This paper introduces a methodology for incorporating metrics for electric-sector reliability into a global Integrated Assessment Model. Using load, resource availability, and system dispatch data with high temporal resolution, we designed a set of reduced-form constraints that guide investment and usage decisions among power plants in IIASA's MESSAGE model. The analysis examines how such reliability metrics impact modeled system build-out, including in scenarios with greenhouse gas (GHG) limits. Scenarios show how carefully chosen model constraints can allow a flexible approach to treating integrations concerns of variable renewable technologies into the electric sector in a high-level energy model.