The following chart shows the calculated PV system output for a system in the Phoenix, Arizona area for a variety of array orientations. The calculations assume an open array in free air such as a pole mount or parking canopy without anything under the modules. Mounting PV modules on a roof reduces the output due to the higher temperatures. PV modules mounted flush with a roof, but with at least 3” of space below the modules and mounting structures that allow some air flow, will have an annual energy reduction of about 6%. Of course, these calculationa assume no shadows on the PV array. The calculations include normal inverter efficiency, wire loss, and an allowance for dirt.
In the chart the upper line shows the roof pitch (4/12 represents 4" of slope per 12" of roof), the angle the pitch represents, and the direction the PV module face (NW=North-West, etc.).The larger number is the annual output in kilo-Watt-hours (kWhr) per year for a PV array with a nominal rating of 1000 Watts. For instance, if the PV array has 20 PV modules with a rating of 310 watts (STC) per module, the array is rated 6.2 kilo-Watts DC (kWdc). To estimate the annual output using this chart, simply select the closest orientation, such as South facing at 3/12 pitch, and multiply the 1668 by 6.2 to get the annual output of 103,416 kWhr.