Self-sufficiency (SS) of buildings with low greenhouse gas (GHG) emissions can be obtained using photovoltaics (PV). To maximize self-consumption - minimizing the import of grid electricity - PV can be coupled with a hydrogen storage system converting the electricity to hydrogen by electrolysis during the summer season, when the on-site production is higher, and using it during the winter season with fuel cells. This article deals with the sizing constraints of solar hydrogen systems at building-scale. The future building for the Smart Living Lab (SLL) in Fribourg (Switzerland) has been taken as case study. It has four stories and a mixed usage (Office-building and Research facilities), with a multi-oriented PV installation in order to produce enough electricity to achieve at least 50% of self-sufficiency. Using the PV production, this study aims to optimise the sizing of a hydrogen storage system allowing to reach the required self-sufficiency ratio. Finally, a comparison of the global efficiency of the system for three different demand-side scenarios.