
Electricity is capable of being generated either centrally, or at different locations based on the requirement of the geographical location, demand or type of use. Most countries generate electricity in large centralized facilities, using fossil fuels, such as coal, gas, nuclear, large solar power plants or hydropower plants. These plants have excellent economies of scale, but usually transmit electricity over long distances and can negatively affect the environment. Distributed generation allows collection of energy from many sources and may give lower environmental impacts and improved security of supply. Historically, central plants have been an integral part of the electric grid, in which large generating facilities are specifically located either close to resources or otherwise located far from populated load centers. These, in turn, supply the traditional transmission and distribution (T&D) grid that distributes bulk power to load centers and from there to consumers. These were developed when the costs of transporting fuel and integrating generating technologies into populated areas far exceeded the cost of developing T&D facilities and tariffs. Central plants are usually designed to take advantage of available economies of scale in a site-specific manner, and are built as "one-off," custom projects.