The technology is dubbed Thermeleon and when the temperature is cold the tiles will be black to better absorb heat, and when the temperature is high they will be white, to better reflect the light and save on cooling costs.
Digital Life: Energy-saving Thermeleon roof tiles
The tiles use polymer encapsulated between layers of flexible plastic layers.
Apparently, things have not quite gone to plan with the prototypes, however... You can read more on physorg.com - Color-changing roof tiles absorb heat in winter, reflect it in summer
Writes the site:
The team, which the students call Thermeleon (rhymes with chameleon, because of its color-changing property), 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 final showdown was held Wednesday night, and the Thermeleon team took first place, earning $5,000 in the process.
It's an interesting idea, but note - these are not solar tiles. And, as one commenter points out:
Now I recall that there are many cities in which most homes have a solar hot water heater on the roof. With this (and deatopmg's comment) in mind, doesn't it seem a bit silly to go through a bunch of effort to deflect energy back to the sky during precisely the periods of time in which the energy is most abundant?
(I know - this is more materials engineering than digital technology, but - hey - I found it interesting, and I'm using 'Digital Life' as a wide-ranging category, and it could reduce the electricity bills!)