The global energy transition calls for scalable, low-carbon solutions. Hydrogen is increasingly seen as a cornerstone of future energy systems—particularly when produced via electrolysis using renewable electricity. The phase-out of conventional power plants with controllable generation and high rotational inertia is affecting grid stability and diminishing the availability of ancillary services. Wind and solar power, while crucial for decarbonization, can currently provide these services only to a limited extent [1]. Consequently, electrolyzers are increasingly being considered for grid support, particularly for the provision of requency Containment Reserve (FCR) and automatic Frequency Restoration Reserve (aFRR) [2]. However, a frequently raised concern is that Alkaline

Electrolysis (AEL) are too slow to provide FCR or aFRR services. While a AEL may not match the dynamics over the complete rated power, it is still possible to participate in ancillary services in a reduced way.

In this work, we extend a privous approach by Dorn et al. [3] and apply it to different large-scale electrolyzer systems. Based on published data from selected projects, we explore how AEL systems can be dimensioned and controlled to meet grid requirements. Our findings indicate that, with appropriate

system design, AEL can be technically capable of providing fast-response ancillary services. The findings offer a practical basis for discussion and invite further exchange—particularly with colleagues working on similar challenges in grid integration of electrolysis.