This paper presents a set of case studies of a 50 kW green hydrogen plant operating at different grid strengths with and without the support of a grid-forming energy storage system using a supercapacitor. The results stem from the ongoing Horizon Europe project Advanced Grid Interfaces for innovative STorage INtegration (AGISTIN) that investigates how energy storage systems can help the integration of industrial loads, such as, electrolyzers.

The green hydrogen plant consists of a 50 kW photovoltaic plant and a 50 kW electrolyzer plant, both operating in grid-following mode, and a 25 kW supercapacitor with 300 Wh, operating in grid-forming mode. They are connected to a low-voltage grid with a varying grid strength.

The paper describes the models of the converters, including the electrolyzer stack, using typical design rules for the filters and the tuning of the controllers. The grid is represented as a Thevenin-equivalent grid, where a short circuit ratio is varied from 5 down to less than 1. The green hydrogen plant is modeled in MathWorks’ Simulink. The studies compare the operation of the green hydrogen plant at different power setpoints and grid strengths, firstly without, and then with the grid-forming energy storage system.

During the strong grid scenario, the simulation results indicate that the photovoltaic plant can power the electrolyzer plant across all setpoints. However, as the grid becomes weaker, the oscillations increase with larger power setpoints occur until the system is not stable. For the studied cases, the grid-forming energy storage system enabled the operation of the green hydrogen plant during the weakest grid conditions.

The results are put into the context of current integration practices and requirements in the European Union and the ongoing activities of the AGISTIN project.