SHADING

Because solar PV systems rely on direct sunlight to create electricity, even a very small amount of shade – for example, the size of a fist – can significantly reduce the output of your system. For optimum performance, the entire array must be located in full sun from about 9am to 3pm during all 12 months of the year.

When looking for objects that may shade part of the array, we must not only consider things like nearby trees, buildings, power poles, and power lines, but also objects on the roof itself. These would include chimneys, antenna, vent pipes, and power masts.

Finally, one must consider the low angle of the sun during the winter months. On the shortest day of the year, the sun is only 14 degrees above the horizon at 9am. It is easy to underestimate the impact of nearby trees and buildings when looking at their shade patterns during the summer months.

If part of your roof is impacted by shade, it does not necessarily mean that a system can't be installed on your roof. Depending on how much of the roof is shaded, it may only mean that the system size must be smaller than what you might otherwise choose to install.

This roof is obviously too shady for a PV System:

This roof gets shade from the tree in the afternoon and shade from the 2-story part of the house in the morning:

This is an example of winter-time shading that may not be apparent in the summer months:

This roof is impacted by shade from the chimney:

This is another example of how long winter shadows can impact the solar window of a roof:

Here is an installation that works around shading from a chimney:

Here is an installation that works around shading from a dormer: