This work concerns a methodology for PV-H2 hybrid system design that consider the weather data and the electrical variables of the subsystems to perform energy balances and to assess the systems in terms of the capacity and operation of the components, and the resulting costs. Two configurations (with and without batteries) and two locations (Madrid and Fisciano) were studied to find the best trade-off between the efficiency and sizes of the subsystems. Directly connected systems operate at intersection points between the PV output and electrolyzer (EL) input curves for different solar irradiance levels, while the battery assisted systems reduce the sizes of EL at the expense of higher energy loss and additional cost of batteries (B). It was found how is not convenient to operate the EL at fixed rate, resulting in high PV and B sizes, as well as power unbalances in winter and summer. Solutions are to run the EL at a minimal load at night and change the intensity of daytime operations to achieve null cumulative energy each season. The H2 supplied by these systems has the merit of being sustainable (renewable) and autonomous (avoiding power constraints in off-grid locations), and the costs are around 6–7 €/kgH2. •A novel methodology for PV-H2 hybrid system design is presented, used and discussed.•Two configurations (direct coupling and battery assisted electrolysis) are compared.•The battery reduces the size of electrolyzer at the expense of higher energy loss.•Changing the electrolyzer operations optimize cumulative energy each season.•The H2 supplied has the merit of being sustainable at costs around 6–7 €/kgH2.