If you've ever wondered why the heat from a car's engine can't be captured and converted into electricity (and who hasn't, frankly?), then you're in good company – that's precisely what a bunch of clever Japanese engineers have just managed to achieve.

The boffins at Tokyo-based Furukawa have solved a tricky engineering problem to create a thermoelectric conversion system that sits between the engine and the exhaust in a car to generate power from the hot gases.

Heat gradient

The tiny devices – 20 are used per car in the current prototype – work because they are made of a mineral that can maintain the heat differential between its two sides that is needed for the generation of electricity.

The skutterudite-based material keeps its hottest face at 720º C, while the opposite side can remain at around 50ºC with the aid of a little water-cooling. This allows the converter to operate properly and generate up to 33W of electricity.

Fuel saving

Apparently, that means 7 per cent of exhaust heat becomes electricity that can partially power a car, thereby reducing fuel consumption by 2 per cent. Furukawa says a commercial version should be ready in about three years.

Oh, and in case you're wondering, "Skutterudite is a cobalt arsenide mineral that has variable amounts of nickel and iron substituting for cobalt". So there.