The integration of electrolysers with renewable energies to provide green hydrogen poses challenges in converter-dominated networks faced with weak grid connection. This paper presents a case study about a grid-connected green hydrogen plant that is part of the ongoing work of the Horizon Europe AGISTIN project. The AGISTIN project investigates the role of energy storages to integrate large industrial loads with renewable electricity. In this work, a photovoltaic plant provides the power to the electrolyser, where both plants operate in grid-following mode. The electrical-equivalent circuit model of the alkaline

electrolyser stack is derived from a measurement campaign. An energy storage system operating in grid-forming mode is added. The converter control is based on literature. Time-domain simulations were performed on a real-time digital simulator using PLECS to investigate the integration of the electrolyser and the photovoltaic plant into a grid with various grid strengths. The results indicate that the grid-forming energy storage system allows operation in weak grids, as well as in island mode operation.