Maximizing Radiation to the Solar Module Panels

Ensure the Site Has Clear Access to the Sun

PV solar modules panels must face the sun to make electricity. As every romantic knows, the sun sets in a brilliant display of color in the west. My mother-in-law tells me that it does the same when it rises in the east, although I cannot personally attest to this statement. Where, then, do you face the modules? The quick answer is to point the panels directly at the sun. However, with the sun moving from east to west during the day and progressively higher in the sky as summer approaches, this might be a rather difficult task.

You have two options:

mount the modules to a fixed location pointing solar south or install a tracking unit that automatically aims the panels directly at the sun. Either way, make sure the location you choose is not impeded by trees, buildings, or other obstructions. Site locations can be difficult to assess due to the seasonal variation in the sun’s track, leaves on deciduous, trees, and neighboring buildings. To help simplify the assessment of a site, consider purchasing or renting a Solar Pathfinder to eliminate any guesswork. This device works on the well-known principal observed by every schoolchild with access to a magnifying glass. As the sun tracks across the sky, light enters the magnifying and focusing dome of the device. The concentrated sunlight falls on specially sensitized paper burning a copy of its path. Gaps in the marking indicate obstructions that will cause unacceptable shading of the solar module panels.

Eliminate Tree Shading

Although you want to protect the south side of your house from the summer sun, the last thing you want to do is to shade ever a very small portion of your PV array. Partial shading will cause a disproportionate reduction in electrical generation to the shaded area. Keep trees well clipped in the sunlight window (between the hours of 9am to 3pm), keeping in mind both winter and summer sun tracking. If you are unsure about shading, consider evaluating your site using the solar pathfinder.

Consider Snow and Ice Buildup in Winter

If you live in a snow area, take winter snow and ice buildup into account when considering PV location. Although PV angles at this time of year are almost vertical, snow and ice will stick to the array. If a coating of fresh, white, powder snow is covering the array, it may take several days for it to fall off without brushing-and you may not want to brush off PV arrays if they’re mounted on a second-story roof.

Ensure That Modules Don’t Overheat in Hot Weather

Solar module panels electrical output fades (just like everyone I know) as the mercury rises. In order to ensure peak operation of the array, modules must not be seated directly on the roof surface. An air gap of 2-3 (5-8 cm) will allow cooling air to circulate under the array, providing maximum power output.

References: The Renewable Energy Handbook, by William H. Kemp.

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