(Image: Rex Features)

A new breed of structures called skutterudites could finally tap the floods of energy our machines waste as heat

Thermodynamics will always take its pound of flesh. Its laws ultimately dictate that more than half of the energy we use in cars, dishwashers, factories and elsewhere is lost as waste heat (see also “Wonder stuff: Electron freeway for cool gadgets“). That’s just an average: for car engines, the proportion is more like two-thirds.

Reclaim even a small amount of that lost heat as electricity, and that would massively boost energy efficiency. Thermoelectric materials allow us to do just that, by coaxing a current from a temperature difference. Wrap a thermoelectric substance around your car’s exhaust, and its waste heat could power the electrics. Incorporate thermoelectric elements into a refrigerator, and heat extracted from its interior could power it. Add them to solar panels and the sun’s heat, not just its light, could be used to make electricity.

Good harvest

Too good to be true? So far, yes. The most efficient thermoelectric material yet discovered, lead telluride, was benched because of fears, and legislation, about the use of lead in electrical equipment. Replace the lead with its less toxic cousin bismuth and you are still at the mercy of the fluctuating price of tellurium, a metallic by-product of copper mining. Decades of research have failed to identify an alternative thermoelectric material to these that can cover its costs commercially.

Even more damningly, the already-mediocre efficiency of most thermoelectric substances drops off still further at high temperatures, making them useless for things like car engines. In thermodynamic terms, …