Green hydrogen, obtained by electrolysis of water with renewable energy, is increasingly recognized as a critical part of the carbon neutral future. Adoption of green hydrogen is largely dependent on the cost of green hydrogen. Scaling up H2 production is necessary to drive down the hydrogen production cost to compete as a commodity gas. Solid Oxide Electrolysis is a well-known process to split water into hydrogen and oxygen by using electrical energy at high temperature. In this study AVL shows how modeling and simulation can be used to optimize balance of plant and system efficiency of solid oxide electrolyzer systems at different scales by different layouts and component selection. Energy flow diagram and temperature for different components will be presented. The real time capability of the overall model, as a crucial prerequisite for a consistent model usage all along the development process, is also demonstrated at some ramp up and ramp down operation conditions.