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Solar Electricity

Building and Site Assessment

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Answering these questions will help you determine if a solar electric system will work
for your building or site.

1. Do you have a south-facing roof?

Because Montana and Wyoming are in the northern hemisphere, PV panels (modules) need to face south for maximum performance. This placement allows panels to take full advantage of the sun’s path in the sky. The sun shines longest on a building’s south side. Southeast- and southwest-facing panels will perform about 5 percent less efficiently.

Yes! — Move to Question #2
No — Options: PV panels can be used as structure such as a porch cover or window awnings. They can also be ground-mounted or pole-mounted. If you cannot place PV panels to face south, a solar electric system will likely not be an efficient investment.

Panels can be mounted on east- or west-facing roofs to face south, but they stick up, are highly visible, and can be unattractive. Architects and builders can address this by designing “solar ready” buildings and integrating solar technology components into their designs.

2. Does your roof have enough space for PV panels?

The rule of thumb for PV panels is 100 square feet of space is needed for every kilowatt (kW) of electricity produced. For thin-film PV materials (such as solar shingles), about 175 square feet of space per kW is needed.

Yes! — Move to Question #3
No — Options: If your roof does not have enough space, review the Options section under the previous question.

3. Is your roof unshaded?

Photovoltaic panels are very sensitive to shading. Any shading will dramatically reduce electricity generation. Installers use a Solar Pathfinder device to determine if there are shading concerns from trees (consider mature height), chimneys, nearby buildings, etc. Keep in mind the sun’s path changes throughout the year. For maximum electricity production, make sure panels will be unshaded year-round (especially from 9 or 10 am until 3 pm).

Yes! — Move to Question #4
No — Options: If the shade is from landscaping, consider removing the plants. Check local and state codes regarding “solar access” rights if a neighbor might produce shade on any solar system you are considering. See the Pre-Installation section of Step 7: Installation. If some shade is inevitable, ask the installer about microinverters.

4. What is the angle of your roof?

Installers typically mount panels directly (flush) on an existing south-facing roof for aesthetics. To maximize electricity generated year-round, mount modules at an angle equal to or close to your site’s latitude (46 degrees for Helena; 41 degrees for Cheyenne). Installers can tilt at an angle best for your site, system type, and electricity needs.

For more summer electricity production, tilt at latitude minus 10 degrees to 15 degrees; for more winter production, tilt at latitude plus 15 degrees

Flat Roofs: Panels can be angled on flat roofs often found on commercial, industrial, and institutional buildings, but should not be placed flat (horizontal) because of snow buildup that will block the sun.

5. Is your roof in good condition?

Most roofs can safely support PV panels and mounting system weight. The rule of thumb is 2 to 5 pounds per square foot depending on the panel type and installation method. For example, a 230 watt crystalline panel (3.5 feet x 5.5 feet) weighs about 50 pounds. An installer should determine if the roof/structure can handle the added weight. Innovative mounting systems can make panel removal easy, but because panels can last 30+ years, it may be less expensive and labor intensive to make needed roof repairs before installing panels.

Yes! — Move to What’s Next?
No — Options: Complete any needed repairs first. If considering a new roof, contact a PV system installer/contractor for roof options/recommendations that might make panel installation easier or less expensive.

What’s Next?

If you answered yes to every question or can make adjustments where you answered no, your building or site is a good solar electric system candidate! A system supplier or installer can provide a more detailed assessment. Next, consider how conservation and efficiency measures can result in an efficient and affordable system; then, learn about system options.