Energy sources & the power mix

You flip the light switch and the lamp comes on. But that electricity has to come from somewhere: maybe from a wind turbine on the coast, from a solar panel on a roof, or from a power plant burning coal. Which source is delivering right now even changes over the course of a day. That is exactly what we look at here.

Many sources, one grid

Electricity is almost always made the same way: something spins a generator, just like you saw with electromagnets. The difference is what drives the spinning. For a wind turbine it is the wind, for a hydro plant it is flowing water, for a coal or gas plant it is hot steam from burnt fuel. Only solar cells are different: they turn light directly into electricity, with no spinning at all. All sources feed into the same grid, and the mixture is called the power mix.

Renewable or fossil?

Wind, sun, water and biomass are called renewable sources: they do not run out, because tomorrow the wind blows again, the sun rises again, and wood or plant waste grows back. Coal and natural gas are fossil sources: they formed millions of years ago from the remains of plants and tiny sea creatures, their supply is limited, and burning them releases CO2, which heats up the climate. That is why many countries are trying to keep growing the renewable share of the power mix.

Why the mix keeps changing

Solar panels deliver the most at midday and nothing at night. Wind turbines only deliver when the wind blows. But since the grid must always generate exactly as much electricity as is being used, other power plants step in when sun and wind are weak. The big challenge is storage: batteries and pumped hydro save surplus electricity for later, for example midday solar power for the evening. A pumped hydro plant pushes water up into a high reservoir and later lets it flow back down through the turbine. There is still too little storage of this kind, so gas and coal plants keep running to fill the gaps.

Watt and kilowatt hour

Two units come up all the time with electricity. Power says how much a plant delivers at this moment and is measured in watts: 1 kilowatt (kW) is 1000 watts, 1 megawatt (MW) is 1000 kW, 1 gigawatt (GW) is 1000 MW. A large wind turbine manages a few MW, a whole country needs a few dozen GW. The amount of energy, by contrast, counts what adds up over time and is measured in kilowatt hours (kWh): a device with 1 kW of power uses exactly 1 kWh in one hour. That is why your electricity bill shows kWh, while the size of a power plant is given in MW or GW.