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 vent stacks, antenna, skylights, power masts, and HVAC equipment.

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 surrounding objects 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 otherwise might choose to install.

Many commercial buildings have large HVAC equipment that shades a sizeable area to their north:

This roof has a large skylight and numerous pipe runs in addition to HVAC equipment. An array on this roof would have to be worked around both the equipment and the shade that the equipment creates:

It would probably not be feasible to fit an array on this roof: