Knowing what direction a roof faces (its azimuth) is important to accurately estimate a roof-mounted PV array’s generation potential. With the use of a compass and magnetic declination, a roof’s orientation can be determined using these few simple steps.
1. Align the base of the compass with the edge of the roof. Most compasses will have an indicating arrow that will be perpendicular to the roof edge.
2. Rotate the compass dial so the needle is aligned to the magnetic north-and-south axis.
3. Adjust the compass dial to compensate for the local magnetic declination. You can find your magnetic declination at bit.ly/CalcDeclination.
a. For eastern declinations, the dial is rotated counterclockwise, subtracting the declination value from the current compass reading.
b. For western declinations, the dial is rotated clockwise, adding the declination value to the current compass reading.
4. The compass bearing that aligns with the indicating arrow is the roof’s azimuth. The photos demonstrate finding roof orientation with an eastern declination of 8°.