The sun is the source of all life on earth. We can also use it to keep our buildings comfortable, provided we understand how, and when, solar energy reaches our site.
The apparent motion of the sun across the sky depends on latitude. At the equator, the sun passes nearly overhead, and follows a steady east-west path, regardless of the time of year. Whereas at the poles, the sun travels round and round the sky all summer, and never rises at all in winter!
But in the temperate zone, from about 30 to 60 degrees of latitude, due to the axial tilt of the earth, the sun climbs higher in the sky, and follows a longer path, in summer than in winter. This is why we have distinct seasons with very different temperatures and amounts of daylight.
On cloudy days, sunlight is scattered across the sky, and most solar energy comes from overhead, instead of directly from the sun.
This image, made with a fixed pinhole camera, shows the sun’s path across the sky each day from the winter to the summer solstice, with cloudy days shown as broken or absent lines, allowing us to see a snapshot of six months’ weather in a single image.
Knowing how solar energy behaves at our location, allows us to capture the right amount at the right time to heat and light our building effectively.
Assuming we’re in the Northern hemisphere, this means having large windows facing south, to capture low sun in winter; while elongating the building along an east-west axis allows the sun to penetrate all the way inside in winter; as can be seen in this passive solar school building in Ladakh, India.
On the other hand, windows that face north, east, west, or up (skylights), should be small, to provide natural lighting without too much heat gain in summer and loss in winter, as in this building in the US.
Other methods for capturing solar energy in the building include the use of glazed sunspaces…
