The location of a skylight is the primary consideration if you want to maximize natural lighting and passive solar heating potential. Skylights on roofs that face north provide fairly constant but cool illumination. Those on east-facing roofs provide maximum light and solar heat gain in the morning. West-facing skylights provide afternoon sunlight and heat gain. South-facing skylights provide the greatest potential for desirable winter passive solar heat gain than any other location, but often allow unwanted heat gain in the summer.
Some units have a solar control film, with a solar heat gain rating.
The slope, or tilt, of the skylight also has a great effect on solar heat gain. A low-slope will admit relatively more solar heat in the summer and less in the winter, exactly the opposite of what is desirable. A general rule of thumb is to achieve a slope equal to your geographical latitude plus 5 to 15 degrees. At least one skylight manufacturer makes a prefabricated, tilted base that increases the angle of a skylight above the roof. Preventing Leaks Leaks are a common problem with skylights.