One of the first things you learn about planning and installing solar thermal systems is the importance of orientation. On a theoretically perfect clear sky day, a collector array that faces true south will produce the greatest heat output, all other factors being equal.
In many situations, solar pros don’t have the option of facing a collector directly true south. Instead, they are constrained by the orientation of a roof, or perhaps the shadows cast by nearby objects such as trees and adjacent buildings. In these cases, using a tool such as the Solar Pathfinder (shown in Figure 1) can help determine the time of day and month when the location will be shaded.