How Power Plants Work — and How to Read a Map of the World's Power Stations

Electricity feels like magic because it arrives invisibly and instantly. But behind the switch is one of the largest machines humanity has ever built — a continent-spanning network of generating stations, wires and transformers, all kept in a delicate, constant balance. This map plots the generating stations: the places where electricity is actually made. Here is what is happening inside them, and how to read what you are looking at.

It (almost) always comes down to spinning a magnet

In 1831 Michael Faraday discovered that moving a magnet near a coil of wire makes electricity flow in the wire. Nearly two centuries later, that single principle still produces the overwhelming majority of the world's power. Every coal, gas, oil, nuclear, biomass, waste, hydro and wind plant is, at heart, a way of spinning a generator — a coil and a magnet in relative motion.

What differs is the source of the spin:

• Thermal plants — coal, gas, oil, biomass, waste and nuclear — make heat, use it to boil water into high-pressure steam, and fire that steam through a turbine to turn the generator. In a coal or biomass plant the heat comes from burning fuel; in a nuclear plant it comes from splitting atoms. The fuel changes; the steam-and-turbine machinery is much the same.
• Hydroelectric plants skip the heat entirely and let falling water push the turbine blades, which is why they cluster in mountainous, rainy places and along great rivers.
• Wind turbines use moving air to turn the blades directly.
• Solar photovoltaic plants are the true exception: they have no moving parts and no turbine. Sunlight knocks electrons loose inside a semiconductor and the current flows straight out. (Solar thermal plants, a smaller category, do use the sun's heat to make steam in the old-fashioned way.)

So the colour of a plant on this map is really a shorthand for how it spins its generator — or, for solar, that it has found a way not to.

Why the mix matters more than the total

Electricity is uniquely hard to store in large amounts, so a grid must generate almost exactly as much power as is being consumed at every instant. Meeting that moving target is why a country needs different kinds of plant working together:

• Baseload — the steady demand that never goes away — is usually carried by big plants that like to run continuously: coal, nuclear, and some gas and hydro.
• Peaks — the daily surges when people wake, cook and cool their homes — are met by plants that can ramp up and down fast, often gas.
• Variable sources — wind and solar — produce only when nature cooperates, so a grid leaning on them needs flexibility: fast-reacting plants, storage (batteries, or pumped-hydro reservoirs), and strong long-distance connections to move power from where it's windy or sunny to where it's needed.

This is why two countries with the same total capacity can run completely different power systems — and why the colours in a country, not just the number of dots, tell the real story.

Capacity is potential, not output

The dots on this map are sized by capacity, measured in megawatts (MW). Capacity is the maximum rate a plant can generate — its top speed. It is not the same as how much electricity the plant actually makes over a year, which depends on how often it runs and is measured in megawatt-hours.

A nuclear station may run near full output almost all year. A solar farm of identical nameplate capacity only generates in daylight, and less in winter or cloud, so over a year it produces far fewer units. The ratio of actual output to theoretical maximum is the capacity factor, and it varies enormously by fuel. So read a big dot as "this plant can produce a great deal" — not as a measurement of how hard it is working. (For the same reason, adding up capacity across a country tells you its built-up generating potential, not its yearly electricity production.)

Reading the map

Each plant is coloured by its primary fuel, folded into nine groups, and sized by capacity. Where many plants sit close together they merge into a cluster, and the cluster takes the colour of the fuel that generates the most power inside it — so a region glows by whatever actually drives its grid, not by whichever fuel simply has the most sites. Zoom in and the clusters break apart into individual stations; click any one for its name, fuel and capacity, and its commissioning year where it's recorded.

Look for the patterns geography writes: Norway and other mountainous, rainy countries running deep blue on hydro; Iceland mixing in geothermal; France a field of nuclear violet; coal-built economies still showing broad bands of red; and the spreading freckles of yellow and aqua where solar and wind have been built out. The map is, in the end, a portrait of how each part of the world chose — and was able — to keep its lights on.

One caution worth keeping in mind: this is a careful snapshot, not a live feed. The newest solar and wind farms may be under-counted, small rooftop solar is largely off the map, and what you see is generating capacity in place, not real-time output. Read it as the shape of the world's power system — and a starting point for understanding the machinery behind the switch.