This article assesses developing-countries’ power sector pathways toward net zero. The Low Emissions Analysis Platform (LEAP) combined with the Next Energy Modeling system for Optimization (NEMO) is used to simulate 100% renewable energy integration into power systems. While many studies have been carried out using LEAP, few have utilized NEMO (the latest optimization add-on for LEAP) for analyzing net-zero pathways of the power sector in developing countries. NEMO enables the inclusion of energy storage capacity in the long-term simulation of power system capacity expansion. Storage is crucial for balancing intermittent renewable energy especially when high penetration of renewable energy is considered. The analysis is applied to three countries in the Global South: Cambodia, Laos, and Myanmar.