Methods and systems for utilizing intermittent renewable power

Abstract

A system for converting intermittent renewable power into chemical fuels includes a DC bus with variable voltage between a first and second DC bus voltage. The system includes a variable renewable power generation unit connected to the DC bus through a first power converter, an electrochemical power conversion system directly connected to the DC bus operating at the variable DC bus voltage, and a power storage system linked to the DC bus via a second power converter that allows electric current flow in both directions.

Description

METHODS AND SYSTEMS FOR UTILIZING INTERMITTENT RENEWABLE POWERCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to provisional application no. 63 / 585,645 filed on Sep. 27, 2023, titled “Methods and Systems for Utilizing Intermittent Renewable Power” which is hereby incorporated by reference herein in its entirety.TECHNICAL FIELD

[0002] The described embodiments relate to renewable power sources.BACKGROUND

[0003] As the world struggles to reduce carbon emissions, deployment of intermittent renewable power systems, such as wind and solar, experiences rapid growth. Currently, these renewable power systems must be connected to the AC electrical grid in order to supply power to consumers. The vast majority of the renewable resources, though, can be found at remote areas of the globe where no grid connection is available. Building new long-distance power transmission lines needed to utilize these resources may be very expensive and can take a long time for project development and execution. Alternatively, renewable power can be converted into chemical fuels, such as hydrogen, methanol, ammonia or liquid hydrocarbons, which can be delivered to the markets by pipelines, tankers, or by rail and can be used in many existing power applications replacing present day fossil fuels.

[0004] Electrochemical devices which convert DC electric power into various chemicals, such as water electrolysis systems, chloralkali plants, or aluminum smelting, have been used for more than a century. Many new systems, such as CO2 electroreduction to carbon monoxide and hydrocarbon fuels are being developed. Currently, these electrochemical systems are designed to receive power on demand from electrical grid through an AC / DC power converter. As the power on the grid is available in excess of the electrochemical device demand, the power converters in present day systems are controlled to draw the amount of electric current required by the electrochemical device. Individual AC / DC power converter has to be installed with each electrochemical device to control the current, which constitutes a large fraction of the system cost.

[0005] In many cases production of chemical fuels from renewable power requires further downstream processing of the chemical components in a chemical conversion plant integrated with the electrochemical devices. These chemical plants have their own balance of plant (BOP) power components, which in present day systems draw power from the grid, and some of these BOP components may require continuous power supply. When using intermittent power sources, this would require large power storage devices installed with the conversion system, which significantly adds to the system cost. These issues make the present-day power control designs not readily suitable for behind-the-meter integration of intermittent renewable power sources with electrochemical power conversion and chemical fuel production systems.SUMMARY

[0006] In various embodiments, a system is designed for converting intermittent renewable power into chemical fuels. This system includes a DC bus with a variable voltage that ranges between the first and second DC bus voltages. A variable renewable power generation system is connected to this DC bus through a first power converter. An electrochemical power conversion system, which operates directly at the variable DC bus voltage, is also connected to the DC bus. Additionally, there is a power storage system that connects to the DC bus via a second power converter and can transfer electric current in both directions between the DC bus and itself.In one embodiment, a system for converting intermittent renewable power into a chemical fuels includes a DC bus having a variable voltage between a first DC bus voltage and a second DC bus voltage; a variable renewable power generation system connected to the DC bus through a first power converter; an electrochemical power conversion system directly connected to the DC bus and operating at the variable DC bus voltage; a power storage system connected to the DC bus through a second power converter configured to flow electric current to and from the DC bus.

[0007] Optionally, in some embodiments, the electrochemical power conversion system chemically reduces carbon dioxide to carbon monoxide and / or to hydrocarbons.

[0008] Optionally, in some embodiments, the system further includes; a plurality of variable renewable power generation systems each connected to the DC bus through a first power converter of a plurality of first power converters; and a plurality of electrochemical power conversion systems each directly connected to the DC bus and operable at the variable DC bus voltage; wherein a number of the plurality of electrochemical power conversion systems isselected such that a total current drawn by the plurality of electrochemical power conversion systems at the second DC bus voltage matches a design current that can be supplied by the plurality of variable renewable power generation systems connected to the DC bus and operable at the second DC bus voltage.

[0009] Optionally, in some embodiments, the design current comprises a maximum current that can be supplied by the plurality of variable renewable power generation systems.

[0010] Optionally, in some embodiments, the electrochemical power conversion system comprises a chemical fuel synthesis plant having a variable balance of plant (BOP) power load connected to the DC bus through a BOP DC / DC or DC / AC power converter.

[0011] Optionally, in some embodiments, the system further includes a power generator directly connected to the DC bus, wherein: the power generator is configured to generate DC power from a chemical generated by the system; and the power generator is configured to supply the DC power to the DC bus at the first DC bus voltage.

[0012] Optionally, in some embodiments, the system includes a chemical storage system configured to store the chemical, wherein the power generator is further configured to generate the DC power from the chemical generated by the system and stored in the chemical storage system.

[0013] Optionally, in some embodiments, the electrochemical power conversion system comprises a water electrolysis system producing hydrogen and oxygen from water.

[0014] Optionally, in some embodiments, the first power converter comprises an AC / DC or DC / DC power converter.

[0015] Optionally, in some embodiments, the second power converter comprises a DC / DC power converter.

[0016] In one embodiment, a method for operating a system for converting intermittent renewable power into a chemical fuel includes: providing a variable setpoint voltage value for a DC bus; controlling a first power converter connecting a variable renewable power generation system to the DC bus to supply a current to the DC bus at the variable setpoint voltage value; directly connecting an electrochemical power conversion system to the DC bus so that the electrochemical power conversion system draws the electric current determined by a polarization curve of the electrochemical power conversion system; controlling a second power converter connecting a power storage system to the DC bus to provide a balancing current to orfrom the DC bus to stabilize a DC bus voltage at the variable setpoint voltage value; and adjusting the variable setpoint voltage value to control the DC bus voltage between a first DC bus voltage and a second DC bus voltage to control a state-of-charge of the power storage system.

[0017] Optionally, in some embodiments, the current comprises a maximum current that the renewable power generation system can supply under existing ambient conditions.

[0018] Optionally, in some embodiments, the method further includes curtailing the current from the variable renewable power generation system when the variable setpoint voltage value reaches the second DC bus voltage.

[0019] Optionally, in some embodiments, the method further includes disconnecting the electrochemical power conversion system from the DC bus when the variable setpoint voltage value reaches the first DC bus voltage.

[0020] Optionally, in some embodiments, the method further includes setting a chemical fuel synthesis plant connected to the DC bus through a BOP power converter to an idle operating state when the variable setpoint voltage value reaches the first DC bus voltage; and starting a power generator configured to supply a second current to the DC bus at the first DC bus voltage; and adjusting the second current to control the state-of-charge of the power storage system.

[0021] Optionally, in some embodiments, the method further includes measuring a total current flowing in or out of the DC bus; detecting shifts in the total current; monitoring a polarization curve for the electrochemical power conversion system, and compensating for changes in the variable setpoint voltage value in response to the detected shifts in the total current.

[0022] Optionally, in some embodiments, the first DC bus voltage comprises a minimum DC bus voltage and the second DC bus voltage comprises a maximum DC bus voltage.

[0023] Optionally, in some embodiments, the first DC bus voltage is lower than the second DC bus voltage.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0024] FIG. 1 is a block diagram of an embodiment of a power conversion system.

[0025] FIG. 2 shows an example of a general relationship between an electrochemical cell voltage and efficiency and the cell current, also known as a polarization curve, for an electrochemical power conversion system of the system of FIG. 1.

[0026] FIG. 3 is an example of a polarization curve for an embodiment of the system of FIG. 1, including three electrochemical conversion systems connected to a direct current (DC) bus.

[0027] FIG. 4 is a block diagram of an embodiment of a power conversion system.

[0028] FIG. 5 illustrates a method 500 for operating a system for converting intermittent renewable power into a chemical fuel in accordance with one embodiment.DETAILED DESCRIPTION

[0029] The systems and methods of the present disclosure address shortcomings of conventional energy systems and provides for dynamic operation of a system integrating a variety of intermittent renewable power sources with electrochemical conversion devices and downstream fuel synthesis plant and balance of plant (BOP) loads to convert intermittent renewable power into chemical fuels without a need for grid connection.

[0030] Referring to FIG. 1 in some embodiments systems and methods of the present disclosure can include: providing a power conversion system for converting intermittent renewable power into chemical fuels, the system including: a direct current (DC) bus 100 having at a variable voltage between a first (e.g., minimum) DC bus voltage and a second (e.g., maximum) DC bus voltage and having electrical connections to power inputs and power outputs; at least one variable renewable power generation system 101 - 103 connected to the DC bus through an alternating current (AC) / DC or DC / DC power converter 121-123; at least one electrochemical power conversion system 131-132 directly connected to the DC bus and operating at the DC bus voltage; a power storage system 134 connected to the DC bus through a DC / DC converter 144; controlling the AC / DC and / or DC / DC power converters 121-123 to maximize current supplied to the DC bus by each variable renewable power generation system at the setpoint or target DC bus voltage; controlling the DC / DC converter 144 of the power storage system to stabilize the DC bus voltage at the setpoint value by supplying balancing current to / from the power storage system 134; adjusting the setpoint DC bus voltage to control the state of charge of the power storage system 134 to a desired value.

[0031] As used herein, “directly connecting", “direct connection” and the like mean an electrical connection between a DC source, such as a bus, with one or more electrochemicalconversion systems without the use of an intervening conversion device (e.g., a DC / DC, DC / AC, AC / AC, or AC / CD converter, rectifier, transformer, boost converter, buck converter, combinations of these, or the like) disposed electrically between the DC source and the electrochemical conversion device. A direct connection encompasses the use of passive components such as fuses, wires, cables, bus bars, splices and active components such as switches, fuses, circuit breakers and other such components that control or enable the flow of electricity, but do not appreciably change its characteristics, allowing for losses such as due to Ohm's Law losses.

[0032] The variable renewable power generation system 101 can be any known renewable system generating electric power output. Wind turbines and photovoltaic solar panels are the most common examples of renewable power systems. Other types, such as hydropower, geothermal power, wave power, or others can also be used in some examples. Some power generation systems can produce AC power, such as, for example, a wind turbine 102, and can be connected to the DC bus 100 through an AC / DC power converter 122. Other power generation systems can produce DC power directly such as, for example, a solar farm 103, and can be connected to the DC bus 100 through a DC / DC power converter 123. Multiple variable renewable power generation systems of different types can be part of the same power conversion system and can be connected to the DC bus 100 through appropriate power converters 121-123. Each power system can be connected to the DC bus 100 through its own power converter. As such, all power systems can operate independently of each other, without being synchronized in terms of voltages, frequencies, and phases.

[0033] Variable renewable power generation systems producing power in the range of up to several megawatts are commonly available on the market. For a power conversion system in the range between several hundred megawatts to several gigawatts tens to hundreds to thousands of power generation systems can be connected to the DC bus 100. Some of these power generation systems can be placed at a distance of up to tens of miles from the DC bus 100. To avoid significant power losses in the power transmission lines 111-113, the power generation systems 101-103 can operate at higher voltages than the DC bus 100 and the AC / DC and DC / DC converters 121-123 can reduce voltage.

[0034] Various types of AC / DC and DC / DC power converters can be used with the methods and systems of the present disclosure. The power converters can be placed in close proximity to the DC bus 100 (e.g., within tens of meters or less) to avoid long-distance transmission at theDC bus voltage. Each power converter 121-123 can be controlled in such a way to maximize the amount of current transmitted from each variable power generation system 101 - 103 to the DC bus 100 at the present setpoint DC bus voltage value and the present generating power of the renewable generation system. The current that each variable renewable power generation system 101 - 103 supplies to the DC bus 100 through the power converter 121-123 can vary depending on the momentary ambient conditions at the location of the power generation system. E.g., wind gust would increase the amount of current that a wind turbine 102 can supply to DC bus 100, while a passing cloud would decrease the amount of current that a solar farm 103 supplies to DC bus 100. Operating each power controller 121-123 to maximize current supplied by each power generating system will utilize total maximum power that could be generated by the power conversion systems under the momentary present ambient conditions. When configuring and operating an electrochemical power conversion system as disclosed herein, there may be two or more distinct maximum currents at which the systems may operate. One is the maximum nameplate or design power (current) that can be supplied by all the renewable power systems. This first maximum current may be used to determine the number of electrochemical systems connected to the DC bus. The second maximum current is the momentary current that each renewable power system can supply to the DC bus under the existing wind and solar conditions (i.e. , ambient conditions), which may be lower than the nameplate current. Power converters may be controlled to provide the maximum momentary current.

[0035] Electrochemical power conversion systems 131-132 consume electrical DC current to generate some form of chemical energy. Examples include, but are not limited to water electrolysis systems, which split water to produce hydrogen and oxygen; chloralkali process, which convert sodium chloride into sodium hydroxide, hydrogen and chlorine; aluminum smelting process, which extracts aluminum from its oxide. More recently, electrochemical processes for direct reduction of carbon dioxide to carbon monoxide and various chemicals are being developed. Any of these electrochemical power conversion systems can be used with the systems and methods of the present disclosure. In some examples, electrochemical power conversion systems that operate at low temperatures can be used and can be rapidly ramped up and down in power and be shut down in response to variation in the amount of power supplied by the variable renewable power generation systems 101 - 103. Examples of low-temperature(e.g., less than about 100°C) electrochemical power conversion systems include alkali, PEM and AEM water electrolysis systems, PEM and AEM based CO2 electroreduction systems.

[0036] Electrochemical power conversion systems 131-132 generally include a series of individual electrochemical cells (i.e., a stack), each cell operating in the range of DC voltages between about IV and 3V. The actual voltage depends on cell current, operating pressure, temperature and may vary in a broad range with changing cell current. Cell voltage is at the low end of the range at low cell current and nearly linearly increases towards the high end of the voltage range as current is increasing, reaching the maximum voltage at the maximum design cell current. The dependence of cell voltage on current is known as the polarization curve of the electrochemical cell, as generally represented in FIG. 2 together with a corresponding cell efficiency curve. Cell voltage starts to rapidly increase at the low and high ends of the linear range of operating current, which results in rapid loss of cell efficiency. Therefore, it is preferred that electrochemical devices are operated within the nearly linear range of the polarization curve. Generally, cells in an electrochemical power conversion system are arranged electrically in series forming a stack where the same current flows through all cells and cell voltages are added up to a total stack voltage. The number of cells in electrochemical power conversion systems 131-132 can be selected such that the operating range of the stack voltage matches the maximum and minimum voltages of the DC bus 100 and stacks can be directly connected to the DC bus 100 to draw the amount of current which corresponds to the instantaneous DC bus voltage according to the stack polarization curve.

[0037] In some examples, multiple electrochemical power conversion stacks 131-132 can be connected to the DC bus 100 in parallel, whereas each stack operating at the same bus voltage and drawing the amount of current corresponding to the polarization curve of each particular stack. Polarization curve for each stack 131-132 connected to the DC bus can be slightly different due to variations in the voltage of individual cells, slightly different operating conditions or stacks age. It is known that electrochemical cell voltages gradually increase with cell aging, so that the polarization curve for each stack will be shifting up in voltage over time.

[0038] An example of three electrochemical stacks having slightly different polarization curves is shown in FIG. 3. More or fewer stacks may be used as desired. When all three stacks are connected to the DC bus and are operating at the same voltage, they will be drawing different current from the bus and the total current will be a sum of all the currents drawn by the stacks connected to the DC bus 100. The size of the stacks should be selected such that atthe maximum DC bus voltage the current drawn through the stack with the lowest polarization curve remains in the desired linear operating range for the electrochemical cell. The number of stacks connected to the DC bus 100 can be selected such that the total current drawn by all stacks at the maximum DC bus voltage corresponds to the maximum design current that can be supplied by all the variable renewable power generation systems connected to DC bus 100.

[0039] The power storage system 134 can be any device capable of storing DC electricity. In some examples, the power storage system 134 is a battery or a bank of batteries.

[0040] The DC / DC converter 144 connecting the power storage system 134 to the DC bus 100 can allow flowing current to and from the power storage system 134. At any moment there can be a balance between the electrical current supplied to the DC bus 100 by all variable renewable power generation systems 101-103 connected to the DC bus 100 through power converters 121-123 and the electrical current drawn by all the electrochemical power conversion systems 131-132 directly connected to the DC bus 100. If the supplied current exceeds the drawn current, then the DC bus voltage will increase to allow for more current flow to the electrochemical power conversion systems according to the polarization curve of these systems. On the contrary when the supplied current decreases, the DC bus voltage will decrease so that less current flow to the electrochemical power conversion systems. To keep DC bus voltage at a setpoint value the DC / DC converter 144 can provide the balancing electrical current to or from DC bus 100. When current flows to the DC bus 100, the state of charge of the power storage system 134 will decrease, and when current flows from the DC bus 100, the state of charge of the power storage system 134 will increase.

[0041] In some examples, the setpoint for voltage of the DC bus 100 can be adjusted to control the state of charge of the power storage system 134 to a desired value. When current flows from the DC bus 100 to the power storage system 134 the state of charge of the power storage system 134 increases. The setpoint voltage of the DC bus 100 can be increased, so that when the state of charge of the power storage system 134 reaches the desired value no current flow from the power storage system 134 is required. When current flows to the DC bus 100 from the power storage system 134 the state of charge of the power storage system 134 decreases. The setpoint voltage of the DC bus 100 can be decreased so that when the state of charge of the power storage system 134 reaches the desired value no current from the power storage system 134 is required. Various control strategies can be used to control setpointvoltage of the DC bus 100 to keep the state of charge of the power storage system 134 to a desired value.

[0042] When excess power is provided by variable renewable power generation systems 101 - 103 beyond the design maximum value, the DC bus setpoint voltage may reach the maximum design value. To avoid damaging the electrochemical power conversion systems 131-132, further increase in power generation can be curtailed. On the contrary, when the amount of power generated by the variable renewable power generation systems 101 - 103 is low, the DC bus setpoint voltage may reach the minimum design value. Under these conditions some of the electrochemical power conversion systems 131-132 can be disconnected from the DC bus 100 to further reduce the current draw. If all the electrochemical power conversion systems 131-132 are disconnected, the system can be set for the idle operation state.

[0043] FIG. 4 illustrates an example of a system similar to the system of FIG. 1 , with system elements of FIG. 4 corresponding to system elements of FIG. 1 being represented by the corresponding 200-series numbers.

[0044] In the example of FIG. 4, the electrochemical power conversion systems 231-232 can be low-temperature water electrolysis systems splitting water into oxygen and hydrogen, low- temperature CO2 electroreduction systems that produce CO or hydrocarbon fuels from CO2 and water, or the like. Downstream chemical conversion systems can be included that further convert H2 produced by water electrolysis systems, or CO produced by CO2 electroreduction systems, into other fuels and chemicals. Examples of these downstream chemical conversion systems can include, but not limited to hydrogen compression or liquefaction, methanol synthesis from H2 and CO2, ammonia synthesis from H2 and N2, methanation reactors producing synthetic natural gas from CO2 and H2, Fischcr-Tropsch synthesis reactors producing hydrocarbons from CO and H2 and similar chemical processes.

[0045] These downstream chemical conversion systems can require electrical power to various power loads for systems operation. These loads can be various compressors, pumps, blowers, electric heaters, metering devices, control systems, etc. Some of these loads may require AC current and some may require DC current. At least one variable balance of plant power load 233 can be connected to the DC bus 100 through an appropriate DC / DC or DC / AC power converter 243 and can be controlled to draw current required by the BOP power load 233. The number of installed electrochemical power conversion systems 231-232 can beadjusted to account for additional current draw from the DC bus 100 by the downstream loads 233.

[0046] A power generator 235 capable of generating DC power can be directly connected to the DC bus 100. Generator 235 produces power during the idle state of the system operation when the variable power generation systems 201-203 cannot provide sufficient current to keep the DC bus voltage at the minimum setpoint value. The power generator 235 may be of any type that can use hydrogen, or the fuel produced and stored in the system to produce DC current. Examples of these power generation devices may be a fuel cell or a DC generator type. The power generator 235 can be directly connected to the DC bus 100 and can be set to produce current at the minimum DC bus setpoint voltage value. During the idle state of the system operation all electrochemical power conversion systems 231-232 and most of the BOP power loads 233 can be disconnected from the DC bus 100. Only the BOP loads that are used for sustaining system operation in the idle state, such as control loads, necessary pumps, heaters, etc., may be connected to the DC bus 100 in the idle state. The DC current supplied by the power generator 235 to the DC bus 100 can be regulated to sustain the state of charge of the power storage device 234 at the desired value.

[0047] The polarization curve of the electrochemical power conversion system 231-232 can depend on various operating parameters, such as temperature, pressure, age, manufacturing tolerances, and water purity. Polarization curves can change with time. Generally, as the system ages, higher operating voltage is required to sustain the same current. To account for these variations in the polarization curve of the electrochemical power conversion systems 231-232, total DC current supplied to the DC bus 100 by all power converters 221-223 and the corresponding DC bus voltage can be monitored to determine the present time I-V curve for the whole system. In case of rapid change in the DC current supply to the DC bus 100 by any of the variable power generation systems 201-203 due to rapid change in ambient conditions, or when switching on or off some BOP power load 233, the DC bus voltage setpoint can be rapidly adjusted to the new value based on the know I-V curve.

[0048] FIG. 5 illustrates an example method 500 for operating a system for converting intermittent renewable power into a chemical fuel. Although the example method 500 depicts a particular sequence of operations, the sequence may be altered without departing from the scope of the present disclosure. For example, some of the operations depicted may be performed in parallel or in a different sequence that does not materially affect the function ofthe method 500. In other examples, different components of an example device or system that implements the method 500 may perform functions at substantially the same time or in a specific sequence.

[0049] According to some examples, the method 500 includes providing a setpoint voltage value for a DC bus at operation 502.

[0050] According to some examples, the method 500 includes controlling a first power converter connecting a renewable power generation system to the DC bus to supply a current to the DC bus at the setpoint voltage at operation 504.

[0051] According to some examples, the method 500 includes directly connecting an electrochemical power conversion system to the DC bus at operation 506. In many embodiments, operations 504 and 506 may be executed in parallel, although in other embodiments, operations 504 and 506 may be executed in a serial fashion in any order.

[0052] According to some examples, the method 500 includes controlling a second power converter connecting a power storage system to the DC bus to provide a balancing current to or from the DC bus to stabilize the DC bus voltage at the setpoint voltage value at operation 508.

[0053] According to some examples, the method 500 includes adjusting the setpoint voltage value between a first DC bus voltage and a second DC bus voltage to control a state-of-charge of the power storage system at operation 510.LISTING OF DRAWING ELEMENTS100 - System DC bus at a variable setpoint voltage101 - Variable renewable power generation system102 - Wind turbine power generation system103 - Solar farm power generation system111 - DC or AC power line, depending on the type of the power generation source, connecting the power source 101 to the power conversion system112 -AC power line connecting wind turbine 102 to the power conversion system113 - DC power line connecting solar farm 103 to the power conversion system121 - DC / DC or AC / DC power converter, depending on the type of the power generation source, converting power from generation system 101 to DC power at the system DC bus voltage122 -AC / DC power converter converting power from wind turbine 102 to DC power at the system DC bus voltage123 - DC / DC power converter converting power from solar farm 103 to DC power at the system DC bus voltage131 - Electrochemical power conversion system directly connected to, and operating at voltage of the system DC bus132 - Another electrochemical power conversion system directly connected to, and operating at voltage of the system DC bus134 - Power storage device144 - DC / DC power converter for supplying power to / from the DC bus 100 and the power storage device 134200 - System DC bus at a variable setpoint voltage201 - A variable renewable power generation system202 - A wind turbine power generation system203 - A solar farm power generation system211 - DC or AC power line, depending on the type of the power generation source, connecting the power source 201 to the power conversion system212 -AC power line connecting wind turbine 202 to the power conversion system213 - DC power line connecting solar farm 203 to the power conversion system221 - DC / DC or AC / DC power converter, depending on the type of the power generation source, converting power from generation system 201 to DC power at the system DC bus voltage222 -AC / DC power converter converting power from wind turbine 202 to DC power at the system DC bus voltage223 - DC / DC power converter converting power from solar farm 203 to DC power at the system DC bus voltage231 - Electrochemical power conversion system directly connected to, and operating at voltage of the system DC bus232 - Another electrochemical power conversion system directly connected to, and operating at voltage of the system DC bus233 - AC or DC balance of plant power loads required for system operation234 - Power storage device243 - DC / AC or DC / DC power converter, depending on the type of the BOP loads, converting DC power from system DC bus 200 to the type of power and voltage required by the BOP loads244 - DC / DC power converter for supplying power to / from the DC bus 200 and the power storage device 234235 - Power generator supplying DC power to DC bus 200 at minimum bus voltage during idle state of the power conversion system

Claims

CLAIMSWhat is claimed is:

1. A system for converting intermittent renewable power into a chemical fuel comprising: a DC bus having a variable voltage between a first DC bus voltage and a second DC bus voltage; a variable renewable power generation system connected to the DC bus through a first power converter; an electrochemical power conversion system directly connected to the DC bus and operating at the variable DC bus voltage; a power storage system connected to the DC bus through a second power converter configured to flow electric current to and from the DC bus.

2. The system of claim 1, wherein the electrochemical power conversion system chemically reduces carbon dioxide to carbon monoxide and / or to hydrocarbons.

3. The system of claim 1, further comprising: a plurality of variable renewable power generation systems each connected to the DC bus through a first power converter of a plurality of first power converters; and a plurality of electrochemical power conversion systems each directly connected to the DC bus and operable at the variable DC bus voltage; wherein a number of the plurality of electrochemical power conversion systems is selected such that a total current drawn by the plurality of electrochemical power conversion systems at the second DC bus voltage matches a design current that can be supplied by the plurality of variable renewable power generation systems connected to the DC bus and operable at the second DC bus voltage.

4. The system of claim 3, wherein the design current comprises a maximum current that can be supplied by the plurality of variable renewable power generation systems.

5. The system of claim 1, wherein the electrochemical power conversion system comprises a chemical fuel synthesis plant having a variable balance of plant (BOP) power load connected to the DC bus through a BOP DC / DC or DC / AC power converter.

6. The system of claim 5, further comprising a power generator directly connected to the DC bus, wherein: the power generator is configured to generate DC power from a chemical generated by the system; and the power generator is configured to supply the DC power to the DC bus at the first DC bus voltage.

7. The system of claim 6, further comprising a chemical storage system configured to store the chemical, wherein the power generator is further configured to generate the DC power from the chemical generated by the system and stored in the chemical storage system.

8. The system of any of the preceding claims, wherein the electrochemical power conversion system comprises a water electrolysis system producing hydrogen and oxygen from water.

9. The system of any one of claims 1 to 6, wherein the first power converter comprises an AC / DC or DC / DC power converter.

10. The system of any one of claims 1 to 6, wherein the second power converter comprises a DC / DC power converter.

11. A method for operating a system for converting intermittent renewable power into a chemical fuel comprising: providing a variable setpoint voltage value for a DC bus; controlling a first power converter connecting a variable renewable power generation system to the DC bus to supply a current to the DC bus at the variable setpoint voltage value; directly connecting an electrochemical power conversion system to the DC bus so that the electrochemical power conversion system draws the electric current determined by a polarization curve of the electrochemical power conversion system; controlling a second power converter connecting a power storage system to the DC bus to provide a balancing current to or from the DC bus to stabilize a DC bus voltage at the variable setpoint voltage value; and adjusting the variable setpoint voltage value to control the DC bus voltage between a first DC bus voltage and a second DC bus voltage to control a state-of-charge of the power storage system.

12. The method of claim 11, wherein the current comprises a maximum current that the renewable power generation system can supply under existing ambient conditions.

13. The method of claim 11, wherein the first power converter comprises an AC / DC or DC / DC power converter.

14. The method of claim 11, wherein the second power converter comprises a DC / DC power converter.

15. The method of claim 11, further comprising: curtailing the current from the variable renewable power generation system when the variable setpoint voltage value reaches the second DC bus voltage.

16. The method of any one of claims 11 to 15, further comprising: disconnecting the electrochemical power conversion system from the DC bus when the variable setpoint voltage value reaches the first DC bus voltage.

17. The method of claim 11, further comprising: setting a chemical fuel synthesis plant connected to the DC bus through a BOP power converter to an idle operating state when the variable setpoint voltage value reaches the first DC bus voltage; and starting a power generator configured to supply a second current to the DC bus at the first DC bus voltage; and adjusting the second current to control the state-of-charge of the power storage system.

18. The method of claim 11, further comprising: measuring a total current flowing in or out of the DC bus; detecting shifts in the total current; monitoring a polarization curve for the electrochemical power conversion system, and compensating for changes in the variable setpoint voltage value in response to the detected shifts in the total current.

19. Any of the preceding claims, wherein the first DC bus voltage comprises a minimum DC bus voltage and the second DC bus voltage comprises a maximum DC bus voltage.

20. Any of claims 1 to 18, wherein the first DC bus voltage is lower than the second DC bus voltage.

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