Open curtains on south facing windows during the day to allow sunlight to naturally heat the home, and close them at night to reduce the chill from cold windows. (realtormag.realtor.org)
This arrangement allows the entire south face of the building to be used as a collector, right up to the peak of the roof. (builditsolar.com)
This is often the case for south facing windows (northern hemisphere), but for windows facing other directions is almost never the case. (elrondburrell.com)