Every so often, someone pulls up a chart of the world’s energy mix, points at the great slab of fossil fuels, and declares that since oil, coal and gas still supply around 80% of global energy, the notion of wind and solar filling that gap is pure fantasy. This is not an argument confined to non-specialists. Dieter Helm, the Oxford economist, does not deny climate change and calls himself a climate realist; yet he too maintains that it is naive to think wind and solar could ever add up to replace that 80% of fossil fuels, that they are necessary but a very long way from sufficient.
The trouble is that the 80% conceals a trap. It measures primary energy, the total energy locked inside the fuel, rather than the energy we actually use. A coal-fired power station runs at roughly 35% efficiency, and a petrol car turns less than a third of the energy in its tank into motion at the wheels. Put another way, close to two-thirds of that 80% never becomes a useful service at all. It leaves as waste heat, dispersing into the air and carrying carbon dioxide with it. Taken across the whole energy system, only about a third of the primary energy we burn, and by some measures rather less, ever ends up as useful work. A large part of that imposing slab on the chart is not something we want. It is the waste itself.
Once this is clear, the task changes shape. What has to be replaced is not 80% of the energy, but the far smaller slice of genuine service that the 80% buys us. The real power of electrification is not that it swaps one unit of electricity for one unit of oil or gas, but that it strips out the great block of waste heat sitting in the middle. An electric car is about three times as efficient as a petrol one, and a heat pump delivers the same warmth using a third to a fifth of the energy a gas boiler needs. Nick Eyre, the Oxford energy researcher, ran the numbers on a simple question: what if the world electrified industry, buildings and transport as far as it could? That step alone, he found, would cut final energy demand by around 40%. The 80% mountain, measured in useful energy, is suddenly a good deal shorter.
In fairness, Helm has a separate set of arguments about the cost of running the supply side, and that is a different subject, not one for this article. But on the 80% itself the point is plain. The figure measures how much we burn, not how much we use. Treat the heat that vanishes during combustion as demand that must be matched unit for unit, and of course the task looks impossibly large. Telling people to be realistic about the energy transition is no bad thing. But the first act of realism is to measure the right quantity. Using a figure inflated by waste heat to prove the transition is hopeless may look rigorous, yet it has miscounted from the very first step.
