Patent Publication Number: US-2022220620-A1

Title: High power water electrolysis plant configuration optimized for sectional maintenance

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a utility application claiming priority to U.S. Provisional Application 63/105,587, filed on Oct. 26, 2020, the entire contents of which I incorporated herein by reference. 
    
    
     FIELD OF INVENTION 
     This disclosure relates to a novel, high power hydrogen production plant using unipolar alkaline water electrolysers configured in such a way so that sectional maintenance can be optimized. 
     BACKGROUND OF THE INVENTION 
     Electrochemical cell technology is designed such that an applied electric current induces reactions within a cell, converting available reactants into desired products. An electrolytic cell, or electrolysis cell, is one preferred method of accomplishing this conversion. Electrolysis cells require the conduction of electricity, typically direct current, from an external source to a polarized electrode. They further require conduction away from an electrode of the opposite polarity, either external to or within the electrochemical cell, to generate products. 
     One desirable configuration of an electrochemical cell is that of the filter press-type electrolyser. Filter press electrolyser electrochemical cells require: mechanical frames with sufficient rigidity, the ability to be connected to (and removed from) an external current source, a “current carrier” to provide a current flow path for electricity to be conducted to the electroactive area, a circulation chamber to provide space for gaseous product generation at the electroactive area, passageways that allow the input and output of reactants and products, and finally a capability to form an external seal that prevents fluids leaking from the interior of the cell to the external atmosphere. 
     Filter press electrolyser electrochemical cells generally come in three configurations, driven by the design of their sub-components: a bipolar cell design, a unipolar cell design, or a monopolar cell design. 
     Monopolar Cell Design 
     A “monopolar” cell design or configuration refers to an electrochemical device based upon a current carrying configuration. This monopolar configuration comprises a current carrying structure, and further provides an electroactive structure of a singular polarity (either anodic or cathodic) on one side of the current carrying structure. As a result, a region of one polarity is provided on the side of the current carrying structure that possesses the electroactive structure. Current is provided into the configuration by a power source and flows in across the current carrier and to the electroactive structure. Typically, the current flows in a parallel direction to the electroactive structure. A half-cell creates the base current carrying unit for a monopolar electrochemical filter press device constructed of positive and negative (anodic and cathodic) half-cell pairs. All monopolar base current carrying units are configured electrically in parallel within a single filter press arrangement, such that one electrochemical cell is formed within a single filter press stack. 
     Bipolar Cell Design 
     The phrase “bipolar configuration” or “bipolar cell configuration” refers to an electrochemical device based upon a current carrying configuration. This bipolar configuration comprises a bipolar wall, defining electroactive areas of opposite polarity on opposing sides of the current carrying structure. Regions of opposite polarity are provided on the opposing sides of the bipolar wall. Current is provided into the configuration by a power source and flows through the bipolar wall orthogonally, creating the base current carrying unit for a bipolar electrochemical filter press device. Multiple electrochemical cells within a bipolar filter press are electrically connected in series, with each individual current carrier typically comprising one anodic and one cathodic side connected by a conductive bipolar wall. The current path in bipolar cells between electroactive structures of different polarities is typically shorter than the equivalent current path in traditional monopolar designs and unipolar designs as described later. 
     In bipolar cells, the current must only travel through one bipolar wall to reach an electroactive structure of the opposing polarity, whereas in traditional unipolar and monopolar cells additional components are required to connect current to opposite polarity electroactive structures. A shorter current path generally creates lower resistance parameters within the conductive surfaces of a singular cell. This has traditionally led to higher voltage losses due to higher electronic resistance voltage loss, and thus lower efficiency, for unipolar and monopolar cells as compared to bipolar cells for similar current densities and similar electroactive structures. 
     Historically, the contribution of electronic resistance to cell voltage losses in traditional unipolar and monopolar designs presented the greatest barrier to the continued commercialization of these technologies. When choosing which direction to take electrolysis technologies in recent decades, leaders in the electrolysis field focused heavily on the advancement of “zero-gap” bipolar cell designs as they reduced the contribution of electronic resistance to cell voltage losses and consequently, for similar current densities and similar electroactive structures, improved plant energy efficiency. Zero-gap designs also allowed bipolar cells to utilize higher current densities. The focus on zero-gap, or near zero-gap, bipolar technology led to an industrial preference for bipolar technology as a whole over monopolar and unipolar technology. However, the utilization of higher current densities does not in itself lead to improved efficiency or improved plant economics. Unipolar and monopolar technologies present many complementary advantages in these areas, which will be discussed further. 
     In addition, in numerous bipolar filter press designs the electrolyte is shared amongst cells within the same filter press and exposed to the full potential gradient of all the individual electrolytic cells that comprise the bipolar filter press. This leads to rapid depolarization upon removal of the forward current, bypass currents during normal operation, and exposure to high potential differences leading to a need for choice of materials able to withstand this environment. 
     Unipolar Cell Design 
     A unipolar cell design or configuration refers to an electrochemical device based upon a current carrying configuration. This unipolar configuration comprises a current carrying structure that provides multiple electroactive structures of the same polarity (either anodic or cathodic) on opposing sides of the current carrying structure. As a result, regions of the same universal polarity are provided on the opposing sides of the current carrying structure. Current is then provided by a power source and flows in across the current carrier and to the electroactive structures. Typically, the current flows in a parallel direction to the electroactive structures. The half-cell creates the base current carrying unit for a unipolar electrochemical filter press device constructed of positive and negative (anodic and cathodic) half-cell pairs. Like the previously described monopolar base current carrying unit, all unipolar base current carrying units are configured electrically in parallel within a single filter press arrangement, such that one electrochemical cell is formed within a single filter press stack. Unipolar designs are distinguished from monopolar designs by the presence and positioning of their electroactive area(s) and the structure of their current carrier(s) among other things. 
     Historically, unipolar cells for alkaline water electrolysis were popularized in a “tank type” configuration. An early tank type unipolar electrolyser is described in U.S. Pat. No. 1,597,552, Electrolytic Cell, Alexander T. Stuart, 1923. A major advancement in tank type unipolar electrode design as described in U.S. Pat. No. 4,482,448, Electrode Structure for Electrolyser Cells, Bowen et al, 1981 introduced the world to large scale hydrogen production from non-fossil energy, the electrolyser design being configured for large total surfaces areas and currents of 120,000 amperes per cell. However, because of the high part count, complex assemblies, resistance within the conductive pathways of a single cell, and difficulties inherent in changing the surface area per cell, “tank type” unipolar water electrolysers, such configurations were generally replaced by comparatively more efficient “filter press type” configurations over time. However, these “tank type” designs eliminated need for mixing electrolyte between cells and the related by-pass currents and very high potential differences across multicell arrays. This generally enabled low costs materials which are stable for over 30 years of operation. These include use of low carbon steel without surface treatments or light nickel plating on carbon steel. 
     Proposed layouts of larger hydrogen production plants using the Electrolyser Inc. Generation I and II cell designs are found in Advanced Unipolar Electrolysis, R. L. LeRoy and A. K. Stuart, 1981. The large-scale designs include several rows of electrolyser cell blocks or cell which consist of several unipolar water electrolysers. Each cell block is electrically connected to the preceding cell block by a substantially u-shaped connection, to thereby form a U-bank. The difference between the large-scale hydrogen production plant using the Generation I cells and the Generation II cells is the floor space size requirement needed to house the cell blocks. Advancements in electrolyser technologies have reduced the facility space from 3020 m 2  using the Generation I cells to 900 m 2  using the Generation II cells, while continuing to maintain the production of hydrogen and general U-bank arrangement. Additionally, a 100-MW large scale hydrogen production plant using unipolar electrolysers was designed and shown as a schematic in Industrial Water Electrolysis: Present and Future, R. L. LeRoy, 1982). 
     This large-scale production plant was modelled after a smaller experimental plant of 600-kW in Varennes, Quebec also using the Generation II advanced unipolar electrolyser. 
     In both the Advanced Unipolar Electrolysis and the Industrial Water Electrolysis: Present and Future papers, although discussing preliminary designs of large-scale hydrogen production plants using unipolar electrolysers, there is little consideration given to how plant operations would proceed given a routine maintenance check, diaphragm replacement, cell overhaul or technical complications due to improper maintenance. Examples of such complications due to improper maintenance could include poor gas purities, overheating, internal cell shortage, caustic leakage or a sudden increase or decrease in cell voltage. For instance, after 25 years of operation, diaphragm replacements may be required. Replacement of one cell block would require the shutdown of the entire plant ceasing the production of hydrogen completely while the individual cell block is removed. Additionally, complete purging of the plant would be required before and after the removal of the cell block. This would lead to additional costs and additional time wasted, as there would be plant downtime and a loss of hydrogen and oxygen production. It would be preferable to be able to perform maintenance without significantly interfering operations. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides a high-power unipolar water electrolysis plant including a rectifier for supplying DC current, a first U-bank electrically connected to the rectifier, and a second U-bank electrically connected in series to the rectifier and to the first U-bank. Each U-bank is formed by a pair of adjacent, first and second longitudinal cell arrays electrically connected to each other. The first and second cell arrays are arranged in a spaced apart, side-by-side arrangement with a service corridor defined therebetween to allow sectional maintenance to be performed on each cell array. The first cell array is disposed on one side of service corridor and the second cell array is disposed on the other side of the service corridor. Each cell array has a plurality of unipolar water electrolyser cells. In addition, each U-bank has input conduits for delivering feed water and cooling water to the plurality of unipolar water electrolyser cells of each cell array, output conduits for carrying hydrogen gas, oxygen gas and cooling water away from the plurality of unipolar water electrolyser cells of each cell array and valving for isolating flow from the output conduits and the input conduits during maintenance of each cell array. 
     In addition, the high-power unipolar water electrolysis plant includes a first jumper being connectable upstream of the first cell array of the first U-bank for electrically isolating the first cell array of the first U-bank, a second jumper being connectable downstream of the second cell array of the first U-bank for electrically isolating the second cell array of the first U-bank, an electrical bypass busbar extension being connectable upstream of the first jumper and downstream of the second jumper for completing the circuit in the high-power water electrolysis plant when the first U-bank is isolated, and a third jumper cooperating with the electrical bypass busbar extension and being operable to redirect the DC current away from the first U-bank toward the remainder of the high-power water electrolysis plant when the first U-bank is isolated. 
     In addition, the power supply may be a rectifier, a rectifier system, solar panels or other direct power generating source connections. The rectifier system comprises a plurality of rectifiers electrically connected in parallel. 
     Where the power supply is a rectifier, the rectifier is configured to permit its amperage output to be increased to compensate for between 5% to 50% of any reduced hydrogen production output on account of the isolation of one of the first and second U-banks during maintenance. 
     In one embodiment, the high-power unipolar water electrolysis plant has a first U-bank and the second U-bank that have the same or substantially the same hydrogen production capacity. 
     Alternatively, the first U-bank and the second U-bank have different hydrogen production capacities. 
     Alternatively, the first cell array of the first U-bank has the same or substantially the same hydrogen production capacity as the second cell array of the first U-bank. 
     Alternatively, the first cell array of the first U-bank has a different hydrogen production capacity than the second cell array of the first U-bank. 
     Furthermore, each cell array of the first U-bank may be configured to receive between 2 MW and 125 MW of power to produce hydrogen. 
     Alternatively, the first cell array of the second U-bank has the same or substantially the same hydrogen production capacity as the second cell array of second U-bank. 
     Alternatively, the first cell array of the second U-bank has a different hydrogen production capacity than the second cell array of the second U-bank. 
     Each cell array may include between 2 and 100 unipolar electrolyser cells. 
     The first cell array of the first U-bank has a first end connected to the adjacent U Bank and a second end connected to one of the power supply or another U-bank. 
     In addition, the first U-bank is disposed parallel or substantially parallel to the second U-bank with a service corridor formed therebetween. 
     Furthermore, the first cell array of the first U-bank is disposed parallel or substantially parallel to the second cell array of the first U-bank. 
     The first and second jumpers are selected from the group consisting of switches and busbar segments. 
     The input conduits of the first U-bank may include a feed water input conduit having a first branched portion in fluid communication with the first cell array and a second branched portion in fluid communication with second cell array, and a cold water input conduit having a first branched portion in fluid communication with the first cell array and a second branched portion in fluid communication with second cell array. 
     Alternatively, the input conduits may include having first feed water input conduit in fluid communication with the first cell array, a second feed water input conduit in fluid communication with the second cell array, a first cold water input conduit in fluid communication with the first cell array and a second cold water input conduit in fluid communication with the second cell array. 
     In addition, the valving includes a first input valve connected to the first feed water input conduit upstream of the first cell array, a second input valve connected to the first cold water input conduit upstream of the first cell array, a third input valve connected to the second feed water input conduit upstream of the second cell array, and a fourth input valve connected to the second cold water input conduit upstream of the second cell array. 
     The output conduits of the first U-bank may include a first hydrogen gas output conduit in fluid communication with the first cell array, a second hydrogen gas output conduit in fluid communication with the second cell array, a first oxygen gas output conduit in fluid communication with the first cell array, a second oxygen gas output conduit in fluid communication with the second cell array, a first cooling water output conduit in fluid communication with the first cell array and a second cooling water output conduit in fluid communication with the second cell array. 
     In addition, the valving includes a first output valve connected to the first cooling water output conduit downstream of the first cell array, a second output valve connected to the first oxygen gas output conduit downstream of the first cell array, a third output valve connected to the first hydrogen gas output conduit downstream of the first cell array, a fourth output valve connected to the second cooling water output conduit downstream of the second cell array, a fifth output valve connected to the second oxygen gas output conduit downstream of the second cell array and a sixth output valve connected to the second hydrogen gas output conduit downstream of the second cell array. 
     The first U-bank may further include a first water seal connected to the first oxygen gas output conduit and the first hydrogen gas output conduit upstream of the second and third output valves, a second water seal connected to the second oxygen gas output conduit and the second hydrogen gas conduit upstream of the fifth and sixth output valves. 
     The first U-bank may further include a first vent exhaust for venting oxygen from the first oxygen water seal, a second vent exhaust for venting hydrogen gas from the first hydrogen water seal, a third vent exhaust for venting oxygen gas from the second oxygen water seal, and a fourth vent exhaust for venting hydrogen gas from the second hydrogen water seal. 
     The first U-bank may further include a first mist eliminator connected to the first oxygen gas output conduit upstream of the second output valve, a second mist eliminator connected to the first hydrogen gas output conduit upstream of the third output valve, a third mist eliminator connected to the second oxygen gas output conduit upstream of the fifth output valve, and a fourth mist eliminator connected to the second hydrogen gas output conduit upstream of the sixth output valve. 
     The first U-bank may further include a first isotope (deuterium) enrichment column connected to the first oxygen gas output conduit upstream of the second output valve, a second isotope (deuterium) enrichment column connected to the first hydrogen gas output conduit upstream of the third output valve, a third isotope (deuterium) enrichment column connected to the second oxygen gas output conduit upstream of the fifth output valve, and a fourth isotope (deuterium) enrichment column connected to the second hydrogen gas output conduit upstream of the sixth output valve. 
     The present disclosure also provides a high-power unipolar water electrolysis plant including a power supply for supplying DC current, a first plurality of U-banks electrically connected to the power supply, and a second plurality of U-banks electrically connected in series to the power supply and to the first plurality of U-banks. Each U-bank of the first and second plurality is formed by a pair of adjacent, first and second longitudinal cell arrays electrically connected to each other and arranged in a spaced apart, side-by-side arrangement with a service corridor defined therebetween to allow sectional maintenance to be performed on each cell array. The first cell array is disposed on one side of service corridor and the second cell array being disposed on the other side of the service corridor, each cell array having a plurality of unipolar water electrolyser cells, and each U-bank of the first and second plurality having input conduits for delivering feed water and cooling water to the plurality of unipolar water electrolyser cells of each cell array, output conduits for carrying hydrogen gas, oxygen gas and cooling water away from the plurality of unipolar water electrolyser cells of each cell array and valving for isolating flow from the output conduits and the input conduits during maintenance of each cell array. 
     In addition, high-power unipolar water electrolysis plant may include a first jumper being connectable upstream of the first cell array of a first U-bank of one of the first or second plurality of U-banks for electrically isolating the first cell array of the first U-bank, a second jumper being connectable downstream of the second cell array of the first U-bank for electrically isolating the second cell array of the first U-bank, an electrical bypass busbar extension being connectable upstream of the first jumper and downstream of the second jumper for completing the circuit in the high-power unipolar water electrolysis plant when the first U-bank is isolated, a third jumper cooperating with the electrical bypass busbar extension and being operable to redirect the DC current away from the first U-bank toward the remainder of the high-power unipolar water electrolysis plant when the first U-bank is isolated. 
     The high-power unipolar water electrolysis plant may include the first plurality of U-banks and the second plurality of U-banks being disposed on either side of a central space defined within the plant. 
     The first plurality of U-banks is laid out according to a first arrangement and the second plurality of U-banks is laid out according to a second arrangement, the first and second arrangements being identical to each other. 
     The high-power unipolar water electrolysis plant is configured to receive between 5 MW and 2 GW of power to produce hydrogen. 
     The high-power unipolar water electrolysis plant is configured to receive between 5 MW and 100 MW of power to produce hydrogen. 
     The high-power unipolar water electrolysis plant is configured to receive between 100 MW and 500 MW of power to produce hydrogen. 
     Alternatively, the high-power unipolar water electrolysis plant may be a high-power monopolar water electrolysis plant. 
     The present disclosure also provides a method of isolating a U-bank in a high power water electrolysis plant having a plurality of u-banks connected in series to a DC power supply. Each U-bank is formed by a pair of adjacent, first and second longitudinal cell arrays electrically connected to each other and arranged in a spaced apart, side-by-side arrangement to allow sectional maintenance to be performed on each cell array. Each cell array has a plurality of unipolar water electrolyser cells. The method of isolating a U-bank in a high power water electrolysis plant includes powering down the high power water electrolysis plant, fluidly isolating the u-bank from feed water and cooling water inputs and hydrogen gas and oxygen gas outputs, electrically isolating the first cell array of the u-bank to be isolated, electrically isolating the second cell array of the u-bank to be isolated, actuating a bypass circuit provided to the high-power water electrolysis plant, and powering up the high power water electrolysis plant, thereby allowing DC current to be redirected away from the U-bank to be isolated toward the remainder of the high-power water electrolysis plant. 
     Fluidly isolating the U-bank further includes closing valves on a plurality of input conduits associated with the u-bank to be isolated so as to prevent the input conduits from supplying feed water and cooling water inputs to each u-bank. 
     Alternatively, fluidly isolating the U-bank further includes flushing out all hydrogen and oxygen gas from the U-bank to be isolated by introducing a purging gas to the U-bank to be isolated, and venting hydrogen and oxygen gas out of a vent exhaust. 
     Alternatively, fluidly isolating the U-bank further includes closing valves on a plurality of output conduits associated with the u-bank to be isolated so as to prevent any backflow of hydrogen and oxygen gas through the output conduits. 
     Electrically isolating the first cell array of the U-bank to be isolated further includes actuating a first jumper connected upstream of the first cell array of the U-bank to be isolated. 
     Electrically isolating the second cell array of the U-bank to be isolated further includes actuating a second jumper connected downstream of the second cell array of the U-bank to be isolated. 
     Actuating a bypass circuit provided to the high-power water electrolysis plant further includes connecting an electrical bypass busbar extension upstream of the first jumper and downstream of the second jumper, and actuating a third jumper cooperating with the electrical bypass busbar extension to complete the circuit in the high-power water electrolysis plant. 
     The method of isolating a U-bank in a high power water electrolysis plant may also include increasing the amount of power from the DC power supply to compensate for the loss in production in high power water electrolysis plant following the fluid and electrical isolation of u-bank to be isolated. 
     The embodiments of the present invention shall be more clearly understood with reference to the following detailed description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  depicts a block diagram of a unipolar alkaline water electrolyser cell showing input reactants entering and resultant products leaving the unipolar electrolyser cell with DC power flowing therethrough to allow for continuous operation and production of hydrogen and oxygen gas. 
         FIG. 2  depicts a block diagram of a U-bank in accordance with an embodiment of the invention, the U-bank comprising two cell arrays and the corresponding input reactants entering and resultant products leaving each cell array of the U-bank, wherein each cell array is comprised of several unipolar electrolyser cells of  FIG. 1 . 
         FIG. 3A  depicts a block diagram modelling the arrangement of several U-banks and the corresponding pathing of input and output conduits, in accordance with an embodiment of the invention. 
         FIG. 3B  depicts a block diagram modelling the arrangement of several U-banks and the corresponding pathing of input and output conduits, in accordance with an alternate embodiment of the invention. 
         FIG. 4A  depicts a block diagram of a single U-bank, with input and output conduits, valving and accessory components such as water seals (or other similar devices), mist eliminators, isotope (deuterium) enrichment columns and gas offtakes for operation within a large scale unipolar alkaline water electrolyser hydrogen production plant. 
         FIG. 4B  depicts a block diagram showing a section of a large high-power unipolar electrolysis plant provided with three U-banks electrically connected to each other in series, the centrally disposed U-bank having an electrical bypass circuit to isolate it during maintenance, the electrical bypass connection configured to allow the U-banks on either side of the centrally disposed U-bank to continue operation while maintenance is performed on the centrally-disposed U-bank. 
         FIG. 5A  depicts a schematic top plan view of a large scale unipolar alkaline water electrolyser plant comprising several U-banks electrically connected to a rectifier/power supply. 
         FIG. 5B  depicts a schematic top plan view of the large scale unipolar alkaline water electrolyser plant of  FIG. 5A  provided with a single electrical bypass circuit. 
         FIG. 6  is a flowchart outlining the steps of a method of isolating a U-bank and electrically bypassing said U-bank to perform maintenance on the cell arrays of said U-bank while allowing the high-power unipolar electrolysis plant and the remaining U-banks to continue operating. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     Various embodiments and aspects of the disclosure will be described with reference to details discussed below. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. The figures are not to scale. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosure. 
     As used herein, the terms, “comprises” and “comprising” are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in the specification and claims, the terms “comprises” and “comprising” and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components. 
     As used herein, the term “exemplary” means “serving as an example, instance, or illustration,” and should not be construed as preferred or advantageous over other configurations disclosed herein. 
     As used herein, the terms “about” and “approximately” are meant to cover variations that may exist in the upper and lower limits of the ranges of values, such as variations in properties, parameters, and dimensions. In one non-limiting example, the terms “about” and “approximately” mean plus or minus 10 percent or less. 
     As used herein, the terms “generally” and “essentially” are meant to refer to the general overall physical and geometric appearance of a feature and should not be construed as preferred or advantageous over other configurations disclosed herein. 
     Unipolar water electrolysis plants have generally been designed with the ability to remove a single unipolar cell from an array of cells. Procedures related to replacement of single unipolar electrolyser cells are known. 
     With the advent of very large-scale hydrogen production system incorporating unipolar water electrolyser cells, the size of an individual array of electrolyser cells could reach 1,000 individual cells connected together through external bus bars to a single power supply. For example, if each cell operated at 2 volts, and 1,000 cells were connected electrically in series, then the single system would be 2,000 volts. In such an embodiment, if the current flowing through the unipolar electrolyser cells were 250,000 amperes, then a 500 MW single hydrogen plant would be created. In low power—(e.g., less than 20 MW) unipolar water electrolysis based hydrogen production systems, isolation of individual cells is adequate and does not impede the output of manufacturing significantly as the absolute number of water electrolysis cells is a relatively low number. For example, only 40 cells would be required. For example, four spare cells could be held ready for substitution and readily replace four operating cells in need of maintenance. To retrofit the entire facility would require 10 shut down and start up procedures which may be quite acceptable over a 30 plus year plant life. However, isolation of individual cells for maintenance purposes may impact the output of manufacturing significantly in large-scale hydrogen production systems which incorporate many hundreds of water electrolysis cells. This would lead to more frequent shutdowns for maintenance of the entire plant. The present invention relates to large-scale unipolar water electrolysis plant designs with the ability to perform sectional maintenance by dividing the population of cells into two or more segments, called U-banks, which can allow isolation not just of a single cell, but also a larger portion of the plant. Sectional maintenance in a high-power unipolar electrolysis plant is advantageous as it allows for electrically isolating U-banks to perform sectional maintenance while allowing other U-banks to continue to receive current and allowing the remainder of the plant to continue to operate. 
     A large-scale unipolar alkaline water electrolyser hydrogen production plant is configured using a single circuit electrical system and a high current, high voltage power supply (i.e. rectifier, solar cells or other direct power generating source connections) favoured by hydrogen plants, such that sections of the hydrogen plant can be isolated without surrendering the benefit of a single electrical circuit or a significant loss in production. 
     As will be discussed further below, this design features blocks of cells, or cell arrays which consist of several unipolar water alkaline electrolyser cells wherein each cell array is connected alongside one another utilizing an electrical connection at one end of the two cell arrays to form a U-bank. Said U-bank consists of two cell arrays connected within a single circuit. With this U-bank configuration, an electrical bypass circuit can be implemented enabling the electrical isolation of a single U-bank, or pair of cell arrays. Isolation allows the individual U-bank to undergo maintenance while the remaining U-banks continue operation and hydrogen production. 
     Maintenance of a cell array may be due to various reasons, including, but not limited to maintenance checks, preventative part replacements, diaphragm replacement, or cell overhaul. For instance, diaphragm replacements are generally required after 20 to 25 years of operation. To perform this replacement without the present invention would require a plant shutdown and a purging of either the cell array containing said cell for maintenance or even the entire plant of all gases and liquids, ceasing all operations and production of hydrogen until the electrolyser cells requiring the replacement has been successfully completed With the present invention, it is possible to quickly isolate and bypass the U-bank with the affected electrolyser cell from the entirety of the plant, allowing for maintenance to be performed while the remainder of the plant continues operations. It is also possible to purge only the isolated U-bank, saving costs and lessening the waste of hydrogen and oxygen. In addition, where a determination to undertake maintenance of the entire hydrogen generation plant, sectional maintenance can allow most or all cells in each section to undergo maintenance without causing a long term shutdown of the entire hydrogen plant. 
     In addition, another advantage of the present invention is that the number of U-banks can be structured so that a specific percentage of the unipolar plant can be isolated for the purpose of sectional maintenance. At a minimum, two U-banks are required. While any number of U-banks may be employed, it is believed that most applications will utilize between 2 to 20 U-banks, and more preferably between 4 to 10 U-banks. Preferably, the operator should have the ability to isolate between 10% and 50% of the plant for maintenance while still operating the remaining portion of the plant. However, this could vary (more or less) in specific implementations.  FIG. 5A  depicts a large-scale unipolar alkaline water electrolyser hydrogen production plant  500  (also referred to herein as high-power unipolar electrolysis plant  500 ). In some embodiments, the high-power unipolar electrolysis plant is capable of accommodating 5 MW to over 2 GW which it uses to generate hydrogen. Preferably, large high-power unipolar electrolysis plants may be configured to receive 100 MW to 500 MW, whereas smaller plants could be configured to receive 5 MW to 100 MW. 
     In  FIGS. 5A and 5B , the high-power unipolar electrolysis plant  500  is shown to have a rectangular or substantially rectangular footprint  524  (also referred to herein as floorplan  524 ). This is for illustration purposes only. A person skilled in the art will appreciate that the unipolar electrolysis plant can have any suitably-shaped footprint or floorplan. Laid out within the footprint  524  is a first series or plurality  532  of U-banks  50  and a second series or plurality  536  of U-banks  50  disposed on either side of a large central space or corridor  528 . In the embodiment shown, the first series  532  of U-banks includes five (5) U-banks—U-banks  50 - 1 ,  50 - 2 ,  50 - 3 ,  50 - 4  and  50 - 5  and similarly, the second series  536  of U-banks also includes five (5) U-banks—U-banks  50 - 6 ,  50 - 7 ,  50 - 8 ,  50 - 9  and  50 - 10 . The configuration or layout of the U-banks  50 , rectifier  504 , corridor  528  in floorplan  524  in the embodiment depicted by  FIGS. 5A and 5B  provides the availability of space for the operation of high-power unipolar electrolysis plant  500 , the movement of electrolyser cells  104  for maintenance around high-power unipolar electrolysis plant  500 , and also the safety, to ensure there is distance between areas with high voltage in the region of the rectifiers. In any embodiment of high-power unipolar electrolysis plant  500 , there are at least two U-banks, and other embodiments may have more than two U-banks or any number of U-banks greater than the ten U-banks depicted in the embodiment of  FIGS. 5A and 5B . Other embodiments of unipolar electrolysis plant could have any number of series U-banks, and may be arranged in a similar or in a different fashion. In still other embodiments, each series could include a greater or lesser number of U-banks. It will also be appreciated that in some instances smaller unipolar electrolysis plants may not have their U-banks grouped in a first and second series. 
     Returning to the current embodiment depicted in  FIGS. 5A and 5B , high-power unipolar electrolysis plant  500  includes a plurality of U-banks  50 - 1 ,  50 - 2 ,  50 - 3 ,  50 - 4 ,  50 - 5 ,  50 - 6 ,  50 - 7 ,  50 - 8 ,  50 - 9  and  50 - 10  electrically connected in series to rectifier  504  (also referred to herein as power source  504 , or DC current power supply  504 ). (U-banks referred to herein generically, as U-bank  50  and collectively, as U-banks  50 ). 
     In the current embodiment, rectifier  504  is connected to a first U-bank  50 - 1  via electrical connection  540 -A. First U-bank  50 - 1  is then connected to a second U-bank  50 - 2  via electrical connection  508 - 2 . Second U-bank  50 - 2  is connected to a third U-bank  50 - 3  via electrical connection  508 - 3 . Final U-bank  50 - 10  is connected to rectifier  504  via electrical connection  540 -B. It will occur to a person skilled in the art that each U-bank  50 -X is connected to a subsequent U-bank  50 -X+1 via electrical connection  508 -X, where X is the final U-bank before electrical connection  540 -B. It will also occur to a person skilled in the art that this architecture and configuration of U-banks  50  is modular, expandable and scalable to any suitable size for particular applications. It will also occur to a person skilled in the art that footprint  524  is not limited to any size or any shape. 
     Rectifier  504  acts as a power supply, supplying DC power to U-banks  50 . Rectifier  504  may receive its power from the power grid as AC power, or alternatively from other AC or DC generating power sources. Rectifier  504  may also be replaced with other DC power sources, such as solar panels, or other high current converters. Each terminal on rectifier  504  is connected to a terminal of a U-bank  50  of the same polarity through electrical connection  508 . In the current embodiment, the positive terminal on rectifier  504  is connected to the positive terminal of U-bank  50 - 1 , and the negative terminal on rectifier  504  is connected to the negative terminal of U-bank  50 - 10 . In completing the circuit, the negative terminal of U-bank  50 - 1  is connected to the positive terminal of U-bank  50 - 2 . It will occur to a person skilled in the art the connections in polarity between each U-bank  50  and rectifier  504  may occur in different configurations depending on the configurations and placements of U-banks  50 . In certain embodiments, the rectifier  504  may be capable of delivering increased amperage or current to the unipolar electrolyser cells in high-power unipolar electrolyser plant  500  to make up for the loss of hydrogen production resulting from sectional maintenance. Preferably, rectifier  504  is capable of delivering between 5% and 50% more amperage or current than normal operating conditions of high-power unipolar electrolysis plant  500 . 
     In the current embodiment depicted in  FIGS. 5A and 5B , rectifier  504  is a single unit. Alternatively, a rectifier system including a group of rectifiers operating in parallel may be used to obtain the desired total current. Rectifier system can be composed of numerous parallel rectifier units with voltages between 100 and 2000 or more volts and current of 30,000 to 500,000 or more amperes. 
     Adjacent U-banks  50  may be arranged in any manner, but are preferably arranged in an adjacent, spaced apart, side-by-side arrangement as shown in  FIGS. 3A, 3B, 5A and 5B , with one U-bank being disposed parallel or substantially parallel to the next adjacent U-bank with a service corridor  520  formed therebetween. The advantage of this arrangement is the placement of service corridor  520  between U-banks  50 , allowing for maintenance of individual cell arrays  512 -A and  512 -B. Placing U-banks  50  adjacent to each other also allows for the consolidation of valving, input conduits and/or output conduits, which items will be described in greater detail below. The preferred dimension of service corridor  520  will be at least the size necessary for removal of a single unipolar cell  104  from the array into the corridor itself so that it can be effectively transported down the corridor. Alternatively, if a suitably designed gantry crane was placed above the specific array where the unipolar cell  104  is to be removed, corridor  520  may be narrower. The design and dimensions of service corridor  520  allows unipolar electrolysis cell  104  to be readily removed towards the outer perimeter of hydrogen plant  500 . 
     Each U-bank  50  includes two longitudinal cell arrays  512 -A and  512 -B (also referred to herein as cell blocks  512 -A and  512 -B, or segmented cell arrays  512 -A and  512 -B), valving, in the nature of isolation valves  416 ,  420 ,  424 ,  440 , and  432  (also referred to herein as valves  416 ,  420 ,  424 ,  440 , and  432 ), a plurality of input conduits  408 , and  412  and a plurality of output conduits  428 ,  436 , and  444 . In the current preferred embodiment, cell arrays  512 -A and  512 -B are arranged in a spaced apart, side-by-side arrangement, with cell array  512 -A being disposed parallel or substantially parallel to cell array  512 -B of the same U-bank. This allows for an additional service corridor  516  to be defined between the cell arrays  512 -A and  512 -B, where cell array  512 -A is disposed on one side of service corridor  516 , and cell array  512 -B is disposed on the other side of service corridor  516 . Service corridor  516  allows for ease of access to either cell array  512 -A or  512 -B for maintenance purposes. The preferred dimensions of the service corridor  516  are generally less than the service corridor  520 , provided there is no intent to withdraw an electrolysis cell towards the central corridor  528 . If the electrolyser cell  104  is to be removed to corridor  528 , then the dimension of corridor  516  must be wide enough to accommodate the effective removal from the array of a water electrolysis cell (which depends on the dimensions of the water electrolysis cell plus an allowance for turning or other adjustments required during the removal or replacement process). 
     It will occur to a person skilled in the art that while service corridors  516  and  520  allow for access to cell arrays  512 -A and  512 -B on either side thereof, hence granting greater access for maintenance, access to cell arrays  512 -A and  512 -B may be restricted to a single side of cell arrays  512 -A and  512 -B, and only service corridors  516  or service corridors  520  may be present. 
     Cell array  512 -A is electrically connected to cell array  512 -B by way of an end cell array bus bar connector  404  (also referred to herein as electrical connection  404 ). The bus bar connector  404  connects to cell array  512 -B at an end thereof opposite to the end at which the electrical connection joins cell array  512 -B to cell array  512 -A. In the embodiment shown in  FIG. 5A , array bus bar connector  404  is along a second side of each series  532  and  536  of U-banks  50 , where the first side and second side of series  532  and  536  are opposite to each other. 
     Each cell array  512 -A and  512 -B includes several unipolar alkaline water electrolyser cells  104  connected to each other electrically in series (also referred to herein as unipolar water electrolyser cell  104 ). Each cell array  512 -A and  512 -B may be configured to receive between 2 MW and 125 MW of power to produce hydrogen. In a preferred embodiment, each cell array  512 -A and  512 -B may include between 2 and 100 unipolar electrolyser cells. In determining the number of U-banks  50  and electrolyser cells  104 , the following design considerations may be taken into account: Given that this design is appropriate for very large unipolar hydrogen plants, the preferred number of cells  104  in a U-bank  50  will equate to the total cells in the unipolar electrolysis plant  500  divided by the desired number of U-banks  50 . The desired number of U-banks  50  is determined by the maximum preferred percentage of total unipolar electrolysis plant  500  which is to be sectioned off for maintenance. A large scale electrochemical process such as aluminum production is known to use a total of 2,000 volts DC across its array of cells and having cell currents at over 500,000 amperes. Large scale unipolar hydrogen plants with such capacity can be envisioned as the demand for hydrogen from water electrolysis grows. The decision by the designer, vendor or owner of the hydrogen plant  500  will determine the percentage of the plant which a sectional maintenance U-bank will be. For a non-limiting example, if the individual voltage of a single water electrolysis cell is 2 volts, then 1,000 water electrolysis cells would be required for a hydrogen plant with similar power capacity of the above mentioned aluminum plant. If the decision for sectional maintenance size is 10% of the overall production, then the resulting layout would have ten U-banks each with 100 unipolar water electrolysis cells. Each array would have 50 cells. If the center-to-center distance between adjacent cells in a single array was 1 m, the array (and hence the U-bank) would be approximately 50 m long. At 2 volts per cell, the voltage of each array would be 100 volts. From a layout  524  perspective having an even number of U-banks with an even number of cells may be optimal, though those skilled in the art could consider alternative designs with as low as three (3) U-banks. As the number of U-banks increases beyond three, the designer will find an even number of U-banks to be preferred. 
     In a preferred embodiment, U-banks  50  includes a first cell array  512 -A and a second cell array  512 -B that have the same hydrogen and oxygen production capabilities/capacities, have the same number of unipolar electrolyser cells  104 , and have the same capacity for accommodating DC power. However, it will occur to a person skilled in the art that U-banks  50  may include a first cell array  512 -A that differs in hydrogen production capabilities, or the number of unipolar electrolyser cells  104 , or a different capacity of accommodating DC power than that of cell array  512 -B. 
     Furthermore, in a preferred embodiment, each U-bank  50  in the same high-power unipolar electrolyser plant  500  has the same hydrogen and oxygen production capabilities/capacities, has the same number of unipolar electrolyser cells  104  in cell arrays  512 -A and  512 -B, and has the same capacity for accommodating DC power. In addition, in a preferred embodiment, each U-bank  50  has the same number of cell arrays. However, it will occur to a person skilled in the art that each U-bank  50  may differ in hydrogen production capabilities, or the number of unipolar electrolyser cells  104  in cell arrays  512 -A and  512 -B, or a different capacity of accommodating DC power, or a differing number of cell arrays. 
     An example of unipolar alkaline water electrolyser cell  104  can be seen in  FIG. 1 . Unipolar water electrolyser cell  104  receives water (H 2 O) and DC electrical power, and will break the water (H 2 O) into hydrogen gas (H 2 ) and oxygen gas (O 2 ) using electricity, and then discharge the hydrogen gas and oxygen gas. Unipolar water electrolyser cell  104  may also allow cooling water to flow through, to ensure that unipolar water electrolyser cell  104  stays cool during the electrolysis process. A further description of an exemplary unipolar electrolyser cell which may make up cell array  512 -A or  512 -B may be found in patent applications PCT/CA2021/050979 and PCT/CA2021/051240, both of which are incorporated by reference. 
     Referring to  FIG. 2 , an example U-bank  50  may be seen, where each cell array  512 -A and  512 -B each receive feed water through feed water input conduit  408  (also referred to herein as water input conduit  408 ), cooling water through cooling water input conduit  412  (also referred to herein as cold water input conduit  412 ) and DC electrical power to perform electrolysis. Once electrolysis has occurred, the hydrogen gas and oxygen gas produced is sent from cell arrays  512 -A and  512 -B through output conduits  436  and  444  respectively to be collected. Cooling water is also sent from cell arrays  512 -A and  512 -B through cooling water output conduit  428  to exit example U-bank  50 . 
     Referring to  FIG. 4A , U-bank  50  also includes a plurality of input conduits and a plurality of output conduits. The input conduits include water (H 2 O) input conduit  408  and cooling water input conduit  412 . Along input conduits  408  and  412 , valving, in the nature of valves  416  and  420 , are present. Valves  416  and  420  control the flow of water and cooling water within their respective input conduits  408  and  412 . More specifically, valve  416  controls the flow of water into cell array  512  along water input conduit  408 , and may even stop the flow of water into cell array  512 -A or  512 -B altogether. Similarly, valve  420  controls the flow of cooling water into cell array  512 -A or  512 -B along cooling water input conduit  412 , and may even stop the flow of cooling water into cell array  512 -A or  512 -B. 
     Output conduits include cooling water output conduit  428 , hydrogen gas output conduit  436 , and oxygen gas output conduit  444 . Output conduits  428 ,  436  and  444  may include valving, in the nature of valves  424 ,  432  and  440 . More specifically, cooling water conduit  428  may include valve  428  to control the outflow of cooling water, and may prevent cooling water from leaving U-bank  50 . Similarly, hydrogen gas output conduit  436  may include valve  432  to control the outflow of hydrogen gas, and to prevent hydrogen gas from leaving U-bank  50 . Oxygen gas output conduit  444  may include valve  440  to control the outflow of oxygen gas, and to prevent oxygen gas from leaving U-bank  50 . Valves  432  and  440  may also prevent any reverse flow of hydrogen gas and oxygen gas returning into U-bank  50 . 
     U-bank  50  may further include a multi purpose water seal  70 , vent exhausts  76  (also referred to as gas offtakes  76 ), mist eliminators  72  and optional isotropic enrichment columns  74  (also referred to as isotope (deuterium) enrichment columns  74 , or enrichment columns  74 ) and any related attachments needed for isotope enrichment. Water seal  70  or similar devices which can prevent reverse flow of gases into the U-bank from other U-banks, provide pressure balancing between oxygen and hydrogen, and provide an overpressure release mechanism for either or both hydrogen and oxygen gases leaving cell arrays  512 -A and  512 -B and entering the hydrogen gas output conduit  436  and the oxygen gas output conduit  444 .  FIG. 4A  depicts a single water seal  70  for both hydrogen gas output conduit  436  and oxygen gas conduit  444 . In this embodiment, water seal  70  has two separate compartments, one compartment for hydrogen gas, and the second compartment for oxygen gas. Alternatively, there may be two separate water seals, one for hydrogen gas and one for oxygen gas, leading to a water seal dedicated to hydrogen gas on hydrogen gas output conduit  436 , and a water seal dedicated to oxygen gas on oxygen gas output conduit  444 . U-bank  50  may further include a deuterium capture system between cell arrays  512 -A and  512 -B, and vent exhausts  76 . Such a system may capture condensates for further deuterium enrichment from the hydrogen and/or the oxygen gases which are enriched in deuterium. Though not shown in the figures, those skilled in the art will understand additional conduits would be required for transport of the enriched deuterium into other U-banks or removal from unipolar electrolyser plant  500  to other enrichment mechanisms or as a finished product. Other such minor streams may be required including floor drains, venting systems, electrical instrumentation wires, gas analysers, and other non-limiting conduits selected by the designer for which isolation or sectional maintenance may require adjustments for isolations. 
     Vent exhausts  76  are located along hydrogen gas output conduit  436  and oxygen gas conduit  444 , prior to valves  432  and  440 , and allow for the release of the hydrogen and/or the oxygen in the event of the down stream valves  432  and  440  being closed or a blockage down stream of the water seal  70 . Purge gas can also flow through the hydrogen and oxygen gas headers and be travel through the exhaust vents  76  when the downstream valves are closed. In a preferred embodiment, there may be up to four vent exhausts  76  for U-bank  50 , a first vent exhaust  76  for venting oxygen from the first oxygen water seal  70  of the first cell array  512 -A, a second vent exhaust  76  for venting hydrogen gas from the first hydrogen water seal  70  of the first cell array  512 -A, a third vent exhaust  76  for venting oxygen gas from the second oxygen water seal  70  of the second cell array  512 -B, and a fourth vent exhaust  76  for venting hydrogen gas from the second hydrogen water seal  70  of the second cell array  512 -B. Purging of the gasses may be performed by closing off valves  432  and  440 , and then allowing pressure to build up so that vent exhausts  76  provides a pressure relief mechanism, and emptying out hydrogen and oxygen gases from U-bank  50 . The purging process may be aided by flushing out the hydrogen and oxygen gases from U-bank  50  using a purging gas. A purging gas may be introduced into U-bank  50  via a purging gas input conduit (not shown in figures). 
     Mist eliminators  72  are located along hydrogen gas output conduit  436  and oxygen gas conduit  444  downstream from water seal  70 , and are used for removal and management of trace aerosols in the gases. In one embodiment, there may be up to four mist eliminators  72  for U-bank  50 , a first mist eliminator  72  connected to the first oxygen gas output conduit  444  upstream of the second output valve  440 , a second mist eliminator  72  connected to the first hydrogen gas output conduit  436  upstream of the third output valve  432 , a third mist eliminator  72  connected to the second oxygen gas output conduit  444  upstream of the fifth output valve  440 , and a fourth mist eliminator  72  connected to the second hydrogen gas output conduit  436  upstream of the sixth output valve  432 . It will occur to a person in the art that there are different possible configurations and arrangements of mist eliminators  72  in U-bank  50 . 
     Isotope (deuterium) enrichment columns  74  are located along hydrogen gas output conduit  436  and oxygen gas conduit  444  downstream from mist eliminators  72 . In one embodiment, there may be up to four enrichment columns  74  for U-bank  50 , a first enrichment column  74  connected to the first oxygen gas output conduit  444  upstream of the second output valve  440 , a second enrichment column  74  connected to the first hydrogen gas output conduit  436  upstream of the third output valve  432 , a third enrichment column  74  connected to the second oxygen gas output conduit  444  upstream of the fifth output valve  440 , and a fourth enrichment column  74  connected to the second hydrogen gas output conduit  436  upstream of the sixth output valve  432 . It will occur to a person in the art that there are different possible configurations and arrangements of isotope (deuterium) enrichment columns  74  in U-bank  50 . 
     It will occur to a person skilled in the art that while water seal  70 , vent exhaust  76 , mist eliminator  72 , and enrichment columns  74 , remain in the same sequence along the hydrogen gas output conduit  436  and oxygen gas output conduit  444 , they may occur anywhere along output conduits  436  and  444 . This will be further discussed below. 
     In the embodiment shown in in  FIG. 4A , input conduits  408  and  412  are provided for each cell array  512 -A and  512 -B within U-bank  50 , and valves  416  and  420  are located on each input conduit  408  and  412  respectively. Input conduits  408  and  412  are preferably made of an insulating material to ensure electrical isolation to U-bank  50 . Alternatively, the connection points between input conduits  408  and  412  and cell arrays  512 -A and  512 -B are made with an insulating material. In the provided embodiment, there are a total of four input conduits, two water input conduits  408 , and two cooling water input conduits  412 . This can also be seen in  FIG. 3A , where each cell array  512 -A,  512 -B has its own input conduits. In alternative embodiments, there may be a single water input conduit  408  supplying U-bank  50 , where the single water input conduit  408  may be split within U-bank  50  into two branches to provide water to each cell array  512 -A,  512 -B, as is shown in  FIG. 3B . Valve  416  (not shown in  FIG. 3B ) may be located along single water input conduit  408  prior to the split, hence controlling the flow of water for the entire U-bank  50 . Alternatively, valve  416  may be located along the branches of water input conduit  408  after the split, hence controlling the flow of water into individual cell arrays. 
     Similarly, cooling water input conduits  412  may have different configurations. Returning to  FIG. 3A , cooling water input conduits  412  may lead to individual cell arrays  512 -A,  512 -B, or alternatively, as depicted in  FIG. 3B , a singe cooling water input conduit  412  may supply U-bank  50 , where it may be split within U-bank  50  into two branches to provide cooling water to each cell array  512 -A,  512 -B. Valve  420  (not shown in  FIG. 3B ) may be located along cooling water conduit  412  prior to the split, or may be located along the branches of cooling water conduit  412  after the split. 
     It will occur to a person skilled in the art that there are different configurations of input conduits  408  and  412  in U-bank  50 . In addition, it will occur to a person skilled in the art that there are different configurations for water conduits and cooling water conduits leading from a water source  304  and conduits leading from a cooling water source  308 , and the distribution and branching of the conduits prior to connecting to input conduits  408  and  412 . For example, in the embodiment as depicted in  FIG. 5A , conduits leading from a water source may be split off into two sub-conduits to supply the two columns of U-banks  50 , after which the two sub-conduits may connect to the plurality of input conduits  408  supplying water to each U-bank  50 . 
     Returning to  FIG. 4A , in the embodiment depicted, output conduits  428 ,  436 , and  444  exist for each cell array  512 -A,  512 -B within U-bank  50 . Output conduits  428 ,  436  and  444  are preferably made of an insulating material, or have electrical isolation breaks, to ensure electrical isolation to U-bank  50 . Alternatively, the connection points between output conduits  428 ,  436  and  444  and cell arrays  512 -A and  512 -B are made with an insulating material. Similar to the previously described embodiments of input conduits  408  and  412 , output conduits  428 ,  436 , and  444  may lead to main conduits  312 ,  316 , and  320  collecting cooling water and the hydrogen and oxygen gas byproducts, or alternatively, output conduits  428 ,  436  and  444  may converge into a single output conduit for each element, and may then exit U-bank  50  into main collecting conduits  312 ,  316 , and  320 . For example,  FIG. 3A  aligns with  FIG. 4A , in that there are output conduits  428 ,  436  and  444  leading away from each cell array  512 -A,  512 -B. More specifically, each cooling water conduit  428  leaves cell array  512 -A,  512 -B and U-bank  50  before joining with main cooling water output conduit  320 . Each hydrogen gas output conduit  436  leaves cell array  512 -A,  512 -B and U-bank  50  before joining with main hydrogen gas output conduit  312 . Similarly, each oxygen gas output conduit  444  leaves cell array  512 -A,  512 -B and U-bank  50  before joining with main oxygen gas output conduit  316 . In this embodiment, water seal  70 , exhaust vents  76 , mist eliminators  72 , isotope (deuterium) enrichment columns  74  are located on each output conduit  436  and  444  leaving cell array  512 -A,  512 -B, and valves  424 ,  432 , and  440  are located on each output conduit  428 ,  436  and  444  leaving cell array  512 -A,  512 -B, prior to joining the main output conduits  312 ,  316 ,  320 . 
     Alternatively, as depicted in  FIG. 3B , output conduits  428 ,  436  and  444  from cell arrays  512 -A,  512 -B may converge prior to leaving U-bank  50  and joining main output conduits  312 ,  316 , and  320 . More specifically, cooling water output conduits  428  from each cell array  512 -A,  512 -B within U-bank  50  may converge into a single cooling water output conduit  428  within U-bank  50 . As the single cooling water output conduit  428  departs U-bank  50 , it joins with the main cooling water output conduit  320 . The two hydrogen gas output conduits  436  leaving each cell array  512 -A,  512 -B within U-bank  50  may converge into a single hydrogen gas output conduit  436  within U-bank  50 . As the single hydrogen gas output conduit  436  departs U-bank  50 , it joins with the main hydrogen gas output conduit  312 . Similarly, the two oxygen gas output conduits  444  leaving each cell array  512 -A,  512 -B within U-bank  50  may converge into a single oxygen gas output conduit  444  within U-bank  50 . As the single oxygen output conduit  444  departs U-bank  50 , it joins with the main oxygen gas output conduit  316 . While not shown, in this embodiment, valves  424 ,  432 , and  440  may be located either on output conduits  428 ,  436 , and  444  leaving cell arrays  512 -A,  512 -B, or the aforementioned converged single output conduits  428 ,  436 , and  444 . Water seal  70 , exhaust vents  76 , mist eliminators  72 , and enrichment columns  74  may also be located on either output conduits  436  and  444  leaving cell arrays  512 -A,  512 -B, or the aforementioned converged single output conduits  436  and  444 , so long as they are located prior to valves  432  and  440 . 
     It will occur to a person skilled in the art that there are different configurations and arrangements of output conduits  428 ,  436  and  444 . Furthermore, it will occur to a person skilled in the art that there are different configurations and arrangements of water seal  70 , exhaust vents  76 , mist eliminators  72 , enrichment columns  74  and valves  424 ,  432 , and  440 . 
     Different pathways for input conduits and output conduits are contemplated including multiple configurations and variations of main input and output conduits, input and output conduits leading to and from u-banks  50 , and the location of flow splitters or branches leading to and from cell arrays  512 -A and  512 -B. 
     It will also occur to a person skilled in the art that different combinations of input conduits and output conduits arrangements are possible. For example, the input conduits on a number of U-banks  50  may be cell array based, whereas the output conduits on the same U-banks may converge and be U-bank based. 
     As previously stated, one advantage of the configuration of U-banks  50  in high-power electrolysis plant  500  is the ability to perform maintenance on cell arrays  512 -A,  512 -B within U-banks  50  without shutting down the entire high-power electrolysis plant  500  for the entire duration of the maintenance task. This is achieved by bypassing the identified U-bank  50  that requires maintenance and increasing the input of water through water input conduits  408  and DC power from rectifier  504  to the remaining U-banks  50  to maintain a steady output, despite the loss of a U-bank  50 . 
     Referring to  FIG. 4B , a section of high-power unipolar electrolysis plant  500  having three U-banks  50 , is depicted. For this section, the three U-banks  50  are labeled as U-banks  50 -(Y−1), U-bank  50 -Y and U-bank  50 -(Y+1). Electrical connection  508 -Y can be seen between U-bank  50 -(Y−1) and subsequent U-bank  50 -Y. Electrical connection  508 -(Y+1) can also be seen between U-bank  50 -Y and U-bank  50 -(Y+1). In the examples provided below, U-bank  50 -Y is identified as requiring maintenance. 
     Bypass electrical connection  80  (also referred to herein as electrical bypass busbar extension  80 ) starts at a first isolation point  204 , and ends at second isolation point  208 , effectively bypassing the identified U-bank  50 -Y that requires maintenance. The bypass electrical connection  80  allows DC power from rectifier  504  to be supplied to the subsequent U-bank  50 -(Y+1) which does not require maintenance, and which is intended to remain operational while U-bank  50 -Y being serviced. Grounding points at isolation point  204  and at isolation point  208  may be desirable or required by electric codes. 
     As shown in  FIG. 4B , bypass electrical connection  80  further includes jumper  60  (also referred to herein as switch  60  or busbar segment  60 ) which allows the opening and closing of the circuit through bypass electrical connection  80 , and jumpers  62  and  64  (also referred to herein as switches  62  and  64  or busbar segments  62  and  64 ). Jumpers  60 ,  62  and  64  may be made of conductive materials such as copper or aluminum (though those skilled in the art will understand alkaline electrolytes should not be allowed onto aluminum jumpers). Jumpers  60 ,  62  and  64  have an open position and a closed position, and may be actuated to change from the open position to the closed position, or may be actuated to change from the closed position to the open position. 
     Jumpers  62  and  64  are operable to cut off power to the first cell array  512 -A and second cell array  512 -B within U-bank  50 -Y. Jumper  62  is located upstream of the first cell array  512 -A of U-bank  50 -Y and once operated, may electrically isolate the U-bank from the main plant bus bar at isolation point  204 . More specifically, jumper  62  may electrically isolate the first electrolysis cell  104  of the first cell array  512 -A. Jumper  64  is located downstream of the second cell array  512 -B of U-bank  50 -Y and once operated, may electrically isolate the entire U-bank from the main plant bus bar. More specifically, jumper  64  may electrically isolate the last electrolysis cell  104  of the second cell array  512 -B. The operation of jumpers  60 ,  62 , and  64  allow for the process of bypassing U-bank  50 -Y. When maintenance on U-bank  50 -Y is needed, jumpers of  62  and  64  may be opened, blocking DC power from continuing through the U-bank  50 -Y that requires maintenance. Once jumpers  62  and  64  have been opened, jumper  60  on bypass electrical connection  80  may be closed to redirect the DC power to the subsequent U-bank  50 -(Y+1), successfully isolating the U-bank  50 -Y without having to discontinue operation of other U-banks  50 -(Y−1) and  50 -(Y+1) for a prolonged period of time. 
     As indicated above, jumpers  60 ,  62  and  64  may also be switches or busbar segments. It will occur to a person skilled in the art that there may be other apparatus to control the opening and closing of the circuit that may replace jumpers  60 ,  62  and  64 . 
       FIG. 5B  depicts bypass electrical connection  80  as part of high-power unipolar electrolysis plant  500 . In this embodiment, the identified U-bank  50  requiring maintenance may be bypassed using bypass electrical connection  80 . For a unipolar electrolyser plant  500  with numerous (e.g., more than 2 to 3) U-banks, bypass electrical connection  80  can be added from time to time to enable the isolation of a specific U-bank requiring maintenance. Alternatively, for a larger unipolar electrolyser plant  500 , bypass electrical connection  80  may be built into the plant during the initial construction. As such, bypass electrical connection  80  may be temporarily placed between isolation points  204  and  208  to bypass the U-bank  50  undergoing maintenance, or bypass electrical connection  80  may be fixed between isolation points  204  and  208  and engaging jumper  64  will close the circuit enabling the bypass of the U-bank  50  undergoing maintenance. Those skilled in the art could design a suitable connection point for bypass electrical connection  80  to isolation points  204  and  208 . As previously stated, the bypass electrical connection  80  enables DC power to continue along the electrical circuit to the following U-bank  50  where regular operation of electrolysis may continue. The isolated U-bank  50  may then undergo the necessary maintenance, repairs or part replacements without disruption to the remaining U-banks  50  within high-power unipolar electrolysis plant  500 . Once maintenance, repairs, or part replacements are complete, the isolated U-bank  50  may be reconnected to the electrical circuit. Also, while  FIG. 5B  shows a single bypass electrical connection  80  for ease of illustration, in a preferred embodiment, it will be appreciated that each U-bank would have its own bypass electrical connection  80 . 
       FIG. 6  depicts a method  600  of bypassing a U-bank  50  for maintenance, wherein power is shut down to high-power unipolar electrolysis plant  500  for only the duration of time where the bypass electrical connection is installed. 
     At block  605 , high-power unipolar electrolysis plant  500  is powered down. This may be done by turning off rectifier  504 , and/or disconnecting rectifier  504  from its AC power source. 
     Once power has been shut off to high-power unipolar electrolysis plant  500 , and hence to all U-banks  50 , the identified U-bank  50  that requires maintenance needs to be isolated both from a fluid standpoint and electrically. Isolation is required, not only for the performance of the maintenance, but also to ensure that other U-banks  50  in high-power unipolar electrolysis plant  500  are not interrupted or disturbed. 
     At block  610 , U-bank  50  to undergo maintenance is fluidly isolated from feed water, and cooling water inputs, and hydrogen gas and oxygen gas outputs. Fluid isolation is achieved by actuating/closing valves  416 ,  440  and  432 . More specifically, valve  416  is closed to prevent supplying feed water to U-bank  50  through water input conduit  408 , and valves  432  and  440  are closed to isolate the hydrogen and oxygen gas leaving U-bank  50  through hydrogen gas output conduit  436  and oxygen gas output conduit  444  and to prevent the backflow of gases generated by other U-banks  50  that may be in operation once the power is turned back on. Purging of U-bank  50  of any hydrogen or oxygen gas may also occur by flushing out all hydrogen and oxygen gas from U-bank  50  by introducing a purging gas to the U-bank  50  prior to the closing of valves  432  and  440 , and venting hydrogen and oxygen gas out of vent exhaust  76 . Those skilled in the art will understand minor custom connecting lines may also be isolated at this point. 
     Valves  420  and  424  may also be optionally closed to isolate U-bank  50  from cooling water. Valves  420  and  424  may be left open if it is desired to cool down the individual electrolysis cells  104  faster than they would otherwise cool down without cooling water flow. Valves  420  and  424  may then be shut down once cooling has been completed prior to maintenance commencing. Once there are no liquids or gases moving through the U-bank  50  to be maintained, it is then considered to be fluidly isolated from the remainder of high-power unipolar electrolysis plant  500 . 
     At block  615 , the first cell array  512 -A of U-bank  50  to undergo maintenance is isolated electrically. Electrically isolating the first cell array  512 -A of U-bank  50  is achieved by actuating/removing jumper  62  and creating an open circuit. More specifically, opening jumper  62  electrically isolates the first electrolysis cell  104  in the first cell array  512 -A. Jumper  62  is located upstream of the first cell array of U-bank  50  to be isolated. 
     At block  620 , the second cell array  512 -B of U-bank  50  to undergo maintenance is isolated electrically. Electrically isolating the second cell array  512 -B of U-bank  50  is achieved by actuating/removing jumper  64  and  64 , hence creating an open circuit, and isolating U-bank  50  from the remainder of the high and creating an open circuit. More specifically, opening jumper  64  electrically isolates the last electrolysis cell  104  in the second cell array  512 -B. Jumper  64  is located downstream of the second cell array of the U-bank  50  to be isolated. 
     Removing jumpers  62  and  64  can be done one after another, in either order. Once the jumpers  62  and  64  have been opened, U-bank  50  undergoing maintenance will be isolated electrically from the other U-banks  50  in high-power electrolysis plant  500 . 
     At block  625 , a bypass circuit provided to the high-power water electrolysis plant  500  is actuated. Electrical bypass busbar extension  80  acts as the bypass circuit and is attached to isolation point  204 , upstream of jumper  62 , and isolation point  208 , downstream of jumper  64 . As previously stated, in certain embodiments, electrical bypass busbar extension  80  may be moved to bypass U-bank  50  undergoing maintenance. In other embodiments, bypass busbar extension  80  is already built into high-power unipolar electrolysis plant  500 , and as such may already be attached to isolation points  204  and  208 . Once bypass busbar extension  80  is connected, jumper  60  may be actuated/closed, and hence closing the circuit along electrical bypass busbar extension  80 . Jumper  60  cooperates with bypass busbar extension  80  to complete the circuit in high-power water electrolysis plant  500 . By completing the circuit, DC current is directed away from U-bank  50  to undergo maintenance, and flows from the previous U-bank  50  (or rectifier  504  if U-bank  50  to undergo maintenance is the first U-bank  50 ) to the subsequent U-bank  50  (or rectifier  504 , if U-bank  50  to undergo maintenance is the last U-bank  50 ). U-bank  50  to undergo maintenance is effectively bypassed electrically. 
     At block  630 , high-power water electrolysis plant  500  is powered up, with the DC power redirected/bypassing the isolated U-bank  50 . Maintenance may now be safely performed on the isolated U-bank  50 . 
     Method  600  may be performed by a control mechanism with a manual disconnect switch, or may be automated with a powered switch. Alternatively, method  600  may also be performed by manually removing a section of the bus bar where the isolation is required. 
     As previously stated, the amount of power from DC power supply  504  may be increased to compensate for the loss in production in high power water electrolysis plant  500  following the fluid and electrical isolation of U-bank  50  to be isolated. 
     It will occur to a person skilled in the art hat blocks  605  to  630  are to be performed with safety protocols in mind, including, but not limited to, the grounding of any points along the circuit to ensure the safety of operators and users. 
     It will occur to a person skilled in the art that isolation of U-bank  50  for maintenance is not limited to a single U-bank  50 . Multiple U-banks  50  may be isolated at the same time, or at different times, and high-power unipolar electrolysis plant  500  may continue to operate. 
     It will also occur to a person skilled in the art that once U-bank  50  has completed maintenance, it may be placed back into service in high-power unipolar electrolysis plant  500  by performing the steps in method  600  in reverse. More specifically, power is turned off to all U-banks, jumper  60  is removed from electrical bypass busbar extension  80 , electrical bypass busbar extension  80  is disconnected from isolation points  204  and  208 , jumpers  62  and  64  are closed to complete the circuit with U-bank  50  in serial with the remaining U-banks in high-power unipolar electrolysis plant  500 , valves leading to and away from U-bank  50  are opened to allow fluid and gases to flow through U-bank  50 , and power is turned on to all U-banks  50 . 
     If incorporated, consider adjustment of the offload tap changer of the rectifier transformer to adjust DC voltage to obtain a higher power factor. For example, if 10% of the plant is isolated, then the nominal voltage from the rectifier power supply will drop by approximately 10%. An off load tap or on load tap changer covering the portion of the voltage reduced due to the removal of U-bank for sectional maintenance may be advised if the rectifier power factor is to be maintained. Additional mechanisms known by those skilled in the art of power supplies may also be implemented. 
     If a constant DC amperage is applied to high-power unipolar electrolysis plant  500  while any number of U-banks  50  are isolated, there will be a reduced output of hydrogen and oxygen gases or recovered isotopes due to fewer U-banks performing electrolysis. Increasing the amperage output of rectifier  504  to the remaining U-banks  50  in high-power unipolar electrolysis plant  500  may compensate for the reduced output. Increasing the amperage rectifier  504  may compensate anywhere between 5% to 50% of loss product output(s) only limited by the practical level of surplus current the water electrolysis plant can operate at. Optimization will depend upon factors such as energy efficiency of the system, The larger the plant  500  is, the more likelihood is that the increase in current may be limited to a smaller percentage of increased current such as 5% to 10%. However the larger the plant  500 , the more likely that the sectional maintenance size of an individual U-bank will be to 5% to 10% of the plants capacity. 
     It is noted that the foregoing disclosure describes the principles of the invention as applied to unipolar water electrolysis systems, however, it will be appreciated that the principles of the invention may also be applied to monopolar water electrolysis systems to similar advantage. In such cases, unipolar water electrolysis cells could be substituted for monopolar electrolyser cells, and all features or combinations of features described in respect of the embodiments relating to unipolar water electrolysis systems could be found as well in embodiments relating to monopolar water electrolysis systems. 
     Although the foregoing description and accompanying drawings related to specific preferred embodiments of the present invention as presently contemplated by the inventor, it will be understood that various changes, modifications and adaptations, may be made without departing from the spirit of the invention.