ORIENTATION

Solar PV systems operate most efficiently when the sun is perpendicular to the surface of the panels; an array facing true south will produce the maximum amount of electricity. In this region, true south is about 11° east of magnetic (compass) south.

This is important for two reasons. First, you will be making a substantial investment in your PV system, so you want to choose the location on your property that provides the best possible orientation for your array. Second, if your system is oriented too far from south, Xcel will not pay you the full amount of the Renewable Energy Credit (REC) since the system is not producing as much as it could.

There is some flexibility with the precise direction that your array faces. In this region, if your array faces 30° east of true south, the output of your system will still be about 99% of optimum. If your array faces 30° west of true south, the output of your system will be about 94% of optimum. These figures are somewhat variable depending on the pitch of your roof. A system that faces due east will produce between 78% and 83% of optimum, and one facing due west will produce between 70% and 80%. If the expected output of an array is less than 90% of optimum, the REC payment from Xcel decreases accordingly.

If the array must be installed on a roof that is oriented too far from south, it is possible to use tilt legs to provide a southern orientation for the array. However, this requires engineering design for wind loads, additional mounting equipment, and a longer installation time, all of which increase the cost of the system. Many customers with east-facing roofs, particularly those concerned with aesthetics, choose to mount the modules flush against the roof and accept the decrease in the Xcel REC payment. The savings realized through avoiding a tilt-up array often offsets the loss in REC funds.

This array is flush-mounted on an east-facing roof that has an 18° pitch. It will produce about 83% of an optimally oriented array:

This is a tilt-up array on a west-facing roof: