Point a thermal camera at two cars parked up after a drive and the efficiency gap between petrol and electric is there in plain sight. The petrol car glows red and orange while the electric car stays almost cold, and all that colour is energy wasted as heat: fuel you paid for that never reached the wheels. It is the clearest illustration you will find of a principle that normally stays hidden under the bonnet.
What the thermal image reveals
In a petrol or diesel engine, most of the energy in the fuel never becomes motion. It becomes heat, lost through the engine block, the radiator, the exhaust gases and the friction of the moving parts. A combustion engine turns only around 30% of the fuel's energy into movement; the rest, close to two thirds, escapes as heat. That is exactly what the camera picks up: a scorching bonnet, a glowing exhaust, a tailpipe blazing in infrared. Every red patch in the image is a slice of your tank that did nothing to move the car a single metre.
Why the electric car stays cold
An electric motor works the other way round. It converts around 85 to 90% of the electricity it receives into movement and gives off very little heat. Under the camera it looks cold because almost all the energy really is going where it should: to the wheels. There is a bonus, too. Under braking, an EV recovers part of that energy and feeds it back into the battery, while a petrol car simply turns it into heat in the brakes and loses it. That is no technical footnote: it is why an electric car costs far less to fuel over the same distance. Compare a tank of petrol with a full charge and the numbers tell the same story as the infrared picture. To get a handle on home charging costs, start with today's electricity prices.
What it means for drivers
The thermal camera is more than a lab toy. It makes visible a principle that feeds straight into your running costs. Every degree of heat a petrol car pours onto the tarmac is money burned without taking you anywhere, and in summer all that heat helps warm our cities too. EVs do pay a small winter penalty, since the cabin has to be heated from the battery rather than by an engine's waste heat, but over the full year the efficiency advantage is clear-cut. Efficiency is not an abstract idea: it is the share of what you pay that actually becomes movement. The same logic applies at home, where the steps in our guide on how to save electricity are all about cutting the energy that goes to waste.