EP4623472A1

EP4623472A1 - Formic acid energy storage system and relative method

Info

Publication number: EP4623472A1
Application number: EP23817029.4A
Authority: EP
Inventors: Manjush GANIGER; Maneesh PANDEY
Original assignee: Nuovo Pignone Technologie SRL
Current assignee: Nuovo Pignone Technologie SRL
Priority date: 2022-11-23
Filing date: 2023-11-21
Publication date: 2025-10-01
Also published as: WO2024110064A1; AU2023384328A1; IT202200024093A1

Abstract

Energy storage system (1000) for producing, storing and consuming energy comprising an electrochemical reduction CO2 cell unit (110) configured to receive electrical energy, in particular from a renewable energy source, and to perform electrochemical reduction process to produce formic acid (CH2O2), a formic acid storage unit configured to store formic acid (CH2O2) in liquid state received from electrochemical reduction CO2 cell unit (110), a formic acid fuel cell unit (130) configured to perform electrochemical oxidation process producing electrical energy from formic acid (CH2O2) received from the formic acid storage unit (120) and a control unit (180) configured to control supply of formic acid (CH2O2) to and from the formic acid storage unit (120). The energy storage system (1000) is also configured to perform a closed-loop recirculation of carbon dioxide (CO2) from the formic acid storage unit (130) to the electrochemical reduction CO2 cell unit (110).

Description

TITLE

Formic acid energy storage system and relative method

DESCRIPTION

TECHNICAL FIELD

[0001] The subject-matter disclosed herein relates to an energy storage system and relative method, in particular for producing and storing formic acid when electrical energy produced from a renewable source is available and producing electrical energy using formic acid when electrical energy is requested and the renewable source is not available.

BACKGROUND ART

[0002] Nowadays, Long Duration Energy Storage (=LDES) systems can play a crucial role in helping reaching flexibility and stability of renewable power plants for power generation, alongside other technologies such as Lithium-ion (Li-ion) batteries and hydrogen storage. Various LDES systems exists, such as thermal, mechanical and chemical.

[0003] In fact, the intermittent nature of renewable energy requires a stable storage system in order to effectively meet the electrical grid energy demand. One of the possible ways to store renewable energy for high demand periods is to convert renewable energy into different chemicals. Previously, there have been studies on various chemicals like methane, methanol, ammonia, etc., as potential sources of energy carriers. However, processes to convert renewable energy to these chemicals are not efficient and/or economical due to two main reasons: Conversion to the chemicals descried above is highly energy intensive, as these conversion reactions are only favorable at high pressures and high temperatures;

Conversion to the chemicals descried above requires hydrogen (H2) as input. Therefore, costs and inefficiencies in the production of hydrogen are also involved in the overall storage efficiency.

[0004] Because of the above reasons, there is a need for less energy intensive and efficient storage system to overcome fluctuating power generation patterns of renewable energy sources. Recently, formic acid properties have been studied in order to exploit this fluid as energy storage media and carrier. For example, from patent document US8562811B2 it is known a process to produce formic acid from carbon dioxide using electrochemical reduction process in order to mitigate emissions of carbon dioxide. From patent document US11131028B2 it is known a method and a system for electrochemical reduction of carbon dioxide to convert carbon dioxide into economically valuable materials such as fuels and industrial chemicals using electrical energy for renewable energy sources. It is to be noted that formic acid is used as a hydrogen storage source, being subsequently catalytically decomposed to hydrogen gas to be sent to a fuel cell system (which may employ also a natural gas feed) in order to produce electricity. However, the solution proposed in US11131028B2 may require energy to perform formic acid decomposition and the possible use of natural gas does not assure the purity of CO2 produced. Therefore, it is desired to have a completely green energy storage system which is more efficient and less expensive.

SUMMARY

[0005] According to an aspect, the subject-matter disclosed herein relates to an energy storage system for producing, storing and consuming energy, comprising: an electrochemical reduction CO2 cell unit comprising a main inlet, a main outlet and at least a first secondary inlet, wherein the electrochemical reduction CO2 cell unit is configured to receive electrical energy at the main inlet and carbon dioxide at the first secondary inlet and to perform electrochemical reduction process, produce formic acid and provide the formic acid at the main outlet; a formic acid storage unit selectively fluidly coupled to the main outlet, the formic acid storage unit being configured to store formic acid in liquid state; a formic acid fuel cell unit selectively fluidly coupled to the formic acid storage unit and comprising a main inlet, a main outlet and at least a first secondary outlet, a control unit, wherein the formic acid storage unit is configured to selectively supply formic acid to the main inlet of the formic acid fuel cell unit, wherein the control unit is configured to control supply of formic acid to and from the formic acid storage unit, wherein the formic acid fuel cell unit is configured to perform electrochemical oxidation process producing electrical energy and carbon dioxide and provide the electrical energy at the main outlet and the carbon dioxide at the first secondary outlet, wherein the first secondary outlet of the formic acid fuel cell unit is fluidly coupled to the first secondary inlet of the electrochemical reduction CO2 cell unit and is configured to perform a closed-loop recirculation of carbon dioxide to the electrochemical reduction CO2 cell unit.

[0006] According to another aspect, the subject-matter disclosed herein relates to a method for producing, storing and consuming energy, the method comprising the steps of

A. producing formic acid (CH2O2) through an electrochemical reduction process performed by an electrochemical reduction CO2 cell unit using carbon dioxide (CO2) and electrical energy produced from a renewable energy source when the renewable energy source is available;

B. storing the produced formic acid (CH2O2) at least for a predetermined time;

C. supplying the stored formic acid (CH2O2) as fuel to a formic acid fuel cell unit for producing carbon dioxide (CO2) and electrical energy through an electrochemical oxidation process when the renewable energy source is not available; wherein the carbon dioxide (CO2) produced at step C is used for producing formic acid (CH2O2).

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig. 1 shows a schematic drawing of a first embodiment of an innovative energy storage system for producing, storing and consuming energy,

Fig. 2 shows a schematic drawing of a second embodiment of an innovative energy storage system for producing, storing and consuming energy comprising further a distillation column in order to increase formic acid concentration at the distillation column outlet,

Fig. 3 shows a schematic drawing of a third embodiment of an innovative energy storage system for producing, storing and consuming energy comprising further distillation column, a gas turbine unit and a steam generation unit, and Fig. 4 shows a schematic drawing of a detail of the third embodiment of Fig. 3 highlighting a control loop with associated instruments to control concentration of formic acid at the outlet of the distillation column.

DETAILED DESCRIPTION OF EMBODIMENTS

[0008] According to an aspect, the subject-matter disclosed herein relates to a system which uses electrical energy from a renewable power plant to produce formic acid (CH2O2) through an electrochemical reduction of CO2 along with water, in an electrochemical cell unit when electrical energy is available, for example when the sunlight produces electrical energy in a solar power plant or when wind speeds is enough to produce electrical energy through a wind power plant. The system then stores energy in the form of formic acid (CH2O2) in a dedicated storage unit to be used when electrical energy is required and is not available from the renewable power plant, for example during night or not windy days. The formic acid (CH2O2) is used as fuel in a formic acid fuel cell unit with air as oxidizer in order to produce electrical energy as output to be supplied to an electric grid (or micro-grid).

[0009] According to another aspect, the subject-matter disclosed herein relates to a method for producing formic acid (CH2O2) through an electrochemical reduction process performed by an electrochemical reduction CO2 cell unit using electrical energy produced from a renewable energy source when the renewable energy is available, storing the produced formic acid (CH2O2) at least for a predetermined time and supplying the stored formic acid (CH2O2) as fuel to a formic acid fuel cell unit for producing electrical energy through an electrochemical oxidation process when the renewable energy is not available.

[0010] Reference now will be made in detail to embodiments of the disclosure, examples of which are illustrated in the drawings. The examples and drawing figures are provided by way of explanation of the disclosure and should not be construed as a limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. In the following description, similar reference numerals are used for the illustration of figures of the embodiments to indicate elements performing the same or similar functions. Moreover, for clarity of illustration, some references may be not repeated in all the figures.

[0011] Fig. 1 shows a schematic drawing of a first embodiment of an innovative energy storage system for producing, storing and consuming energy referred in the following as “energy storage system 1000” or simply as “system 1000”. As it will be better described in the following, the energy storage system 1000 is configured to consume electrical energy to produce formic acid, in particular electrical energy generated from a renewable power source when the renewable power source is available, in particular when a surplus of electrical energy generated from a renewable power source is available, to store formic acid at least for a predetermined time and to produce electrical energy from formic acid store, in particular when the renewable power source is not available.

[0012] With non-limiting reference to Fig. 1, the system 1000 comprises an electrochemical reduction CO2 cell unit 110, configured to perform electrochemical reduction process and produce formic acid (CH2O2), and a formic acid fuel cell unit 130, configured to perform electrochemical oxidation process and produce electrical energy using formic acid (CH2O2) as fuel. As a non-limiting example, the electrochemical reduction CO2 cell unit could be an alkaline electrolyzer or similar device. As a non-limiting example, the formic acid fuel cell unit could be a PEM fuel cell or similar device. The system 1000 further comprises a formic acid storage unit 120 which is selectively fluidly coupled to the electrochemical reduction CO2 cell unit 110 and the formic acid fuel cell unit 130 and configured to store formic acid (CH2O2) in liquid form, in particular to store formic acid at least for a predetermined time. As a non-limiting example, the formic acid storage unit could be a tank or similar device.

[0013] The electrochemical reduction CO2 cell unit 110 has a main inlet 111 configured to receive electrical energy (see the dashed arrow from 105 to 110 in Fig. 1). Advantageously, the main inlet 111 is coupled to an electrical energy power source, in particular a renewable power plant 105. According to a preferred embodiment, the electrochemical reduction CO2 cell unit 110 receives electrical energy from the renewable power plant 105 to perform electrochemical reduction process, in particular using one or more stacks of the electrochemical reduction CO2 cell unit 110. The electrochemical reduction CO2 cell unit 110 has further a first secondary inlet 112; in particular, the first secondary inlet 112 is configured to receive carbon dioxide (CO2). Advantageously, the electrochemical reduction CO2 cell unit 110 has further a second secondary inlet 113, in particular configured to receive water (H2O), in order to perform the electrochemical reduction process according to the following reaction and consuming electrical energy:

CO₂ + 2H₂O + Electricity HCOOH + O₂ + H₂

[0014] The electrochemical reduction CO2 cell unit 110 has further a main outlet 119, to which is provided the formic acid (CH2O2) resulting from the reaction, and secondary outlets 118, in particular two secondary outlets, a first one configured to supply hydrogen (H2) and the second one configured to supply oxygen (02) resulting from the reaction.

[0015] As already mentioned above, electrical energy is needed to start and possibly develop the electrochemical reduction process. Advantageously, the electrical energy is provided only when electrical energy from renewable energy source is available, i.e. the formic acid (CH2O2) is produced intermittently. However, according to the innovative energy storage system 1000, the formic acid storage unit 120 is configured to store formic acid (CH2O2), so that formic acid (CH2O2) may be available even if electrical energy from renewable energy source is not available.

[0016] Advantageously, the system 1000 comprises a first valve 181 upstream to the formic acid storage unit 120, in particular between the electrochemical reduction CO2 cell unit 110 and the formic acid storage unit 120. The first valve 181 is configured to selectively fluidly couple/decouple (respectively when the first valve 181 is opened/closed) the electrochemical reduction CO2 cell unit 110 and the formic acid storage unit 120, in particular the main outlet 119 and the formic acid storage unit 120. Advantageously, the formic acid (CH2O2) is stored at ambient conditions, for example 20°C and 1 bar, so that no additional energy is required to store formic acid (CH2O2); in other words, the formic acid (CH2O2) is stored in the formic acid storage unit 120 in liquid state.

[0017] The system 1000 further comprises a control unit 180. As a non-limiting example, the control unit could be a computer, programmable controller, microprocessor or similar device. As it will be better described in the following, control unit 180 is configured to control at least supply of formic acid (CH2O2) to and from the formic acid storage unit 120, in particular by opening/closing valves. However, control unit 180 may be configured to control other elements of the system 1000. For example, the control unit 180 may check the availability of electrical energy from renewable power plant 105 and/or regulate the electrical energy supply to the electrochemical reduction CO2 cell unit 110 and/or activate one or more stack of the electrochemical reduction CO2 cell unit 110 and/or control flow rate of carbon dioxide (CO2) at the first secondary inlet 112 and/or control flow rate of water (H2O) at the second secondary inlet 113 and/or control supply of formic acid (CH2O2) to the formic acid storage unit 120, in particular control opening/closing of the first valve 181 and/or control the amount of formic acid (CH2O2) stored in the formic acid storage unit 120.

[0018] As already mentioned above, the formic acid storage unit 120 is selectively fluid coupled to the formic acid fuel cell unit 130 and is configured to selectively supply formic acid (CH2O2) to the formic acid fuel cell unit 130, in particular to a main inlet 131 of the formic acid fuel cell unit 130. Advantageously, the formic acid fuel cell unit 130 has further a first secondary inlet 132, in particular configured to receive air (A), in order to perform the electrochemical oxidation process using formic acid (CH2O2) as fuel and producing electrical energy according to the following reaction:

[0019] The formic acid fuel cell unit 130 has further a main outlet 139, to which is provided the electrical energy resulting from the reaction, and at least a first secondary outlet 138 configured to supply carbon dioxide (CO2) resulting from the reaction. It is to be noted that the carbon dioxide (CO2) produced through the electrochemical oxidation process is pure. Advantageously, the formic acid fuel cell unit 130 has further a second secondary outlet 137 configured to deliver water (H2O) resulting from the reaction. It is to be noted that according to the purity of the inlet flows, in particular of the air (A), the formic acid fuel cell unit 130 may further supply other substance at the second secondary outlet 137 or at another dedicated secondary outlet, for example nitrogen (N2) from air.

[0020] Advantageously, the system 1000 comprises a second valve 182 downstream to the formic acid storage unit 120, in particular between the formic acid storage unit 120 and the formic acid fuel cell unit 130. The second valve 182 is configured to selectively fluidly couple/decouple (respectively when the second valve 182 is opened/closed) the formic acid storage unit 120 and the formic acid fuel cell unit 130, in particular the formic acid storage unit 120 and the main inlet 131. Advantageously, the control unit 180 is further configured to control supply of formic acid (CH2O2) to the acid fuel cell unit 130, in particular control opening/closing of the second valve 182 and/or control flow rate of air or oxygen (A) to the first secondary inlet 132.

[0021] Advantageously, with non-limiting reference to Fig. 1, the system 1000 further comprises a pump 125 located upstream of the main inlet 131 of the formic acid fuel cell unit 130, in particular between the second valve 182 and the main inlet 131. In particular, the pump 125 is configured to pump formic acid (CH2O2) from the formic acid storage unit 120 to the main inlet 131, in order to supply formic acid (CH2O2) to the formic acid fuel cell unit 130 when electrochemical oxidation process is requested, i.e. when electrical energy is requested. Advantageously, the control unit 180 is further configured to control actuation of the pump 125.

[0022] In particular, the formic acid fuel cell unit 130 has a main outlet 139 configured to be electrically coupled to an electric grid or micro-grid 195 (see the dashed arrow from 130 to 195 in Fig. 1). More in particular, when the electric grid or micro-grid 195 needs electrical energy (i.e. there is demand of electrical energy) and renewable power source is not available, the formic acid fuel cell unit 130 may perform electrochemical oxidation process, in particular using one or more stacks of the formic acid fuel cell unit 130, using stored formic acid (CH2O2) as fuel and generate electrical energy to be supplied to the electric grid or micro-grid 195. Advantageously, the control unit 180 is further configured to activate one or more stack of the formic acid fuel cell unit 130 and/regulate the electrical energy supply to the electric grid or microgrid 195 in order to meet the power demand requirements. [0023] With non-limiting reference to Fig. 1, the first secondary outlet 138 of the formic acid fuel cell 130 is fluidly coupled to the electrochemical reduction CO2 cell unit 110, in particular to the first secondary inlet 112, and is configured to perform a closed-loop recirculation of carbon dioxide (CO2) to the electrochemical reduction CO2 cell unit 110. In other words, the carbon dioxide (CO2) produced by the system 1000 through the electrochemical oxidation process may be also consumed by the system 1000 through the electrochemical reduction process, so that the system 1000 may be a zero-CO2 emissions system, i.e. without releasing any CO2 to the atmosphere. Advantageously, as it will be better explained in the following, the carbon dioxide (CO2) may be stored for a certain time before being supplied to the first secondary inlet 112.

[0024] Advantageously, as shown for example in Fig. 1, the closed-loop recirculation of carbon dioxide (CO2) may be provided with a CO2 storage unit 140 configured to store the carbon dioxide (CO2) produced by the formic acid fuel cell 130. As a nonlimiting example, the CO2 storage unit could be a tank or similar device. In particular, the CO2 storage unit 140 is fluidly coupled to the first secondary outlet 138 of the formic acid fuel cell 130 and to the first secondary inlet 112 of the electrochemical reduction CO2 cell unit 110. Advantageously, the control unit 180 is further configured to control the amount of carbon dioxide (CO2) stored in the CO2 storage unit 140.

[0025] With non-limiting reference to Fig. 1, the system 1000 may further comprise a third valve 183 and a fourth valve 184 located respectively upstream and downstream of the CO2 storage unit 140 and configured to allow/disallow carbon dioxide (CO2) supply to and from the CO2 storage unit 140. Advantageously, the control unit 180 is further configured to control opening/closing of the third valve 183 and the fourth valve 184. [0026] Advantageously, carbon dioxide (CO2) is stored at pressure higher than ambient pressure, for example to reduce CO2 storage unit size. The system 1000 may further comprise a blower 145 located upstream of the CO2 storage unit 140 and configured to increment carbon dioxide (CO2) pressure before being stored in the CO2 storage unit 140. Advantageously, the control unit 180 is further configured to control actuation of the blower 145.

[0027] It is to be noted that, according to the formic acid fuel cells currently available on the market, the concentration of formic acid (CH2O2) produced by the electrochemical reduction CO2 cell unit 110 and utilized by the formic acid fuel cell unit 130 may be around 50%wt. However, since formic acid (CH2O2) concentration affects the fuel cells performance, it would be advantageous to take into account future developments of formic acid fuel cells which may allow them to operate with various concentrations of formic acid (CH2O2).

[0028] With non-limiting reference to Fig. 2, it is shown a second embodiment of an innovative energy storage system 2000 which is similar to the embodiment shown in Fig. 1 but further comprises a distillation column 250 configured to increase concentration of formic acid (CH2O2). It is to be noted that elements in Fig. 2 which have similar reference number of the elements of the first embodiment 1000 shown in Fig. 1 may be identical or similar to the elements in Fig. 1 and perform the same or similar functions.

[0029] In particular, as shown in Fig. 2 (and also in Fig. 3), the distillation column 250 is located downstream of the electrochemical reduction CO2 cell unit 210 and has a main inlet 221 which is fluidly coupled to the main outlet 219 of the electrochemical reduction CO2 cell unit 210, in order to receive formic acid (CH2O2) from the main outlet 219. Advantageously, the distillation column 250 is configured to increase concentration of formic acid (CH2O2) before being stored in the formic acid storage unit 220. [0030] In particular, as shown in Fig. 2 (and also in Fig. 3), the distillation column 250 is located upstream of the formic acid storage unit 220 and has a main outlet 229 which is fluidly coupled to the formic acid storage unit 220, in particular to the first valve 281 which allow/disallow the formic acid (CH2O2) supply to the formic acid storage unit 220, in order to supply concentrated formic acid (CH2O2) to the formic acid storage unit 220.

[0031] According to a possibility, the distillation column 250 may be for example a tray column or a packed column which receives steam (S) at a secondary inlet 222 of the distillation column 250 and formic acid (CH2O2) from the main inlet 221 and perform formic acid distillation in order to increase formic acid concentration and supply concentrated formic acid (CH2O2) to the formic acid storage unit 220.

[0032] As it will better explain in the following with the aid of Fig. 3, which shows a third embodiment of an innovative energy storage system 3000 similar to the second embodiment of Fig. 2, a steam generator, advantageously a heat recovery steam generator 370, may supply the steam (S) to the secondary inlet 322 of the distillation column 350. It is to be noted that elements in Fig. 3 which have similar reference number of the elements of second embodiment 2000 shown in Fig. 2 may be identical or similar to the elements in Fig. 2 and perform the same or similar functions. In particular, the heat recovery steam generator 370 shown in Fig. 3 has an inlet 371 configured to receive water (W) in liquid form and an outlet 372 fluidly coupled to the distillation column 350, in particular to the secondary inlet 322 of the distillation column 350, and configured to supply steam (S) to the distillation column 350.

[0033] With non-limiting reference to Fig. 3, the system 3000 further comprises a gas turbine unit 360, typically receiving air (A) and a fuel (F) in order to perform a combustion and produce electrical power, which may be advantageously supplied to the electric grid or micro-grid 395. The gas turbine unit 360 further produces exhaust gases (EG) due to combustion; advantageously, the heat recovery steam generator 370 is fluidly coupled to the gas turbine unit 360 so that the heat recovery steam generator 370 may exploit the residual heat capacity of exhaust gases (EG) and transfer heat from exhaust gases (EG) to water (W) in order to produce steam (S). Even more advantageously, the system 3000 further comprises a control valve 375 located downstream of the outlet 372 of the heat recovery steam generator 370 and configured to regulate the amount of steam (S) supplied to the distillation column 350, in particular to regulate the concentration of the formic acid (CH2O2) at the main outlet 329 of the distillation column 350.

[0034] In particular, the operation of the distillation column 350 will be now described with the aid of Fig. 4, which shows a schematic drawing of a detail of the third embodiment of Fig. 3 where a control loop is highlighted. Advantageously, the control unit 380 or a sub-unit of the control unit 380 is further configured to control operation of the control valve 375. In particular, with non-limiting reference to Fig. 4, the control unit 380 may receive (or store) information about the desired concentration of formic acid (CH2O2) at the main outlet 329 of the distillation column 350, in particular a concentration setpoint SP, a first measure of concentration of formic acid (CH2O2) at the main inlet 321 of the distillation column 350 and a second measure of concentration of formic acid (CH2O2) at the main outlet 329 of the distillation column 350. Advantageously, the control unit 380 may control the opening/closing of the control valve 375 according to the concentration setpoint SP, the first measure and the second measure, in order to regulate the supply of steam (S) to the distillation column 350 and therefore regulate the concentration of formic acid (CH2O2) at the main outlet 329 of the distillation column 350. [0035] It is also to be noted that, according for example to Fig. 2 and Fig. 3, the distillation column 250 and 350 may have also a first secondary outlet 237 and 337 which is configured to discharge excess water (in liquid or gas phase) from the distillation column 250 and 350; advantageously, the first secondary outlet 237 and 337 may be fluidly coupled to the electrochemical reduction CO2 cell unit 210 and 310, in particular to the first secondary inlet 213 and 313 in order to supply excess water back to the electrochemical reduction CO2 cell unit 210 and 310. With non-limiting reference to Fig. 4, the distillation column 350 may have also a second secondary outlet 328 which is configured to discharge catholyte that may have been drag from the electrochemical reduction CO2 cell unit 310, in particular from the cathode, to the distillation column 350; advantageously, the second secondary outlet 328 may be fluidly coupled to the electrochemical reduction CO2 cell unit 310, in order to supply catholyte back to the electrochemical reduction CO2 cell unit 310.

[0036] According to another aspect, the subject-matter disclosed herein relates to an innovative renewable power plant for producing electrical energy, for example a solar power plant or a wind power plant, which is configured to produce and supply electrical energy. The innovative renewable power plant is further configured to selectively supply electrical energy to an energy storage system as described above, in particular to the electrochemical reduction CO2 cell unit of an energy storage system. Advantageously, the renewable power plant is electrically coupled to the innovative energy storage system when renewable power source is available; even more advantageously, the renewable power plant is electrically coupled to the innovative energy storage system when the renewable power plant produces excess electrical energy, in particular with respect to an electrical energy demand to the renewable power plant. [0037] According to still another aspect, the subject-matter disclosed herein relates to a method for producing, storing and consuming energy comprising the steps of:

A. producing formic acid (CH2O2) through an electrochemical reduction process performed by an electrochemical reduction CO2 cell unit 110 using carbon dioxide (CO2) and electrical energy produced from a renewable energy source when the renewable energy source is available;

B. storing the produced formic acid (CH2O2) at least for a predetermined time, in particular in a formic acid storage unit 120;

C. supplying the stored formic acid (CH2O2) as fuel to a formic acid fuel cell unit 130 for producing carbon dioxide (CO2) and electrical energy through an electrochemical oxidation process when the renewable energy source is not available.

[0038] It is to be noted that the carbon dioxide (CO2) produced in step C during the electrochemical oxidation process is used in the electrochemical reduction CO2 cell unit 110 for producing formic acid (CH2O2) through the electrochemical reduction process performed in step A. According to a preferred embodiment, the method comprises further the steps of:

D. storing the carbon dioxide (CO2) produced by the formic acid fuel cell unit 130 in a CO2 storage unit 140 for a predetermined time;

E. supplying the stored carbon dioxide (CO2) to the electrochemical reduction CO2 cell unit 110.

In particular, step D may be performed during step C.

In particular, step E may be performed during step A.

Claims

CLAIMS Energy storage system (1000, 2000, 3000) for producing, storing and consuming energy, the system comprising: an electrochemical reduction CO2 cell unit (110) comprising a main inlet (111), a main outlet (119) and at least a first secondary inlet (112), wherein the electrochemical reduction CO2 cell unit (110) is configured to receive electrical energy at the main inlet (111) and carbon dioxide (CO2) at the first secondary inlet (112) and to perform electrochemical reduction process, produce formic acid (CH2O2) and provide the formic acid (CH2O2) at the main outlet (119); a formic acid storage unit (120) selectively fluidly coupled to the main outlet (119), the formic acid storage unit (120) being configured to store formic acid (CH2O2) in liquid state; a formic acid fuel cell unit (130) selectively fluidly coupled to the formic acid storage unit (120) and comprising a main inlet (131), a main outlet (139) and at least a first secondary outlet (138), a control unit (180), wherein the formic acid storage unit (120) is configured to selectively supply formic acid (CH2O2) to the main inlet (131) of the formic acid fuel cell unit (130), wherein the control unit (180) is configured to control supply of formic acid (CH2O2) to and from the formic acid storage unit (120), wherein the formic acid fuel cell unit (130) is configured to perform electrochemical oxidation process producing electrical energy and a carbon dioxide (CO2) and provide the electrical energy at the main outlet (139) and carbon dioxide (CO2) at the first secondary outlet (138), wherein the first secondary outlet (138) of the formic acid fuel cell unit (130) is fluidly coupled to the first secondary inlet (112) of the electrochemical reduction CO2 cell unit (110) and is configured to perform a closed-loop recirculation of carbon dioxide (CO2) to the electrochemical reduction CO2 cell unit (110). The energy storage system (1000) of claim 1, wherein the main inlet (111) of the electrochemical reduction CO2 cell unit (110) is configured to be electrically coupled to a renewable power plant (105) and to receive electrical energy from the renewable power plant (105). The energy storage system (1000) of claim 1, wherein the main outlet (139) of the formic acid fuel cell unit (130) is configured to be electrically coupled to an electric grid or micro-grid (195) and to supply electrical energy to the electric grid or micro-grid (195). The energy storage system (1000) of claim 1, further comprising a pump (125), wherein the pump (125) is located upstream of the main inlet

(131) of the formic acid fuel cell unit (130) and is configured to pump formic acid (CH2O2) from the formic acid storage unit (120) to the main inlet (131). The energy storage system (1000) of claim 1, further comprising a CO2 storage unit (140) fluidly coupled to the first secondary outlet (138) of the formic acid fuel cell unit (130) and to the first secondary inlet (112) of the electrochemical reduction CO2 cell unit (110), the CO2 storage unit (140) being configured to store carbon dioxide (CO2) at least for a predetermined time. The energy storage system (1000) of claim 5, further comprising a blower (145) located upstream of the CO2 storage unit (140), wherein the blower (145) is configured to increment carbon dioxide (CO2) pressure before being stored in the CO2 storage unit (140). The energy storage system (2000, 3000) of claim 1, further comprising a distillation column (250) comprising a main inlet (221) and a main outlet (229), wherein the main inlet (221) of the distillation column (250) is fluidly coupled to the main outlet (219) of the electrochemical reduction CO2 cell unit (210), wherein the main outlet (229) of the distillation column (250) is fluidly coupled to the formic acid storage unit (220), wherein the distillation column (250) is configured to receive formic acid (CH2O2) from the main outlet (219), increase concentration of formic acid (CH2O2) and supply concentrated formic acid (CH2O2) to the formic acid storage unit (220). The energy storage system (3000) of claim 7, further comprising a gas turbine unit (360) configured to produce exhaust gases (EG) and a heat recovery steam generator (370) fluidly coupled to the gas turbine unit (360), wherein the heat recovery steam generator (370) comprises an inlet (371) and an outlet (372), wherein the inlet (371) is configured to receive water (W) in liquid form, wherein the heat recovery steam generator (370) is configured to transfer heat from exhaust gases (EG) to water (W) in order to produce steam (S) and to supply steam (S) to the outlet (372). The energy storage system (3000) of claim 8, wherein the outlet (372) of the heat recovery steam generator (370) is fluidly coupled to the distillation column (350), wherein the distillation column (350) is configured to receive steam (S) from the outlet (372). The energy storage system (3000) of claim 9, further comprising a control valve (375) downstream of the outlet (372) of the heat recovery steam generator (370), wherein the control valve (375) is configured to regulate the amount of steam (S) supplied to the distillation column (350). The energy storage system (3000) of claim 10, wherein the control unit (380) is further configured to control operation of the control valve (375) according to at least a concentration setpoint (SP), a first measure of concentration of formic acid (CH2O2) at the main inlet (321) of the distillation column (350) and a second measure of concentration of formic acid (CH2O2) at the main outlet (329) of the distillation column (350). Renewable power plant for producing electrical energy, wherein the renewable power plant is selectively electrically coupled to the energy storage system (1000, 2000, 3000) of claim 1, wherein electrical energy provided to the electrochemical reduction CO2 cell unit (110) is produced from the renewable power plant. Method for producing, storing and consuming energy, the method comprising the steps of:

B. storing the produced formic acid (CH2O2) at least for a predetermined time;

C. supplying the stored formic acid (CH2O2) as fuel to a formic acid fuel cell unit for producing carbon dioxide (CO2) and electrical energy through an electrochemical oxidation process when the renewable energy source is not available; and wherein the carbon dioxide (CO2) produced at step C is used for producing formic acid (CH2O2). The method for producing electrical energy of claim 13, wherein the method comprises further the steps of:

D. storing the carbon dioxide (CO2) produced by the formic acid fuel cell unit in a CO2 storage unit for a predetermined time;

E. supplying the stored carbon dioxide (CO2) to the electrochemical reduction CO2 cell unit.