We knew our site had inherent limits on solar access because of the lot orientation, the house placement (as regulated by zoning), and the shading of nearby large trees. Before making the final decision on whether to install solar collectors, we needed to verify the solar potential.
To do this we used a tool called a "Solar Pathfinder®". Any trees, buildings, or other objects that will cast shadows on a collector or photovoltaic panel are reflected in it's plastic dome, showing shading patterns at the site for the entire year. While observing the reflection, a wax pencil is used to trace around the reflected shadows on a sunpath diagram.
Above: Master Plumber and Solar Installer Douglas Dypold makes a sunpath diagram from a tall step ladder.
Above: The Solar Pathfinder includes a reflective dome, a compass and a leveling bubble.
The bad news: Unfortunately, the rooftop solar prognosis for our site does not look favorable. Shade cast on the roof plane by two huge, beautiful Elm and Sugar Maple trees leaves us only a relatively narrow "solar window". That meant that for much of the year, a solar collector would only "see" direct sun from about 10:30 AM through 2:30 PM. Even in the best of the three diffrent locations we tested, economical solar energy via collectors is not yet viable.
Our conclusion: Someday the trees may no longer standing. Until that day, we'll be grateful for their cooling shade in summer. In the meantime, we installed the piping in the walls into the attic, insulated and ready for the time when solar collection is feasible.