Wouldn’t it be nice to get rid of all your venetian blinds or cumbersome curtains? That’s the aim of electrochromic or photoelectrochromic windows, which borrow from thin-film photovoltaic (PV) technology to deposit micron-thin layers of electrochromic materials on top of window glass. With a small electric charge, the materials in the window change the window from clear to tinted instantly. In addition, the windows are able to significantly help reduce heating and cooling costs since it keeps infrared radiation from entering or leaving the house or office building.
The difference between electrochromic and photoelectrochromic tinting windows is in how the electrochromic mechanism is powered. Electrochromic windows are tinted by an outside electrical force, while photoelectrochromic windows are self-powered. Photoelectrochromic devices generate electricity through dye-sensitized electrodes that provide power to lithium ions in the window’s electrochromic layer, which will color it.
When photoelectrochromic windows are struck by sunlight the electrodes absorb some of the light and convert it to electricity. The electric flow causes iodide ions to migrate through a thin solution into a electrochromic layer. The electrochromic element of the window is activated by the electricity and causes it to change color, adding tint or an opaque quality to the window.
As sunlight wanes, the electricity stored in the electrochromic layer is ejected, reducing the coloration in the window and again making it clear. This allows the window to automatically adjust to the sunlight that hits it. However, the process also can be controlled by other means, allowing the window’s tint or opacity to be controlled externally. This makes it ideal for shading bedroom windows for instance.
Electrochromic technology has been tested since the 1980s, but it has always been prohibitively expensive at about $1,000 per square meter, making it unfeasible for consumer applications. And NREL, the National Renewable Energy Laboratory, has said that earlier versions of the electrochromic windows failed far too early to provide a long-lasting, cost-effective, consumer-ready product. NREL is working to create electrochromic and photoelectrochromic windows that will last for at least 20 years.
But at least two companies, Velux and Sage Electrochromics are now ready to bring such windows to market. Sage’s, technology was tested by NREL. Sage predicted that prices for its windows will fall 70% by 2015 because of performance, production and volume increases.