ROOF PITCH

Solar PV systems operate most efficiently when the sun is perpendicular to the surface of the panels. Because the height of the sun varies over the course of the year, the best year-round angle for an array is approximately equal to the latitude where the array is located. In this region, that angle is 40° .

However, decreasing the tilt of the array does not cause a dramatic decrease in energy output until the tilt drops below about 15° . A south-facing array tilted at 15° from horizontal will produce about 93.5% of optimum, and one tilted at 23° will perform at 97% of optimum. For aesthetics and cost reasons, most customers choose to go with a flush-mounted array if the pitch of their roof is around 18° or greater.

A tilt-up array is recommended for flat roofs. Here's a photo of a tilt-up array on a flat roof: