Nick Orf, one of the team of students, demonstrates Thermeleon.
When I wrote a post entitled Arguments Against White Roofs in Northern Cities are Specious, I was complaining about the roofers who say that in cooler climates, white roofs can mean higher heating bills. It was a controversial issue: dark or light? Now Gizmodo describes how MIT students are giving us two mints in one: Thermeleon, a roofing tile that changes from dark to light depending on the temperature. It recently took first price in a school competition.
The best of both worlds: a roof that reflects in summer, absorbs in winter
They describe how it works:
When the polymer phase separates from the gel, the solution becomes a mixture of polymer and solvent and because the polymer and solvent have different refractive indices the mixture becomes strongly scattering (white colored). When the mixture cools below the transition temperature the polymer re-dissolves in the liquid and the solution is clear and colorless. The pictures below illustrate the change in color when the tile is subjected to hot and cold temperatures.
Most roofs in traditional homes have unheated attics, so the benefits of heat gain in winter are negligible. But if you have an occupied and insulated attic and a steep enough roof to shed snow, this could be very useful. More information at their website Thermeleon, MIT News and Gizmodo.
More on white roofs:
Arguments Against White Roofs in Northern Cities are Specious
How To Help Prevent Global Warming On Your Roof
Lighter Roofs Could Save $1Billion USD Annually
White Roofs to Sweep the World, Fight Climate Change