For more than 100 years, electricity has been reliably provided to end users through a centralized generation and transmission model. Large coal, hydro and (later) nuclear generating facilities produced huge amounts of electricity and, through a spider’s web of high voltage transmission lines, sent the power to distribution substations which in turn, through a secondary set of lower voltage feeders, distributed the power out to the end users. And when the end user flipped the switch, their lights would go on. This system was very reliable.
Source: Renewable Energy