Energy consumption: an environmental problem

We are living in air-conditioned comfortable houses, going to school or office using city transport network such as trains and subway cars which run every few minutes, and sending and receiving data to and from any place in over the world through the Internet instantaneously (Fig. 1) [1]. We are, however, scarcely acknowledging the fact that today's conveniently working society is supported by the enormous consumption of electric energy, and if supply of electricity is stopped, this society will be thrown into a terrible chaos. Electricity, like air and water, is so wide spread that nobody may recognize its existence. Progress in urbanization and advancement of the networked information society is giving electricity more and more importance as the main energy source for our social life. In view of the increase in its demand, the electric power system has come to face three adversely affecting issues, namely, steady electricity supply (energy security), decrease of electricity price and economic growth (economic growth), and harmonization with environment (environmental protection) [1,2] (Fig. 2). Load leveling, electric energy storage technology, and renewable or new energy power generation systems such as photovoltaic and wind-power generation are being developed as the effective measures to solve these types of trilemma syndrome, but it is true that we have not found the fundamental solution yet.