid from the fluid source flows through the outer channel in a first direction and the heated fluid flows through the inner channel in a second direction, opposite the first direction. Thus, thermal energy from the heated fluid in the inner channel is transferred to the fluid in the outer channel. As a result, excess heat from the thermal energy storage system is recoverable. Advantageously, the outer surface of the pipe is kept relatively cool (compared to a conventional pipe). Thus, it is easier to attach the pipe to another system / process. That is, using this counter current design, it is possible maintain the outer portions of the pipe at a relatively low temperature whilst recovering energy that may otherwise be lost.

[0114] It may be that the outer channel is in fluidic communication with an input to the thermal energy storage system for receiving fluid to be heated. That is, recovered heat is supplied to the energy storage system, thereby improving overall energy efficiency. It may be that the fluid input to the thermal energy storage system surrounds the fluid output to the thermal energy storage system.

[0115] The inner channel may be fully enclosed by the outer channel along at least a portion of its length.

[0116] The fluid source may comprise a pump (e.g., a pump which draws cool air from the surroundings or the exhaust of another process).

[0117] It may be that the inner channel is defined by a wall having an inner surface and an outer surface. In some embodiments, the pipe comprises an insulation layer. In some embodiments the insulation layer is provided on (e.g., directly on) the inner surface of the inner channel.

[0118] The pipe may comprise structures extending from the outer surface of the inner channel for providing additional cooling. The structures may comprise protrusions (e.g., fins).

[0119] The inner channel may be configured to be in fluidic communication with a fluid input of an apparatus / process using the heated fluid generated by the thermal energy storage system. The outer channel may be configured to be in fluidic communication with a fluid output of the apparatus. Thus, a closed system may be achieved. Advantageously, this facilitates recovery of waste energy from the apparatus.

[0120] The pipe may be connectable to a pressure release valve for avoiding over pressurisation during heating. The pipe may be connectable to a compressor for pressurising the system, if necessary. Thereby, the gas conditions within the closed system can be better controlled.

[0121] According to another aspect of the invention, there is provided a closed system comprising a thermal energy storage system for generating heated fluid and an apparatus configured to use the heated fluid. The thermal energy storage system comprises a pipe having an inner channel and an outer channel surrounding the inner channel, wherein the inner channel is in fluidic communication with the fluid output of the thermal energy storage system and a fluid input of the apparatus. The outer channel is in fluidic communication with a fluid output of the apparatus. The system may comprise a pressure release valve for avoiding over pressurisation during heating. The system may comprise a compressor for pressurising the system, if necessary. The system may comprise a means for removing moisture from fluid circulating within the closed system (e.g., a condenser). Thus, reducing chemical reactions which may degrade the system. Thereby the service life of the system can be increased.

[0122] The inner channel may be configured to be in fluidic communication with an input of an apparatus using the heated fluid generated by the thermal energy storage system. The outer channel may be configured to be in fluidic communication with a fluid output of the apparatus. Thus, a closed system may be achieved. Advantageously, this facilitates recovery of waste energy from the apparatus.

[0123] The pipe may be connected to an attachment comprising a first attachment inlet for receiving fluid from a fluid source, and a first attachment outlet for supplying fluid to the inner channel. The attachment further comprises a first conduit configured to extend between the first attachment inlet and the first attachment outlet through the outer channel of the pipe.

[0124] According to another aspect of the invention there is provided an attachment for fluid mixing. The attachment may be for co-operation with any of the pipes described herein above.

[0125] The attachment comprises a first attachment inlet for receiving fluid from a fluid source, and a first attachment outlet for supplying fluid to the inner channel. The attachment further comprises a first conduit configured to extend between the first attachment inlet and the first attachment outlet. In embodiments where the attachment is for cooperation with any of the counter-current pipes described herein above, the first conduit may be configured to extend through the outer channel of the pipe.

[0126] In use, fluid received into the inner channel via the attachment can be used to adjust the temperature (typically to cool) the fluid exiting the pipe. Advantageously this means that processes / systems with different requirements (in terms of the fluid temperature required) can be supplied. It may be that the attachment comprises a plurality of conduits each having a corresponding attachment outlet for supplying fluid from the fluid source to the inner channel. The conduits may be arranged so that they are spaced (e.g., equally spaced) around the inner pipe. The attachment may further comprise an intermediate region for accommodating fluid between the conduits and the fluid source. The intermediate region may be configured to extend around the circumference of the pipe.

[0127] In use, fluid from the thermal energy storage system will flow from the thermal energy storage system and exit the pipe via an inner channel outlet defining the end of the inner channel. The inner channel may comprise mixing structures for enhancing fluid mixing, typically arranged between the or each attachment inlet and the inner channel outlet. The mixing structures may comprise a mesh, or any other structure configured to generate turbulence.

[0128] The or each conduit may be shaped to limit pressure drop over the system. For example, the or each conduit may be shaped to facilitate smoothly varying changes in flow direction. The or each conduit may be shaped to have a constant cross-sectional area along its length. The or each conduit may be shaped to have a smoothly varying cross sectional area along at least a portion of length. The or each conduit may comprise smooth inner walls (i.e., the walls in contact with the fluid).

[0129] The or each conduit may be orientated to limit pressure drop over the system (e.g., compared to a system having conduits orientated at 90 degrees to the inner channel). It may be that the or each conduit is angled relative to the inner pipe at a first angle so that a major component (i.e., the largest component) of the direction of fluid entering the inner channel from the conduit is parallel to the direction of fluid flow through the inner channel. That is, the flow directions of the fluid along at least part of the conduit and the fluid already flowing through the inner channel are at least partly aligned before mixing, thereby reducing pressure drop over the system. The first angle may be less than 60 degrees, less than 50 degrees, or less than 45 degrees.

[0130] It may be that the thermal energy storage system comprises outer casing surrounding the insulation and thermal energy storage mass. The outer casing may be fluid tight. That is, fluid may be prevented from exiting or entering the thermal energy storage mass, apart from via the fluid inlet or fluid outlet. It may be that the thermal energy storage system comprises a fluid tight envelope surrounding the thermal energy storage mass. The fluid tight envelope may be defined by an outer casing and an inner casing. Typically the thermal energy storage system comprises a fluid inlet for receiving fluid to be heated and a fluid outlet for outputting heated fluid. It may be that the fluid tight envelope is configured to prevent fluid exiting or entering the thermal energy storage mass, apart from via the fluid inlet or fluid outlet.

[0131] The inner casing and outer casing may define a chamber. The chamber may accommodate further insulation. It may be that, in use, the chamber is held at a negative pressure (e.g., using a vacuum pump). Thereby providing a particularly efficient thermal energy storage system.

[0132] According to another aspect of the invention there is provided a thermal energy storage system comprising a thermal energy storage mass and a fluid tight envelope surrounding the thermal energy storage mass. Typically the thermal energy storage system comprises an inlet for receiving fluid to be heated and an outlet for outputting heated fluid. It may be that the fluid tight envelope is configured to prevent fluid exiting or entering the thermal energy storage mass, apart from via the fluid inlet or fluid outlet. The fluid tight envelope may be defined by an outer casing and an inner casing, wherein the inner casing and outer casing together define a chamber for accommodating insulation. The thermal energy storage system may further comprise insulation accommodated within the chamber. It may be that, in use, the chamber is held at a negative pressure (e.g., using a vacuum pump). Thus, the heat retention of the system is improved.

[0133] It may be that at least a subset of the fluid channels / passages within the thermal mass extend along the vertical direction. In embodiments having an inner thermal mass and an outer thermal mass, it may be that any fluid passages / channels extending through the inner thermal mass extend along the vertical direction.

[0134] It may be that both the fluid input and fluid output are arranged below the thermal storage mass. It may be that both the fluid input and fluid output are arranged above the thermal storage mass.

[0135] It may be that the fluid input is connectable to a plurality of pumps for providing fluid to be heated. The thermal energy storage system may further comprise barriers impermeable to the fluid for guiding the fluid from the fluid input, through the thermal storage mass, to the fluid output.

[0136] It may be that the thermal energy storage system comprises a mixer for diluting heated fluid outputted by the thermal energy storage system. It may be that the mixer is connectable to a pump for providing cool fluid. It may be that the mixer is connectable to a plurality of pumps for providing cool fluid. It may be that the fluid output comprises an end portion in contact with the mixer. The end portion may be hardened (e.g., coated with a hardened material). The end portion may comprise a composite hardened material as described herein defining at least one surface in contact with the fluid.

[0137] According to another aspect of the invention there is provided a mixer for diluting heated fluid from a thermal energy storage system. The mixer having a base portion connectable to a fluid output of the thermal energy storage system. The mixer comprises an input for accepting cool fluid for diluting the heated fluid. In use, the mixer may be in direct contact with the fluid output. The mixer may be configured to protect (e.g., shield) the base portion from the heated fluid.

[0138] In particular, the mixer may be configured to direct the cool fluid around at least part of the base portion. Additionally, or alternatively, the mixer may comprise a seal between the base portion and the fluid output defined at least in part by a first surface.

[0139] The seal may comprise a material having a low thermal conductivity (e.g., relative to the first surface) to limit the transfer of heat from the first surface to the base portion so that the structural integrity of the base portion is not comprised (e.g., so that melting, sublimation or debonding of the base portion is avoided). The seal may comprise ceramic fibres. The seal may comprise ceramic fibres surrounded by a woven outer layer.

[0140] Thus, the mixer is protected from thermal damage caused by the heated fluid outputted from the thermal energy storage system. Accordingly, the mixer may be made from a relatively low-cost material (i.e., it is not necessary to use a material capable of withstanding high temperatures), thereby manufacturing costs can be reduced. The mixer may comprise a mixer outlet for outputting cool fluid around at least part of the base portion. The mixer outlet may be one of a plurality of mixer outlets arranged around the base portion.

[0141] The mixer may be configured to direct the cool fluid along a direction different from the direction of flow of the heated fluid. Thus, this arrangement generates turbulence, and improves cooling.

[0142] The mixer may include a structure for generating turbulence (e.g., a grid or protrusion).

[0143] In embodiments involving a seal, the seal may comprise a compressible material. The base may be shaped so that it extends around the seal. The mixer may comprise a seal compressor for compressing the seal (e.g., an elastic element or biasing element).

[0144] According to another aspect of the invention there is a method for supplying fluid to an input of the thermal energy storage system (e.g., to a mixer of the thermal energy storage system, or to a fluid input for receiving fluid to be heated by the thermal energy storage system). The method comprises providing a first pump in fluidic communication with the input, and a second pump in fluidic communication with the input. The method further comprises supplying fluid to the thermal energy storage system using the first pump operating in a first configuration and the second pump operating in a second configuration, wherein the first configuration corresponds to the first pump operating at its maximum efficiency.

[0145] Thus, it is possible operate one of the pumps at their maximum efficiency (thereby saving energy) whilst still providing the required fluid.

[0146] The method may comprise determining the required fluid output of the second pump based on the fluid output of the first pump when operating in the first configuration, and the fluid requirements of the thermal energy storage system. The method may comprise controlling the second pump to provide the determined required fluid output of the second pump. The method may comprise determining the fluid requirements of the thermal energy storage system. According to another aspect of the invention, there is provided a valve for controlling fluid flow within a thermal energy storage system. The valve comprising a composite hardened material defining at least one surface. The composite hardened material may comprise ceramic. The composite hardened material may comprise a fibrous and / or porous material. The fibrous and / or porous material may comprise ceramic (e.g., ceramic fibres). Typically, in use, the surface is in contact with the fluid. Regions (e.g., pores) defined by structures (e.g., fibres) of the fibrous and / or porous material may be filled with another material. This material may comprise a silicate compound.

[0147] The valve may comprise an aperture for allowing the passage of fluid therethrough, and a first portion for selectively blocking the aperture. It may be that the first portion is moveable (e.g., slidable) between a first configuration and a second configuration, wherein, in the first configuration the aperture is open and, the second configuration, the aperture is closed.

[0148] According to another aspect of the invention, there is provided a method for manufacturing a valve for a thermal energy storage system. The method comprising providing a first structure defining at least part of the valve body. The first structure may comprise a porous and / or fibrous material. The method further comprises applying a carrier liquid to at least part of the first structure. The method may further comprise applying heat to cause the carrier liquid to solidify and encapsulate the fibrous and / or porous material. The carrier liquid may comprise ceramic. The porous and / or fibrous material may comprise ceramic (e.g., ceramic fibres). The carrier liquid may comprise a silicate compound.

[0149] According to another aspect of the invention there is provided a thermal energy storage system comprising a thermal energy storage mass and insulation surrounding the thermal energy storage mass. The thermal energy storage system further comprises an electrical heating element for heating the thermal energy storage mass. The electrical heating element is connectable to an external electricity supply via a connector rod. The connector rod is moveable such that electrical connection between the electrical heating element and external electricity supply is maintained when the position of the electrical heating element moves due to thermal expansion of the thermal energy storage mass. Thus, the different thermal expansion of different parts of the thermal energy storage system is accommodated, thereby avoiding damage / degradation. It may be that the thermal energy storage mass comprises an outer thermal storage mass surrounding an inner thermal storage mass, wherein the electrical heating element is arranged within the inner thermal storage mass. The connector rod may extend between the electrical heating element, through the outer thermal storage mass. The connector rod may be pivotally connected the electrical heating element. Advantageously, heat that may be lost to the surroundings due to thermal conduction along the connector rod can be recovered by the outer thermal storage mass, thereby improving heat retention.

[0150] According to another aspect of the invention there is provide a thermal energy storage system comprising a thermal energy storage mass arranged adjacent to a first layer. The first layer may be an insulating layer. The first layer may surround the thermal storage mass. The thermal energy storage system may comprise a moveable seal extending between the first layer and the thermal energy storage mass for restricting fluid flow therebetween. The thermal energy storage mass and / or the first layer may comprise a groove for supporting a first end of the moveable seal.

[0151] In some embodiments, the thermal energy storage mass comprises a groove for supporting a first end of the moveable seal and the second end of the moveable seal is supported by the first layer.

[0152] In some embodiments, the first layer comprises a groove for supporting a first end of the moveable seal and the second end of the moveable seal is supported by the thermal energy storage mass.

[0153] By providing a thermal energy system comprising a moveable seal as described herein fluid flow can be restricted between two parts that move relative to each other (e.g., due to different amounts of thermal expansion).

[0154] According to another aspect of the invention there is provided a support for an electrical conductor for use in a thermal energy storage system (e.g., an electrical conductor for connecting to an electrical heating element). The conductor support comprises a channel for supporting a portion of an electrical conductor. In use, the channel is angled relative to the vertical direction so that the weight of the electrical conductor is supported. Thus, deformation of the electrical conductor element due to self- weight / creep is prevented, thereby improving the performance and lifetime of the electrical conductor.

[0155] In some embodiments the channel is helix shaped.

[0156] The support may be configured to allow electrical connection to the electrical conductor at a first point between a first end and second end of the electrical heating element. The support may be configured to allow electrical connection to the electrical conductor at multiple points between a first end and second end of the electrical heating element.

[0157] According to another aspect of the invention there is a thermal energy storage system comprising an inner thermal storage mass surrounded by an outer thermal storage mass. The thermal energy storage system further comprises an electrical heating element for heating the inner thermal storage mass. The electrical heating element is configured for electrical connection to an external electricity supply. The electrical heating element may comprise a first portion that extends into the outer thermal storage mass so that an end of the first portion is arranged within the outer thermal storage mass. The end of the first portion may be configured to be connectable to a further conductor arranged within the outer thermal storage mass. It may be that the first portion of the electrical heating element comprises a first material and the further conductor comprises a second material different from the first material. It may be that the second material has a lower heat tolerance (e.g., lower melting point) compared to the first material. The first material may be ceramic. The second material may be metal. The thermal energy storage system may comprise insulation between the inner thermal storage mass and the outer thermal storage mass.

[0158] The outer thermal storage mass helps to cool the first portion of the electrical heating element. Thus, it is possible to use a heating element having a heat tolerance in the inner thermal storage mass (where the highest temperatures will be reached) and make the electrical connections from the electrical heating element to the electrical connections (typically metal) within the outer thermal storage mass. Since the electrical heating elements do not need to extend out of the thermal energy storage system, less thermal energy is conducted from the inner and outer thermal storage masses to the surrounding layers (or external surroundings), thereby heat retention is improved. It may be that the thermal energy storage mass is an inner thermal storage mass surrounded by an outer thermal storage mass. It may be that the insulation is arranged between the inner thermal storage mass and the outer thermal storage mass. In this way, heat retention is further improved.

[0159] It will be understood that the disclosure of the features described hereinbefore extends to their disclosure in any combination with any one or more of the other features herein described, apart from combinations which would be inherently incompatible.

[0160] It will also be understood that any of the features or combinations of features described hereinbefore can be part of a thermal energy system having a fluid input, a thermal energy storage mass, and a fluid output for outputting heated fluid generated through heat exchange between the thermal energy storage mass and fluid received through the fluid input.

[0161] Description of the Drawings

[0162] An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

[0163] Figure 1 is a schematic diagram of a thermal energy storage system having a counter current pipe;

[0164] Figure 2 is a schematic diagram of a thermal energy storage system having a counter current pipe and a mixing attachment;

[0165] Figure 3 is a schematic diagram of a thermal energy storage system having a closed system;

[0166] Figure 4 is a schematic diagram of a module of a thermal energy storage system according to the invention;

[0167] Figure 5 is a schematic diagram of an arrangement of modules of a thermal energy storage system according to the invention;

[0168] Figure 6 is a schematic diagram of a module of a thermal energy storage system according to the invention;

[0169] Figure 7 and Figure 8 are schematic diagrams of an arrangement of modules (along with U-shaped electrical heating elements) of a thermal energy storage system according to the invention; Figures 9-11 are schematic diagrams of an arrangement of modules of a thermal energy storage system according to the invention;

[0170] Figure 12 is a schematic diagram of a module of a thermal energy storage system according to the invention;

[0171] Figure 13 is a schematic diagram of part of a module of a thermal energy storage system according to the invention;

[0172] Figure 14 is a schematic diagram of a thermal energy storage system according to the invention having a number of switchable electrical heating elements;

[0173] Figure 15 is a schematic diagram of an arrangement of modules of a thermal energy storage system according to the invention;

[0174] Figure 16 is a schematic diagram of a module of a thermal energy storage system according to the invention;

[0175] Figure 17 is a schematic diagram of part of a module of a thermal energy storage system according to the invention;

[0176] Figures 18-19 are schematic diagrams of parts of modules of thermal energy storage systems having slidable seals according to the invention;

[0177] Figure 20 is a schematic diagram of a module of a thermal energy storage system according to the invention;

[0178] Figure 21 is a schematic diagram of part of a module of a thermal energy storage system according to the invention;

[0179] Figure 22 is a schematic diagram of a module of a thermal energy storage system according to the invention;

[0180] Figures 23-24 are schematic diagrams of modular thermal energy storage systems according to the invention;

[0181] Figure 25 is a schematic diagram of a mixer for a thermal energy storage system;

[0182] Figure 26 is a schematic diagram showing a cross-section of a mixer for a thermal energy storage system;

[0183] Figure 27 is a schematic diagram showing fluid flow through a mixer for a thermal energy storage system;

[0184] Figure 28 is illustrative of the relative efficiency of different pump choices;

[0185] Figure 29 is a schematic diagram of a valve for a thermal energy storage system;

[0186] Figures 30-31 are schematic diagrams showing a thermal energy storage system having a movable conductor rod; Figure 32 is a schematic diagram showing a slidable seal for a thermal energy storage system;

[0187] Figure 33 is a schematic diagram of modular thermal energy storage systems according to the invention;

[0188] Figure 34 is a schematic diagram of an arrangement of modules of a thermal energy storage system according to the invention;

[0189] Figures 35-36 are schematic diagrams of supports for an electrical conductor for use in a thermal energy storage system;

[0190] Figure 37 is a schematic diagram of a connection between an electrical heating element and a further conductor within an insulation layer of a thermal energy storage system;

[0191] Figure 38 is a flowchart illustrating a method of heating the thermal energy storage mass of a thermal energy storage system according to the invention;

[0192] Figure 39 is a schematic diagram of a controller for controlling a thermal energy storage system according to the invention; and

[0193] Figure 40 is a schematic diagram of a portion of a thermal energy storage system.

[0194] Detailed Description of an Example Embodiment

[0195] Figure 1 schematically illustrates a system for cooling the hot gas pipes used to transport gas from a thermal storage system whilst recovering energy that may otherwise be lost.

[0196] The illustrated system comprises a thermal storage system 1 that supplies heat through a heat exchanger 2 to a gas, which is piped out of the system through pipe 3, which is fully enclosed by pipe 4 that is used to supply cold air to heat exchanger 2.

[0197] To control the temperature of pipe 3 insulation 5 can be added inside the pipe or features can be added to the outside of pipe 3 to cool it such as fins or other methods to increase surface area or induce turbulence in the flow. The cool gas can be supplied to pipe 4 through a manifold 6 and or be drawn from an attached process 7 to add active cooling and heat recovery to that process. The cold air is supplied through a pump 9, which draws air from atmosphere 10 or the exhaust of a process. The inlet air can also be used to cool the interface between the pipe and the process integrated to the thermal storage system.

[0198] In Figure 2 a system for controlling the temperature and mass flow rate from a thermal storage system is shown. Cold air is input 35 to the main pump 36 where it is heated within a thermal storage system as shown in Figure 23, a secondary pump known as a dilution pump 37 draws cold air from an inlet 38 which is then injected into manifold 39. The cold gas from the manifold is then injected through pipes 40 that pierce pipes 3,4 and insulation 5. Cold gas then mixes with hot gas, which can then be input to a process 7. Mass flow can be controlled by controlling the mass flow of pumps 36 and 37. Mixing can be enhanced using flow devices including but not limited to meshes and turbulence generators at the cost of pressure drop if it is advantageous. The pipes 40 pass through the outer pipe 4 and deliver cool gas to the hot gas pipe can be shaped to minimise pressure drop. In an implementation where the counter current cold inlet pipe 4 is not used the pipes 39 will go directly from the manifold to the hot pipe 5.

[0199] Figure 3 is an alternative embodiment of the system described in Figure 1 where the thermal store supplies hot gas to an external process 7 through an inlet 66 and then takes the exhaust gas from the process 67 and direct it into the inlet of the thermal store. By sealing the inlet and outlet of the thermal store to the host process a closed system can be achieved. The advantages of a closed system include recovery of the waste energy from the host process and control of the gas conditions within the system. For example, by increasing the gas pressure within the closed system heat transfer can be enhanced. T o allow the control of pressure and to allow for gas expansion when heating and gas cooling when discharging additional components are added. A pressure relief valve to atmosphere 68 is connected to the gas path pipework 69 to avoid over pressurisation during heating. This valve or another valve could also be set to allow gas from atmosphere in during cooling and depressurisation and to maintain a set pressure above atmospheric levels. A compressor 70 is connected to the gas path pipework 71 to allow gas to be added to pressurise system.

[0200] Controlling the gas conditions would also allow the reduction of component degrading chemical and electrochemical reactions taking place within the thermal store and host process increasing service life. One example of this would be moisture removal to reduce electrochemical reactions this could be achieved by installing within the closed system heat pump condensation and draining, absorption into glycols, absorption onto desiccants, freeze drying, freeze concentration and osmotic concentration methods. Another example is oxygen removal to reduce component degrading chemical reactions. This could be achieved by adding chemicals to the closed system that would react with oxygen to form a non-component degrading gas, for example carbon to form carbon dioxide. Other methods might include adding cryogenic distillation, pressure or vacuum swing adsorption or membranes within the closed system to selectively remove oxygen from the gas within the closed system. The above are given as examples however other methods of removing degrading components may be useful in some applications. Removal of degrading chemicals from atmospheric air that enters an open cycle arrangement (Figure 1) may also be beneficial in some scenarios.

[0201] Figure 4 schematically illustrates a brick-based module having an integrated thermal mass, heat exchanger and heating element that can be used to assemble a key elements of a thermal storage system.

[0202] The illustrated component comprises a thermal mass formed as a brick 11 that can be made with a metal or ceramic material. Features are added to the brick to increase solid to gas heat transfer than when in combination with other brick form passages 12 suitable for heat exchange between the thermal mass of the brick and a gas used to transport energy. Into one surface of the brick, a trench 13 is formed to allow the laying of electrical heating elements 14. Heat transfer between element 14 and the brick 11 can be further enhanced by filling the trench with a powdered solid material, one example of which would be a ceramic powder such as magnesium oxide; this also provides support for the element. To ensure powder does not escape into the heat exchanger passages 12 ceramic paste can be used to seal between brick layers (Figure 5) and block escape. This paste will harden over time or as the thermal storage system is heated to form a solid barrier. To form electrical circuits between elements in parallel trenches another trench 15 is cut at one end of the brick to allow connection between elements.

[0203] Figure 5 shows several brick-based modules which are stacked to form an integrated arrangement of heaters, thermal mass, and gas to solid heat exchanger passages. Multiple bricks stacked vertically form long heat exchange passages 16 providing advantageous surface area for heat exchange, low pressure drop and a means of passing hot gas from the top of the integrated thermal mass to the bottom. Multiple bricks laid next to each other form trenches 17 where long heating elements can be supported with good contact to the thermal mass they heat. Multiple bricks layer next to each other form trenches 18 where electrical communication between elements 14 can be placed. In the embodiments shown heat exchangers have vertical arrangements and elements and link trenches are horizontal however, other orientations are possible depending on the thermal storage system requirements. It may also be advantageous for the trench 13 to contain multiple elements 14.

[0204] Figure 6 shows an alternative embodiment where heat exchanger passages are square 12 or curved 73 to best balance heat exchange area, pressure drop and manufacturability. The conductor bridge between parallel (or radial) bricks can be a trench 74 between heat exchanger passages 12.

[0205] In Figure 7 an alternative embodiment shows flat element 75 which features U shape geometry so a single element can have both connections at the same end. Gaps between bricks 76 should be left during assembly in any constrained direction to allow thermal expansion during heating with all above embodiments.

[0206] In Figure 8 it is demonstrated how multiple elements 75A and 75B in contact with different bricks can be joined together to a to form a single heater circuit. In this embodiment the connections are made and supported within a separate connector brick 77 however the required slots could be integrated in a core brick if advantageous. In combination with the cross-sectional area and element length this allows the element to be matched with the supply voltage for a given heat output. In the embodiment shown in Figure 8 a single circuit is connected in serial however a parallel or mixture of serial and parallel connections may be an advantageous configuration. The negative and positive terminals 78, 79 are connected to electricity. Connection between separate elements in the vertical plane can be achieved by pieces of material 80 connected with joining process or by forming the entire heater from a continuous piece of material. Connection piece 80 is shaped to be supported by a slot in the conductor brick 77 to increase service life. In addition to this it allows for greater thermal expansion of the bricks without vertical connector failure. Connection between separate elements in the horizontal plane can be achieved by pieces of material 81 . The element and connector piece are supported by a slot in the brick. Vertical connections can be made with same way but the supporting slots in the conductor brick 77 which can be shaped to minimise creep as shown in Figure 35 and Figure 36.

[0207] In Figure 9 an arrangement of modules for enabling low-cost assembly, scalability and management of differential thermal expansion is displayed. The diagram on left is an exploded view and on the diagram on the right is as assembled. Here a thermal storage system is constructed using modules. Modules 82A, 82B and 82C represent three identical groupings of thermal mass, insulation, heating elements and seals as further detailed in Figure 12. When assembled three Modules 82A, 82B and 82C are placed together between a gas input and output module 83 and a gas turning module 84 used to reverse the flow from the collector brick 24 to the core bricks. Gas enters at inlets 85A and 85B, which could be linked by pipework to a plenum chamber or manifold, and is first heated by passing through the collector bricks 24 then reverses direction in a cavity 84 before flowing back through inner thermal mass to be further heated. The gas exits through 86 to supply a downstream process. This gas flow is further described in Figure 23. Any number of modules 82 can be added to configure the performance and capacity of the resulting thermal storage system.

[0208] In Figure 10 one possible arrangement of six single modular combination of thermal mass, heating elements and insulation 82A to F are shown divided by lines 87 to form a thermal store. Here The cool gas is inlet at 85A and 85B and flows through all modules 82A-F is reversed by gas turning module 84 before exiting at 85A and 85B as described by Figure 9. The flow rate through the system is limited by the acceptable pressure drop and energy loss or by the properties of the duct materials to a particular velocity. This velocity is dependent duct area and hence the total area of the gas path therefore a single modular combination of thermal mass, heating elements and insulation 82A-F will have a maximum allowable mass flow rate determined by economic and engineering considerations. In Figure 10 six modules 82A-F are arranged sequentially to maximise the length of the gas passages, the result will be to maximise the gas exit temperature and stored energy utilisation through the thermocline effect for a six modules configuration.

[0209] In an alternative thermal store configuration Figure 11 six modules 82A-F are configured in two groups. Cool gas enters the inlets 85A to 85D either from individual pumps or from a single pump with a four-way manifold feed gas from atmosphere or the host process exhaust. It passes through each group of three modules then exits through the outlets86A and 86B where it can be combined to feed the host process. The gas flow reversed in gas turning module 84A and 84B In Figure 11 double the mass flowrate can be provided to the host flow rate compared to Figure 10 whilst maintaining the same gas path and duct 12 velocity within the thermal store. The disadvantage of the configuration shown in Figure 11 when compared to Figure 10 is lower gas exit temperature and stored energy utilisation. By adjoining the flow reversing cavity 84A from on three module group to the flow reversing cavity 84B from the other three module group thermal losses are reduced when compared to stand alone groups of modules. Standalone groups of modules maybe advantageous in some scenarios.

[0210] At Figure 12 the single modular combination of thermal mass, heating elements and insulation is shown as a thickness of one brick and one element however in some scenarios it may be advantageous to have the modular multiple bricks and elements thick. The inner thermal mass is surrounded by the inner insulation 20 and a seal 87 which is further detailed in Figure 18. The inner insulation 20 is surrounded by the collector bricks 20 which are an integration of thermal mass and a gas path to allow heat from the bricks to be extracted to the gas. The collector bricks 20 can be configured to give the best ratio of thermal mass, pressure drop and surface area for heat exchange. Configurations could include single ducts, multiple ducts, or honeycombs. The collector brick layer is surrounded by a further layer of insulation 24 with a seal 88 like that detailed in Figure 18 and 19. To allow easy configuration of storage capacity and other performance characteristics whilst lowering cost by making key components universal throughout a range of thermal store sizes. Simple filling elements 89A-F are used in the inner and outer thermal mass brick layers these filler elements will be made of insulation or thermal mass materials dependent on their location. Conductor bricks 77A-D are used at the connector end of each row of core bricks 11 to facilitate electrical connections. The collector bricks 20 are made with a uniform 2D cross-section to allow them to be produced with a low-cost extrusion process. However, there shape may also be achieved using pressing and other processes. In use the entire modular combination of thermal mass, heating elements and insulation would be supported by a structural frame work that may be further insulated.

[0211] Figure 13 shows the location of a flat element 75 in a single modular combination of thermal mass, heating elements and insulation by removing bricks. To configure the thermal stores charging, the serial and parallel connections of electrical heating elements 75 within a slice can be controlled. For example, it may be advantageous to wire all heating elements from a single modular combination of thermal mass, heating elements and insulation 82 as shown in figure 11 and 12 in serial and wire them to a single phase of a three-phase supply. In other scenarios it may be advantageous to have the module 82 as shown in figure 11 and 12 electrically subdivided into three which are the each supplied with one phase of three-phase supply.

[0212] In Figure 14 one possible electrical heater configuration is demonstrated. A bank of heating elements is formed by connecting full modules 82A-C heating elements inside the inner thermal mass 23 in serial, each bank 90A, 90B and 90C is connected to a single-phase supply 91 through a switch 92A-92C. A method of maximising charging rate from a given supply power is described in relation to Figure 38.

[0213] Figure 15 shows a system with components removed to show features. As before bricks 11 are used together to form gas passages 12 for heat exchange from bricks to gas. Geometry at the top 93 and geometry at the bottom 94 of the brick 11 interlock to aid assembly and structural integrity. The layers of bricks are also offset 95 to further interlock the brick. In the embodiment shown the element 75 is supported on a flat on the top of the brick and the bottom of the brick has a slot 96 which is detailed in Figure 16 that when seated in slot 93 ensures there is a gap between the top of the element 75 and the bottom of the brick above to allow thermal expansion of the element 75. The element 75 is designed as a flat sheet with material removed to form a conductor path of rectangular cross-section to maximise the available volume taken up by heating element material and maximise surface area for heat transfer. The design shown in Figure 13 and Figure 15 maximises the volume filled by high energy density materials and hence energy density of the thermal store. Individual heating elements are connected as shown in Figure 8. The position of the connector support bricks 77 is shown in Figure 12.

[0214] In an alternatively embodiment the brick could be used upside down with the heating element 75 supported in slot 96.

[0215] In Figure 16 the core brick geometry has indented features on a maximum of two sides. In the case shown at Figure 16, the indented features are provided on the heat exchange surfaces 12A and 12B. The element grove 96 and interlocking geometry 93 have a constant cross section, this enables the bricks to be manufactured in part by a low-cost pressing process. Although all brick edges are shown as sharp throughout the above descriptions, they could also be radiused to allow certain manufacturing processes.

[0216] In Figure 17 a section is removed from the single modular combination of thermal mass, heating elements and insulation shown in Figure 12 to highlight an insulation arrangement. Although it may be advantageous to have a single type of insulation between the core bricks 11 and collector brick 20 a multi-layer approach may be beneficial in some scenarios. In Figure 17 two layers of insulation are used. The inner 97 may have higher temperature resistance than the outer layer 98 but the temperature gradient between the hotter core bricks 11 and colder collector bricks 20 may allow both insulation layers to be used within their typical operating limits without excessive damage. It may also be necessary to protect the inner 97 and outer layer 98 of high- performance insulation with a layer of more robust low performance insulation 99 or solid material so that it is protected from gas flows or disturbance during maintenance disassembly as further detailed in Figure 21.

[0217] In Figure 18 a section is removed from the single modular combination of thermal mass, heating elements and insulation shown in Figure 12 to highlight a sealing arrangement. In this embodiment the inner insulation 100 is made shorter than the outer 98 to create a slot for a compressible seal 87. The seal shown is round however a square or rectangular profile may also be useful. It would also be possible to have a slot cut out of a piece of insulation as shown in Figure 12 where seal 88 is placed in a slot cut from the outer insulation 24. In some embodiments having the compressible seal on all four sides of the system (top, bottom, left side and right side) will be advantageous to managing leakage and thermal expansion. In an alternative embodiment the compressible seal may only be used at the top of the module where the effects of thermal expansion are largest and the other sides will either use insulation panels connected at edges ora multi insulation layer approach as discussed in Figure 17 with overlaps to block gas leaks.

[0218] When two or more modular combination of thermal mass, heating elements and insulation shown in Figure 12 are assembled to form a thermal store (Figure 9) the resulting seal is shown in Figure 19. In Figure 19 the seal 87 is compressed on flat face 101A and 101 B of the next modular combination of thermal mass, heating elements and insulation. This sealing arrangement allows assembly of small module in addition to allowing sealing when modules move at a different rate to its neighbour due to the combined effect of temperature difference and thermal expansion. The seal 87 slides up and down the smooth surface 101A it is in contact with. This sealing arrangement allows a large amount of vertical movement due to the sliding seal and a smaller amount of horizontal movement due to seal compression.

[0219] Figure 20 demonstrates how various types and grades of insulation could be used in combination to allow high heat retention and access to the inner thermal mass for maintenance of component such as heating elements, sensors, and others. Although a uniform distribution of insulation types may be advantageous in some situations as shown in Figure 12 maintenance access without disturbing high-performance insulation may be useful in others. In Figure 20 the inner thermal mass assembly made of core bricks 11 is surrounded on three sides by high thermal performance insulation as shown previously in Figure 12 and Figure 17 however one side is replaced by a plurality of smaller removable insulation blocks 18T of a lower performance but more robust and handleably insulation that can be removed whilst the panels on the other 3 sides remain in place. The thickness of the plurality of insulation blocks 102 can be increased to give equivalent heat retention as the high-performance insulation panels. The collector bricks 20 outer insulation blocks 103 are also a plurality or removable blocks. The outer support structure must also be removable on one side to enable maintenance from a single side. Figure 21 shows a module having high performance insulation which can be protected during maintenance. High performance insulation panels 104A and 104B are covered by pieces 105A-D of a more robust material which can be solid, insulated or a treated fibre or porous material (Figure 29). Therefore, during maintenance when insulation blocks 102A-F is removed the high-performance insulation panels 104A-B are protected.

[0220] In Figure 22 a module of a thermal energy storage system configured to allow for differential thermal expansion is shown. By ensuring that all components such as bricks and insulation layers end at the same horizontal location lines of movement 107A and 107B can be planned so that when high temperature high thermal expansion components such as the core thermal mass is heated it can move more than its surrounding components. This movement is exaggerated in Figure 22 for illustrative purposes. Additional seals of the type shown in Figure 19 can be added normal to the lines of movement 107A and 107B (in to page, Figure 19) to improve gas path sealing when movement occurs.

[0221] It may be advantageous to transport a thermal storage system to the site of use in a fully or partially constructed form however it may be necessary to leave gaps between components such as bricks to allow thermal expansion when the system is heated without damage. By planning lines of movement 107A and 107B within the single modular combination of thermal mass, heating elements and insulation 82 shown in figure 12 pressure can be temporarily applied to the top of a portion of module 82 to lock the components in place during transport. For example, a uniform pressure could be applied horizontally between points 107A and 107B to reduce the bricks 11 ability to move. For example, this pressure could be provided by a mass under the action of gravity or pneumatically or hydraulicly with a bladder or by an elastic material. Alternative approaches of locking the brick 11 assemblies shown in Figure 12 and Figure 20 could include placing spacers made of a material that would melt or sublimate under the action of heat once the thermal store was charged for the first time. These spaces could be fitted between bricks during assembly or in the gas flow ducts 12 shown in Figure 12. Another approach could involve fitting expandable rods in the gas flow ducts 12 during transport that could be removed on site.

[0222] Figure 23 demonstrates how an internal envelope with internal insulation can be used to allow a vacuum chamber to be formed around an entire thermal storage system whilst, key internal components can be subject to gas at a positive pressure for use as a heat exchange medium and or to provide a favourable chemical environment for key components which can include but is not limited to heating elements.

[0223] Figure 23 is a diagram of one possible embodiment of a thermal storage system. This thermal storage system is configured to heat from an electrical source, heat gas for some external use and retain heat for long periods between discharges. Gas flow through the system is represented by grey outlined arrows. Gas enters the system through an inlet 18 the gas then passes through passages in the outer concentric thermal mass 19, which could be constructed with bricks. In an alternative embodiment the outer thermal mass 19 could be a packed bed of granulated material contained between the inner insulation 20 and the envelope 21. If the heat transfer fluid must be sealed from the thermal mass a labyrinth of pipe or pipes can be passed through the packed bed to contain the gas.

[0224] Once the gas has passed through the outer concentric thermal masses on the sides and top of the storage system into the inner thermal mass through an opening or pipe 22. The gas then passes through the inner thermal mass 23 which could be an integration of thermal mass, heat exchanger and heating element into a brick-based module as shown in Figure 5 or be some other arrangement like a packed bed of thermal mass. Once heated the gas exits the system through a duct or pipe 24 that passes through the inner and outer thermal masses 19, 23 the insulation components 20, 24 and the envelope 21 and vacuum chamber 26. The hot gas outlet 25 connects to an external process.

[0225] Heat is retention in the system is enhanced by an arrangement of thermal masses, insulation, and walls. The central thermal mass 23 is enclosed within an insulated layer 20 which is intern enclosed within a second thermal mass 19 this is then enclosed within a gas tight envelope 21. A further layer of insulation 23 exists between the envelope 21 and the vacuum chamber 26.

[0226] In a modified embodiment, the gas tight envelope 21 can be removed and a nonvacuum tight container can be used in place of 26, lowering the cost of the system but decreasing heat retention. To ensure that flow is properly directed around the thermal storage system impermeable barriers are erected using solid walls and passages between sections. For example, the envelope 21 acts with the insulation 20 to guide the gas through the thermal mass integrated heat exchangers 19. Before a passage 22 at the top of the insulation allows transfer of the gas into the inner thermal mass.

[0227] In an alternative embodiment Figure 24 gas enters and exits the top of the system this and entry and exit from the side may be advantageous in some situations. Here two pumps 58 and 59 are combined in a mixer 61 A to supply air to the thermal store from atmosphere or the host process exhaust. A second pair of pumps 56 and 57 are combined to supply air to a mixer 61A then in mixer 62 which cools the hot air exhausted from the core of the thermal store 23. Check valves 60A-D are used to prevent backflow whilst only one of the pumps is operating. It may be advantageous to have a single or any number of pumps depending on use. This a pump approach can also be applied to the thermal store configurations embodied in Figure 1 ,2, 3, 9 10 and 11

[0228] In Figure 25 a mixer 62 from figure 24 is shown. The mixer connects to the duct that outputs hot gas from the thermal storage system. During extraction cold air is input to pipe 108 which is split into smaller pipes 109A-F (109F is obscured) for distribution which inject air into the mixer to combine and cool the hot gas from the thermal store entering at 110. Mixed gas exits at an outlet 111 to further duct work to the external process. The mixer has several features that allow it to be made of a low temperature material at low cost and contain gas at a temperature that could weaken or damage its structure. These are detailed in Figure 26.

[0229] Figure 26 is a cross-sectional view of the mixer shown in Figure 25. It may be necessary to protect the mixer structure 115 from the hot gas from the thermal store input through duct 110 the first way this is achieved is by shielding the mixer walls by imputing the gas around the perimeter of the base 112 of the mixer. The second approach is to isolate the mixer from the hot duct 110 with a low thermal conductivity seal element 113 around the perimeter of the inlet Duct 114 this is detailed in Figure 27

[0230] In Figure 27 the details of the mixer seal area are shown. A compressible seal 113 made of a single high temperature material or combination of high temperature material contacts the top of the duct 110. This seal 113 could be of round, square or rectangular profile and is constrained by feature 116.

[0231] To allow the mixer structure to be made of a low temperature material cool gas is introduced at inlet 117 that cools and protects the mixer walls 118 from hot gas until it mixes to lower the gas flow temperature. In some use scenarios mixing can be enhanced by angling cold gas inlets to create swirl, adding turbulence generation features such as grids and protrusions into the flow. In alternative embodiments of the mixer cold gas could be introduced from an annulus or plenum chamber feed by any number of inlet pipes and screens or meshes could be added to make flow distribution more uniform.

[0232] The seal 113 can be compressed by the action of gravity on the mixer 62 or compression on the seal can be controlled, enhanced, or reduced using a sprung or elastic element. These arrangements also allow for movement and thermal expansion. The top surface of the duct 110 in contact with seal 113 can be hardened as discussed in Figure 29 or protected by a harder material as discussed in Figure 21.

[0233] During system discharge the price of electricity to operate the discharge pumps 56-59 in figure 24 it is likely to be high therefore it is advantageous to operate the pump its most energy efficient setting. However, it may also be necessary to vary the flow rate to suit the downstream process. Therefore, it may be advantageous to operate multiple pumps to allow the combined discharge to be delivered at maximum efficiency. An example of this is given in Figure 28 where a typical pump efficiency vs mass flow rate is given. If a mass flow rate of 0.5 is required from a pump that has a maximum output of 1 it can be operated at setting 63 however, greater efficiency may be achieved by operation operating 2 pumps with a maximum flow rate of 0.5 at setting 64 and 65 and combining their output.

[0234] Figure 29 shows a valve for selectively closing the exit duct 110 from the inner thermal mass 23 to reduce heat losses from natural convection whilst the thermal store is storing or charging cycle. In Figure 29 a sliding piece of solid material 119 is slid across the duct in a grove 120 to close it and form a gate valve which can be actuated manually or with an actuator switched by control system. Alternative embodiments could use circular, square or rectangular duct with a gate or butterfly valve or a passive non-return valve that is lifted by the gas flow when the extraction pumps are in use and returns by gravity or an elastic element when there is no gas flow. The ideal location for the valve is as close as possible to the inner thermal mass whilst allowing external access for actuation.

[0235] To provide location selective wear resistance, thermal conductivity, and strength to high temperature components such as the walls of the duct 110 the grove 120 or the gas input and output module 83 and a gas turning module 84 in figure 9 a composite construction approach is used. For example, in the duct 110 or module 83 and 84 the surface requires wear resistance from the fast-flowing gas whilst the remaining material requires sufficient strength to support loads whilst having low thermal conductivity to minimise thermal losses. The construction method involves constructing these components using assemblies of simple shaped porous or fibrous ceramic material that are then impregnated with a ceramic in a carrier liquid at required location such as a gas path surface. When heated the liquid evaporates away and the ceramic in the liquid bonds or adheres to itself and to the porous or fibrous material to form a densified composite material. The amount of liquid impregnated in the surface is controlled to ensure that only the required depth of hardened material is produced as an excessive depth will increase thermal conductivity and increase heat loss. Where simple shapes are joined to form components such as the duct 110 the ceramic carrying liquid can be used at the interface between discreate pieces to provide sealing and adhesion. Where additional strength is required in the joint requires methods can be used to increase contact surface area or to interlock separate pieces.

[0236] These may include serrations, castellations, tongue and grove, dovetail, or lap joints. The ceramic carrying liquid can be applied externally or passages can be left in the joint to allow internal injection of liquid.

[0237] Figure 30 and Figure 31 show a system having a connector rod 121 for making the electrical connections from the heating elements 75 in the inner thermal mass 23 to the exterior of the thermal storage system where it can be connected to an external electricity supply. Figure 30 represents the thermal store in a cold state and Figure 31 after significant heating. During the heating process the inner thermal mass 23 heats to higher temperatures to the outer thermal mass 19 and the surrounding insulation layers. The consequences of this are that the thermal expansion of the material within the inner thermal mass 19 causes the heating element 75 to move vertical a greater amount than the outer thermal mass. As the electrical connection must pass through the outer thermal mass 19 and the surrounding insulation layers and is made of a solid material which must move and flex to accommodate the differential thermal expansion. In the embodiment above the connector rods 121 are supported by and pivot within the outer thermal mass with appropriate clearance left through the solid material. This allows the connections to the external electricity supply from the connector rods 121 to move and be joined with flexible rods or cables within the outer insulation layer 24. This configuration also allows differential thermal expansion between modules as shown in Figure 9, if they are used. The second benefit of this configuration is that heat that may be lost through conduction from the core to the exterior of the system through the connector rod 121 is captured in the outer thermal mass 19 for recovery during the next extraction cycle.

[0238] Where sealing is required to maintain airflow direction a device as shown in Figure 32 can be used. A loose piece of sheet material 27 can be supported in a grove 29 cut into a thermal mass brick 11 and held against a surface such as an insulation layer 28 or the envelope or another solid wall by gravity to form a gas seal. This sheet would be free to move and allow thermal expansion of connected components.

[0239] To provide structural and stability support it may be necessary to provide an additional element as shown in Figure 33 for a thermal storage system as envisioned in Figure 23. For example, support 30 is to add stability to the thermal core made of brick. To ensure that the thermal bridge created is minimal the support may be made with a ceramic in the form of a rod, tube, or honeycomb. Profile is kept to a minimum as the supports may penetrate insulation layers. Similar structural elements 31 may be used to transfer load from outer thermal mass bricks through insulation layers to the central thermal mass. The load of the thermal core bricks may be distributed onto a plate 32, which could be a single piece of material or an assembly of overlapping plates. Load from this plate could be distributed to the outer thermal mass brick using a ceramic in the form of a rod, tube, or honeycomb 33. In the case where the base of the envelope is of a curved form as shown in Figure 33 a flat base can be created either by filling the base 34 with packed and levelled granular material, a liquid / paste ceramic that solidifies with heat or time. Alternatively, a brick-based structure can be made that could also integrate a heat exchanger to recover energy from the thermal mass created in the base 34. Figure 34 shows an arrangement of brick-based modules. This arrangement enables the use of individual heater element parts having reduced sizes to ease assembly and maintenance of a thermal storage system. When bricks 11 are stacked in layers the trenches 13 and link trenches 15 align to allow complex element 14 shapes. To ease assembly and simplify maintenance these complex elements can be separated into small parts 42 and then welded in place during assembly 43.

[0240] Figure 35 shows a connector for reducing the effects of creep on electrical conductors that are experiencing high temperature used to connect heater planes in a thermal storage system. In the first embodiment, the electrical conductor in the form of a helix

[0241] 45 is supported by a helical slot in a ceramic material 44. The angle / pitch of the groove is calculated to ensure the conductor is supported such that it won’t stretch due to selfweight and creep. An electrical connection can be taken off the helix at the correct level

[0242] 46 to power an element on a heater plane as shown in Figure 5 and Figure 34.

[0243] In a second embodiment Figure 36 the conductor wire 47 is straight and passes through holes in ceramic blocks 48 to gain the height between heater planes without leaving the hot wire conductor subject to excessive degradation from unsupported selfweight and creep. An electrical connection can be taken off from the end of the block 48 at the correct level 49 to power an element on a heater plane as shown in Figure 5 and Figure 34. It may also be beneficial in some systems to use square or rectangular profile conductors in square or rectangular slots, which can be open on one side for access as shown in Figure 8.

[0244] In Figure 37 an arrangement for electrically connecting high temperature ceramic heating elements that heat a thermal storage system to exterior electrics is shown.

[0245] In a thermal storage system, that uses concentric thermal masses as shown in Figure 23 high temperature ceramic heating elements 50 that can heat the central thermal mass 51 can be implemented by extending the ceramic portion through the first layer of insulation 52 to the outer thermal mass 53 where the temperature is low enough to allow a metallic conductor 54 to be joined to the ceramic. This metallic conductor can then exit the outer layers of insulation 55 and any other layers to the exterior of the thermal storage system where a connection can be made to an external electricity supply. Figure 38 is a flowchart illustrating a method 300 of heating the thermal storage mass of a thermal energy storage system. The method 300 involves a step 310 of providing a first electrical heating element and a second electrical heating element in contact with the thermal storage mass. The method involves a step 320 of operating the first electrical heating element at a first power level and the second electrical heating element is operated at a second power level. The method also involves a step 330 of operating the first electrical heating element at a third power level less than the first power level, and operating the second electrical heating element at a fourth power level greater that the second power level.

[0246] A key limiting factor on the service life of electrical heating elements is the maximum temperature they operate. Figure 38 shows a method of limiting element temperature whilst maintaining necessary heat transfer from elements to the thermal storage mass. As an element heats it increases the temperature of the surrounding thermal mass however as the thermal mass has a thermal inertia and a resistance to heat transfer the material directly in contact with the elements is hotter than the material surrounding it and a thermal gradient is formed. The surrounding material acts to cool the element as it dissipates power therefore for a given power dissipation the element temperature increases with the temperature of surrounding material. By switching the heating element off the thermal mass close to the element cools and becomes uniform with its surroundings and cools the element. By pulsing the element on and off maximum element temperature can be minimised.

[0247] If an electrical power of 1 is available in the thermal store shown in Figure 14 and each bank of elements 90A, 90B and 90C can absorb a power of 1 switches 92A-C can be operated to ensure only one banks are heating at any time once they reach a predetermined temperature that has been chosen to maximise element life the heater bank is switched off and allowed the heating element to relax whilst another is switched on until it reaches maximum temperature.

[0248] Figure 39 is a schematic diagram of a controller 200 for controlling a thermal energy storage system. The controller 200 in this example is realised by one or more processors 210 and a computer-readable memory 220. The memory 220 stores instructions which, when executed by the one or more processors 210, cause the thermal energy storage system (i.e., the electrical heating elements of the thermal energy storage system) to operate as described herein. Figure 40 illustrates how a storage system component such as the gas input and output module 83, gas turning module 84 and the module 82 in figure 9 can be constructed with the multi-layer insulation approach discussed in figure 17 and components used to aid this. Figure 40 is a sectional view of a gas turning module where it is advantageous to use multiple layers of insulation 122-125 of different material properties to lower cost and lower heat loss from the system. To add additional strength to the structure features such as a web 126 can be added. This web can be made using a castable ceramic or ceramic fibre or a premade shape of ceramic or ceramic fibre that is bonded or doweled to the surface. To aid the strength and stiffness of the structure and hold together multiple layers of insulation, ceramic dowels pins and bolts could be inserted through holes 127 at any location that would be advantageous. Bolts could have head and nuts made of ceramic of increases in cross-section provided by castable ceramics hardened after assembly. It may also be advantageous to remove these ceramic dowels pins and bolts after assembly and fill the holes with an insulating material. It may also be advantageous in some scenarios to use castable ceramic fibre insulation to construct the entire structure or use large sheets of premade insulation boards for flat sections and key cast additional protrusions 128 into boards (e.g., by roughening / reshaping the surface of the boards to provide increased surface area and / or features to interlock with the additional protrusions - can also be referred to as over-moulding). The insulation boards may comprise the composite hardened material as described herein.

[0249] In summary, there is provided a module for a modular thermal energy storage system. The module has a thermal storage mass, an electrical integration channel, and a fluid channel. The electrical integration channel is for at least partly enclosing a portion of an electrical heating element extending through the module. The fluid channel is for fluidic communication with a fluid input and a fluid output of the modular thermal energy storage system. The electrical integration channel is separate and different from the fluid channel. The present invention also relates different types of modules for a modular thermal energy storage system, modular thermal energy storage systems themselves, and methods for heating the thermal energy storage mass of a thermal energy storage system.

[0250] These and other modifications and improvements may be incorporated without departing from the scope of the present invention. Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to and do not exclude other components, integers, or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0251] Features, integers, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

Claims1. A module for a modular thermal energy storage system, the modular thermal energy storage system having a fluid input, a plurality of modules, an electrical heating element for heating at least a subset of the plurality of modules, and a network of channels for heat exchange between fluid introduced via the fluid input and the plurality of modules to generate heated fluid, and a fluid output for outputting the heated fluid, the module comprising: a thermal storage mass; an electrical integration channel for at least partly enclosing a portion of the electrical heating element extending through the module; a fluid channel for fluidic communication with the fluid input and fluid output; and wherein the electrical integration channel is separate and different from the fluid channel.

2. The module according to claim 1 wherein the fluid channel is one of a plurality of fluid channels each configured to be in fluidic communication with the fluid input and fluid output when in use.

3. The module according to claim 1 or claim 2 wherein the electrical integration channel extends along a first direction and the or each fluid channel extends along a second direction, different from the first direction, and optionally wherein the first direction is perpendicular to the second direction.

4. The module according to any preceding claim wherein the module comprises: a first face associated with the electrical integration channel, wherein the electrical integration channel extends along the first face between a second face and a third face, and a fourth face associated with the fluid channel, wherein the fluid channel extends along the fourth face between a fifth face and the first face.

5. The module according to any preceding claim wherein, in use, the or each fluid channel is configured such that the thermal storage mass is in direct contact with the fluid, and / orthe electrical integration channel is configured such that the thermal storage mass is in direct contact with the electrical heating element.

6. The module according to any preceding claim wherein the or each fluid channel is configured to partly define a fluid pipe enclosed along its length when the module is arranged adjacent to a further module having the same orientation, wherein the or each fluid pipe is defined in part by a fluid channel of the module and in part by a respective fluid channel of the further module, and / or wherein the electrical integration channel is arranged so that the electrical heating element can extend through the module and an additional module, having the same orientation, along a respective electrical integration channel.

7. The module according to any preceding claim wherein the module comprises a first end, wherein the electrical integration channel comprises an outlet arranged before the first end, and wherein the module further comprises a trench region for supporting a first portion of the electrical heating element extending between the outlet and the first end and for allowing access to the first portion of the electrical heating element.

8. The module according to any preceding claim wherein the electrical integration channel extends along a first direction, wherein the module is further configured to support a portion of the electrical heating element extending along a further direction different from the first direction, wherein the further direction is angled relative to the vertical direction, or wherein the module is further configured to cooperate with a connector module configured to support a portion of the electrical heating extending element along a further direction different from the first direction, wherein the further direction is angled relative to the vertical direction.

9. The module according to any preceding claim further comprising a retaining portion configured to cooperate with a corresponding portion of a further module to engage the module with the further module, and optionally wherein the retaining portion comprises a protrusion configured to engage with an indentation of the further module, and further optionally wherein the protrusion is defined by a portion of the electrical integration channel.

10. A module of a thermal energy storage system, the thermal energy storage system having a fluid input, a thermal energy storage mass, and a fluid output for outputting heated fluid generated through heat exchange between the thermal energy storage mass and fluid received through the fluid input; the module comprising: a thermal energy storage mass having an exposed portion in thermal contact with the surroundings; and insulation extending around the circumference of the thermal energy storage mass; wherein the module is attachable to at least one other module such that, in use, heat can be transferred between attached modules via the exposed portion.

11. The module according to claim 10, wherein the thermal energy storage mass comprises a plurality of thermal storage mass modules according to any of claims 1- 9.

12. The module according to claim 10, wherein the thermal energy storage mass comprises an outer thermal mass extending around the circumference of an inner thermal mass, and optionally wherein the inner thermal storage mass comprises a plurality of thermal storage mass modules according to any of claims 1-9.

13. The module according to claim 12, wherein the outer thermal storage mass comprises a plurality of outer storage mass modules, wherein each outer storage mass module comprises at least one fluid passage for fluidic communication with the fluid input and fluid output, and optionally wherein the or each outer storage mass module is shaped to have a uniform cross-section, and / or optionally wherein at least a subset of the outer storage mass modules are removable.

14. The module according to claim 12 or 13, the module further comprising inner insulation between the inner thermal storage mass and the outer thermal storage mass, wherein the inner insulation and the outer thermal storage mass each comprise a movable portion for allowing access to the inner thermal storage mass.

15. The module according to any of claims 10-14 having a second module portion between a first module portion and a third module portion, wherein the second module portion is slidable relative to the first module portion and the third moduleportion, wherein the second module portion comprises a first portion of the thermal energy storage mass and at least part of the insulation.

16. The module according to claim 15 wherein the first portion of the thermal energy storage mass comprises a plurality of separate mass portions, wherein, in a first configuration, the plurality of separate mass portions are prevented from moving relative to one another, and optionally wherein, in the first configuration, the module comprises a retaining element in a retaining configuration for preventing relative movement between at least a subset of the plurality of separate mass portions, wherein the retaining element is configured to change away from the retaining configuration in response to heating of the first portion of the thermal energy storage mass to allow relative movement between the plurality of separate mass portions.

17. A modular thermal energy storage system having a plurality of modules according to any of claims 1-16, each module being attachable to at least one other module.

18. The modular thermal energy storage system according to claim 17 having a first module according to any of claims 10-16 and a second module according to any of claims 10-16, wherein the first module is connected to a fluid input module comprising the fluid input and the fluid output, and wherein the second module is connected to a fluid turning module having a chamber for directing fluid from the fluid input through the first module and the second module to the fluid output.

19. The modular thermal energy storage system according to claim 18, further comprising a third module according to any of claims 10-16 and a fourth module according to any of claims 10-16, wherein the third module is connected to a further fluid input module comprising a further fluid input and a further fluid output, and wherein the fourth module is connected to a further fluid turning module having a further chamber for directing fluid from the further fluid input through the third module and the second module to the further fluid output, wherein the fluid turning module and further fluid turning module are arranged adjacent to one another.

20. A method for heating the thermal energy storage mass of a thermal energy storage system comprising:providing a first electrical heating element in contact with the thermal energy storage mass; providing a second electrical heating element in contact with the thermal energy storage mass; regulating the temperature of the first electrical heating element and the second heating element by switching between a first regulation mode and a second regulation mode; wherein, in the first regulation mode, the first electrical heating element is operated at a first power level and the second electrical heating element is operated at a second power level; and in the second regulation mode, the first electrical heating element is operated at a third power level less than the first power level, and the second electrical heating element is operated at a fourth power level greater that the second power level.

21. The method of claim 20 wherein the second power level is less than the first power level, and the third power level is less than the fourth power level.

22. The method according to claim 21 wherein the first power level corresponds to the same target power as the fourth power level, and / or wherein the third power level corresponds to same target power as the second power level.

23. The method according to claim 21 or 22, wherein the third power level corresponds to the first electrical heating element being switched off and / or wherein the second power level corresponds to the second electrical heating element being switched off.

24. A controller configured to carry out the method of any of claims 20-23.

25. A computer program product comprising instructions which, when the program is executed on a computer processing means, causes the computer processing means to carry out the method of any of claims 20-23.

26. An electrical heating element suitable for integration with any of the modules of claims 1-16, modular thermal energy storage systems of claims 17-19 or use with any of the methods of claims 20-23.

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