Bipolar plates are the heart of electrolysers, which are used to produce hydrogen. Depending on the manufacturing process, stacks can consist of hundreds of such bipolar plates, whereby a single defective plate can negatively impact the performance of the entire stack. Because of this, it makes sense to monitor the voltage of each plate separately. Weidmüller has developed solutions for this purpose. With these solutions measured values can be recorded and processed reliably, safely and economically, even in potentially explosive areas.
Green hydrogen is both, a source of energy and a source of hope. This makes it an ideal supplement to more volatile power sources like photovoltaics and wind energy. In addition, some electrolysis processes also allow for the use of waste heat. Accordingly, there are a wide range of possible sites where electrolysers can be deployed. These might include cement plants, offshore wind turbine systems, or a company’s facility where hydrogen might be generated to operate industrial trucks, for example forklift trucks. As diverse as their designs and processes may be: in principle, all electrolysers require two electrodes, separated by a membrane. The cell voltage for separating hydrogen molecules into H2 and O2 is around 2.5 V. For a stack of 100 bipolar plates, this would be 250 V. However, depending on the stack size and interconnection, it can also be several hundred to well over a thousand volts. The operation of the plates is subject to ageing processes, although a service life of up to 20 years is expected. The worst cell always determines the overall performance of the stack. In this case, adjusting the stack parameters can keep efficiency high and detect cell degradation. To do so, the plates must be continuously and individually monitored via condition monitoring, so-called single cell monitoring. Weidmüller has developed specific solutions to implement this monitoring from a technical and practical standpoint, through close coordination with electrolyser manufacturers.
Safe measurement points on the stack
As indicated, a stack may include hundreds of cells located in a zone 1 or 2 explosion hazard area. Therefore, it is essential to comply with the high requirements for the explosive zone. The connecting cables to the bipolar plates must be connected securely and must be routed out of the explosive zone via the shortest possible route. Weidmüller provides the entire chain of components necessary to do so. From the plate contact to data pre-processing and the bus connection including data communication and data analysis.
The temperature in the stack during the most common processes (PEM and alkaline electrolysis) is 60–100°C. In this case, contacts can be designed using commonly available blade receptacles and silicone lines with a resistance class up to 125°C.
“In addition to single connections, multipol connections are also possible by using unique connectors mouted on a Printed Circuit Board”, explains Matthias Kaspar, Application Manager Hydrogen at Weidmüller and adds: “Multiple boards can be connected with just one plug-in process. The temperature-related expansion of the stack must be taken into consideration – this offers significant time savings for typical stacks used in PEM electrolysis.” Weidmüller maintains in-house electronic production, meaning the company can offer custom stack solutions.
There are a range of Weidmüller components available for the voltage tap and potential transmission to the evaluation unit, such as plug-in connectors and signal distribution boxes. These allow for custom, stack-specific solutions.
Interface solutions to meet customer needs: mechanical ...
There are many different types of electrolysis systems, whether for installation in covered warehouses or as modular container solutions. The latter can also be operated largely independently and in a decentralised manner. Such converted shipping containers are already being considered for installation in conjunction with offshore wind turbine systems. No matter the type, signals must be collected and routed reliably. Comprehensive system monitoring includes not only monitoring the cell voltages, but also other parameters such as power consumption, temperatures, system pressure, flow rates, etc. “Weidmüller has developed passive Ex signal distribution boxes with M12 ports to connect the sensors”, says Matthias Kaspar. “In contrast to most other products on the market, these can even be used in zone 1”, states the Application Manager. Up to 16 sensors or valves can be controlled via Y-lines. Components can be exchanged easily if maintenance is required. Another highlight are pluggable adapter bonnets that can be used to test the connected sensors or actuators without central control. The solution is ideal for the modular system structure of containers, in which signals from the sensors and actuators are collected decentral and routed to an encapsulated controller.
… and electronic
However, Weidmüller offers not only wiring but also data pre-processing. This is handled by the u-remote station approved for potentially explosive conditions (Ex approval) for zone 2. The processed data is transmitted to a gateway or router. Weidmüller provides variants for all common fieldbus protocols like PROFINET, Modbus TCP and of course, Ethernet to connect a controller. In addition to the LAN connection, connection to the customer’s or Weidmüller's own cloud is also possible via IoT boxes. This means that even remotely stationed systems can be monitored externally. This allows not only the user, but also the system manufacturer to access the system for diagnostics, service, or support.
In addition, Weidmüller offers specialised housings approved for use in explosive areas in which commonly available industrial components can be installed. Barriers are used for galvanic separation, allowing for safe connections up to zone 0. This allows the user to route signals easily, safely, and efficiently from zone 0 to the controller.
Stack monitoring and more
As mentioned above, a seamless CMS (condition monitoring system) involves a wide range of monitoring tasks. This includes recording power consumption upstream of the rectifier. With precise measurement data, the operator can decide for themselves when service is needed. Likewise, the stack can be maintained at an optimal operating point by changing other parameters, depending on the applicable situation. This is certainly an economical approach for remote systems.
Weidmüller is continuously working to develop additional components for its CMS portfolio, such as the u-sense vibration sensor to monitor pumps and compressors. Their vibrations indicate the wear and tear on bearings, or other imminent faults. Thanks to their battery operation, Bluetooth connection and individual attachment options, these sensors can also be installed subsequently. Other sensors are currently being developed, such as for monitoring preload force. Stacks are held with pre-tensioned springs so that they can expand in case of temperature changes without leaking. Continuous monitoring eliminates the need for regular adjustments using a torque wrench.
Weidmüller also has an accredited laboratory in-house to develop project-specific solutions that meet applicable standards. This means the company can provide all modules, from stack connection to data analysis for CMS and predictive maintenance in hydrogen generation. All components meet the highest requirements and directives, including the ATEX directive and UL standards.
