Decarbonization and idle cropland reclaiming pose critical policy challenges. Agrivoltaic systems (AVSs), which merge agriculture and photovoltaics, offer a promising solution by reducing land use conflicts between agriculture and energy production. This study develops a GIS-based methodology to identify reclaimable idle croplands and assess the AVS’s contribution to agriculture and photovoltaic energy in Japan’s Kansai region. Using official geographic data and excluding high-risk areas, this study employs GIS for quantitative analysis. Our method detected more reclaimable idle cropland than previous studies. Focusing on food security while limiting AVS installations to reclaimable idle croplands could still generate up to 4564.08 GWh of electricity (0.8% of regional consumption) and 930.82 tons of soybeans (6.2% of regional yield). Under a more stringent scenario that excludes areas less suitable for solar power, 5 of 227 municipalities could achieve 15% electricity self-sufficiency through AVS. This research uncovers the existence of reclaimable idle croplands that could not be detected by existing methods and a decentralized power source available alongside food security maintenance. These insights will inform decarbonization and agricultural policy and guide the development of supportive and regulatory AVS frameworks.