Accelerating development in Sub-Saharan Africa will require massive expansion of access to electricity -- currently reaching only about one-third of households. This paper explores how essential economic development might be reconciled with the need to keep carbon emissions in check. The authors develop a geographically explicit framework and use spatial modeling and cost estimates from recent engineering studies to determine where stand-alone renewable energy generation is a cost effective alternative to centralized grid supply. The results suggest that decentralized renewable energy will likely play an important role in expanding rural energy access. But it will be the lowest cost option for a minority of households in Africa, even when likely cost reductions over the next 20 years are considered. Decentralized renewables are competitive mostly in remote and rural areas, while grid connected supply dominates denser areas where the majority of households reside. These findings underscore the need to de-carbonize the fuel mix for centralized power generation as it expands in Africa.