Direction: The Surface Direction is shown in compass orientation. Twelve directions are shown, including the cardinal directions and 30 degrees each side of cardinal. Though the actual orientation of a surface is used to calculate PV energy generation, the direction shown here is the closest of the twelve general directions.
Tilt: The Surface Tilt is measured from an upward-facing horizontal orientation. For example, a vertical wall has a tilt of 90 degrees. A flat roof has a tilt of 0 degrees, and a pitched roof surface is between 0 and 90 degrees. A floor has a tilt of 180 degrees. Only surfaces with a tilt of less than 120 degrees are considered for PV analysis.