Extra information regarding Solar Azimuth

Detailed write up regarding Solar Azimuth by the Solcast Modelling Team

By definition azimuth is the angular measurement in a horizontal plane, usually measured in degrees, clockwise from a reference direction, which is typically north. More specifically, solar azimuth refers to how much the observer would need to turn in order to be directly facing the Sun from geographic north. In combination with the [Solar Zenith] angle it can be used to map the Sun’s position in the sky at a particular moment from a specific location on Earth. The diagram below showcases the Solcast definition of azimuth.

Notice that in the context of Solcast API and Toolkit the azimuth angle increases counterclockwise meaning that an azimuth angle of 90 degrees will be pointing west. Some use cases have the azimuth angle increasing clockwise, so be careful when comparing to other sources.

If we follow the movement of solar azimuth during the typical day the following will be observed:

Morning: At sunrise, the solar azimuth angle is negative as the sun rises over the eastern horizon. As the morning progresses, the solar azimuth angle heads westward either through north or south depending on where you are in the world.

Solar Noon: At solar noon, which is when the sun is highest in the sky, the solar azimuth angle is 180° (south) for locations in the northern hemisphere. For locations in the southern hemisphere, solar noon corresponds to a solar azimuth angle close to 0° (north).

Afternoon: After solar noon, the solar azimuth angle continues westward as the sun descends in the western sky towards the horizon.

Over the course of a full day (including night time), solar azimuth varies across the full -180 to 180 degree range, as the Earth turns once on its axis. It is this constant variation over the course of the day that allows sundials to work.

While the range of azimuth values each day don’t change, the ones we observed during sunlight hours do have seasonal changes.In the summer months, the sun's path travels a longer path across the sky, resulting in sunrise and sunset azimuth angles that are further apart. The reverse is true during winter when the shorter days mean sunrise and sunset angles are closer together. The figure below showcases how the Azimuth angle varied during the days of the winter and summer solstices at the Sydney Opera House.

The change in solar azimuth over the course of the day is what single axis trackers are designed to account for, facing the Sun to minimize the angle of incidence and generate more power.