Color changing roof tiles that change based on temperature could be an interesting cheaper alternative to covering your roof with solar panels. While solar panels are still likely your best bet, these color changing titles can help you save money as well. They work on the simple premise that something black in color absorbs more sunlight/heat then something white in color which reflects more. When it gets hot, the tiles turn white. When it gets cold, the tiles turn black. This change saves you money on both your heating and cooling bill.
"The ideal situation, then, would be to get the advantage of white roofs when it's hot and black roofs when it's cold.
Now, there may be a way to have both. A team of recent MIT graduates has developed roof tiles that change color based on the 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 just when it's needed.
The team's lab measurements show that in their white state, the tiles reflect about 80 percent of the sunlight falling on them, while when black they reflect only about 30 percent. That means in their white state, they could save as much as 20 percent of present cooling costs, according to recent studies. Savings from the black state in winter have yet to be quantified."