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Energy Efficient Window Coatings that Please the Eye

Energy Efficient Window Coatings that Please the Eye

NREL partnerships expand market reach and provide more energy saving options.

Start with a novel concept. Pursue related fundamental research. License intellectual property to companies. Understand technical barriers to greater market penetration of the technology. Partner with companies to overcome these barriers. Help a successful industry develop as a result and provide end-users with more options to choose from to save energy and gain other desired benefits. NREL has a long track record of following this path in the field of dynamic windows—windows with glass that changes properties based on environmental and user demands to improve the energy efficiency and aesthetics of buildings.

From Great Idea to Next-Generation Materials

A photo of an office space with windows that are darker in the upper portion and clear in the lower portion.

The dynamic electrochromic windows in this office can darken in the upper portion to block unwanted light, glare, and heat while the lower portion remains clear.
Photo from Sage Electrochromics

In 1973, even before coming to NREL, Satyen Deb conceived of making a window that incorporated tungsten oxide thin films that had adjustable properties. Once at NREL (then, the Solar Energy Research Institute), he and his colleagues continued to pursue this technology as a device that changes color when voltage is applied—an "electrochromic" device—thus controlling the amount of light and heat transmitted through it (see sidebar).

Since the 1990s, NREL has obtained patents on key aspects of electrochromic materials, devices, and processes, and has made this intellectual property available for licensing. Various companies have entered into development partnerships and/or license agreements to explore and capitalize on NREL electrochromic innovations: SAGE Electrochromics, Inc.; Eclipse Energy Systems, Inc.; e-Chromic Technologies, Inc.; as well as for hydrogen sensor (Nuclear Filter Technology) applications.

NREL Senior Scientist Chaiwat Engtrakul, who currently conducts research in electrochromic materials, explains, "NREL and SAGE are working together to develop innovative nanocomposites that can be used in new window designs. These next-generation materials are enabling window features desired by designers and consumers and will help grow the market penetration of this technology."

One feature that will bolster market acceptance relates to aesthetics: most architects and building occupants would prefer clear windows on one extreme and dark gray glass on the other. Addressing this preference, the SAGE electrochromic coatings have no perceptible tinting in the clear state and, when combined with the standard tungsten oxide electrochromic layer, have the potential to result in the desired dark gray.

Another feature relates to performance, namely, the length of time it takes to switch between the clear and darkened states. The device switching speed depends on the ambient temperature and the area of the glass. NREL and SAGE are researching electrochromic materials that exhibit increasingly fast switching rates that consumers find desirable.

Saving Energy, Helping Companies and Consumers

Neil Sbar, vice president of Energy and Technology Applications at SAGE, concludes, "We're confident that the next-generation materials being conceived through our research and development will boost the penetration of dynamic window applications within the buildings market. The ultimate impact will be a substantial decrease in energy usage over existing window technologies."

In other electrochromic research, NREL scientists are exploring avenues for retrofitting these coatings to existing glass windows. This ability would expand the options available to remodelers for the almost 20 billion square feet of windows currently installed in U.S. commercial and residential buildings.

NREL's seminal and ongoing work in dynamic window technologies, including key collaborations with industry partners, exemplifies how a national laboratory can serve as a valuable resource to companies needing to overcome technical market barriers to bring new energy technology options to consumers.

Energy Saving Homes and Buildings

Spring 2014 / Issue 6

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  • Kim Adams | Managing Editor
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