This study identified areas suitable for photovoltaic (PV) and onshore wind systems, with few or no competing land uses. All contiguous land in Japan was classified into 15 independent land-use types according to their regulation level. Four types were determined as soft-restriction areas suitable for development: devastated farmland, grassland, bareland, and scrubland. Legally prohibited land in nature reserves was then excluded from these areas. The remaining area was deemed available for both renewable energy systems. Analysis by geographic information systems (GIS) revealed that the total area of land available for PV and wind turbine development is 3,428 km2 or 0.9% of all contiguous land in Japan. In 72% of this area, these systems may have to compete with other development projects, including each other. Considering factors such as electricity demand and the slope of the land, the installation of onshore wind turbines in areas of competing development is shown to be important. If an onshore wind capacity of 25 GW was to be installed in areas with competing development and a PV capacity of 64 GW in the non-competing areas, it would result in 130.2 TWh/year, which represents 15% of the total annual electricity demand of Japan in 2018.