Definition Energy systems are set of production, transformation, and transmission of energy sources. The structure of energy systems is not the same around the globe and differences exist among developing and developed worlds, among developing countries, and even within the country. An important difference in the structure of energy systems is between rural and urban areas in developing countries. In urban areas, much of the energy is used for commercial activities and the share of the household sector in total energy consumption is very low. On the contrary, in rural areas, the household sector is the major consumer of energy. The supply of energy in rural areas is basically met from traditional sources like fuelwood, crop residues, animal dung, etc. So, Rural energy systems refer to systems in which energy is mainly supplied from traditional sources (fuelwood, crop residue, animal dung) and may also include biogas, solar, and micro-hydro at a small scale. Another characteristic of the Rural energy systems is, here the household sector is the highest contributor in total energy demand and the main use of energy is for cooking and space heating in cool places. The energy requirement of other sectors is insignificant, and households are the major consumer of energy.