Cellular networks in developing regions continue to rely heavily on diesel for energy to provide network coverage due to the paucity of reliable grid power which directly impacts the network's economic viability and long-term sustainability. At the other extreme, solar powered cellular installations have gained prominence but have faced their own adoption challenges including inability to provide adequate and reliable 24x7 power supply, need for large land footprints and lack of eficient power storage. In this paper, we perform a detailed economic cost analysis comparing diesel powered cellular networks with solar powered cellular networks. The key goal of this paper is to establish the cross-over boundary beyond which solar powered installations are better than diesel powered alternatives. We perform a detailed analysis based on actual diesel consumption data from a large telecom operator in a developing region. Using our model, we can also easily perform an extended analysis based on future projections on solar eficiencies and future cellular network designs.