Electrochromic windows in zero energy buildings allows an automatic control of the amount of light and heat that passes through the windows of buildings and vehicles. They can change from transparent to dark by an electric signal. Electrochromic windows can be darkened (a small voltage applied to the windows will cause them to darken) in a hot climate where solar heating is not desired or for privacy reasons, or lightened electronically where solar heating is desired (reversing the voltage causes them to lighten). This function can be controlled by an electronic thermostat.
However, installation of standard electrochromic windows is more complicated than ordinary windows since they require an electrical source. But advanced electrochromic technologies such as photo electrochromic windows would work without the use of an external control circuit, powered by solar energy.
This technology have the potential to save substantial amounts of energy in zero energy buildings, and may replace traditional solar control technology making traditional window shades, tints and blinds obsolete.