There are several completely different definitions that have appeared since the term was used for nothing more that national electricity grids. One commonly used definition today is, "An electricity distribution system mainly based on direct current, designed to facilitate large scale sustainable power generation in remote areas for use in centers of consumption, one of whose fundamental attributes will be enhancement of the market for electricity." Nowadays supergrid is a loose term used for the next generation of land based electric power distribution holistically incorporating a multitude of new technologies and remote sources of power generation and storage. New distribution technology may include superconducting cables. Innovative power storage may include batteries the size of a house with circulating electrolyte or giant versions of vehicle traction batteries or even traction batteries that have come to the end of their useful life in vehicles. It may include photovoltaics on millions of houses and the optimal charging and discharging of batteries in millions of electric vehicles. The key thing is that all this is optimally managed as one flexible, scalable system.