Won’t properly insulated windows keep out heat from the sun?
Keeping warm air inside is not the same as keeping out infrared (i.e. heat) contained in sunlight. A well-insulated window uses multiple panes and air barriers to minimize thermal losses between inside and outside. Clear glass and plastic prevent most ultraviolet (UV) in sunlight from passing through the window, but they do not block most infrared. This means that heliostat systems can be used effectively for direct space heating through most windows, including very well-insulated ones. In warmer climates, some people do choose to use somewhat tinted windows that block out infrared. This window technology is also compatible with heliostats; it allows users in warm climates to use heliostats for natural lighting without also delivering 600 watts of thermal energy (heat) per heliostat.
