If you delve into the world of window shopping-- and I'm not talking abou the phenomenon of looking without buying -- lots of companies make promises about energy efficiency. Most of these are focused on insulating through multiple panes or glazes, or on their ability to let in lots of sunlight in the winter to maximize solar heating. Electrochromic glass (also called smart glass), however, uses electricity to change the glass from opaque to translucent. It can happen with the push of a button, or it can be programmed to change over the course of a day as the sun moves, using a centralized system.
Electrochromic glass uses nanotechnology, with layers of ceramic plates between glass that are thinner than a hair. These ceramic plates are coated with materials like tungsten oxide, which change from clear to dark with a quick, low-voltage burst of electricity. Reversing the charge changes it back. Not only does electrochromic glass save energy by reducing the load on an HVAC system, but it can also provide lighting in the form of skylights and can eliminate the need for shades or other window coverings.