Solmetric provides a free online tool that can determine your roof’s azimuth. Just enter your address and use a screen cursor to point to the edge of your roof (see bit.ly/SolmTools). To use the tool, you will need to register on Solmetric’s website.
Select “Roof Azimuth Tool” from the drop-down menu under the “Support” tab at the top of Solmetric’s home page. Log in with your username and password, and a map of the United States will appear with a text box at the top to enter the property address. Once the address has been entered, an overhead image of the property will appear for viewing. Next, click on the “Azimuth Tool” button located at the top of the satellite image just to the right of the address text box. A crosshair will appear for you to move and establish a reference point for measuring the roof azimuth. Use the crosshair to click on two points at either end of the roof edge. Once the two points have been established, the tool automatically draws a line along this roof edge indicating the orientation to true south, which is also shown in the “Azimuth (true)” text box. (See “PV Site Evaluation” for an example.)
If you have location services enabled, the compass app on your smartphone likely corrects for magnetic declination automatically. Just align the phone with the roof edge and read the value. However, be aware that interference can create inaccurate readings.