Roof tiles that change color with temperature

A team of recent Massachusetts Institute of Technology (MIT) graduates have made roof tiles that change color with temperature, as described in MIT News.

The tiles turn white in hot weather and black in cold weather, thus moderating the temperature inside the building.

When it's cold, in winter and at night, the tiles are black, absorbing more sunlight which helps reduce the need for heating.

When black, the tiles reflect only 30% of sunlight. When white, the tiles reflect 80% of sunlight, which helps keep temperatures down inside the building.

Moreover, light-reflecting materials could help reduce smog, the urban heat island effect and global warming.

The team named the roof tile Thermeleon, to make it rhyme with chameleon. The tile contains commercially-available polymers and solvents, sandwiched in between a clear flexible plastic top layer and a black layer at the back.

As long as the temperature stays below a certain point (different levels can be set by varying the formula), the polymer remains dissolved in the solvent, and the black backing shows through, absorbing sunlight.

When it's hot, the polymer condenses to form tiny droplets, whose small sizes scatter light, resulting in a white surface that reflects more sunlight.

Because the materials are common and inexpensive, team members think the tiles could be manufactured at a price comparable to that of conventional roofing materials, but there are a number of uncertainties. The biggest remaining question is over durability, and answering it will require testing through repeated hot-cold cycles.

The team is also working on adding tiny capsules with their polymer-solvent mixture to paint, enabling their color-changing material to be painted or sprayed onto existing roofs, pavement or roads.

Such tiles and paint do well complement the bricks and concrete that I discussed in the article carbon-negative building, as well as transparent spray-on films that could be added to parts of buildings (such as windows) to convert sunlight into electricity, as mentioned in a comment underneath. Government incentives, such as discussed in Green Building Feebate, could further help make such applications more attractive.