Electrolyzer with a variable number of active electrolytic cells

Abstract

1. A system comprising: an electrolytic cell having a plurality of electrolytic cells arranged in a cell stack, the electrolytic cells being electrically connected in series and grouped into two or more cell groups, each cell group having electrical contacts at opposite ends; an electrical circuit having one or more switches, each switch coupled between a respective electrical contact of a cell group and configured to selectively disconnect the cell group from the cell stack by electrically bypassing the cell group through a lower resistance path, thereby varying the number of active electrolytic cells in the cell stack; and a controller configured to determine the number of active electrolytic cells based on a variable amount of direct current (DC) electrical energy supplied to the cell stack by an electrical energy source, and to control the one or more switches based on the determination.

Description

[Technical Field]

[0001] The present disclosure relates generally to electrolytic cells, and more particularly to electrolytic cells in which the number of active electrolytic cells may vary. [Background technology]

[0002] Electrolyzers use electricity to split water into hydrogen and oxygen in a chemical process called electrolysis. The electricity needed for the electrolysis process can be obtained from renewable resources, such as solar or wind power. However, using electricity from such renewable resources poses various challenges. For example, electricity supplied by renewable sources can be intermittent and variable. Therefore, a need exists for electrolyzers that can operate efficiently under a variety of input power conditions. Summary of the Invention

[0003] One aspect of the present disclosure provides a system comprising: an electrolyzer having a plurality of electrolytic cells arranged in a cell stack, the electrolytic cells being electrically connected in series and grouped into two or more cell groups, each cell group having electrical contacts at opposite ends; an electrical circuit having one or more switches, each switch coupled between a respective electrical contact of a cell group and configured to selectively disconnect the cell group from the cell stack by electrically bypassing the cell group through a lower resistance path, thereby varying the number of active electrolytic cells in the cell stack; and a controller configured to determine the number of active electrolytic cells based on a variable amount of direct current (DC) electrical energy supplied to the cell stack by an electrical energy source, and to control the one or more switches based on the determination.

[0004] Varying the number of active electrolysis cells in this manner can allow the electrolyzer load to be adapted to a variable DC output from an electrical energy source, such as a renewable energy source (e.g., a solar photovoltaic system) and / or a battery. That is, the electrolyzer load can be optimized to maximize the amount of electrical energy transferred from the electrical energy source to the electrolyzer for hydrogen production. Furthermore, the variable DC output can be applied "directly" to the cell stack without the need for intermediate power electronics such as an inverter or DC-DC converter.

[0005] The electrolyzer may be physically implemented in different ways. For example, a cell stack may comprise a single cell stack having a first electrical contact with an anode at one end of the cell stack, a second electrical contact with a cathode at the other end of the cell stack, and one or more intermediate electrical contacts. Alternatively, the cell stack may comprise a first substack and a second substack electrically connected in series, each substack having a first electrical contact with an anode at one end of the substack and a second electrical contact with a cathode at the other end of the substack. The second substack may have one or more intermediate electrical contacts. Additionally, the cell stack may comprise multiple second substacks.

[0006] The cell groups may have the same number of electrolytic cells or different numbers of electrolytic cells. For example, the different numbers of electrolytic cells may be defined by a geometric progression expressed as 2(n-1), where n≧0. This may allow the electrolytic cells to be disconnected in a "binary" manner, which may minimize the number of external switches while still retaining the ability to disconnect / connect any number of electrolytic cells in the second substack with one-cell adjustment accuracy. Other combinations of the number of electrolytic cells may also be used. Furthermore, with respect to the total number of electrolytic cells in a cell stack, the number of "variable" electrolytic cells may comprise approximately 25%-10% of the total number of electrolytic cells, while the number of "fixed" electrolytic cells may comprise approximately 75%-90% of the total number of electrolytic cells.

[0007] The system may include two or more electrolyzers and their respective electrical circuits, and a switching circuit for switching the connection between the electrolyzers from a series connection to a parallel connection and vice versa. The controller may be configured to control the switching circuit to connect the electrolyzers in series or parallel, determine the number of active electrolysis cells for each of the electrolyzers, and control the respective electrical circuits based on the determination. In this manner, the electrolyzers may be managed as a pool of electrolyzer cells, and their serial or parallel electrical connection to a DC source may be dynamically modified by an external switch to achieve a specific goal. For example, multiple electrolyzers may be connected in parallel to a DC source when the DC source supplies a relatively high current and a relatively low voltage, while these multiple electrolyzers, or some of them, may be electrically connected in series when the DC source supplies a relatively low current and a relatively high voltage. Dynamic allocation of electrolysis cells to parallel or serial electrical connections may optimize system costs, enhance hydrogen production, promote a modular approach, and improve system reliability and fault tolerance.

[0008] The electrical energy source may comprise one or more of a renewable energy source or an electrical energy storage device.

[0009] The controller may implement a maximum power point tracking (MPPT) algorithm for the renewable energy source in determining the number of active electrolytic cells.

[0010] The number of active electrolysis cells can be varied such that the load on the electrolyzer can be optimized when the amount of electrical energy supplied to the cell stack is adjusted. For example, the controller can implement an energy management policy that adjusts the amount of DC electrical energy supplied to the cell stack. The amount of DC electrical energy can be adjusted based on the time of day, weather conditions and forecasts, hydrogen production demand, and / or any other factors. The energy management policy can define a first amount of electrical energy to be immediately used by the electrolyzer and a second amount of electrical energy to be stored or otherwise used. The first and second amounts of electrical energy can be total amounts of electrical energy generated by the electrical energy source. The controller can automatically determine the energy management policy or can receive the energy management policy.

[0011] The controller may further determine the number of active electrolysis cells based on one or more of an operating condition of the electrical energy source, an operating condition of the cell stack, or an operating condition of the electrical energy storage device.

[0012] For example, the operating conditions of the electrical energy source may include one or more of the irradiance level on a solar PV array, the temperature of the solar PV array, the voltage and current generated by a wind turbine or other type of generator. The operating conditions of the cell stack may include the temperature of the cell stack. The operating conditions of the electrical energy storage device may include one or more of the state of charge (SoC) of the electrical energy storage device, or the voltage of the electrical energy storage device.

[0013] The controller may be configured to divide the electrical energy between the electrolyzer stack and another electrical energy utilization system, and control the relative amount of electrical energy supplied to each through appropriate determination of the number of active electrolysis cells. For example, the electrical energy utilization system may include an energy storage battery or a grid-tied inverter.

[0014] The controller may be configured to regulate the utilization of energy stored in the battery and into the electrolyzer through appropriate determination of the number of active electrolysis cells.

[0015] The system may further include a plurality of voltage sources configured to supply a maintenance voltage to the disconnected cells or entire cell stack when not in use. The controller may be further configured to control the electrical circuit to electrically isolate one or more of the cells, thereby allowing a maintenance voltage to be applied to the inactive cell or cells while the remainder of the stack is electrically connected and operating. This may reduce gas crossover problems and extend electrolysis cell life. The controller may be further configured to control the electrical circuit to short-circuit one or more unused cells to protect against polarity reversal when disconnected from stack operation.

[0016] The system may further include a battery for storing electrical energy used by the cell stack and for smoothing fluctuations in the electrical energy provided by the electrical energy source. Thus, the variable amount of DC electrical energy may include electrical energy provided by the renewable energy source and electrical energy provided by the battery. The controller may adjust the utilization rate of the electrical energy stored in the battery by modifying the number of active cells in the electrolyzer stack. As described above, when implementing an energy management policy, the controller may further adjust the relative amount of renewable electrical energy directed to the cell stack and the remaining amount stored in the battery for later use.

[0017] Another aspect of the present disclosure is an electrolyzer comprising a plurality of electrolysis cells arranged in a cell stack, the electrolysis cells being electrically connected in series and grouped into two or more cell groups, each cell group having externally accessible electrical contacts at both ends to allow the cell group to be electrically disconnected from the cell stack during operation of the electrolyzer, thereby varying the number of active electrolysis cells in the cell stack.

[0018] Another aspect of the present disclosure provides a controller comprising a processor and a memory, the memory storing instructions that, when executed by the processor, cause the processor to determine a number of active electrolytic cells to be used from among a plurality of electrolytic cells arranged in a cell stack of an electrolyzer, the electrolytic cells being electrically connected in series and grouped into two or more cell groups, each cell group having externally accessible electrical contacts at both ends, the determination being based on a variable amount of direct current (DC) electrical energy supplied to the cell stack by an electrical energy source and / or according to a user-defined policy; and instructions to control one or more switches, each coupled between the electrical contacts of a respective one of the cell groups, to selectively disconnect one or more of the cell groups from the cell stack based on the determination.

[0019] The processor may be further configured to control one or more voltage sources and associated electrical switches to apply a maintenance voltage to one or more groups of cells that are not in use. The processor may be further configured to apply a short circuit to one or more groups of cells that are not in use.

[0020] The processor may further be configured to: determine a first number of active electrolytic cells to be used from among a first plurality of electrolytic cells arranged in a first cell stack of a first electrolytic cell, the first plurality of electrolytic cells being electrically connected in series and grouped into two or more cell groups, each cell group having externally accessible electrical contacts at both ends; and, based on the determination, control one or more first switches to selectively disconnect one or more of the cell groups from the first cell stack; determine a second number of active electrolytic cells to be used from among a second plurality of electrolytic cells arranged in a second cell stack of a second electrolytic cell, the second plurality of electrolytic cells being electrically connected in series and grouped into two or more cell groups, each cell group having externally accessible electrical contacts at both ends; and, based on the determination, control one or more first switches to selectively disconnect one or more of the cell groups from the second cell stack; and control a switching circuit to connect the first electrolytic cell and the second electrolytic cell in series or in parallel.

[0021] The present disclosure will be more fully described with reference to the accompanying drawings, in which like numbers refer to like elements throughout. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a graph of current-voltage curves of a PEM electrolyzer at different temperatures. [Figure 2] 2 is a table showing data on the current-voltage curve at 50° C. in FIG. 1. [Figure 3] 3 is a table showing a subset of the data in FIG. 2. [Figure 4] 1 is a graph of current-voltage curves of a PV plant under various irradiances. [Figure 5] 1 is a graph of current-voltage curves of a PV plant under different temperatures; [Figure 6] 1 is a graph of the current-voltage relationship of a PV plant and two cell stacks with different numbers of electrolysis cells. [Figure 7] FIG. 1 is a schematic diagram of an electrolytic cell. [Figure 8] FIG. 1 shows a schematic diagram of how bipolar plates form electrical contact between the cathode and anode in an electrolyzer cell stack. [Figure 9] 1 is a schematic diagram of an electrolytic cell with different numbers of electrolytic cells. [Figure 10-12] 1 is a schematic diagram of an electrolytic cell with a variable number of active electrolytic cells. [Figure 13] FIG. 10 is a schematic diagram illustrating a binary switching scheme for varying the number of active electrolytic cells. [Figure 14] FIG. 14 is a diagram illustrating the operation of the binary switching scheme shown in FIG. 13. [Figure 15-17] FIG. 1 shows a schematic diagram of how multiple electrolyzers can be electrically connected in parallel or in series. [Figure 18] FIG. 1 is a schematic diagram of a system including an electrolyzer with a variable number of active electrolysis cells connected to a renewable energy source. [Figure 19] 1 is a schematic of a system including an electrolyzer with a variable number of active electrolysis cells connected to a battery. [Figure 20] FIG. 1 is a schematic diagram illustrating hydrogen crossover in an electrolysis cell. [Figure 21] 1 is a graph showing the voltage-current relationship in an electrolysis cell. [Figure 22] FIG. 11 is a schematic diagram of the electrolytic cell of FIG. 10 with a maintenance voltage function. [Figure 23] FIG. 2 is a schematic diagram of a controller. [Figure 24-25] 24 is a flowchart showing the operation of the controller of FIG. 23. DETAILED DESCRIPTION OF THE INVENTION

[0023] Throughout this specification and the claims, the following terms have at least the meaning explicitly associated therewith herein, unless the context clearly indicates otherwise. The meanings identified below are not intended to limit the terms but merely provide illustrative examples of the terms. The meanings of "a," "an," and "the" are plural inclusive. As used herein, the term "comprising" means including, but not limited to, and should be interpreted in the manner typically used in patent contexts. The use of broader terms such as "comprises," "includes," and "having" should be understood to support narrower terms such as "consisting of," "consisting essentially of," and "comprised substantially of." As used herein, the word "example" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as an "example" should not necessarily be construed as preferred or advantageous over other implementations.

[0024] overview

[0025] The present disclosure provides electrolyzers in which the number of active electrolytic cells can be varied. Several principles for determining the number of active electrolytic cells are described with reference to Figures 1-6. It will be understood that not all principles need to work. Furthermore, although these principles are described in the context of proton exchange membrane (PEM) electrolyzers and PV power sources, they may be applied more generally to other types of electrolyzers, including, but not limited to, alkaline water electrolysis (AWE), anion exchange membrane (AEM), solid oxide electrolyzers (SOE), as well as other types of power sources and other types of DC power.

[0026] Figure 1 shows experimental current-voltage curves for a PEM electrolyzer operating at currents ranging from 0 A to 40 A for different water temperatures. The operating cell voltage ranges from 1.2 V to 2.4 V. 2 Assuming an effective cell area of ​​0.05A / cm for a current of 2A, the current density is 2 to 1A / cm for a current of 40A 2 In this example, the electrolytic cell is below 60°C and has a current of 0.1 A / cm 2 ~0.9A / cm 2 The cell is designed to operate at optimum efficiency for low current densities in the range of . Hydrogen production is proportional to the current flowing through the cell. The graph shows the thermodynamic limit U REV Below = 1.229 V, the current is zero, thus indicating no hydrogen production, while the thermal neutral limit U TN = 1.481 V, hydrogen production is minimal. In the latter case, the cell uses some heat to dissociate the water and becomes cold if no extra heat is supplied to the system.

[0027] FIG. 2 shows the electrolyzer cell operating voltage for each current, as well as the corresponding lower heating value (LHV) and higher heating value (HHV) efficiencies (η LHV and η HHV). The highlighted areas, corresponding to capacity factors ranging from 20% to 85%, indicate electrolyzer HHV efficiencies ranging from 77% to 91%. The corresponding cell voltage range is from 1.62V to 1.93V. Taking two exemplary operating points of a PEM electrolyzer, e.g., (10A, 1.64V) and (28A, 1.823V), and assuming a PV array producing (10A, 32.8V) at maximum power point (MPP) conditions, it can be seen that for the first operating point (10A, 1.64V), an electrolyzer stack with 20 active electrolyzer cells can provide the optimal load (20×1.64V=32.8V), while for the second operating point (28A, 1.823V), an electrolyzer stack with 18 active electrolyzer cells can provide the optimal load (18×1.823V=31.8V). Therefore, different numbers of active electrolyzer cells may provide different optimum loads at a given electrolyzer operating temperature for two different operating power points of the PV array.

[0028] FIG. 3 is a table showing that electrolysis cells can operate at different currents, e.g., from 1 A to 40 A, with different cell voltages associated with each current. At a given time, a renewable electricity source, such as a PV panel, may have a specific combination of current and voltage that defines the MPP. As an example, at an MPP current of 10 A, an operating point of 1.64 V may be most appropriate for one electrolysis cell. These MPP voltages and currents are therefore "ideal" for a PV-electrolyzer combination when an appropriate number N of electrolysis cells are connected in series, each operating at an MPP current of 10 A, with the MPP voltage equal to the sum of the individual cell voltages (Vmpp=N×1.64 V).

[0029] Figures 4 and 5 show the IV curves of a 60-cell PV panel under different solar irradiation conditions and different temperatures, respectively. As shown in Figure 4, the current generated by the PV panel is directly proportional to the irradiance, i.e., it increases with irradiance. The voltage also increases, but logarithmically, so the voltage increase is small in comparison. As shown in Figure 5, the temperature increase is proportional to the current for a given 1000 W / m 2Although this can significantly reduce the voltage of a PV panel, the current generated by a PV panel only increases slightly with increasing temperature, and therefore the total power generated by a PV panel decreases significantly with increasing temperature.

[0030] Figure 6 is a graph showing some of the principles operating in combination in a system with an electrolyzer having direct current coupled to a PV array. In the graph, the solid and dashed lines are photovoltaic IV curves at different levels of irradiance G. Each solid line (photovoltaic IV curve) has two corresponding dashed lines (corresponding photovoltaic IV curves). These show the effect of varying the number of PV panels in series (N s ) and the effect of varying the number of PV panels in parallel (N p The normal thick dotted lines in the graph are electrolyzer IV curves for two electrolyzer stacks (denoted as EC1 and EC2, respectively) at different temperatures between 20°C and 80°C (at 10°C intervals). The electrolyzer stacks EC1 and EC2 have different numbers of electrolytic cells. The effect of having different numbers of electrolytic cells is shown in N c In the graph, I SC is the short circuit current, and V OC is the open circuit voltage. The graph in Figure 6 shows the following:

[0031] (1) Any given maximum power point V on the photovoltaic IV curve MPP For the appropriate number N c electrolyzer cells may be required. For example, electrolyzer EC1 has too few cells to optimize the use of PV power at a given value of irradiance G.

[0032] (2) The number of electrolyzer cells that is optimal at higher irradiation levels may not necessarily be optimal at lower irradiation levels. That is, the number of electrolyzer cells in electrolyzer EC2 is 1000 W / m 2(Region A is above 1000 W / m, as shown by the good overlap of the curves in the region labeled A in the graph of Figure 6.) 2 It can be observed that the MPP of the PV plant at irradiation is Vmpp(1000), the number of electrolyzer cells in the electrolyzer EC2 is 100 W / m 2 irradiances of 100 W / m may not be very suitable (as shown by the poor overlap of the curves in the region labeled B in the graph of Figure 6). 2 (The equation for Vmpp(100) is the MPP of the PV plant at irradiance. Therefore, at lower irradiance levels, more electrolyzer cells may be required. This may seem counterintuitive, but at low irradiance levels, the electrolyzer cells must operate at a lower current density, i.e., a lower voltage per cell, and therefore, there is a need to have more cells in series.

[0033] (3) The temperature change of the electrolyzer stack is related to the V of the photovoltaic IV curve. MPP This can have a significant impact on the search for MPP, and if the temperature of the electrolyzer stack is different, a different number of active electrolyzer cells may be used to match a given MPP.

[0034] (4) Number of PV panels in series N s can be used to establish an index operating point for the electrolyzer stack, in particular the number of electrolytic cells N c and the number of PV panels in series, N s can be pre-selected to be compatible and produce good overlap in the IV curves of the electrolyzer and the PV plant under most operating conditions of irradiation and temperature.

[0035] It is therefore contemplated that the number of active electrolytic cells may be determined according to one or more of the following:

[0036] (1) The number of active electrolytic cells can be determined based on the variable amount of electrical energy supplied to the cell stack by the electrical energy source. For example, the number of active electrolytic cells can be determined based on the amount of electrical energy supplied to the cell stack at a given operating point of the PV power source (e.g., I MPPT ,V MPPT ) to adapt the electrolyzer to the input voltage (e.g., the total MPP voltage of the PV power source). By "adapt," we mean that the load on the electrolyzer can be optimized to maximize the amount of electrical energy transferred from the PV power source for hydrogen production. In other words, the number of active electrolysis cells can be varied so that the operating voltage of the electrolyzer can be matched to the input voltage (e.g., the total MPP voltage of the PV power source). For example, the number of active electrolysis cells, N, can be varied such that N multiplied by the single cell voltage is equal to the total voltage (V) delivered by the PV power source. MPP ) can be chosen to approximate

[0037] (2) The number of active electrolytic cells may be determined based on the operating conditions of the electrical energy source, such as irradiance levels.

[0038] (3) The number of active electrolysis cells may be determined based on the operating conditions of the electrolyzer, such as the temperature of the cell stack. As used herein, the term "operating conditions" may generally refer to any of a variety of conditions that can be measured or calculated. Operating conditions may relate to the current or real-time environmental or operating state of the device or system being monitored. Thus, operating conditions may include environmental conditions that may affect the operation of the device or system being monitored.

[0039] (4) A maximum power point tracking (MPPT) algorithm can be used to determine the number of active electrolytic cells. The number of active electrolytic cells, N, is an integer, so the MPPT algorithm determines whether only a discrete number of electrolytic cells contribute to the total voltage (V MPP ) can be selected to match the total voltage (V MPPHowever, as the number of active electrolytic cells increases, i.e., as the operating voltage of the electrolyzer increases, the "discrete" MPPT algorithm (I EL ,V EL ) points are selected by the "continuous" MPPT algorithm (I EL ,V EL ) point. That is, as the voltage increases, e.g., above 100 V, the "discretization" effect disappears, and "discrete" MPPT optimization may produce the same optimal results as a "continuous" MPPT algorithm. For example, tests have shown that with a low PV operating voltage of approximately 35 V to 40 V and 23 electrolysis cells, 99.4% of the PV MPPT energy can be delivered to the electrolyzer. This percentage is expected to exceed 99.5% as the operating voltage exceeds 100 V.

[0040] Generally, the systems described herein include a DC source, an electrolyzer, a battery (if present), and switching electronics configured to dynamically switch a variable number of electrolytic cells into and out of an electrical circuit defined by the electrolyzer depending on one or more parameters, such as the policies a user wants the system to implement. A first example of what the systems described herein can achieve is tracking the MPP (maximum power point) of a PV field under any realistic conditions of PV irradiation, PV temperature, and stack temperature without introducing appreciable conversion losses. A second example of what the systems described herein can achieve is dynamically configuring the electrolyzer to share a predetermined allocation of energy from the PV field, while another allocation is sent to a battery-based storage system. In this case, the systems described herein can split renewable energy into two parts as desired by the user. A third example of what the systems described herein can achieve is maintaining a constant amount of energy sent to the electrolyzer, while excess energy is stored in a battery for later use.

[0041] Exemplary Electrolyzer Configurations

[0042] Referring to FIG. 7, the components of an electrolyzer stack typically include a membrane electrode assembly (MEA), bipolar plates, compression plates, and current collectors. The MEA forms the core of the electrolysis cell. Multiple MEAs can exist within a stack. For example, the electrolyzer stack shown in FIG. 7 includes two MEAs and can therefore be referred to as a two-cell electrolyzer stack. Generally, an MEA includes a porous or ionomer membrane, a catalyst, a porous layer, gas and water flow ducts, and both electrodes (anode and cathode) without external connections. Adjacent MEAs are electrically coupled within the stack by bipolar plates, so that the anode of one MEA is in electrical contact with the cathode of the adjacent MEA (or vice versa). The bipolar plates further have water and gas flow ducts to enable the multi-cell stack to operate as a single electrolyzer stack. The stack is terminated with metal compression plates, which are used to apply pressure to the internal elements. Compression can be achieved by tightening multiple threaded rods (not shown) that run along the length of the stack. The stack can have metal plates called current collectors, which have electrical contacts to an external circuit to power the cells. Typically, electrolyzer stacks have only two current collectors. Current collectors are usually monopolar plates, which are thicker than bipolar plates because they must transfer all of the stack current to the external electrical contacts, while bipolar plates transfer current from one cell to the adjacent cell. Gaskets (not shown) are interposed between each element to ensure gas / water tightness and electrical insulation, as needed. Gaskets can be made of rubber, plastic, elastomer, etc. It should be noted that stacks of polymer electrolyte membranes (PEMs), anion exchange membranes (AEMs), and alkaline water electrolyzers (AWEs) can have similar configurations.

[0043] Figure 8 shows a schematic of how a conventional bipolar plate forms an electrical contact between the cathode (-) of one MEA and the anode (+) of an adjacent MEA. Generally, bipolar plates are not accessible from outside the cell stack for power supply purposes. Rather, each end of the electrolyzer stack has a monopolar plate, which is a single electrode contact. For example, the electrolyzer stack shown in Figure 8 has an end plate (anode) on the left and an end plate (cathode) on the right. The anodes and cathodes at both ends of the stack should not be confused with the anodes and cathodes of the MEAs. The monopolar plates are thick enough to carry the total current sent to the electrolyzer. The current flowing through the entire electrolyzer is the sum of the current I flowing through each individual cell connected in series. cell The voltage of the electrolyzer stack U stack is the individual voltage U of all cells cell is the sum of

[0044] Figure 9 shows a schematic of a typical electrolyzer stack with different numbers of electrolyzer cells. A one-cell electrolyzer stack has one MEA, an anode at one end of the stack, and a cathode at the other end of the stack. This stack does not have bipolar plates. Two-cell and four-cell electrolyzer stacks have two and four MEAs 104, respectively, and one anode and one cathode located near the compression plate, i.e., two current collectors. This means that the number of active electrolyzer cells is fixed, all electrolyzer cells are active, and the same current flows through them all.

[0045] It should be noted that actual electrolyzers are more complex than those shown in the previous figures and may include additional elements such as porous transport layers (PTLs) and gas diffusion layers (GDLs) through which H and O gases may diffuse after separation. Furthermore, bipolar plates and end plates may have the additional function of guiding fluids or gases within the stack and are therefore often referred to as flow field plates to emphasize this particular function. For convenience and to avoid unnecessary complexity, the PTLs and GDLs may be considered part of the MEA shown in the previous figures.

[0046] The electrolytic cells described herein may be equipped with additional (internal) current collectors to allow for external control of the number of active cells. Thus, the electrolytic cells described herein may be "dynamically sized" cells where some of the cells are active and some of the cells are inactive by bypassing the cells using an external switch.

[0047] FIG. 10 schematically illustrates an electrolyzer 102 comprising a single-cell stack with an intermediate electrical contact 103 disposed between a cathode 105 at one end of the stack and an anode 107 at the other end of the stack. As one example, the intermediate electrical contact 103 may be disposed on a bipolar plate so that the bipolar plate also functions as a current collector. Existing bipolar plates may be modified to provide this additional function. As another example, the intermediate electrical contact 103 may be disposed on a "dedicated" current collector disposed between two bipolar plates. This may provide a robust path for current toward the external electrical contact. Such a "dedicated" current collector may be different from a current collector located near the end plate because it may ensure continuity of the liquid / gas flow paths (pipes) within the stack. The intermediate electrical contact 103 and the anode 107 are connected to a circuit 112 comprising one or more switches. The cathode 105 is connected to switch SW0. Therefore, the intermediate electrical contact 103, the cathode 105, and the anode 107 are also referred to herein simply as "electrical contacts" that may be connected to an external circuit. Generally, the term "circuit" refers to a combination of several electrical devices and conductors that, when interconnected to form a conductive path, perform some desired function. The term "switch" broadly encompasses any device for making, breaking, or changing a connection in an electrical circuit. When a switch opens or closes, it breaks a connection or makes a connection, respectively. Examples of switches include diode and transistor structures, electromechanical switches (e.g., relays), etc.

[0048] As shown, the circuit 112 comprises three switches SW1, SW2, SW3 connected in parallel to the three intermediate electrical contacts 103, i.e., one switch is provided for each intermediate electrical contact 103. A controller (not shown) selectively drives the switches SW1, SW2, SW3 to electrically disconnect or connect one or more of the electrolysis cells 104 to the cell stack (i.e., to the active electrolyzer circuit), thus enabling a "variable length" electrolyzer stack to be realized in a simple manner. For example, when the switch SW1 is "closed," current circulates through the lowest resistance path of the closed switch SW1, thus bypassing the electrolysis cells 104 electrically connected in parallel to the switch SW1. By selectively opening and closing the switches SW1, SW2, SW3, a variable number of active electrolysis cells 104 can be formed. This variable number of active electrolysis cells can be used to adapt the operating characteristics of the electrolyzer 102 to a renewable energy source 114 (which may be a PV field generator or any other DC source whose voltage is compatible with the stack adjustment interval). The variable (switchable) electrolysis cells can act as a variable load, which can compensate for PV array (I,V) variations depending on temperature and irradiation, and can also compensate for different stack temperatures. Here, S0 is a general switch used to activate / deactivate the entire electrolyzer stack 102.

[0049] FIG. 11 schematically illustrates an electrolytic cell 102 with multiple electrolysis cells, including a first substack 108 electrically connected in series to a second substack 110. As used herein, the term "substack" generally refers to a portion of a cell stack (i.e., a group of electrolysis cells) having an anode at one end of the substack and a cathode at the other end of the substack. It will be understood that the terms "substack" and "group of cells" may be used interchangeably in some cases. In other cases, a "substack" may include a "group of cells." For example, the first substack 108 does not have an intermediate electrical contact, making the first substack 108 equivalent to a group of cells. The second substack 110 includes two intermediate electrical contacts 103, as described above with respect to FIG. 10, making the second substack 110 equivalent to a group of cells (three groups of cells). Additionally, the first substack 108 may be referred to as a "fixed" substack because it provides a fixed number of active electrolysis cells 104 to the cell stack 102. The second substack 110 may be referred to as a "variable" substack because it provides a variable number of active electrolysis cells 104 to the cell stack 102.

[0050] The intermediate electrical contacts 103 of the second substack 110 can be positioned to define multiple cell groups according to a "binary rule" approach to minimize the number of power switches (contactors) required. This will be explained in more detail later, but by way of example, the cell groups constituting the second substack 110 can include 1, 2, 4, 8, and 16 cells, respectively, i.e., a total of five cell groups and six external contacts. This means that the second substack 110 can be dynamically configured to have any active cell size within the [0...31] cell range. This configuration has the advantage that the second substack 110 can be provided as an "add-on" device (with all necessary electrical contacts) to an existing electrolyzer stack with a fixed number of cells.

[0051] FIG. 12 schematically illustrates an electrolytic cell 102 comprising a first (fixed) substack 108 and multiple second (variable) substacks 110. The substacks 108, 110 are electrically connected in series. A circuit 112 is connected to the cathode 105 and anode 107 of the second substack 110 (as well as the anode 107 of the first substack 108). Thus, the cathode 105 and anode 107 of the substack 110 may function as electrical contacts. However, any of the substacks 110 may include additional intermediate electrical contacts, as described above with respect to FIGS. 10 and 11. The number of substacks 110 may depend on requirements such as the ability to adjust the number of active cells with fine granularity (e.g., to one-cell accuracy). Having more substacks may increase cost and complexity in terms of electricity, water, and gas plumbing. On the other hand, having more substacks can also add redundancy, since, for example, if one of its cells is damaged, the entire substack can be bypassed.

[0052] The proportion of electrolysis cells 104 in a substack 110 may comprise approximately 15% to 20% of the total number of electrolysis cells 104 in the electrolyzer 102. The precision of regulation in the substack 110 increases as the operating voltage increases. As an example, as described above, for an operating voltage of 100 V corresponding to approximately 60 electrolysis cells 104, a "discrete" MPPT algorithm may have an efficiency of approximately 99.5%, while for a voltage of 400 V, this efficiency may increase to over 99.7%. The PV array voltage and electrolyzer operating voltage and regulation range may be predetermined to improve compatibility.

[0053] It will be understood that the number of electrolysis cells shown in Figures 10-12 is exemplary only, and the number of electrolysis cells that may be electrically disconnected from the cell stack may be one or any larger number.

[0054] It will be appreciated that the electrolytic cell 102 can be any type of acidic or alkaline electrolytic cell, provided that it is made up of a number of electrolytic cells (plates), some of which have directly accessible electrical contacts to their internal electrodes.

[0055] Binary Grouping

[0056] 13 and 14, the cells 104 may be grouped so that they can be switched on and off in a "binary" manner. Such binary grouping may minimize the number of switches required while maintaining single-cell adjustment accuracy. As shown in FIG. 13, the variable-cell electrolyzer 102 includes a first substack 108 (only one shown) having two electrical contacts (anode and cathode) at each of the input and output, and multiple second substacks 110, each having electrical contacts (anode and cathode) at both ends. As mentioned above, the first and second substacks 108, 110 may be conveniently referred to as a fixed substack and a variable substack. In this example, the variable substack 110 includes four switchable electrolysis cell groups, each having one, two, four, and eight cells. The circuit 112 may include four switches S1, S2, S4, and S8 corresponding to the four switchable cell groups.

[0057] In operation, when all bypass switches S1, S2, S4, and S8 are closed, the variable substack 110 is completely bypassed by current. Cells can be inserted into the current path by placing the corresponding switches in the open position. In this example, different open / close combinations of switches S1, S2, S4, and S8 can result in any combination of 0 to 15 cells (i.e., 2 4 = 16 combinations). (Generally, 2 for N switches. N(There are possible combinations.) Some of the different combinations of switch states for circuit 112 are shown in FIG. 14. The label "EC" indicates the corresponding number of active cells. For example, in the state corresponding to EC=1 (one active cell from the variable substack 110), switch S1 is open and switches S2, S4, and S8 are closed. This causes current from output electrical contact 118 to bypass groups 2, 4, and 8, resulting in only group 1 being active. Similarly, in the switch state corresponding to EC=5 (five active cells from the variable substack 110), switches S1 and S4 are open and switches S2 and S8 are closed. This causes current from output electrical contact 118 to bypass groups 2 and 8, resulting in only groups 1 and 4 (substacks) being active. As another example, in a switch state corresponding to EC=14 (14 active cells from the variable group 110), switches S2, S4, and S8 are open and switch S1 is closed. This causes current from the output electrical contact 118 to bypass the 1 cell group, resulting in the 2 cell group, 4 cell group, and 8 cell group (sub-stack) being active. Thus, when the bypass switch is closed, the current flows through the closed low resistance switch (a short circuit with a sub-milliohm resistance) instead of across the electrolyzer cell group (sub-stack), thereby bypassing (i.e., removing) the corresponding cell group (sub-stack) from the electrolyzer circuit.

[0058] It will be appreciated that other cell grouping combinations can be used to arrive at the desired total number of switchable cells and reduce the number of switches. For example, if the total number of switchable cells required in the electrolyzer is low, the group with the largest number of cells, i.e., 2 (N-1)The groups can be smaller than those calculated by the binary rule: for example, instead of having four groups with 1, 2, 4 and 8 cells respectively, four groups with 1, 2, 4 and 4 cells respectively, or 1, 2, 4, N cells (N=1...7) respectively, can be provided, provided that this number of cells is sufficient for electrolyzer voltage regulation purposes.

[0059] Multiple electrolyzers in series or parallel

[0060] The electrolyzer cell switching architecture described above can be further improved if, instead of a single electrolyzer of rated power, two (or more) electrolyzers are provided, which can be electrically connected in parallel or in series by a controller depending on the operating conditions of the overall system.

[0061] STC (standard test conditions) at 25°C and 1000W / m 2 Under normal irradiation of V OC Consider a PV panel with (1000)=50V. V OC has a positive logarithmic dependence on irradiance (i.e., increases with increasing irradiance) and is 2 to 100 W / m 2 When it comes to irradiation, V OC This indicates a 10% loss of voltage, so V OC (100) = 45. Since the MPPT system must maximize the power output P = V × I, Vmpp is always V for a given exposure. OC is lower than I, which by definition OC V when =0 OC Vmpp(1000)=41.V, which means V OC Although 18% lower than 25°C, Vmpp(100) can be as low as 37 V. The voltage of a PV panel for temperatures different from 25°C is given by "V OCThe temperature coefficient of the electrolyzer cell switching system may be calculated using the "temperature coefficient of V" with typical values ​​of -0.25% / °C to -0.30% / °C. If the PV panel operates in the range of -10°C (low sun, cold winter) to +80°C (high level irradiation, hot summer), the electrolyzer cell switching system may be able to compensate for voltage variations relative to the STC corresponding to cold winter (-35°C) negative variations and hot summer (+55°C) variations; these variations are expressed as V OC Add 3.5V to V OC This corresponds to subtracting 5.5 V from the voltage. The following principles can therefore be relevant for direct coupling with an electrolytic cell:

[0062] (1) The current is proportional to the solar irradiation, and the voltage increases only logarithmically.

[0063] (2) Temperature increase has a significant effect on PV voltage, decreasing the voltage linearly with temperature up to 85°C-90°C, which is the maximum temperature allowed for PV panels.

[0064] (3) An increase in temperature linearly increases the current, but the coefficient is smaller than that of voltage, so power P = V × I decreases with temperature.

[0065] A typical PEM electrolyzer operates at 1.6 V / cell at low loads (10% of rated power), 2 V / cell at 100% load, and intermediate voltages at intermediate loads. This means that to match a given input voltage, more electrolyzer cells are needed at low input currents and fewer cells at high currents. Another effect to consider in PV fields is temperature. At high levels of solar irradiance, this is typically associated with high ambient temperatures, and in any case, the panels themselves heat up several tens of degrees above ambient. High PV temperatures reduce the PV voltage, inevitably resulting in suboptimal utilization of the electrolyzer when coupled to a PV plant, since the effective power (at a fraction of the cells) is lower than the rated electrolyzer power (using all the cells, which is impossible). Therefore, at high temperatures, the PV voltage is lower than at lower temperatures. However, high levels of irradiation always result in high PV panel temperatures (except in exceptional conditions when high levels of irradiation are combined with cold, strong winds that cool the panels), so high levels of irradiation are almost always combined with partial utilization of the cell stack.

[0066] As an example, a practical PV electrolyzer system may have at least two PV panels connected in series, with a total V OC = 100 V. The problem of underutilization of the stack with the PV source may be unavoidable with a single stack, but can be greatly improved with two stacks, i.e., a modular electrolyzer, where the electronic switching system has the option to use cells from both stacks in series when solar energy is low, and both stacks in parallel when solar irradiation is at high levels.

[0067] The above-described system can be adapted to drive multiple electrolyzers connected to a single renewable power source and to dynamically modify the electrical topology to maximize system performance and minimize costs. In particular, having two or more electrolyzer stacks that can be connected in series or parallel depending on operating conditions may provide one or more of the following advantages:

[0068] A typical electrolyzer stack will operate at a lower voltage per cell when the current is low, or in other words, when the electrolyzer load factor is low. Under insufficient load conditions, the stack efficiency is maximized because the operating voltage of the cells is close to the thermal neutral voltage of 1.481 V. As the current increases, the cells operate at higher voltages and lower efficiencies. Some indicative values ​​of the voltage-current characteristics of a typical electrolyzer are shown in the table below. It can be observed that the maximum efficiency of the stack does not necessarily map to the highest efficiency of the entire system, and parasitic loads, such as the energy required to operate a cooling system, can shift the optimum point away from the minimum current. A typical electrolyzer can be operated up to 110% or 120% of its rated load without damage, but obviously, the voltage per cell will increase further and the efficiency will decrease further. [Table 1]

[0069] Each one is V OC Consider a solar PV string driving an electrolyzer system made from 500 W half-cell monocrystalline PV panels characterized by typical characteristics of V = 50 V, Vmpp = 41 V, and Impp = 12.2 A. Using 20 such panels connected in a 2s10p configuration (2 panels in series, 10 pairs of panels in parallel), V OC A 10 kW plant is obtained operating at a nominal voltage of =100 V and Vmpp=82 V, capable of a maximum current of 122 A. There are at least three alternative configurations for attaching electrolyzers to such a PV string.

[0070] (1) One electrolyzer operated by conventional power electronics with a rated current of 120A.

[0071] (2) One electrolyzer rated at 120 A current and operated by the cell switching electronics described herein.

[0072] (3) Multiple smaller electrolyzers operated by the cell switching electronics described herein, for example, two smaller electrolyzers each having a maximum current rating of 60 A.

[0073] First, the electrolyzer "length" (i.e., the number of cells required) for both the large electrolyzer and multiple small electrolyzers in these three configurations is verified. The stack operating voltage depends on both solar irradiance and PV panel temperature. There are other dependencies, such as stack temperature, but these are not considered here to keep the example simple, and in any case, they do not significantly modify the final conclusions.

[0074] Table 2 below shows the 2 (100% load), 500W / m 2 (50% load), and 100W / m 2 The table shows the number of cells required to accurately match the PV field Vmpp at different operating conditions, from -20°C to +90°C for different solar irradiations (10% load) and PV panel temperatures. OC Temperature dependence of I SC Temperature dependence of V on solar irradiation OC The model is constructed using all parameters of a typical PV panel, including the dependence of the electrolyzer cell operating voltage on three different loads. As mentioned above, stack temperature is not considered for simplicity, but may be considered in practice. Note that the number of cells shown in the table is a decimal that can be calculated and rounded to the nearest integer value. [Table 2]

[0075] The design temperature interval for the PV panel is chosen as a subset of the table values ​​in the range [-10...+80] °C. It can be observed that when the load is 10% and the PV panel temperature is very low at -10 °C, corresponding to an extreme winter, the maximum number of cells is required, i.e., 53 cells. Low load is synonymous with low solar irradiation and low current circulating in the cells.

[0076] Conversely, the minimum number of cells required to match the MPP of the PV string, i.e., 35 cells, corresponds to the maximum current and maximum temperature of the PV panel of 80°C.

[0077] Finally, it can be observed that certain combinations of load and temperature in the table are extremely rare or short-lived, i.e., 1000 W / m 2 High levels of solar irradiation at -10°C will heat the PV panel several tens of degrees Celsius above ambient temperature, so it is not possible to have a PV panel at -10°C and full power output for more than a few minutes. The same is true for the right side of the table, where irradiation is 100 W / m². 2 If this is the case, the PV panel will cool down to the ambient temperature quickly and will not be able to stay at 80°C for a long time.

[0078] Figure 15 compares a conventional fixed plate electrolyzer driven by a DC-DC converter with an electrolyzer 102 in which direct connection to the electrolyzer cells is made by a switching circuit 112. Options (1) and (2) are analyzed.

[0079] As shown in the top part of Figure 15, when a single electrolyzer is coupled to conventional power electronics such as a controlled rectifier that is ultimately coupled with a buck or boost converter, the fixed number of plates is approximately 45. This number ensures adequate coupling efficiency at the average operating conditions of the PV field, but results in significant losses when operating at full irradiation (100%), where fewer cells are more suitable, as well as when operating at low levels of irradiation (10%), where more cells are required (see Table 2 above).

[0080] When a single electrolyzer is combined with the switching electronics described herein, it does not introduce losses, but the stack is slightly longer than conventional electronics and has 52 switchable cells instead of 45 fixed cells. This ensures an "ideal" combination with a wide range of operating conditions and can handle a PV panel temperature range of [-10...+80]°C.

[0081] Recall the observation noted with respect to Table 2 that certain combinations of temperature and load are unlikely. The present disclosure contemplates the use of two smaller 60 A stacks instead of a single larger 120 A stack; this may allow a series connection of the two stacks to be used in conditions of low load and low temperature, while a parallel connection may be used in conditions of high levels of solar irradiance and high PV temperature. The required length of the stack and the number of cells required will be evaluated below to determine whether there is an advantage to doing so.

[0082] FIG. 16 shows how the cell switching architecture described herein can be applied to two smaller stacks (40 cells each, 60 A) instead of a single stack (52 cells, 120 A). Assuming the system is at 10% load and the PV temperature is 10°C, Table 2 shows that the correct number of cells is 50. The controller 120 can easily configure this number of cells by connecting two electrolyzer stacks in series. The modification for multiple electrolyzer stacks is to add an auxiliary switch SW-AUX to control the insertion / removal of the largest group of cells (27 cells) from each stack 102. For solar irradiation below 50%, the system processor typically uses a "series connection" of two stacks 102. When there are many cells to insert / remove from the current path, the series connection can track the MPP of the solar PV even at very low loads, such as 5%, or at extremely low temperatures. The reduced membrane area of ​​the 60A stack 102 limits the crossover problem and allows hydrogen production to remain active even at low irradiation levels.

[0083] When illumination exceeds 50% and the current exceeds the 60 A limit, the switching electronics reconfigure the electrical connections and operate two smaller stacks 102 in parallel, thereby doubling the managed current to 120 A. Under high illumination conditions, the PV panel heats up, making it virtually impossible for the PV panel to have a low or negative temperature, which significantly limits the number of cells that can be switched on and off. Also, the current is consistently within the 60 A to 12 A range, so the electrolyzer voltage range is also limited to a narrow range (1.8 V to 2.0 V). This allows for the creation of shorter stacks with 40 plates, sufficient to track the MPP of solar PV cells under high illumination and high temperature conditions. As another example, Figure 17 shows a configuration with two stacks connected in parallel, both consisting of 38 of the 40 active cells, corresponding to 100% illumination and a temperature of 50°C.

[0084] It is important to note that for clarity, Figures 16 and 17 separately show series and parallel connections of electrolyzers 102. The system may include additional circuitry (e.g., nodes, connections, switches, etc.) not shown in these figures that allows the electrolyzers 102 shown in each of these figures to be selectively connected in series or parallel, i.e., switching circuitry for switching the connections between the electrolyzers 102 from a series connection to a parallel connection and vice versa.

[0085] In summary, the advantages of a parallel / series configuration of two smaller stacks using the switching architecture described herein instead of a single larger stack may include one or more of the following:

[0086] (1) A smaller cell stack (e.g., two 60A stacks) requires fewer plates than a single stack (e.g., 40 versus 53 for a single stack).

[0087] (2) There may not be a significant cost increase for using multiple smaller cell stacks with half the current plates compared to the cost of a single stack.

[0088] (3) Multiple stacks can increase redundancy, allowing the hydrogen plant to continue operating even if one stack fails, and facilitating maintenance of a single stack.

[0089] (4) A series configuration in which multiple cells are switched on and off may enable lossless tracking of the MPP even at very low levels of solar irradiation and solid-state temperature.

[0090] (5) The reduced membrane area of ​​smaller cell stacks may make it possible to operate PV plants even at low levels of irradiation (e.g., 5% of rated system power) without significant hydrogen crossover problems.

[0091] (6) The switching architecture can manage two or more stacks in a series / parallel combination, allowing for gradual upgrades of plant capacity and facilitating the development of low-cost modular stacks.

[0092] (7) Stacks with different power and various numbers of plates can be combined into an EC pool, preserving previous investments.

[0093] (8) With multiple stacks operating in series / parallel and controlled by the same controller, it is possible to scale up the plant size to very large powers (>10 MW) easily and without managing too high currents in each switch.

[0094] It is to be understood that there can be two or more electrolyzers connected to the DC energy source, preferably an even number which can be connected in parallel.

[0095] FIG. 18 shows an exemplary system comprising an electrolyzer 102 and control electronics 119. The control electronics 119 may comprise a controller 120 that may be configured to define and maintain an optimal operating point for the electrolyzer 102. In particular, the controller 120 may dynamically adjust the load of the electrolyzer 102, i.e., the operating voltage, current, and power of the electrolyzer 102, to achieve different objectives, such as (i) tracking the MPP of the power source 114 to maximize the extracted energy, (ii) defining the proportion of renewable energy that is sent directly to the electrolyzer 102 and the proportion that is sent to a storage system (not shown) for later use, and (iii) adjusting the rate of power extraction from the storage system to reach a target number of hours of use of the electrolyzer 102. The second and third objectives are described below with reference to FIG. 19. In general, the controller 120 may achieve these objectives by selectively commanding the switches SW1, SW2, SW3 of the circuit 112 to activate / deactivate cells (plates) in the corresponding cell group 110 of the electrolyzer 102.

[0096] The controller 120 may receive, measure, calculate, or otherwise obtain data regarding the operation of the electrolyzer 102 and / or the PV power source 114. For example, the controller 120 may measure the current / voltage (in the figure, "V PV " and "I PV ") and measure the MPP value(s) (indicated as "V MPP " and "I MPP ") and / or obtain or calculate the electrolyzer input and / or output water temperatures from temperature sensors (generally indicated as "T Ein " and "T Eout ", specifically "T E11 " and "T E21"). Based on one or more of these values, the controller 120 may determine the number of active electrolytic cells in the electrolytic bath 102. The controller 120 may output one or more signals (commands) to the circuit 112 to activate / deactivate the variable cells 110 of the electrolytic bath 102 using the switches SW1, SW2, SW3 (e.g., as described above with respect to Figures 10-12) to adjust the operating point of the electrolytic bath 102 in terms of voltage, current, and power.

[0097] 18, circuit 112 includes electromechanical switches SW1, SW2, SW3 operated by a magnetic coil 124 via an actuator 122. However, any suitable switch technology may be used, including, for example, solid state switches such as MOSFETs, IGBTs, and other power semiconductors.

[0098] M PP The voltage is determined by the irradiation conditions and the PV panel temperature (in the figure, "IRR" and "T PV "). Their values ​​may be sensed differently, for example, by connection to the PV power source 114, or by using a reference PV power source 128 and a reference MPPT electronic load 126 (shown in FIG. 18). Alternatively, they may be emulated using irradiance and ambient temperature sensors. However, connection to the PV power source 114 may be advantageous because it can take into account environmental conditions, such as wind conditions, that may affect the temperature of the PV panels of the PV power source 114.

[0099] The controller 120 may perform a "hill climbing" type optimization by modifying the number of active electrolyzer cells in small increments to maximize the power absorbed by the solar field. The controller 120 may also be configured to perform auxiliary functions such as obtaining predictions regarding the energy production of the PV array 114 to optimize energy management policies, transmitting operation data, performance data, and / or alarm data to external systems.

[0100] By way of example and not limitation, for hydrogen production at a 240 kW to 20 MW scale, the operating voltage of the electrolyzer 102 may be in the range of 120 VDC to 1000 VDC, the switch current may be in the range of 1,000 amps to 10,000 amps, and the number of switches N may be 4 to 7 depending on the operating voltage of the stack, as shown in the table below. A number of switches N=7 allows for the insertion / removal of 0 to 127 plates from the stack, which corresponds to a voltage regulation interval of 256 V and is more than enough to regulate a 1000 VDC stack. Smaller stacks have N=4 or N=5 switches, as shown in Table 3 below. [Table 3]

[0101] This means that even for very large plants, the switch SW [1...N] This means that the switch SW corresponding to the variable cell group 110 can be operated at a relatively low voltage difference, a favorable condition for reducing arcing problems that can deteriorate the contacts. For clarity, FIG. 18 does not show the switch S0 of FIGS. 10-12, but this can be provided as a general switch in the form of a high-voltage contactor. However, it is expected that the switch S0 will be largely inactive, for example, when taking the entire electrolyzer 102 offline. On the other hand, the switch SW corresponding to the variable cell group 110 [1...N] can be operated more frequently and therefore can be implemented using solid state switches based on MOSFETs.

[0102] It will be appreciated that the system shown in Figure 18 may use other types of power sources, such as wind power. For example, the operating point of a wind turbine may be defined by the wind speed Vw, the blade pitch angle θ, and the rotor speed Ω. The controller 120 may determine the number of active electrolytic cells accordingly.

[0103] 19 , the system described herein may support the use of a battery unit 136 to store electrical energy generated by the power source 114 for later use by the electrolyzer 102. In the system shown, the task of tracking the MPP of the power source 114 to maximize the extracted energy may be delegated to an MPPT charge controller 134, which may further ensure that the battery unit 136 is charged at the correct voltage. Meanwhile, the controller 120 may regulate the load on the electrolyzer 102. The controller 120 may also adjust the amount of renewable energy diverted to the battery unit 136 and / or schedule the use of energy stored in the battery unit 136 by the electrolyzer 102. For example, during the day, the controller 120 may determine the amount of energy to be immediately used by the electrolyzer 102 and the amount of energy diverted to the battery unit 136, and during the night, it may regulate the discharge rate of the battery unit 136 to the electrolyzer 102. The battery unit 136 may therefore be used to maintain a controlled and uniform current density in the electrolyzer 102, for example to reduce or eliminate the periods when the electrolyzer 102 is offline and / or to reduce dynamic fluctuations in current when it is online. Operating the electrolyzer 102 at a controlled, approximately constant current can significantly extend its lifespan, as the wear effects associated with using the electrolyzer in highly dynamic conditions can be reduced or eliminated. Of course, it will be understood that the functions of the MPPT charge controller 134 and the controller 120 can be performed by the same controller.

[0104] The battery unit 136 may include a battery management system 140 configured to continuously check the battery cells (1...N) and maintain them within the correct voltage / current operating range. The battery management system 140 may also implement different safety mechanisms to protect the battery unit 136 from improper users, external equipment malfunctions, and to extend its lifespan. An active balancer 138 may be used to equalize the state of charge (SoC) of each cell (1...N). The battery unit 136 may further include a coulomb meter 142 and a shunt 144. The coulomb meter 142 measures the voltage and current (in the figure, "V"). BAT " and "I BAT Any suitable battery technology may be used, such as a lithium LFP battery.

[0105] The system in Figure 19 can use wind, grid, and / or PV power. In the case of a combination of wind and solar power, the wind voltage can be matched to the current battery level using an AC-DC converter (if the wind turbine generates AC) or a DC-DC converter (if the wind turbine generates DC). For example, a wind turbine generating AC can be introduced into the system by adding a three-phase rectifier, a leveling circuit (capacitance, inductance), and multiple DC-DC high-voltage chargers in parallel to match the leveled DC current to the battery voltage. This is the same architecture that can be used for PV power sources, and it is simple and scalable.

[0106] Some advantages of having power storage may include: The electrolyzer 102 may be smaller because the battery unit 136 may provide the ability to operate 24 hours per day using a PV power source that typically only harvests energy for 6 to 12 hours per day, depending on the season and country. Furthermore, the battery unit 136 may compensate for fluctuations in the PV power, and therefore the electrolyzer 102 may be powered with an approximately constant current. Also, it may be easier to integrate multiple power sources.

[0107] Referring now to Figure 20, PEM electrolyzers can be subject to a problem known as "hydrogen crossover" (also known as permeation or diffusion), i.e., the unwanted diffusion of H2 gas through the membrane from the anode to the cathode. This has been identified as one of the main causes of degradation of the perfluorinated ionomer membranes (Nafion) typically used in PEMWEs and PEMFCs. Hydrogen crossover increases with increasing battery temperature, pressure, and humidity. Hydrogen crossover can result in lower conversion efficiencies, require the addition of catalysts to recombine the permeated H2 with local O2 to produce water, or lead to the generation of highly corrosive peroxide radicals that cause degradation of both the PEM and the catalyst layer, or can result in currents of 10-20 mA cm after prolonged operation. -2 This can result in hydrogen permeation rates in excess of the typical hydrogen permeation rate through very thin PEMs, typically 1 mA cm -2 The last point is that aged thin (e.g., 57 μm) Nafion membranes can be used in PEM stacks with low current densities (0.5 A / cm) without causing significant hydrogen crossover problems. 2 This may be relevant because the current density is less than 500 mA / cm 2 If lower, the permeation H2 is about 10 mA / cm 2 , which corresponds to a current of 500 mA / cm 2 In this situation, the proportion of H can reach 2% of the H₂O₂ mixture, which is not far from the 4% limit.

[0108] H2 molecular diffusion through Nafion membranes can occur in both dry and hydrated PEMs, but hydration makes the process more effective. Nafion is an ionomer (a polymer made from ions) used in PEM cells to separate electrodes while allowing proton (H+) flow. The H2 diffusion problem is independent of the H2 / O2 side pressure differential but is inversely proportional to the membrane thickness; thinner, hydrated PEM membranes are at their worst, with more hydrogen molecules diffusing to the other side. On the other hand, thinner Nafion membranes also have lower overpotentials (better voltage performance). Therefore, a difficult trade-off exists in PEMs: using thinner membranes is desirable to improve cell performance, but this makes the H2 diffusion problem unmanageable, risking the waste of significant PV power during periods of low-level irradiation. The H2 diffusion of other membrane types, such as Zirconium and anion exchange membranes (AEMs), is typically 1 / 20 to 1 / 40 times slower than that of Nafion membranes. However, even with these membranes, hydrogen crossover can be a problem.

[0109] When power is removed from the electrolyzer, there is no production of H2 and O2, while the permeation mechanism remains active. This situation can become critical in the anode compartment, where the existing O2 gas is gradually diluted by H2 gas diffused from the cathode compartment. In the absence of an electric field, these H2 molecules have no way to return to the cathode, and therefore the proportion of H2 in O2 gradually increases, eventually exceeding the 4% explosive limit. The abundance of H2 in the O2 environment and favorable pH conditions can lead to the formation of peroxides and chemical attack on the PEM membrane or the entire MEA. Another condition that can lead to corrosion and oxidation is the sudden change in potential that occurs upon sudden interruption of the DC voltage to the electrolyzer.

[0110] The systems described herein may incorporate a voltage source configured to apply a conditioning or polarization voltage to a single cell, a group of cells, or an entire electrolyzer stack when they are not in use, or before / after they are in use. This possibility may be useful not only for PEM electrolyzers, but also for AWE and AEM electrolyzers. For example, the polarization voltage may be a constant maintenance voltage. For example, a constant maintenance voltage in the range of 1.0 V to 1.5 V per electrolysis cell (i.e., approximately U REV A reversible water dissociation voltage (=1.229 V) can be applied for long periods of time. This can reduce corrosion and passivation phenomena, control hydrogen diffusion, extend the life of the electrolyzer cell, and limit pH changes within the cell. Applying a small polarization voltage in the range of 1.0 V to 1.5 V may hinder diffusion and return some of the H+ protons to the cathode side. The purpose of the polarization voltage applied to unused cells is to maintain good purity of the produced oxygen and hydrogen gas, slow down membrane aging and corrosion, oxidation, and passivation of electrolyzer components, and extend the service life of the electrolyzer with acceptable performance. The presence of the voltage polarization mechanism may be less relevant in AWE and AEM electrolyzers, which are more resistant to hydrogen diffusion. However, AWE and AEM electrolyzers are much more susceptible to corrosion phenomena than PEM electrolyzers due to their non-precious metal electrodes and catalysts. Therefore, ultimately, all electrolyzer types can utilize the voltage polarization mechanism proposed for inactive cells. Another effect of the polarization voltage mechanism can be to limit pH changes in the cathode / anode compartment when the current is removed. These changes certainly occur in PEM cells and lead to partial loss of catalytic performance, the formation of peroxides and other strong oxidizing radicals, attack of the Nafion (PFSA, perfluorosulfonic acid) proton exchange membrane, and corrosion or passivation of conductive metal parts. Controlling pH conditions by applying a regulating (polarization) voltage can control these degradation phenomena and extend the life and performance of the electrolyzer.

[0111] As shown in FIG. 21, when the voltage applied per cell for maintenance is small, for example, 1.0 V to 1.5 V per cell (i.e., the water electrolysis reversible voltage U per cell is approximately 1.229 V), REV ), the corresponding current density is smaller (10 mA / cm 2 less), i.e., there may be an impact on hydrogen / oxygen production and only a minimal impact on the use of externally supplied DC electrical energy.

[0112] 22 shows how the circuit 112 of FIG. 10 can be modified to provide a protection mechanism against the aforementioned problem. In addition to switches SW1-SW3 for deactivating / activating cell groups 1-3, the system includes N+1=4 auxiliary switches SW1-SW3 for applying sustain voltages to each cell group. a , SW1 2a , SW2 3a , and SW3 0a The switch SW0 functions as a contact breaker for the entire stack. a , SW1 2a , SW2 3a , and SW3 0a where "open" means inactive and "closed" means active. This is opposite to switches SW1-SW3, where "closed" means inactive (bypass), i.e., when switches SW1-SW3 are closed, current flows through the low resistance path of the closed switch instead of across the cell, thereby bypassing (deactivating) the corresponding cell group N.

[0113] As shown, the two cell groups are in "maintenance mode," with the V1 maintenance voltage applied to cell group 1 and the V3 voltage applied to cell group 3. Cell group 0 and cell group 2 are both active, with electrolyzer current flowing through them. When a cell group is active, it does not require maintenance. The maintenance voltage V0 can also be applied to cell group 0 (the fixed portion of the stack) when the entire stack is not in use. Circuit 112 of Figures 11 and 12 can be modified in a similar manner.

[0114] Therefore, in essence, auxiliary switches can be installed for each cell group to electrically isolate it from the rest of the stack. Multiple DC sources operating at different voltages can be used to "maintain" the correct voltage within different-sized cell groups. A maintenance voltage can be applied to the entire electrolyzer when not in use to extend its lifespan. The maintenance voltage can be a polarization voltage near 1.23 V per cell (reversible voltage) used to reduce corrosion / passivation phenomena within the cell when it is not active. In this case, the electrolyzer cell can be transformed into a battery cell with a complete polarity reversal, where the cathode becomes the anode and the anode becomes the cathode. With polarity reversal, the internal electrochemical conditions within the cell change drastically, with corrosion and catalyst passivation more relevant for alkaline electrolyzers with non-precious metal catalysts.

[0115] It should be noted that the simple act of shorting a cell or group of cells when they become inactive can provide some protection against polarity reversal and subsequent corrosion. This can occur automatically if unused cells are bypassed by shorting their corresponding relays / contactors. The above methods can also be combined, where, for example, a polarization voltage is applied for a short period to stabilize cell conditions, while permanent shorting of the cells ensures protection against long-term inactivity.

[0116] Therefore, the use of an appropriate regulated voltage may have one or more of the following advantages: The regulated voltage may inhibit or limit changes in the acidic / basic conditions of the cell components when transitioning from an active to an inactive use state and vice versa. This may avoid or mitigate undesirable effects such as corrosion, oxidation, and the formation of aggressive chemicals such as hydrogen peroxide, which may damage the cell components and / or reduce catalytic activity (passivation), ultimately resulting in a shortened electrolyzer lifespan or reduced efficiency. The regulated voltage may address the issue of electrolyzer cell lifetime and significantly reduce gas crossover problems in unused cells or the entire electrolyzer. The gas crossover problem may be more relevant for electrolyzers operating under high pressure (both absolute and differential pressure) and for thinner membranes. The regulated voltage may reduce damage to electrolyzer components resulting from dynamic use conditions, which occurs in renewable energy sources such as PV. The regulated voltage may reduce damage to cell components caused by switching cell components on and off.

[0117] FIG. 23 is a schematic block diagram of the controller 120. The controller 120 may include a processor 150, a memory 152, a communication interface 154, an input interface 158, and an output interface 160. The controller 120 may be configured to perform the operations described below with respect to FIGS. 24 and 25. While the components of the controller 120 are described in some cases using a functional language, it should be understood that specific implementations involve the use of specific hardware. The processor 150 may communicate with the memory 152 via a bus for passing information between the components of the controller 120. The memory 152 may be non-transitory memory and may include, for example, one or more volatile and / or non-volatile memories. That is, for example, the memory may be an electronic storage device (e.g., a non-transitory computer-readable storage medium). The memory 152 may be configured by a programming device 156 to store information, data, content, applications, instructions, etc. to enable the controller 120 to perform various functions in accordance with the examples described herein.

[0118] Processor 150 may be embodied in several different ways, for example, it may include one or more processing units configured to execute independently. Additionally or alternatively, it may include one or more processors configured to cooperate via a bus to enable independent execution of instructions, pipelining, and / or multithreading. Use of the term “processor” may be understood to include a single-core processor, a multi-core processor, multiple processors internal to controller 120, and / or a remote or “cloud” processor. In one example, processor 150 may be configured to execute instructions stored in memory 152 or otherwise accessible to processor 150. Alternatively, or additionally, processor 150 may be configured to execute hard-coded functions. Thus, whether configured by hardware or a combination of hardware and software, processor 150 may represent an entity capable of and suitably configured (e.g., physically embodied as an integrated circuit or other electronic device) to perform operations according to the present disclosure. Alternatively, as another example, if processor 150 is embodied as an execution unit of software instructions, the instructions, when executed, may specifically configure processor 150 to perform the algorithms and / or operations described herein.

[0119] The input interface 158 and the output interface 160 may be any device or circuit, embodied either in hardware or a combination of hardware and software, through which the processor 150 can receive information from and transmit information to external devices. The inputs 157 may be values ​​related to the operation of the electrical energy source and / or electrolyzer and / or power storage device, and the outputs 161 may be signals (commands) for operating one or more switches and / or voltage sources, as described above.

[0120] Communications interface 154 may be any device or circuit, embodied in either hardware or a combination of hardware and software, configured to transmit and receive data from a network and / or any other device, circuit, or module in communication with controller 120. In this regard, communications interface 154 may include, for example, a network interface to enable communication with a wired or wireless communications network. For example, communications interface 154 may include one or more network interface cards, antenna(s), buses, switches, routers, modems, and supporting hardware and / or software, or any other devices suitable for enabling communication over a network. Additionally or alternatively, communications interface 154 may include circuitry for interacting with antenna(s) to cause transmission of signals via the antenna(s) or to process reception of signals received via the antenna(s). These signals may be transmitted by the controller 120 using any of several wireless personal area network (PAN) technologies, such as Bluetooth® v1.0-v3.0, Bluetooth Low Energy (BLE), infrared radio (e.g., IrDA), ultra-wideband (UWB), inductive radio transmission, 3G, 4G, 5G, etc. Additionally, it should be understood that these signals may be transmitted using Wi-Fi, near field communication (NFC), Worldwide Interoperability for Microwave Access (WiMAX), or other proximity-based communication protocols. The communication interface 154 may be used by the controller 120 to receive forecast data and transmit performance, operational, and / or alarm data, as described above.

[0121] Furthermore, computer program instructions and / or other types of code can be loaded into a computer, processor, or other programmable device to produce a machine, such that the computer, processor, or other programmable device executing the code on the machine creates means for implementing various functions, including those described with reference to the components of controller 120. The computer program instructions can be stored in at least one non-transitory computer-readable storage medium (e.g., computer software stored on a hardware device). Exemplary non-transitory computer-readable media can include, but are not limited to, one or more types of hardware memory, non-transitory tangible media (e.g., one or more magnetic storage disks, one or more optical disks, one or more USB flash drives), computer system memory or random access memory (DRAM, SRAM, EDO RAM, etc.), etc.

[0122] Figure 24 shows a flowchart including a series of operations for improved operation of an electrolytic cell. The operations shown in Figure 24 may be performed by, with the assistance of, and / or under the control of, controller 120, for example, as described above. In this regard, performance of the operations may involve one or more of processor 150, memory 152, input interface 158, output interface 160, or communication interface 154.

[0123] As shown in block 10, the processor 150 may determine the number of active electrolysis cells to be used, as described above. This may include, for example, measuring the current / voltage from the electrical energy source, obtaining or calculating the MPP value(s), and / or obtaining the electrolyzer input and / or output water temperature from a temperature sensor. In block 20, the processor 150 may control one or more switches to electrically disconnect one or more switches, as described above. For example, the processor 150 may generate and send a signal to operate a relay in an external circuit, a signal to operate a transistor in an external circuit, etc. For example, with reference to FIG. 18 , a signal may be output to the actuator 122 to actuate the relay 124 to selectively open or close the switches SW1, SW2, and SW3. The operation may include a feedback loop 30 that the controller 120 repeatedly executes in blocks 10 and 20.

[0124] 25 is another flowchart including a series of operations for improved operation of the electrolyzer. The processor 150 may repeat the operations at a given period (e.g., every 10 seconds). In block 170, relevant values ​​are read from the electrical energy source(s) (e.g., voltage, current, power, temperature, irradiance, wind speed, turbine rotation speed, etc.), from the electrolyzer (e.g., temperature), and / or from the battery (e.g., state of charge, voltage). These input values, along with updated forecasts (e.g., next day solar irradiance forecast, weather forecast) and / or updated user policies, become inputs to the processor 150 (block 172).

[0125] In the case of a single electrolyzer stack, the flowchart proceeds to the left branch, and the processor 150 can determine the correct number of electrolyzer cells to use (block 174), for example, to match the MPP of the PV string. Then, in block 176, the processor 150 can activate / deactivate one or more switches to select the correct number of cells to connect in series. For example, the processor 150 can generate and send signals to operate a relay or solid-state device. In particular, with reference to FIG. 18 , a signal can be output to the actuator 122 to activate the relay 124 to selectively open or close the switches SW1, SW2, SW3. In block 178, a polarization voltage can optionally be applied to excluded (inactive) cells.

[0126] In the case of multiple electrolyzer stacks, the flowchart proceeds to the right branch, where the processor 150 can determine whether the current operating conditions require a series or parallel connection of the stacks (block 182). In blocks 184 and 186, internal configuration (number of active cells) can be performed for each stack. The process for each stack can be similar to the process performed in blocks 174 and 176 in the left branch. In block 188, an auxiliary switch set can be used to achieve a series or parallel connection of the stacks depending on the current operating conditions. Optionally, in block 190, a maintenance voltage can be activated on the disconnected cells.

[0127] After the actions for the branch are executed, the processor 150 may wait a predetermined period of time (e.g., 10 seconds) and the procedure may begin again as shown by the feedback loops 180, 192. Of course, other predetermined periods may be implemented.

[0128] 25 operations described for processor 150 may be used in both systems having one stack and systems having multiple stacks connected in individual series or parallel. However, it will be appreciated that processor 150 need not be configured to perform operations for multiple electrolyzer stacks when used in a system having a single electrolyzer stack (and vice versa), i.e. the method may only include operations for one branch, depending on the configuration of the system.

[0129] The electrolyzer architecture described herein can be implemented with a wind turbine generator or battery storage (coupled to any type of renewable energy source, including a wind turbine generator). The wind turbine can have a DC or AC output. For a DC output, the interface to the electrolyzer system can be direct, provided the turbine voltage and electrolyzer voltage are within a compatible range. For an AC output, a rectifier and leveling stage are typically provided, since the alternator is synchronized with the wind and has a variable frequency that differs from the 50 / 60 Hz grid. A DC-AC power converter can be used to convert the leveled DC power to AC power.

[0130] The controller 120 can dynamically modify the electrolyzer configuration for different applications. For example, if all the power from the wind turbine is used for hydrogen production, the controller 120 can adjust the electrolyzer load without DC-DC power conversion and associated losses. If the power from the wind turbine is used for hydrogen production and supplies electricity to the grid, the controller 120 can send a portion of the wind power to the electrolyzer for hydrogen production, and the remainder is converted to AC power (via a DC-AC inverter) and sent to the grid. If an electrical storage device (battery) is installed, the controller 120 can discharge the electrical storage device at a desired rate to the electrolyzer to achieve a desired energy usage policy.

[0131] Without the capital investment savings of a solar PV inverter, the potential savings for wind power applications may be lower than with PV. However, it is still an advantageous solution because there are no conversion losses, the cost of the switching electronics is lower than that of a full-power DC-DC converter and is more reliable, in light wind operation the electrolyzer operates at high efficiency (which is not achievable with electrolyzers with a fixed number of cells coupled to a DC-DC converter), and the switching circuitry can protect against polarity reversal of unused cells or groups of cells at no extra cost.

[0132] As described in Figures 15-17 and the associated accompanying text, the single switchable cell electrolyzer can be replaced with two or more separate (modular) electrolyzers, providing the controller 120 with the option to run them in series or in parallel to match current operating conditions, e.g., to track the MPP of directly connected PV strings. Using multiple electrolyzers instead of a single electrolyzer may have the advantages of better modularity and fault tolerance. However, in the context of the present disclosure, the use of multiple separate electrolyzers may even be advantageous from a cost perspective, considering that they can have a smaller number of cells than a single electrolyzer. That is, in practice, the controller 120 operates two electrolyzers in series (the active number of cells inside each electrolyzer) when the PV plant operates under low-power, low-current, and low-temperature conditions (where more cells are needed to match the MPP of the PV string), while the controller 120 modifies the electrical connection to a parallel connection when the PV string operates under higher-power, higher-current, and high-temperature conditions (where fewer cells are needed to match a different MPP). As shown in Figures 15-17 and the associated text, the size of a single electrolyzer used in a flexible series / parallel combination can be even smaller, i.e., have fewer internal cells, than a fixed-number-of-cell electrolyzer used with conventional, high-cost DC-DC or AC-DC power supplies. From an economic point of view, apart from other advantages, two half-size electrolyzers can be less costly than a single full-size electrolyzer with a larger number of cells over a larger area. A half-size electrolyzer can provide up to 50 W / m 2 ~100W / m 2 It can also operate at very low solar irradiation levels of 1000 kJ / s, in which case a single electrolyser would cease operation as insufficient current density would result in hydrogen crossover problems.

[0133] Numerous other implementations and modifications will occur to those skilled in the art to which this disclosure pertains having the benefit of the teachings presented in the foregoing description and the associated drawings. Accordingly, it should be understood that the present disclosure is not limited to the specific examples described herein, and that modifications and other implementations are intended to be included within the scope of the appended claims. Furthermore, while the foregoing description and the associated drawings describe particular exemplary combinations of elements and / or functions, it should be understood that alternative implementations may provide different combinations of elements and / or functions without departing from the scope of the appended claims. In this regard, combinations of elements and / or functions other than those expressly described above are also contemplated, as may be set forth in some of the appended claims, for example. Although specific terms are used herein, these terms are used in a generic and descriptive sense and are not intended to be limiting.

Claims

1. an electrolytic cell having a plurality of electrolytic cells arranged in a cell stack, the electrolytic cells being electrically connected in series and grouped into two or more cell groups, each cell group having electrical contacts at both ends; an electrical circuit having one or more switches, each switch coupled between the electrical contacts of each of the cells and configured to selectively disconnect the cells from the cell stack by electrically bypassing the cells via a lower resistance path, thereby varying the number of active electrolysis cells in the cell stack; a controller configured to determine the number of active electrolysis cells based on a variable amount of direct current (DC) electrical energy supplied to the cell stack by an electrical energy source, and to control the one or more switches based on the determination; and A system comprising:

2. 10. The system of claim 1, wherein the electrolyzer comprises a single cell stack having a first electrical contact with an anode at one end of the cell stack, a second electrical contact with a cathode at the other end of the cell stack, and one or more intermediate electrical contacts.

3. 10. The system of claim 1, wherein the electrolytic cell comprises a first sub-stack and a second sub-stack electrically connected in series, each sub-stack having a first electrical contact with an anode at one end of the sub-stack and a second electrical contact with a cathode at the other end of the sub-stack.

4. The system of claim 3 , wherein the second substack has one or more intermediate electrical contacts.

5. The system of claim 3 or claim 4, wherein the cell stack comprises a plurality of the second sub-stacks.

6. The system of any one of claims 1 to 5, wherein at least two of the groups of cells have the same number of electrolysis cells.

7. The system of any one of claims 1 to 6, wherein at least two of the groups of cells have different numbers of electrolysis cells.

8. The different number of electrolysis cells is 2 （ｎ－１） 8. The system of claim 7, wherein the eigenvalues ​​are defined by a geometric progression expressed as:

9. 2. The system of claim 1, wherein the system comprises two or more electrolytic cells and respective electrical circuits, and a switching circuit for switching a connection between the electrolytic cells from a series connection to a parallel connection and vice versa, and the controller is configured to control the switching circuit to connect the electrolytic cells in series or in parallel, determine a number of active electrolytic cells for each of the electrolytic cells, and control the respective electrical circuits based on the determination.

10. The system of any one of claims 1 to 9, wherein the source of electrical energy comprises one or more of a renewable energy source or an electrical energy storage device.

11. 11. The system of claim 10, wherein the controller implements a maximum power point tracking (MPPT) algorithm for the renewable energy source in the determination of the number of active electrolytic cells.

12. The system of any one of claims 1 to 11, wherein the controller implements an energy management policy that regulates the amount of DC electrical energy supplied to the cell stack.

13. The decision further states: the operating conditions of said electrical energy source; the operating conditions of the cell stack; or Operating conditions of the electrical energy storage device The system according to any one of claims 1 to 12, based on one or more of:

14. 14. The system of claim 13, wherein the operating conditions of the electrical energy source include one or more of an irradiance level on a solar PV array, a temperature of the solar PV array, and a voltage and current generated by a wind turbine or other type of generator.

15. The system of claim 13 , wherein the operating conditions of the cell stack include a temperature of the cell stack.

16. 14. The system of claim 13, wherein the operating conditions of the electrical energy storage device include one or more of a state of charge (SoC) of the electrical energy storage device or a voltage of the electrical energy storage device.

17. 17. The system of any one of claims 1 to 16, wherein the controller is configured to divide electrical energy between the electrolyzer stack and a separate electrical energy utilization system, and controls the relative amount of electrical energy supplied to each through appropriate determination of the number of active electrolysis cells.

18. 20. The system of claim 17, wherein the electrical energy utilization system comprises an energy storage battery or a grid-tied inverter.

19. 19. The system of any one of claims 1 to 18, wherein the controller is configured to regulate the utilization of energy stored in the battery and pumped into the electrolyzer through appropriate determination of the number of active electrolysis cells.

20. 20. The system of any one of claims 1 to 19, further comprising a plurality of voltage sources configured to provide a sustaining voltage across the disconnected group of cells or cell stack when not in use.

21. 21. The system of any one of claims 1 to 20, wherein the controller is further configured to control the electrical circuitry to electrically isolate one or more of the cells, thereby allowing a maintenance voltage to be applied to an inactive cell or cells while the remainder of the stack is electrically connected and operational.

22. 22. The system of claim 1, wherein the controller is further configured to control the electrical circuit to short out one or more unused groups of cells to protect against polarity reversal when disconnected from stack operation.

23. 1. An electrolytic cell comprising a plurality of electrolytic cells arranged in a cell stack, the electrolytic cells being electrically connected in series and grouped into two or more cell groups, each cell group having externally accessible electrical contacts at both ends to allow the cell group to be electrically disconnected from the cell stack during operation of the electrolytic cell, thereby varying the number of active electrolytic cells in the cell stack.

24. a controller comprising a processor and a memory, the memory, when executed by the processor, causing the processor to: instructions for determining a number of active electrolysis cells to be used from a plurality of electrolysis cells arranged in a cell stack of an electrolyzer, the electrolysis cells being electrically connected in series and grouped into two or more cell groups, each cell group having externally accessible electrical contacts at both ends, the determination being based on a variable amount of direct current (DC) electrical energy supplied to the cell stack by an electrical energy source and / or according to a user-defined policy; instructions for controlling one or more switches respectively coupled between the electrical contacts of each of the cells to selectively disconnect one or more of the cells from the cell stack based on the determination; Remember the controller.

25. 25. The controller of claim 24, wherein the processor is further configured to control one or more voltage sources and associated electrical switches to apply a maintenance voltage to one or more groups of cells that are not in use.

26. 26. The controller of claim 24 or claim 25, wherein the processor is further configured to apply a short circuit to one or more groups of cells that are not in use.

27. The processor further comprises: determining a first number of electrolytic cells to be used from a first plurality of electrolytic cells disposed in a first cell stack of a first electrolytic cell, the first plurality of electrolytic cells being electrically connected in series and grouped into two or more cell groups, each cell group having externally accessible electrical contacts at both ends; and controlling one or more first switches based on the determination to selectively disconnect one or more of the cell groups from the first cell stack; determining a second number of electrolytic cells to be used from a second plurality of electrolytic cells disposed in a second cell stack of a second electrolytic cell, the second plurality of electrolytic cells being electrically connected in series and grouped into two or more cell groups, each cell group having externally accessible electrical contacts at both ends; and based on said determination, controlling one or more second switches to selectively disconnect one or more of the cell groups from the second cell stack; Controlling a switching circuit to connect the first electrolytic cell and the second electrolytic cell in series or in parallel The controller according to any one of claims 24 to 26, configured to:

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