Windows are an important element in passive solar home designs, which can reduce heating, cooling, and lighting needs in a house.
Passive solar design strategies vary by building location and regional climate. The basic techniques involving windows remain the same—select, orient, and size glass to control solar heat gain along with different glazings usually selected for different sides of the house (exposures or orientations). For most U.S. climates, you want to maximize solar heat gain in winter and minimize it in summer.
Source: EERE, U.S. Department of Energy