Cheaper Color-Changing Window

By Katherine Bourzac in Technology Review, December 3 2009

Thirty percent of the energy used by buildings in the United States is spent making up for heat loss or gain through windows. That adds up to about $40 billion in electricity costs each year. Windows that change color in response to changes in the weather can help save on electricity costs by absorbing sunlight in the winter and reflecting it in the summer. Such windows have existed for awhile, but they are expensive and not widely used. Now researchers are developing cheap printing methods for making these electrochromic systems, and hope to make electrochromic films that can be cut to fit existing windows.

Electrochromic windows sandwich materials that change color when a small electrical field is applied across them. This change is triggered by changes in light or temperature measured by sensors. "With electrochromic windows, everything happens dynamically--you don't have to think about it," says Anne Dillon, senior scientist at the National Renewable Energy Laboratory (NREL). "The problem is, they're too expensive."

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