Author: Eduardo López González (INTA) - The intermittent nature of renewable energy sources has a significant influence on the operating conditions of electrolyzers for renewable hydrogen production. Relevant Key Performance Indicators (KPIs) of water electrolysis-based renewable hydrogen production systems are directly related to these operating conditions.
Electrolyzers typically use a modular architecture based on several stacks, to improve the overall system energy efficiency and extend their lifetime. Commercial electrolyzers are usually connected to AC grids, so AC/DC converters, or rectifiers, are required to supply power to the stacks. Depending on the number of stacks, they can be connected in series to a single rectifier, which manages the operating conditions of all the stacks in the chain. Moreover, these chains can be connected in parallel, to increase the flexibility of the operation, at the cost of increasing the complexity of the control system.
Different control strategies can be to optimize the global performance of the system. These strategies mainly consider the allocation of the available power among stacks and chains, as well as the on-off switching of individual stacks and chains. Power allocation will be evenly shared among the operating stacks in a chain, but the power allocated to each chain could be different, set by the rectifier.
Among the available water electrolysis technologies, Proton and Anion Exchange Membrane (PEM and AEM) electrolysis offer a suitable dynamic response and transient times regarding their integration with renewable energy sources. This work addresses the simulation and experimental validation of different operating strategies for three multi-stack systems based on different technologies and number of stacks. The proposed strategies dynamically distribute power demand among the stacks, according to different criteria: maximum hydrogen production, maximum operating efficiency and minimum degradation.