Most governments have an interest in unused energy, because of high oil price and climate change. Particularly, it is very important to urban governments which have less renewable energy than other local governments. So Seoul, the capital of Korea, established a plan for the development of unused energy in 2007. But it has some problems related to the feasibility of this plan. So this paper checked and reviewed the economic feasibility of unused energy development cases in four cities by using three sub elements: technology, infrastructure, institution. As a result, it discovered that these urban governments have technological feasibility because they are located near big river or ocean. And they used the existing infrastructure and received the institutional subsidies from central governments in order to increase the economic feasibility of unused energy development projects. In conclusion, local governments of Korea have to try to seek how they can utilize the existing infrastructure for unused energy development in the situation that there are few institutional supports from the central government.