Switch 2.0: A modern platform for planning high-renewable power systems. Switch 2.0 is an open-source platform for planning transitions to low-emission electric power systems, designed to satisfy 21st century grid planning requirements. Switch can plan investments and/or operations while considering detailed models of emerging technologies for renewable integration. Applications include integrated resource planning, basic research, and economic, technical or policy analysis. Power system elements include unit commitment, part-load efficiency, fuel supply curves, planning and operating reserves, storage, demand response, hydroelectric networks, and policy constraints. Switch’s novel architecture allows users to compose customized models by choosing built-in modules à la carte or writing custom modules.