It is vital to understand the shading on the rooftop, particularly in urban areas where surrounding buildings and
structures can cast shadows on the roof. Even a small portion of shading on a PV array can significantly reduce
output because of how the panels and array are electrically configured.
Ideally, all portions of the roof should be unshaded for at least 6 hours a day, preferably between 9 a.m. and 3 p.m.
The shading analysis has to be carried out for all sunshine hours throughout the year to account for the seasonal
variation of the sun path. This helps in the selection of the best location to mount the solar modules and gives a
more accurate estimation of the annual output of the PV system.
Shading analysis methods range from simple manual methods to more complex three-dimensional (3D) rendering.
This handbook explains both methods.
The manual method will give a quick impression of the solar window (aperture) of the sky, immediately showing
the structures that block the site from collecting full solar radiation. To apply this method, capture an image of the
360-degree view of the sky from the roof using an instrument such as the Solar Pathfinder (a reflective dome that
also includes a chart of the solar path) or using a camera with a fish-eye lens pointed vertically. Capture the sky view
from various locations on the roof, measuring the location and direction at each position with a compass and GPS