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In the Energy Efficient Future, Our Buildings Will Wear Sunglasses

NREL researchers are developing color-changing energy efficient windows that can cut heating and cooling costs“Sunglasses” for windows could be the key to cutting energy consumption in homes, offices, and any other type of building.  The National Renewable Energy Laboratory (NREL) has been working on energy efficient windows that work like self-adjusting sunglasses, and they could shave about 1/8 off the total energy used by buildings.  With buildings accounting for about 40% of U.S. energy consumption, that’s a huge chunk of savings.


NREL has been working on the project under the Electrochromic Initiative and Windows Technology program since the 1980’s, using lessons learned from photovoltaics, particularly thin film solar cell technology.  There are still some kinks to work out, but the research is progressing and NREL’s research partner Sage Electrochromics is predicting that the cost of the windows will drop with improved performance.

Energy Efficient “Dynamic Windows”

Electrochromatic windows can help maintain an even temperature indoors by changing color to block out more sun on warm days, and to retain more heat on cold days.  According to NREL, the “dynamic windows” contain two layers of electrodes separated by an ion conductor layer.  The three layers are only one micron thick, about the same as thin film solar cells, and they are manufactured by a similar process. The window changes color when an electric field is applied, which can be done automatically through sensors integrated into a building’s electrical field.  The electricity it takes to power about 1500 square feet of dynamic window is only about the same as a light bulb, and computer simulations show that the difference would mean a big drop in electricity consumption  — up to 49% for air conditioning and 51% for lighting.

NREL Aiming for High Performance, Low Cost Dynamic Windows

One of NREL’s goals is to develop a dynamic window performs at more than double the conventional manufacturer’s warranty, to twenty years or more.  To that end the agency is working with electrode layers made of nickel and tungsten oxides, which do not degrade under light.  NREL is also developing a way to manufacture the dynamic layers through low-cost methods, similar to the method NREL is already developing for “printable” thin film solar cells.  Another cost savings could be achieved by printing the electrochromatic film on plastic instead of glass, which in turn could make dynamic windows easier to apply as a retrofit on existing windows.

Windows that Make Energy Instead of Taking It

Because of the dynamic window’s close connection to photovoltaic technology, NREL researchers foresee the development of windows that actually produce excess energy.  It’s another key step in transforming buildings from power consumers into mini-generators by integrating solar components into building elements including solar roof tiles and solar walls.

Update: On March 4 DOE announced that it has offered a $72 million loan guarantee to SAGE in support of financing a new 250,000 square foot factory in Faribault, MN to churn out high volumes of the company’s electronically tinted SageGlass, in anticipation of vigorous demand for the product.  The construction project is expected to create more than 200 jobs.

Image: Sunglasses by Vironevaeh on

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Tina specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Views expressed are her own. Follow her on Twitter @TinaMCasey and Spoutible.


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