# Sun Position

The sun position is calculated according to the algorithm set out in [10]. Please see this document for more detailed information about the calculations involved. For any given calculation interval (hour, ten-minute period etc), the date and time at the middle of the period is used to calculate a sun position representative of the entire period. For intervals with sunrise or sunset, the period is defined for the time the sun is above sea-level. The figure below shows the sun position in a right-hand reference frame where the \(x\text{-axis}\) is east, the \(y\text{-axis}\) is north, and \(z\text{-axis}\) is vertical.

Solar zenith, \(\theta_\text{z}\): The solar zenith angle is the angle between the vertical and a vector pointing to the sun at the plant location. Hence a solar zenith angle of 0° indicates that the sun is directly overhead.

Solar azimuth, \(\gamma_{\text{s}}\): If a line from the observer to the sun is projected onto the horizontal plane passing through the nominal position of the observer (PV plant), the solar azimuth angle is the angle between a line running to true north and the projected line, measuring going clockwise around the observer as seen from above.

*Solar vector given by its zenith and azimuth*

Note that the sun position calculated includes a refraction correction.