Southern Africa faces the dual challenge of providing affordable energy to meet rapidly growing electricity demand while limiting carbon emissions and socio-environmental impacts. To develop optimal electricity pathways for Southern Africa under varying technology and fuel cost projections and energy policies, we combined open source geospatial, hydrologic, and electricity grid-investment models that represent renewable resources in high spatiotemporal detail. We found that if technology and fuel prices continue to follow current trends, wind and solar technologies can become the dominant sources of electricity in the region by 2040. Importantly, no new coal capacity was built in any scenario except when inter-regional transmission was constrained. Further, despite the abundant hydropower potential in the region, fewer than half of planned hydropower projects were cost-competitive, thus supporting river conservation efforts. Through continued build-out of renewable energy technologies and coordinated expansion of inter-regional transmission lines and electricity trade, Southern Africa could maintain its GHG emissions in 2040 at 2020 levels. Limiting coal plant lifetimes to 45 years (20 years less compared to reference) could halve emissions, but results in 13% higher total annual system costs. Alternatively, an 80% clean energy target resulted in a similar 50% reduction in annual GHG emissions by 2040 but costs only 6% or USD $3/MWh more than reference. Our study shows feasible pathways for Southern Africa to develop an affordable and low-carbon electricity system. View external publication here