WO2026017387A1

WO2026017387A1 - Electrolysis system for hydrogen production

Info

Publication number: WO2026017387A1
Application number: PCT/EP2025/068276
Authority: WO
Inventors: Albert Bos; Ahmadreza RAHBARI
Original assignee: Xintc BV
Current assignee: Xintc BV
Priority date: 2024-07-16
Filing date: 2025-06-27
Publication date: 2026-01-22
Anticipated expiration: 2027-01-16

Abstract

The invention relates to an electrolysis system for hydrogen production, comprising: A DC Power source, in particular with a fluctuating power revenue, comprising: a positive power bar; and a negative power bar; A plurality of electrolyser modules, each electrolyser module comprising: A plurality of electrolyser cells; At least a first common liquid input connection; At least one common positive electric pole; At least one common negative electric pole; A liquid circuit for supplying an electrolyte to the liquid input connection of each of said electrolyser modules, connecting the electrolyser modules hydraulically; A controllable electric circuit, configured for selectively connecting and disconnecting one of: the positive electric pole of at least one of the electrolyser modules; or the negative electric pole of said at least of the electrolyser modules; to or from the respective positive or negative power bar; characterised in that the controllable electric circuit is further configured for selectively connecting and disconnecting the other of: the positive electric pole of said at least one of the electrolyser modules; and the negative electric pole of said at least one of the electrolyser modules; to or from the respective positive power bar or the respective negative power bar.

Description

Electrolysis system for hydrogen production

The present invention relates to an electrolysis system for hydrogen production. Systems for this purpose are known in the art. The system according to the invention in particular lies in the field of green production of hydrogen, also referred to as "green hydrogen". Green production means that the energy source used for the hydrogen production is green, for example a solar or wind energy source.

The difficulty with these energy sources is that they do not provide a continuous amount of power. Such fluctuating power level however makes it difficult to operate an electrolyser in an efficient way.

It is a goal of the present invention to provide a solution for this problem and to propose an electrolysis system suitable for green hydrogen production.

The invention therefore proposes an electrolysis system for hydrogen production, comprising a DC Power source, in particular with a fluctuating power revenue, comprising a positive power bar; and a negative power bar, a plurality of electrolyser modules, each electrolyser module comprising a plurality of electrolyser cells, at least a first common liquid input connection, at least one common positive electric pole, at least one common negative electric pole, a liquid circuit for supplying an electrolyte to the liquid input connection of each of said electrolyser modules, connecting the electrolyser modules hydraulically, a controllable electric circuit, configured for selectively connecting and disconnecting one of the positive electric pole of at least one of the electrolyser modules; or the negative electric pole of said at least of the electrolyser modules, to or from the respective positive or negative power bar, wherein the controllable electric circuit is further configured for selectively connecting and disconnecting the other of the positive electric pole of said at least one of the electrolyser modules and the negative electric pole of said at least one of the electrolyser modules to or from the respective positive power bar or the respective negative power bar.

By enabling the positive and negative poles of the electrolyser modules to be selectively connected and disconnected from the DC power source, the electrolyser system according to the invention has become a modular and scalable electrolyser system, suitable for enhancing the efficiency and adaptability of green hydrogen production. The amount of electrolyser modules that is connected to the power source may be matched with the actual power generation.

For this purpose, the present invention proposes a method for operating a electrolysis system for hydrogen production comprising multiple electrolyzer modules, arranged in parallel to a common DC bus bar system, wherein the common bus bar system is powered by multiple solar panels, also referred to as Photo Voltaic modules or PV modules. The solar panels may be electrically connected to the bus bar system in an arrangement that is made out of any combination of series and parallel connected solar panels.

Electrolyser modules that are connected to both power bars and thus may generate hydrogen are referred to as active in the remainder of this application. Electrolyser modules that are disconnected with at least one of their positive or negative power connections and thus cannot generate hydrogen are referred to as idle in the remainder of this application. Electrolyser modules that are disconnected with both their positive and negative power connections from the power bars are referred to as floating or in a floating state. The invention introduces a novel method for operating an array of parallel electrolyser modules with any combination of active or idle configurations.

In a preferred embodiment, the system according to the invention comprises a controller, for selectively connecting and disconnecting the positive and negative electric poles of each electrolyser module simultaneously, thus connecting the electrolyser modules electrically in parallel or completely disconnecting the electrolyser modules.

The floating state configuration, in combination with the system's ability to handle intermittent green power sources such as solar and wind energy, minimizes parasitic currents between active and idle electrolyser modules, thereby optimizing overall system performance and efficiency. Multiple idle electrolyser modules in a floating state configuration, are shown to significantly reduce parasitic mutual currents between the said electrolyser modules. The amount of parasitic mutual currents is even lower than in a grounded open-circuit state.

The system according to the invention further represents an advancement in the field of modular alkaline electrolysis and green hydrogen production, offering a practical and efficient solution to the challenges posed by integrating renewable energy with hydrogen production systems.

The present invention addresses these challenges by introducing a highly modular and scalable electrolyser system specifically designed for green hydrogen production. This system employs a novel method of operating an array of electrolyser modules, electrically parallel.

The electrolyser modules are connected to a manifold which manages electrolyte flow circulation through the entire system. The electrolyte flow channels in the manifold, can be a potential source of parasitic currents between the electrolyser modules if one or some or turned off (idle state) during the operation of the whole system. Parasitic currents are defined as unwanted electrical currents that can flow elsewhere in the system where the electrons are not used for to produce hydrogen.

Parasitic currents can cause energy losses and reduce the overall efficiency of the system. The present invention adapts operating any combination of active electrolyser modules (producing gas) and idle electrolyser modules (not producing gas). Every parallel working electrolyser module is connected to the voltage source on its positive electric pole and the ground on its negative electric pole. It is shown that putting the idle electrolyser modules to a floating state, will minimize parasitic currents between the electrolyser modules through the manifold. In a floating state, both poles of the idle electrolyser module are disconnected, isolating the electrolyser module entirely from the voltage source and ground. This configuration reduces parasitic currents from flowing through the idle electrolyser modules, which is a common problem in other configurations where the electrolyser module might still be partially connected to the power system.

By leveraging the floating state configuration in combination with the ability to handle intermittent green power sources such as solar and wind energy, the system ensures minimal parasitic currents between active and idle electrolyser modules. This innovation not only optimizes the overall performance and efficiency of hydrogen production but also provides the flexibility needed to adapt to the variable nature of renewable energy sources.

In a further embodiment, in a system according to the invention the controllable electric circuit comprises mechanical switches such as relays or more preferably electronic switches such as IGBTs or MOSFETs for connecting and disconnecting the positive electric connection and negative electric connection with the respective positive and negative power bar.

Said controllable electric circuit may further be configured for dynamically connecting and disconnecting positive electric connections and negative electric connections of electrolyser modules with the positive and negative power bar in dependence of a power output of DC Power source.

In a further embodiment, the electrolyser modules each comprise a second common liquid input connection, wherein the system comprises two inlet manifolds for distributing anolyte and catholyte to respective first and second common liquid input connections of the cells.

The electrolyser modules may further comprise two separate outlet manifold channels, for cathodic and anodic compartments of said electrolyser modules respectively, to collect a two-phase flow comprising liquid electrolyte and produced hydrogen and oxygen from the electrolyser cells.

The liquid circuit may be configured for circulating the electrolyte continuously through the electrolyser modules, irrespective of the connections of their electric circuit. Hereby, in idle state the cells are quickly filled with liquid, which reduces gas crossover in the cells (H2 diffuses to the O2 side, and O2 to the H2 side) because this only occurs when completely filled with liquid, via the gas dissolved at the molecular level. In cells where gas bubbles would remain in the cells, a supply of gas occurs, with a very short diffusion path and the gas crossover is a lot higher. As an addition and or alternative to the configurations described above, a string of multiple electrolyser modules in series connection may be applied instead of a single electrolyser module. Such configuration makes it possible to apply the invention with higher voltages of the DC power source.

The invention will now be elucidated into more detail with reference to the following figures. Herein:

Figure 1 shows an electrical equivalent circuit of an electrolyser module according to the invention;

Figure 2 shows a schematic diagram of an electrolysis system according to the invention with electrolyser modules in a floating state;

Figure 3 shows a schematic diagram of an electrolysis system according to the invention with electrolyser modules in a grounded open state;

Figure 4 shows the results of computing the parasitic currents between electrolyser modules via the cathodic route in an electrolysis system according to the invention;

Figure 5 shows the results of computing the parasitic currents between electrolyser modules via the anodic route in an electrolysis system according to the invention;

Figure 6 shows a first schematic representation of parasitic currents in electrolyser modules in grounded open-circuit state, via the cathodic route;

Figure 7 shows a second schematic representation of parasitic currents in electrolyser modules in the grounded state via the anodic route;

Figure 8 shows a third schematic representation of parasitic currents in electrolyser modules in floating states;

Figures 9-13 show self explanatory graphs of electrical quantities in an electrolysis system according to the invention.

Figure 1 shows an electrical equivalent circuit 10 of an electrolyser module comprising multiple a plurality of electrolysis cells 1-N. Such electrolyser module may be referred to as an alkaline stack. Through this electrolyser module, a current l_stack may flow. In this circuit, the first cell 1 and the last cell N are explicitly shown, while cells 2 to (N-l) are represented as repeat units. The equivalent circuit accounts for various resistances (listed below) that impact the performance and efficiency of the electrolysis process. The electrolyser module comprises two inlet manifolds coupled to the electrolysis cells, responsible for distributing anolyte and catholyte to every cell, and two separate outlet manifold channels for cathodic and anodic compartments, to collect a two-phase flow (liquid electrolyte and produced gas) from each electrolysis cell 1-N. Each half-cell comprises separate inlets and outlets for the cathodic and anodic compartments, ensuring efficient distribution and collection of electrolytes and gases. R^: resistance catholyte inside the cathodic compartment. The following equivalent ohmic resistances are considered.

R : Resistance of the catholyte inside the cathodic compartment.

Rg"_e°: Resistance of the anolyte inside the anodic compartment.

R_sep: Resistance due to activation overpotential and membrane thickness.

Rcat-: Resistance of the catholyte inlet of the cell.

R'ano- Resistance of the anolyte inlet of the cell.

R°at : Resistance of the catholyte outlet of the cell, including bubbles from the produced gas. R°no^: Resistance of the anolyte outlet of the cell, including bubbles from the produced gas. Rma,c^: Resistance of the catholyte inlet channel manifold.

Rma,c^: Resistance of the catholyte outlet channel manifold, including bubbles from the produced gas.

Rma,a^: Resistance of the anolyte inlet channel manifold.

Rma,a^: Resistance of the anolyte outlet channel manifold, including bubbles from the produced gas.

Figure 2 shows a schematic diagram 20 of an electrolysis system according to the invention with idle electrolyser modules in a floating state. The system comprises multiple electrolyser modules 21, 22, 23, each capable of operating independently or collectively. These electrolyser modules are connected electrically in parallel to a busbar 24 with a common positive electric pole 21 A, 22 A, 23 A and electrically grounded 25 with a common negative electric pole 21 B, 22 B, 23 B.

The busbar 24 forms a primary electrical connection point for the active electrolyser modules 21, providing a stable connection to the voltage source 26.

The ground Connection 25 serves to ground each electrolyser module 21, 22, 23 on the opposite side of the busbar connection 24, ensuring a reference point for the system.

A liquid circuit delivers an electrolyte solution to each electrolyser module. Thereby an electrolyte solution flows continuously through the electrolyser modules, irrespective of their operational state (active or idle). Only the part of the electric circuit comprising the common liquid input connections is shown.

A manifold manages the distribution of the electrolyte solution among the electrolyser modules and potentially provides a path for parasitic currents. In this configuration, idle electrolyser modules 22, 23 are shown with both poles disconnected using an open switch. This configuration isolates the idle electrolyser modules 22, 23 entirely from both the voltage source 26 and ground 25, thereby minimizing parasitic currents.

The open switch disconnects both poles of the idle electrolyser module. In this floating state, parasitic currents can exit the active electrolyser modules via the manifold and enter the idle electrolyser modules. These currents return to the active electrolyser module, as the idle electrolyser modules are fully isolated from any reference point.

By employing the floating configuration for idle electrolyser modules, the system effectively minimizes parasitic currents that might otherwise flow from active electrolyser modules via the electrolyte solution through idle electrolyser modules to one of the busbar poles. Every idle electrolyser module acts in effect as an additional resistance path (back and forth) to the parasitic currents. This configuration is particularly beneficial when integrating with intermittent green power sources such as solar or wind energy, ensuring optimal system efficiency. Due to the large fluctuations in power supply, relatively many modules can be in the idle state over time. The floating configuration then minimizes leakage currents.

Figure 3 shows a schematic diagram 30 of an electrolysis system according to the invention in a grounded open state. In this configuration, idle electrolyser modules 22, 23 are shown disconnected from the voltage source 26 but remain connected to the ground 25. This configuration significantly impacts the reduction of parasitic currents by providing a direct path to ground 25. An open switch is used to disconnect the idle electrolyser modules 22, 23 from the voltage source. Despite being disconnected from the voltage source 26, the ground connection remains intact, ensuring that parasitic currents are maximized by providing a low-resistance return path to ground. This holds true when the module is disconnected from the ground bar but still connected to the positive bar.

The grounded open-circuit state configuration is essential in minimizing parasitic currents that might otherwise, with grounded open-circuit, flow from active electrolyser modules to idle electrolyser modules through the electrolyte solution and return through the ground. This approach ensures that the overall system operates efficiently, even when integrating intermittent green power sources such as solar or wind energy.

Figure 4 shows the results 40 of computing the parasitic currents between electrolyser modules in a modular alkaline electrolysis system. This figure illustrates the impact of employing a floating state configuration for idle electrolyser modules on the parasitic current exiting from the cathodic inlet of the electrolyser module to the manifold. Specifically, it demonstrates that when the idle electrolyser modules are placed in a floating state, thereby removing their connection to the ground and positive pole simultaneously, the parasitic current is reduced by approximately two to three orders of magnitude. This significant reduction indicates that a floating state configuration introduces a substantially longer resistance path with higher resistance for parasitic currents.

In the context of this figure, electrolyser modules 1 to 11 (x-axis) are designated as active electrolyser modules and are represented by circles, whereas electrolyser modules 12 to 15 are designated as idle electrolyser modules and are represented by triangles. The data clearly shows that the parasitic currents between the idle electrolyser modules diminish as the distance from the active electrolyser modules increases. This shows the effectiveness of the floating state configuration in mitigating parasitic current flow in the electrolysis system according to the present invention.

Figure 5 provides a comparative analysis 50 of floating and grounded configurations for anodic currents using the same model that was used for generating figure 4. When idle electrolyser modules are configured to a floating state, removing their ground connection, the figure demonstrates how this impacts the anodic currents. The anodic pathway acts as a return pathway for parasitic cathodic currents. Therefore, the parasitic currents enter the manifold from a cathodic side and return through an anodic side towards the active electrolyser modules. In the floating state configuration, the parasitic current must exit via the active stacks, as the idle stacks are not grounded. It is also clear that the parasitic currents for floating electrolyser modules are two orders of magnitude smaller than the parasitic anodic currents for the idle electrolyser modules in a grounded state.

This shows the efficiency of the floating state in providing a higher resistance path for parasitic currents, when managing idle and active electrolyser module configurations to optimize system performance according to the present invention.

Figure 6 provides a schematic representation 60 of parasitic currents in an active electrolyser module and the pathways through grounded electrolyser modules. The figure illustrates how parasitic current flows via the catholyte pathway through the manifold system between electrolyser modules. In the grounded electrolyser modules, parasitic currents escape through the ground connection, demonstrating the behaviour of parasitic currents when the idle electrolyser modules are not in a floating state. This configuration highlights the pathways and potential points of parasitic current loss within the system. Figure 7 shows the anodic pathway.

Figure 7 provides a schematic representation 70 of parasitic currents in active electrolyser modules and the pathways through grounded electrolyser modules. The figure illustrates how parasitic current flows via the anolyte pathway through the manifold system between electrolyser modules. In the grounded electrolyser modules, parasitic currents escape through the ground connection, demonstrating the behaviour of parasitic currents when the idle electrolyser modules are not in a floating state. This configuration highlights the pathways and potential points of parasitic current loss within the system.

Figure 8 is a schematic representation 80 of parasitic currents in active electrolyser modules and the pathways through floating electrolyser modules. In this configuration, the catholyte and anolyte pathways form a long continuous pathway from the active electrolyser modules and back to the active electrolyser modules, through the floating electrolyser modules, via the cathodic and anodic pathways of the manifold. This figure demonstrates how, in the floating state, parasitic currents are forced to travel through a longer path with significantly higher ohmic resistance, thereby minimizing the parasitic losses. The comparison with the figures 6 and 7 emphasizes the efficiency and effectiveness of the floating configuration in reducing parasitic currents within the system.

Solar panels have a voltage-current characteristic that mainly reflects a current source, wherein the amount of current is dependent on the amount of light the panel is exposed to.

The Current-Voltage Characteristic of a solar panel is the output voltage of a PV module or system as a function of the output current. The general l-V characteristic of a PV system is shown in figure 9.

The Power-Voltage Characteristic of a solar panel is its output power as a function of its output voltage. The general P-V characteristic curve is shown in figure 10.

The following parameters affect the performance of a PV module:

Open-Circuit Voltage (Voc): This is the maximum voltage output of a PV cell. Voc occurs when the current in the circuit is equal to zero.

Short-Circuit Current (Isc): The short-circuit current is the maximum current output of a solar cell. This occurs when the solar cell is short-circuited and hence, the voltage is zero.

Figure 11 shows the Voc and Isc of a solar cell in the general l-V curve:

As can be seen in the image, the highest current on the l-V curve is the Isc which occurs when the voltage is equal to zero. Also, the highest voltage output of the solar cell is when the current equals zero and it is the Voc- Even on the P-V curve, the highest voltage output is the Voc- Another point on the graph is the 'MPP' which stands for Maximum Power Point. This is the maximum power output of a solar cell. It is known that Power is equal to the product of the Voltage and the Current (P = V x I). Hence, on the l-V curve, the Power is represented by the area under the curve. The Maximum Power Point is the set of coordinates of an l-V curve that give the maximum power output. These coordinates are written as Voltage at Maximum Power Point (V_Mpp) and Current at Maximum Power Point (IMPP). On a P-V curve, the MPP is the highest point attained by the curve on the Y-axis. The method according to the invention comprises connecting an amount of electrolyzer modules to the common DC bus bar system that has a common power consumption that is at or within a predetermined range from the Maximum Power Point.

In particular, according to the invention, it was found that operating the electrolyzer modules at 3- 5%, and more in particular at about 4% below the Maximum Power Point, a yield of 3-5% more Hydrogen can be obtained. This is shown in figures 12 and 13.

Claims

1. Electrolysis system for hydrogen production, comprising:

• A DC Power source, in particular with a fluctuating power revenue, comprising: o a positive power bar; and o a negative power bar;

• A plurality of electrolyser modules, each electrolyser module comprising: o A plurality of electrolyser cells; o At least a first common liquid input connection; o At least one common positive electric pole; o At least one common negative electric pole;

• A liquid circuit for supplying an electrolyte to the liquid input connection of each of said electrolyser modules, connecting the electrolyser modules hydraulically;

• A controllable electric circuit, configured for selectively connecting and disconnecting one of: o the positive electric pole of at least one of the electrolyser modules; or o the negative electric pole of said at least one of the electrolyser modules; to or from the respective positive or negative power bar; characterised in that the controllable electric circuit is further configured for selectively connecting and disconnecting the other of: o the positive electric pole of said at least one of the electrolyser modules; and o the negative electric pole of said at least one of the electrolyser modules; to or from the respective positive power bar or the respective negative power bar.

2. System according to claim 1, comprising a controller, for selectively connecting and disconnecting the positive and negative electric connections of each electrolyser module simultaneously, thus connecting the electrolyser modules electrically in parallel or completely disconnecting the electrolyser modules.

3. System according to any of the proceeding claims, wherein the controllable electric circuit comprises mechanical switches such as relays or electronic switches such as IGBTs or MOSFETs for connecting and disconnecting the positive electric connection and negative electric connection with the respective positive and negative power bar.

4. System according to any of the preceding claims, configured for dynamically connecting and disconnecting positive electric connections and negative electric connections of electrolyser modules with the positive and negative power bar in dependence of a power output of DC Power source.

5. System according to any of the preceding claims, wherein the electrolyser modules each comprise a second common liquid input connection, wherein the system comprises two inlet manifolds for distributing anolyte and catholyte to respective first and second common liquid input connections of the cells.

6. System according to any of the preceding claims, wherein the electrolyser modules comprise two separate outlet manifold channels, for cathodic and anodic compartments of said electrolyser modules respectively, to collect a two-phase flow comprising liquid electrolyte and produced hydrogen from the electrolyser cells.

7. System according to claim 6, wherein the liquid circuit is configured for circulating the electrolyte continuously through the electrolyser modules, irrespective of the connections of their electric circuit.

8. System according to any of the preceding claims, comprising multiple electrolyser modules in a series connection, wherein the circuit is configured for selectively connecting and disconnecting one of: o a common positive electric pole of at least one of the multiple electrolyser modules in series connection; or o the negative electric pole of said at least of the multiple electrolyser modules in series connection; to or from the respective positive or negative power bar; characterised in that the controllable electric circuit is further configured for selectively connecting and disconnecting the other of: o the positive electric pole of said at least one of the multiple electrolyser modules in series connection; and o the negative electric pole of said at least one of the multiple electrolyser modules in series connection; to or from the respective positive power bar or the respective negative power bar.

9. Method for hydrogen production, comprising: selectively connecting and disconnecting one of: o a common positive electric pole of at least one of multiple electrolyser modules in series connection; or o a negative electric pole of said at least of the multiple electrolyser modules in series connection; to or from a respective positive or negative power bar; characterised by selectively connecting and disconnecting the other of: o the positive electric pole of said at least one of the multiple electrolyser modules in series connection; and o the negative electric pole of said at least one of the multiple electrolyser modules in series connection; to or from the respective positive power bar or the respective negative power bar.