This invention relates generally to energy generation. More specifically, although not exclusively, this invention relates to a method and system for the storage and conversion of thermal energy to electrical energy.

Energy has different forms including, for example, thermal, electrical, chemical, and mechanical energy. Different forms of energy have different grades. For example, electrical energy is the highest grade energy, whereas thermal energy is the lowest grade energy. As a result, the conversion between these energy forms has different efficiencies. For example, the conversion of thermal energy to electrical energy (the most popular energy conversion in fossil-fuelled power plants) has an efficiency of approximately 35%. In contrast, direct conversion of electrical energy to thermal energy has a much higher efficiency and indirect conversion of electrical energy to thermal energy via heat pumps can be higher still.

Different energy forms and different application requirements have led to the development of many energy storage technologies, e.g. mechanical, electrochemical, chemical, thermal and electromagnetic storage. For example, mechanical based energy storage technologies, which are primarily for large scale applications, include pumped hydro, and conventional compressed air energy storage. In practical applications, integration of these different energy storage technologies are often needed. An example of a coupled mechanical and thermal energy storage method is advanced adiabatic compressed air energy storage.

Electrochemical based storage methods include the use of lithium-ion batteries and sodium-sulfate batteries. Thermal energy storage technologies include both sensible and latent heat storage technologies, whereas thermochemical energy storage technologies often comprise both thermal and chemical storage as a coupled technology.

One of the performance indicators of a particular energy storage technology is round trip efficiency, which is defined as the energy output from an energy storage device (system) divided by energy input into the energy storage device (system). The current way of quoting round trip efficiency of energy storage technologies is confusing, and in many cases, misleading, because it does not take into account the energy source form and the end use form. In most cases, the round trip efficiency takes the electrical energy form as default, namely, electrical energy discharged out from a storage device delivered by electrical energy charged into the device. However, the majority of electrical energy comes from fossil fuel burning power plants. Therefore, it is unfair to make comparisons. The situation is even more confusing if coupled or hybrid energy storage technologies are considered.

Electrical energy plays a central role in the modern world and as a result, infrastructures have been built around the world for mining, processing and transporting fossil fuels to power plant, electrical generation, transmission and distribution. Currently, electrical generation is mostly from conventional fossil fuelled power plants with an average efficiency of approximately 35% and the rest is discharged to the environment in the form of low grade heat (this itself represents a challenge that the world has been trying to address for many years). Despite significant efforts in the development of renewable energy technologies in the past few decades, renewable power generation only comprises a very small fraction of the total electrical generation. The large-scale replacement of fossil fuel generation is less likely in short to medium terms. Therefore, enhancement of conventional power generation efficiency is still highly important, which also represents one of the greatest challenges in the energy sector.

The majority of electricity generation is currently achieved through burning fossil fuels to produce thermal energy (heat) first, then converting the thermal energy to mechanical energy and finally conversion to electrical energy to be transmitted and distributed to the end user. Thermal energy takes a large portion in the energy demand by the end user. This would imply that, in many cases, the end users need to turn electrical energy back to heat. Although this step is highly efficient (close to 100% for direct conversion, or a few times higher if heat pumps are used), significant losses can be identified immediately. Therefore, the use of thermal energy to generate electrical energy, which is then used to generate thermal energy, is a wasteful process.

Additionally, much of the secondary heat or low grade heat that is generated in industrial processes, and during the generation of electricity from both renewable and non-renewable sources, is often wasted. This thermal energy may be used to generate electricity. However, there is a shortage of efficient and economically viable technologies that are capable of storing thermal energy, which enable said thermal energy to be converted to electrical energy‘on demand’. It is therefore a non-exclusive object of the invention to provide an efficient and scalable method and system for storing thermal energy, and to transfer said thermal energy directly to the end user. It is a further non-exclusive object of the invention provide an efficient and scalable method and system for the storage and conversion of thermal energy (from renewable and non renewable sources) into electricity, the system and method exhibiting a high round trip efficiency (calculated by inclusion of the energy source).

Accordingly, a first aspect of the invention provides a method of converting thermal energy to electrical energy, the method comprising:

(i) harvesting thermal energy from a source;

(ii) using the thermal energy to drive one or more chemical reactions;

(iii) using one or more reaction products of the one or more chemical reactions to drive an electrochemical cell to produce electrical energy.

A further aspect of the invention provides a method of converting thermal energy to electrical energy, the method comprising:

(i) harvesting thermal energy from a source;

(ii) using the thermal energy to drive one or more chemical reactions;

(iii) using one or more reaction products of the one or more chemical reactions to drive an electrochemical cell to produce electrical energy; wherein the one or more chemical reactions preferably comprises a reaction of a non- stoichiometric perovskite oxide; and the one or more reaction products comprises oxygen, the oxygen being used to drive an electrochemical cell to produce electrical energy.

Advantageously, the one or more reaction products of the one or more chemical reactions may be used to store electrochemical energy. For example, the reaction products may be stored for a period of time,’t’, before being used to drive an electrochemical cell to produce electrical energy so as to enable the production of electrical energy‘on demand’.

In embodiments, the method may further comprise (iv) using one or more waste products from the electrochemical cell (formed by producing electrical energy) in the one or more chemical reactions of step (ii). For example, step (ii) and step (iii) may undergo a“chemical looping mechanism”. This is a term known to those skilled in the art, which we be further explained below.

Advantageously, in embodiments in which the waste products from the electrochemical cell are used as reactants in the one or more chemical reactions that are driven by thermal energy of step (ii), the method does not require the addition of further reactants to continuously produce electrical energy from thermal energy. This creates a“closed” system in which electrical energy can be continuously generated from thermal energy without intervention.

In embodiments, the one or more chemical reactions may comprise a reaction of a metal (M) oxide, for example M ₂ O ₂ , e.g. U ₂ O ₂ ; and/or the one or more reaction products to drive an electrochemical cell to produce electrical energy may comprise oxygen. In embodiments, the one or more chemical reactions may comprise a reaction of a metal (M) oxide, for example M ₂ O, e.g. U ₂ O, e.g. and carbon; and/or the one or more reaction products to drive an electrochemical cell to produce electrical energy may comprise lithium (Li).

In embodiments, the metal (M) may be or comprise aluminium, germanium, calcium, iron, lithium, magnesium, potassium, sodium, silicon, tin, and/or zinc. In these embodiments, the method may comprise one or more chemical reactions of one or more metal oxides to produce oxygen. In these embodiments, the method may comprise one or more chemical reactions of one or more metal oxides to produce the elemental metal, e.g. metallic aluminium, germanium, calcium, iron, lithium, magnesium, potassium, sodium, silicon, tin, and/or zinc, said oxygen and/or elemental metal being usable to drive an electrochemical cell, e.g. a metal-air battery, to produce electrical energy. In these embodiments, the metal air battery may comprise the same metal element as the metal oxide usable in the one or more chemical reactions, e.g. the metal-air battery may be a alkali metal -air battery, for example a lithium-air battery and the metal oxide may be or comprise one or more of U ₂ O ₂ and U ₂ O (or the alkali metal oxide analogues).

A further aspect of the invention provides a method of converting thermal energy to electrical energy, the method comprising:

(i) harvesting thermal energy from a source;

(ii) storing the thermal energy; (iii) converting the thermal energy into electrochemical energy;

(iv) converting the electrochemical energy into electrical energy.

The method may further comprise in step iii) producing oxygen via a reaction of a non- stoichiometric perovskite oxide. The method may comprise, in step iv) using oxygen to drive an electrochemical cell to produce electrical energy.

The electrochemical energy may be stored for a period of time,’t’, before conversion into electrical energy so as to enable the provision of electrical energy‘on demand’.

Further aspects of the invention relate to apparatus, e.g. apparatus for operating the method of the invention, the apparatus comprising a reaction vessel, for example a reaction vessel for operating step (ii) or (c) of the method and an electrochemical cell, e.g. an electrochemical cell for providing electricity according to step (iii) or (d) of the method.

The apparatus may comprise a first conduit to allow one or more of the reaction products of step (ii) to communicate with the electrochemical cell and a second conduit to allow the reaction products of the electrochemical cell to communicate with the reaction vessel.

The thermal energy of step (i) or (a) may be harvested from any suitable source. For example, the thermal energy may be harvested from one or more of a renewable source (e.g. solar, wind, tidal, and biomass), a non-renewable source (e.g. fossil fuels, nuclear), a clean fossil fuel, industrial waste heat, and/or heat generated from off-peak electricity either directly or via heat pumps.

The thermal energy of step (ii) may be stored in a series of thermal energy storage (TES) modules. The thermal energy may be converted into electrochemical energy in a thermal- electro converter (TEC). The electrochemical energy may be converted into electrical energy, i.e. electricity, in the thermal-electro converter (TEC).

Step (iii) may further comprise the use of chemical compounds suitable for converting thermal energy into electrochemical energy, for example, by using the stored thermal energy of step (ii) to drive chemical reactions or transformations that result in the conversion of the thermal energy into electrochemical energy. A further aspect of the invention provides a system for converting thermal energy to electrical energy, the system comprising:

(i) at least one module for storing thermal energy;

(ii) a first unit for converting thermal energy into electrochemical energy; and

(iii) a second unit for converting electrochemical energy into electrical energy;

wherein the first unit for converting thermal energy into electrochemical energy comprises a non-stoichiometric perovskite oxide for use in one or more oxidation and/or reactions to produce reaction products, e.g. oxygen, for use in the second unit to convert electrochemical energy into electrical energy.

The at least one module for storing thermal energy may be or comprise a series of thermal energy storage (TES) modules. The first unit and the second unit may be a thermal-electro converter (TEC). The first unit may be or comprise a thermal charge unit. The second unit may be or comprise an electro discharge unit.

In embodiments, the at least one module for storing thermal energy may comprise one or more of phase change materials (PCMs), inorganic salts, hydrocarbons, ceramic, salt hydrate, water, mineral oils, synthetic oils, pebbles/rocks/gravels, and so on and/or a thermochemical based material.

In embodiments, the second unit may comprise or be a metal-air, e.g. lithium-air, flow battery or a fuel cell, e.g. an oxygen-carbon monoxide fuel cell.

For the avoidance of doubt, any of the features described herein apply equally to any aspect of the invention.

A yet further aspect of the invention provides a system, the system comprising a series of thermal energy storage (TES) modules and a thermal-electro converter (TEC), the thermal- electro converter (TEC) comprising a thermal charge unit and an electro discharge unit, wherein thermal energy is exchanged between the series of thermal energy storage (TES) modules and the thermal-electro converter (TEC).

The function of the series of thermal energy storage (TES) modules is to store and exchange thermal energy. In embodiments, the series of thermal energy storage (TES) modules comprise a first thermal energy storage (TES) module and a second thermal energy storage (TES) module. Additionally or alternatively, the series of thermal energy storage (TES) modules may comprise a first thermal energy storage (TES) module, a second thermal energy storage (TES) module, and a 3 ^rd , 4 ^th ,... , n ^th thermal energy storage (TES) module. Each of the first, second, and/or ... n ^th (if present) thermal energy storage (TES) modules may comprise a material or materials that is/are suitable for the storage of thermal energy, i.e. suitable for storing heat in sensible and/or latent and/or chemical forms. For example, the types of material suitable for the storage of thermal energy may comprise one or more of phase change materials (PCMs), inorganic salts, hydrocarbons, ceramic, salt hydrate, water, mineral oils, synthetic oils, pebbles/rocks/gravels, and so on and/or a thermochemical based material.

The first, second, and/or ... n ^th (if present) thermal energy storage (TES) module may comprise the same type of material for the storage of thermal energy, or may each comprise a different type of material for the storage of thermal energy. The type of materials selected for use in the first, second, and/or ... n ^th thermal energy storage (TES) module may be suitable for the storage of thermal energy at different temperatures, e.g. a range of temperatures. For example, the type of materials suitable for the storage of thermal energy may cover a working temperature between approximately -196 °C and approximately +1800 °C.

In embodiments, the first thermal energy storage (TES) module, the second thermal energy storage (TES) module, and/or ... the n ^th (if present) thermal energy storage (TES) module of the series of thermal energy storage (TES) modules may be connected in parallel, in series, or in their combination. The first thermal energy storage (TES) module, the second thermal energy storage (TES) module, and/or ... the n ^th (if present) thermal energy storage (TES) module may be used to store thermal energy in a cascading manner according to energy grade, i.e. temperature. For example, the first thermal energy storage (TES) module, the second thermal energy storage (TES) module, and/or ... the n ^th (if present) thermal energy storage (TES) module may comprise a first, a second, and/or an ... n ^th material for the storage of thermal energy, the materials being different, the first material being suitable for transferring thermal energy at a temperature (T1) to the second material, and/or for transferring thermal energy at a different temperature (T2) to the ... n ^th material. The stored thermal energy within the series of thermal energy storage (TES) modules may originate from a single source, or may originate from a range of sources. For example, the stored thermal energy within the thermal energy storage (TES) module may originate from one or more of a renewable source (e.g. solar, wind, tidal and biomass), a non-renewable source (e.g. fossil fuels), a clean fossil fuel, industrial waste heat, and/or heat generated from off-peak electricity either directly or via heat pumps.

The function of the thermal-electro converter (TEC) is to convert thermal energy (from the series of thermal energy storage (TES) modules) into electrochemical energy, and to convert said electrochemical energy into electrical energy, i.e. electricity. The thermal- electro converter (TEC) comprises a thermal charge unit and an electro discharge unit. The thermal charge unit converts thermal energy to electrochemical energy and stores said electrochemical energy. The electro discharge unit converts said stored electrochemical energy to electrical energy for power grids, which supplies electricity to the end user or the consumer.

The thermal charge unit may comprise chemical compounds suitable for converting thermal energy into electrochemical energy. The chemical compounds suitable for converting thermal energy into electrochemical energy may undergo chemical transformations or reactions, i.e. chemical reactions may be performed in the thermal charge unit to convert thermal energy to electrochemical energy. The chemical reactions may be oxidation and reduction reactions (redox reactions). The chemical reactions may produce reaction products. The reaction products may be used to store the electrochemical energy generated in the thermal charge unit. The reaction products may be used in the electro discharge unit to convert electrochemical energy to electrical energy.

The chemical compounds may comprise solid nonstoichiometric perovskite oxides MO _y and MO _y-d. For example, the solid nonstoichiometric perovskite oxide MO _y may comprise or may be Ba ₂ Cao.66Nbi.34-xFe _x 06-5 (0<x£1).

The chemical compounds may further comprise alkali metal oxides, e.g. lithium oxides, e.g. U2O2 and/or UO2. The sodium and/or potassium analogues may be used, as may those of higher alkali metals. The chemical compounds may undergo oxidation and reduction reactions, i.e. redox reactions, to produce reaction products. The oxidation and reduction reactions may comprise one or more of the following pairs:

(Reaction 1)

(Reaction 2) or

(Reaction 3)

(Reaction 4)

Reactions 3 and 4 may also be carried out with other alkali metals.

The reaction products may comprise carbon monoxide, carbon, oxygen, and/or lithium. The reaction products may be used in the electro discharge unit to convert electrochemical energy into electrical energy.

The reaction products may be stored until required, i.e. so that electrical energy may be generated in the electro discharge unit on demand. The thermal charge unit may comprise a process wherein chemical compounds undergo a chemical looping mechanism, i.e. reactants undergo a first chemical reaction (e.g. an oxidation or reduction) to form products, said products then undergo a further chemical reaction (e.g. an oxidation or reduction) to form further products, the further products being chemically identical to the reactants of the first reaction.

For example, the chemical looping mechanism may involve first chemical compounds that undergo a first chemical reaction to produce first reaction products, said first reaction products are used in the electro discharge unit to generate electricity by undergoing chemical transformations to produce chemical waste products, said chemical waste products are used as reactants in a second chemical reaction to regenerate the first chemical compounds for use as reactants in the first chemical reaction.

Additionally or alternatively, the chemical looping mechanism in the thermal charge unit may comprise chemical compounds (reactants) that undergo a first chemical reaction to produce first reaction products, said first reaction products are used as reactants in a second chemical reaction to produce second reaction products, said second reaction products are used as reactants in a third chemical reaction to produce third reaction products, said third reaction products are used as reactants in a fourth chemical reaction to produce fourth reaction products, said fourth reaction products are used in the electro discharge unit to generate electricity by undergoing chemical transformations to produce chemical waste products, said chemical waste products are the regenerated reactants of the first chemical reaction. The series of thermal energy storage (TES) modules may provide thermal energy to the thermal-electro converter (TEC) to drive the chemical reactions, producing reaction products that are used for the conversion of electrochemical energy into electrical energy. The chemical compounds within the thermal charge unit of the thermal-electro converter (TEC) may be heated to initiate or drive chemical reaction(s). The chemical compounds may be preheated before undergoing a chemical reaction, by thermal energy stored in the series of thermal energy storage (TES) modules. Advantageously, it has been found that preheating the reactants before the chemical reaction is initiated maximises the overall energy efficiency of the system. The thermal energy generated in the electro discharge unit of the thermal-electro converter (TEC) may be exchanged with and stored in the thermal energy storage (TES) module.

The thermal charge unit may comprise a fluidised bed and/or a moving bed and/or a packed bed. The fluidised bed and/or moving bed and/or packed bed may comprise the chemical compounds suitable for converting thermal energy into electrochemical energy.

The electro discharge unit may comprise components suitable for converting electrochemical energy into electrical energy as in an anode and a cathode of batteries and/or fuel cells, for example those conventionally used in alkali metal-ion batteries (e.g. Li-ion batteries) and CO/O ₂ fuel cells. For example, the electro discharge unit may be an electrochemical cell, fuel cell, and/or a battery cell or half battery cell.

The reaction products of the chemical transformations (performed within the thermal charge unit) may be used at the anode and/or the cathode of the electro discharge unit to perform chemical transformations, e.g. electrochemical reactions, to generate electricity. The chemical transformations, e.g. electrochemical reactions, may generate chemical waste products. The chemical waste products may comprise carbon dioxide and/or U ₂ O ₂ .

The chemical waste products generated in the electro discharge unit may be recycled for use as reactants in the thermal charge unit. The thermal energy exchange between the series of thermal energy storage (TES) modules and the thermal-electro converter (TEC) may be performed using a heat exchanger and/or a heat transfer fluid or fluids (HTF). The series of thermal energy storage (TES) modules and/or the thermal-electro converter (TEC) may comprise a heat exchanger and/or a heat transfer fluid or fluids (HTF) for transferring and/or exchanging thermal energy from the thermal energy storage (TES) module to the thermal-electro converter (TEC) or vice versa.

The heat transfer fluids (HTF) may comprise one or more of gases, e.g. air, argon, helium, nitrogen, or mixtures thereof. Alternatively, the heat transfer fluids (HTF) may comprise one or more liquids such as thermal oils, molten salts, water, glycol, water/glycol mixtures, hydrocarbons, synthetic hydrocarbons, refrigerants, fluid-solid two-phase mixtures, and/or phase change fluids.

The heat transfer fluid(s) (HTF) may be selected according to the temperature required for each reaction in the thermal charge unit of the thermal-electro converter (TEC). The heat exchanger may comprise a plate, a tube-in-shell, a packed bed, a moving bed, and/or a fluidized bed.

The series of thermal energy storage (TES) modules may supply thermal energy to the thermal-electro converter (TEC) only. Alternatively, the series of thermal energy storage (TES) modules may further provide thermal energy directly to the end user, i.e. decentralised from, and not via, the grid.

Electrical energy generated in the thermal-electro converter (TEC) may be transmitted to a grid, and/or to the end user.

The system may be centralised, i.e. the end user is supplied with electrical energy generated in the system via a grid. Alternatively, the system may be decentralised, i.e. the end user is supplied directly with electrical energy generated in the system, and not via a grid. The grid and/or the system may be centralised or decentralised depending on the location, application and scale.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. For the avoidance of doubt, the terms“may”,“and/or”,“e.g.”, “for example” and any similar term as used herein should be interpreted as non-limiting such that any feature so-described need not be present. Indeed, any combination of optional features is expressly envisaged without departing from the scope of the invention, whether or not these are expressly claimed. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is an integrated energy conversion system, according to an embodiment of the invention;

Figure 2 is an embodiment of the thermal-electro converter of Figure 1 ; and

Figure 3 is a further embodiment of the thermal-electro converter of Figure 1. Referring now to Figure 1 , there is shown an integrated energy conversion system 10, according to an embodiment of the invention. The integrated energy conversion system 10 comprises a heat source 11 , a series of thermal energy storage (TES) modules 12, a thermal-electro converter (TEC) 13, a grid 14, and an end-user 15. The thermal-electro converter 13 comprises a thermal charge unit 13a and an electro discharge unit 13b.

There is further shown an energy transfer pathway A (between the heat source 11 and the series of thermal energy storage (TES) modules 12), a heat exchange pathway B (between the series of thermal energy storage (TES) modules 12 and the thermal-electro converter 13), an electricity transmission pathway C (between the thermal-electro converter 13 and the grid 14), an electricity transmission pathway D (between the grid 14 and the end user 15), and an optional heat exchange pathway E (between the series of thermal energy storage (TES) modules 12 and the end user 15). The heat source 11 comprises thermal energy from any source, or thermal energy from a combination of sources. For example, the heat source 11 may be thermal energy that has been harvested from renewable sources such as solar, wind, tide, and biomass. The heat source 11 may be thermal energy that has been harvested from non-renewable sources such as fossil fuels, industrial waste, and thermal energy generated by off-peak electricity. The heat source 11 may comprise means to convert other energy sources into thermal energy.

The series of thermal energy storage (TES) modules 12 comprises thermal energy storage materials that have suitable properties for the storage of all forms of thermal energy, e.g. sensible heat and/or latent heat and/or thermal chemically stored heat. In this embodiment, the thermal energy storage materials comprise Phase Change Materials (PCM) and materials for thermochemical based energy storage for high energy density and compactness. The thermal-electro converter (TEC) 13 comprises the thermal charge unit 13a and the electro discharge unit 13b. The thermal charge unit 13a comprises materials suitable for chemical looping, /.e. undergoing a series of chemical reactions to produce reaction products, for the conversion of thermal energy to electrochemical energy, in a thermal charge process. The electro discharge unit 13b is a fuel cell, and comprises materials suitable for generating electricity on demand by electrochemical reaction of said reaction products, in an electro discharge process.

In this embodiment, the grid 14 is centralised. Alternatively the grid 14 may be decentralised, or may be a dedicated electrical supply pathway or other electricity supply pathway.

The end-user 15 is a consumer of electrical energy and/or thermal energy.

In use, thermal energy from the heat source 11 is transferred to the series of thermal energy storage (TES) modules 12 for storage (energy transfer pathway A). Thermal energy is then transferred from the series of thermal energy storage (TES) modules 12 to the thermal- electro converter 13 (heat exchange pathway B) in a cascade manner according to temperature. The thermal energy in the thermal-electro converter 13 is used to perform a series of chemical reactions at the thermal charge unit 13a to convert the thermal energy to chemical energy. The chemical energy is transferred from the thermal charge unit 13a to the electro discharge unit 13b to generate electricity when it is required. In this way, the thermal charge unit 13a functions as an electrochemical energy store. The electricity is then transferred to the grid 14 (electricity transmission pathway C), which transmits electricity to the end-user 15 on demand (electricity transmission pathway D).

The end-user 15 may optionally receive heat energy from the series of thermal energy storage (TES) modules 12 (heat exchange pathway E) in addition to electricity from the grid 14 (electricity transmission pathway D).

Additionally, heat exchange pathway B may operate in both directions, /.e. heat generated in the thermal-electro converter 13 may be transferred to the series of thermal energy storage (TES) modules 12.

Referring now to Figure 2, there is shown a thermal-electro converter 13’, according to an embodiment of the invention. The thermal-electro converter 13’ is an example of the thermal-electro converter 13 shown in Figure 1. The thermal-electro converter 13’ comprises a thermal charge unit 13a’ and an electro discharge unit 13b’, wherein like references from Figure 1 are designated with a prime (‘). The thermal charge unit 13a’ comprises a reactant solid nonstoichiometric perovskite oxide MO _y 1a, and a product solid nonstoichiometric perovskite oxide MO _y.§ 1 b, which undergo a chemical looping mechanism in the conversion of thermal energy to electrochemical energy.

The thermal charge unit 13a’ further comprises a heat exchanger unit 21 , an oxygen separation unit 22. A source of gas phase of argon and oxygen 23, oxygen 24, argon 25, and carbon monoxide 26 are provided. The electro discharge unit 13b’ further comprises a source of carbon dioxide 27, a heat exchanger unit 28 (which may comprise the heat exchanger unit 21 of thermal charge unit 13a’, or may be separate), an anode 29, and a cathode 30.

The thermal charge unit 13a’ provides a location for two chemical reactions to take place, namely Reaction 1 and Reaction 2.

(Reaction 1)

(Reaction 2) Reaction 1 and Reaction 2 are involved in a chemical looping process as follows. Reaction 1 reduces the reactant solid nonstoichiometric perovskite oxide MO _y (1a) to the product solid nonstoichiometric perovskite oxides MO _y.§ (1 b) to produce oxygen for use in the electro discharge unit 13b’. In this embodiment, the reactant solid nonstoichiometric perovskite oxide MO _y 1a is Ba2Cao _. 66Nbi _. 34- _x Fe _x C>6-5 (0<x£1). Oxygen (the product of Reaction 1) is used, along with carbon monoxide (the product of Reaction 2) in the electro discharge unit 13b’ to produce carbon dioxide (the reactant of Reaction 2) in the electro discharge unit 13b’, which is used in Reaction 2 to oxidise MO _y.§ (1 b) (the product of Reaction 1 ) back to MO _y (1 a) (the reactant of Reaction 1 ) and to generate carbon monoxide. Therefore, Reaction 1 produces the reaction product oxygen (O2) and Reaction 2 produces the reaction product carbon monoxide (CO), both of which are fed into the electro discharge unit 13b’ for the conversion of electrochemical energy to electricity. The electro discharge unit 13b’ is a fuel cell, in which the oxygen and carbon monoxide reaction products from the thermal charge unit 13a’ are converted into carbon dioxide (CO2) and electricity. The carbon dioxide 27 waste product produced at the anode 29 of the electro discharge unit 13b’ is then recycled and fed back into Reaction 2, in which it performs as a reactant.

The following half reactions (i) and (ii) occur at the cathode and anode respectively.

(i) (Cathode)

(ii) 2CO + 20 ² 2C0 ₂ + 4e (Anode)

Reaction 1 occurs at approximately 700 °C in an argon environment. The argon may be pre-heated using the thermal energy from the series of thermal energy storage (TES) modules 12 of Figure 1 in heat exchange pathway B. This improves the efficiency of the integrated energy conversion system 10. Heat exchange pathway B may be performed, for example, using the heat exchanger unit 21. The heat exchanger unit 21 may comprise liquid heat transfer fluids (HTF) and a pump, or gaseous heat transfer fluids (HTF) and a blower.

Upon completion of Reaction 1 , the argon environment contains oxygen from the reduction of the reactant solid nonstoichiometric perovskite oxide MO _y (1 a). The heat exchanger unit 21 is used to transfer thermal energy from the gas phase of argon and oxygen 23 in the thermal charge unit 13a’, which has a temperature of approximately 700 °C, to the series of thermal energy storage (TES) modules 12 (heat exchange pathway B). The oxygen separation unit 22 is used to remove oxygen 24 from the gas phase of argon and oxygen 23. The argon 25 is then recycled for use in Reaction 1. In this way, thermal energy is stored electrochemically in the product solid nonstoichiometric perovskite oxide MO _y.§ (1 b) (this being the product of Reaction 1 , but also the reactant of Reaction 2).

Reaction 2 takes place either subsequent to Reaction 1 , or in parallel with Reaction 1. The gaseous carbon dioxide 27 from the electro discharge unit 13b’ is pre-heated to approximately 700 °C using the heat exchanger unit 28. Once heated, the gaseous carbon dioxide 27 is used as a reactant in Reaction 2. Reaction 2 may take place in the same reaction chamber (not shown) or a different reaction chamber to Reaction 1. In Reaction 2, the MO _g -d (the product of Reaction 1 , reactant of Reaction 2) undergoes oxidation to regenerate MO _y (the reactant of Reaction 1), and the carbon dioxide undergoes reduction to produce carbon monoxide 26. The carbon monoxide 26 may be stored before use in the electro discharge unit 13b’. The chemical looping process in the thermal charge unit 13a’, i.e. Reaction 1 and Reaction 2, may be performed using a fluidised bed, in which solid MO _y (1 a) is reduced to solid MO _y.§ (1 b) in the charge process and oxidised to give MO _y (1 a) while converting C0 ₂ to CO in the discharge process.

A theoretical calculation shows that the thermal charge efficiency of this particular embodiment could be as high as 86% without considering heat exchange and storage between the reacting gases and the series of thermal energy storage (TES) modules 12. Therefore, it is believed that the eventual efficiency could potentially be even higher.

The carbon monoxide 26 produced in Reaction 2 is fed to the anode 29, and the oxygen 24 produced in Reaction 1 is fed to the cathode 30, of the electro discharge unit 13b’, wherein a reaction between the two takes place. The carbon monoxide 26 is oxidised and the oxygen 24 is reduced to produce carbon dioxide 27, and to generate electricity. As described above, the carbon dioxide 27 is then fed back into Reaction 2 to complete the cycle. The carbon dioxide may be stored in a tank before use in Reaction 2. Theoretical calculations show that the efficiency of the CO fuel cell could reach 79% when it is operated at 0.8 V.

Referring now to Figure 3, there is shown a thermal-electro converter 13”, according to a further embodiment of the invention. The thermal-electro converter 13” is a further example of the thermal-electro converter 13 shown in Figure 1. The thermal-electro converter 13” comprises a thermal charge unit 13a” and an electro discharge unit 13b”, wherein like references from Figure 1 are designated with a double prime (”).

The thermal charge unit 13a” comprises reactants (e.g. U2O2 3a, UO2 3b, Li 3c), and a further reactant (e.g. solid nonstoichiometric perovskite oxide MO _y 5a), and a product (e.g. solid nonstoichiometric perovskite oxide MO _y.§ 5b), which are able to undergo a chemical looping mechanism in the conversion of thermal energy to electrochemical energy.

The thermal charge unit 13a” further comprises a heat exchanger unit 31 , an oxygen separation unit 32, a heat exchanger unit 33, and a heat exchanger unit 34.

The electro discharge unit 13b” further comprises an anode 35 and a cathode 36. The thermal charge unit 13a” provides a location for four chemical reactions to take place; Reaction 3, Reaction 4, Reaction 5, and Reaction 6.

(Reaction 3) 2U2O2 ® -> 2Li ₂ 0 ( _S > + O2 _¾ >

(Reaction 4) 2Li ₂ 0 _(S) + C _(S) -> 4Li _(g) + C0 _{2 ¾} >

(Reaction 5) 1/5 MOy(s) -^ 1/5 MOy-§ (s) + ½ 02 (g) (Reaction 6) 1/d MO _{g.d (S)} + CO2 (g) -> 1/5 MO _{y (S)} + C ( _S >

Reaction 3, Reaction 4, Reaction 5, and Reaction 6, are involved in a chemical looping process as follows. Reaction 3 reduces liquid U2O2 (3a) to solid U2O (3b). Reaction 4 reduces solid U2O (3b) (the product of Reaction 3) using solid carbon (the reaction product of Reaction 6) to produce gaseous Li (3c), which is oxidised in the electro discharge unit 13b” by reaction of oxygen (the product of Reaction 3 and Reaction 5) to produce U2O2 (3a) (the reactant of Reaction 3). Reaction 5 reduces the reactant solid nonstoichiometric perovskite oxide MO _y (5a) to the product solid nonstoichiometric perovskite oxide MO _y.§ (5b). In this embodiment, the solid nonstoichiometric perovskite oxide MO _y is Ba2Cao _. 66Nbi _. 34- _x Fe _x C>6-5 (0<x£1). Reaction 6 oxidises MO _y.§ (5b) (the product of Reaction 5) back to MO _y (5a) (the reactant of Reaction 5) using carbon dioxide (the product of Reaction 4).

Therefore, Reaction 3 and Reaction 5 both produce oxygen (O2) as a reaction product, and Reaction 4 produces metallic lithium as a reaction product, both of which are fed into the electro discharge unit 13b” for the conversion of electrochemical energy to electricity. The electro discharge unit 13b” is a battery, in which the oxygen and lithium reaction products from the thermal charge unit 13a” are converted into U2O2 and electricity. The following half reactions (i) and (ii) occur at the anode and cathode respectively.

(i) Li ®· Li ⁺ + e- (Anode)

(ii) 2Li ⁺ + 0 ₂ + 2e- ®· Li ₂ 0 ₂ (Cathode) The U2O2 produced at the cathode 36 of the electro discharge unit 13b” is then fed back into Reaction 3, in which it performs as a reactant.

Reaction 3 involves the reduction of liquid U2O2 in the electro discharge unit 13b”, to solid U2O. Reaction 3 also produces oxygen for use in the electro discharge unit 13b”. Reaction 3 occurs at approximately 450 °C in an argon environment. The argon may be pre-heated using the thermal energy from the series of thermal energy storage (TES) modules 12 of Figure 1 in heat exchange pathway B. This improves the efficiency of the integrated energy conversion system 10. Heat exchange pathway B may be performed, for example, using the heat exchanger unit 31. The heat exchanger unit 31 may comprise liquid heat transfer fluids (HTF) and a pump, or gaseous heat transfer fluids (HTF) and a blower.

Upon completion of Reaction 3, the argon environment contains oxygen from the reduction of liquid U2O2 (3a). The heat exchanger unit 31 is used to transfer thermal energy from the gas phase of argon and oxygen in the thermal charge unit 13a”, which has a temperature of approximately 450 °C, to the series of thermal energy storage (TES) modules 12 (heat exchange pathway B). The oxygen separation unit 32 is used to remove oxygen from the gas phase of argon and oxygen. The argon is then recycled for use in Reaction 3.

Reaction 4 takes place after Reaction 3. Reaction 4 involves the reduction of solid U2O (3b) using solid carbon (the product of Reaction 6) to gaseous Li (3c) at approximately 887 °C. The reaction temperature may be controlled by the series of thermal energy storage (TES) modules 12 of Figure 1. The gaseous Li (3c) is condensed to liquid Li, and may be stored in a tank (not shown) for use in the electro discharge unit 13b”. Reaction 4 also produces carbon dioxide.

Reaction 5 reduces solid nonstoichiometric perovskite oxides MO _y (5a) to solid MO _y. s (5b) to produce oxygen for use in the electro discharge unit 13b”. In this embodiment, the solid nonstoichiometric perovskite oxide MO _y (5a) is Ba2Cao _. 66Nbi _. 34- _x Fe _x C>6-5 (0<x<1). Reaction 5 occurs at approximately 700 °C in an argon environment. The argon may be pre-heated using the thermal energy from the series of thermal energy storage (TES) modules 12 of Figure 1 in heat exchange pathway B. This improves the efficiency of the integrated energy conversion system 10. Heat exchange pathway B may be performed, for example, using the heat exchanger unit 33. The heat exchanger unit 33 may comprise liquid heat transfer fluids (HTF) and a pump, or gaseous heat transfer fluids (HTF) and a blower. Upon completion of Reaction 5, the argon environment contains oxygen from the reduction of the solid nonstoichiometric perovskite oxide MO _y . The heat exchanger unit 33 is used to transfer thermal energy from the gas phase of argon and oxygen in the thermal charge unit 13a”, which has a temperature of approximately 700 °C, to the series of thermal energy storage (TES) modules 12 (heat exchange pathway B). The oxygen separation unit 32 is used to remove oxygen from the gas phase of argon and oxygen. The argon is then recycled for use in Reaction 5.

Reaction 6 takes place after Reaction 5. The gaseous carbon dioxide (the product of Reaction 4 which occurs at ~887°C) is adjusted to approximately 700 °C using the heat exchanger unit 34 (the carbon dioxide temperature can also be higher than 700°C so that, upon exchange heat with MO _(y. ¾ gives a reactor temperature of approximately 700°C). Once heated, the gaseous carbon dioxide is used as a reactant in Reaction 6. Reaction 6 takes place in the same reaction chamber as Reaction 5. In Reaction 6, the MO _y.§ (the product of Reaction 5) undergoes oxidation to regenerate MO _y (the reactant of Reaction 5), and carbon dioxide undergoes reduction to produce solid carbon. The solid carbon is then used as a reactant in Reaction 4.

It should be noted that the same starting materials, i.e. 1/5 MO _y -5 _(S) + C0 _{2 (g)} are used in both Reaction 2 (of Figure 2) and Reaction 6. However, the products are different; Reaction 2 produces carbon monoxide, whereas Reaction 6 produces solid carbon. The reaction conditions, e.g. temperature, pressure, the use of catalysts, the C0 ₂ feed rate, and the reaction time, determine which reaction proceeds dominantly and the composition of the products. Therefore, selectivity towards carbon monoxide or solid carbon may be controlled with the reaction conditions and catalysts that are used in the process.

Reaction 3 and Reaction 4 may be performed with a first fluidised/packed/moving bed, and/or Reaction 5 and Reaction 6 may be performed with a second fluidised/packed/moving bed.

The process described for Reactions 3 to 6, and shown in Figure 3 for the thermal-electro converter 13”, is a closed loop.

In this embodiment, the electro discharge unit 13b” is a Li-air/Li-0 ₂ flow battery. The gaseous Li (product of Reaction 4) is condensed into liquid Li (with heat recovered and stored) and is fed to the anode 35, and the oxygen produced in Reaction 3 and Reaction 5 is fed to the cathode 36 of the electro discharge unit 13b”, wherein a reaction between the two takes place. Lithium is oxidised and oxygen is reduced to form U2O2, and to generate electricity. As described above, the U2O2 is then fed back into Reaction 3 to complete the cycle. The reaction product U2O2 is in its solid form. However, once heated up to above 200°C, it becomes the liquid form. It can be stored in a tank and pumped to the reaction chamber (not shown) for Reaction 1 in the thermal charge unit 13a”. In this embodiment, the efficiency of the electro discharge unit 13b” (Li-air/Li-0 ₂ flow battery) from theoretical calculation can be as high as 90%.

A theoretical calculation shows that the thermal charge efficiency of this particular embodiment is 74% without considering recovery and recycle of thermal energy via the series of thermal energy storage (TES) modules 12. Therefore, the efficiency could potentially be even higher.

The main advantages of the method and system of the present invention include: (a) the conversion of thermal energy into electrochemical energy through thermal-electrochemical approach, which has the potential to replace the conventional low energy efficiency fossil fuelled power plants; (b) integration of energy storage enables the provision of peak shaving and time shift of energy supply to meet the demand and hence increase the system flexibility; (c) the use of thermal energy storage enables the supply of thermal energy directly on top of electrical energy supply and hence further increases the flexibility; and (d) the integration enhances the overall energy efficiency of both conventional and renewable energy generation systems in a cost-effective manner with reduced emissions.

The method and system of the present invention integrates scalable energy conversion and storage technologies whilst using thermal energy from any source. The stored thermal energy in the series of thermal storage modules may be transmitted as electricity to the end user via the grid, or may be transmitted as thermal energy (without conversion to electricity) to the end user directly.

The efficiency of the disclosed method and system is much higher than known and conventional technologies. Additionally, the disclosed method and system may be a centralised or a decentralised energy system, depending on location, application, and scale. It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention. For example, other alkali metals may be used in place of lithium.

It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.