Monitor electrolysis stacks

Stacks - "plate stacks" - are the heart of electrolysers used to produce hydrogen. Depending on the manufacturing process, a stack consists of several hundred such bipolar plates, with a single defective plate affecting the performance of the entire stack. Therefore, it makes sense to monitor the voltage on each plate separately. Weidmüller has developed solutions for this purpose that allow the measured values to be recorded and processed safely, reliably and economically, even in potentially explosive atmospheres.

Green hydrogen is a source of hope and energy in equal measure, an ideal complement to the volatile power generators photovoltaics and wind power. In some electrolysis processes, waste heat can also be used. The possible locations for electrolysers are correspondingly diverse. They can be cement plants, offshore wind power plants or a factory site where hydrogen is produced, for example, for the operation of industrial trucks. As different as the designs and processes may be: in principle, two electrodes and a membrane in between are always needed. The cell voltage to separate the hydrogen molecules into H2 and O2 is about 2.5 V.

For a stack with 100 bipolar plates, this results in 250 V. However, depending on the stack size and wiring, it can be several hundred to well over 1,000 volts. The operation of the plates is subject to ageing processes, although a service life of up to 20 years is assumed. In this case, the worst cell always determines the overall performance of the stack. In this case, by adjusting the stack parameters, the efficiency can be kept high and the degradation of the cells can be detected. This requires that the plates are continuously monitored individually by condition monitoring, a so-called single cell monitoring. Weidmüller has developed specific solutions for the technical and practical implementation in close cooperation with electrolyser manufacturers.

Reliable measurement tapping on the stack

As mentioned, a stack can comprise several hundred cells that are located in a Zone 1 and 2 hazardous area. It must therefore be ensured that the high requirements for the hazardous area are met. The connecting cables to the bipolar plates must make safe contact and lead out of the hazardous area by the shortest route. For this purpose, Weidmüller provides the entire chain from the plate contact to the data pre-processing and the bus connection to the data communication and data analysis.

In the most common processes, PEM and alkaline electrolysis, the temperature in the stack is between 60 °C and 100 °C. The contact can be made here with the help of a contacting system. The contacting can be realised here with common flat receptacles and commercially available silicone cables of the resistance class up to 125 °C.

"In addition to individual contacting, multiple contacting is also possible. In this case, the contacts are applied to PCBs," explains Matthias Kaspar, Applications Manager for the Hydrogen Division at Weidmüller, and adds: "In this way, several boards can be contacted in a single plug-in process. The temperature-related expansion of the stack must be taken into account - for the typical stacks of PEM electrolysis, this means enormous time savings." Weidmüller has its own electronics manufacturing facility and can therefore offer customised plug-in solutions.

There is a range of Weidmüller components available for voltage tapping and potential transmission to the evaluation unit, such as connectors and signal distribution boxes. These enable individual and stack-specific solutions.

Interface solutions according to customer requirements: mechanical ...

Electrolysis plants are available in a wide variety of designs, for installation in covered halls or as modular container solutions. The latter can also be operated decentrally, largely independently. There are already considerations to install such converted overseas containers in connection with offshore wind power plants. In any case, the signals must be collected and safely routed. In the case of comprehensive monitoring of the plant, this includes not only the cell voltages, but also other parameters such as power consumption, temperatures, plant pressure or flow rates.

"Weidmüller has developed passive Ex signal distribution boxes with M12 connections for connecting the sensors," says Matthias Kaspar. "Unlike most other products on the market, these can even be used in Zone 1," continues the applications manager. Using Y-cables, up to 16 sensors or valves can thus be controlled. In case of maintenance, the components can be easily exchanged. Another highlight is the pluggable adapter bonnets, which can be used to test the connected sensors or actuators without central control. The solution is ideal for the modular system structure of containers, where the signals from the sensors and actuators are collected decentrally and routed to an encapsulated control system.

... and electronic

However, Weidmüller not only provides the wiring, but also the data pre-processing. This is done by the u-remote station with Ex approval for Zone 2. The data prepared in this way is passed on to a gateway or router. For connection to a controller, Weidmüller provides variants for all common fieldbus protocols such as PROFINET, Modbus TCP and of course Ethernet. In addition to the LAN connection, a connection via IoT boxes to the customer's cloud or Weidmüller's own cloud is also possible. This means that even remotely located systems can be monitored externally. In addition to the user, the system manufacturer can also access the system for diagnostics, service and support.

In addition, Weidmüller offers special Ex-approved enclosures in which standard industrial components can be installed. By means of barriers for galvanic isolation, safe connections up to Zone 0 are also possible. This enables the user to route signals from Zone 0 to the controller simply, safely and economically.

Stack monitoring and more

As already mentioned, a complete CMS (Condition Monitoring System) includes many monitoring tasks. Recording the power consumption upstream of the rectifier is also part of this. With precise measurement data, the operator can decide for himself when a service makes sense. Likewise, the stack can be kept at an optimised operating point depending on the respective situation by means of other parameter settings. This is certainly economical for remote installations.

Weidmüller is constantly developing further components for its CMS portfolio, for example the u-sense vibration sensor for monitoring pumps and compressors. Their vibration behaviour provides information about the wear of bearings or other impending faults. Thanks to battery operation, Bluetooth connection and individual mounting options, this sensor is also suitable for retrofitting. Other sensors, for example for monitoring preload forces, are under development. The stacks are held in place with pre-tensioned springs so that they can expand with temperature changes and do not leak. Permanent monitoring makes regular retightening with a torque spanner unnecessary.

Weidmüller also has its own accredited laboratory to develop project-specific solutions in line with standards. This enables the company to provide all modules from stack contacting to data analytics for CMS and predictive maintenance in hydrogen generation. All components comply with the highest requirements and guidelines, including the ATEX directive and UL standards.