How does electricity get from a power plant to your plug?

When you flip a switch, the electricity that lights the room was made a moment ago, probably far from your home. It travelled along an electrical grid: an interconnected network of power stations, substations, long-distance transmission lines and local distribution lines that carries electricity from the people who produce it to the people who use it. Every plug in a house is the last inch of a machine that can span a whole country.

The journey has three stages. First comes generation. Power stations are typically built close to their energy source and far from crowded areas, and most use generators driven by heat engines, falling water or wind. Second comes transmission, the bulk movement of power over long distances. Here the trick is voltage: for a given amount of power, transmission is more efficient at higher voltage and lower current, so transformers at the power station raise the voltage first. Third comes distribution. Near towns, a substation lowers the voltage to a medium level, lines carry it along the streets, and a last transformer near your building steps it down to the low voltage your sockets give you, about 120 or 240 volts in the United States.

There is one strange rule about this machine: electricity is consumed at the moment it is produced. So generation and demand have to be balanced across the whole grid, all the time. That is why the grid is built as a web with spare routes. If one line fails, power is simply rerouted while it is repaired.

It is easy to forget how new and uneven this is. About 840 million people, mostly in Africa, still had no access to grid electricity in 2017, although that was down from 1.2 billion in 2010.