Energy-saving roof tiles

A team of MIT graduates has developed roof tiles that change colour based on temperature. The tiles become white when it's hot, allowing them to reflect away most of the sun's heat. When it's cold, they turn black and absorb heat only when it is required.

The team's laboratory measurements showed that in their white state, the tiles reflected about 80 per cent of the sunlight falling on them, while when black they reflected about 30 per cent. That means in their white state, they could save as much as 20 per cent of present cooling costs. Savings from the black state in winter have yet to be quantified.

The team, which the students call Thermeleon, was one of the competitors in this year's Making and Designing Materials Engineering Contest (MADMEC), a competition for teams of MIT students (or 2009 graduates). Now in its third year, the contest this year was specifically devoted to projects aimed at improving energy efficiency through innovative uses of materials. The Thermeleon team took first place, earning $5,000 (£3,155).