All solar contractors will perform a site assessment as part of a proposal.
Some questions to ask prospective installers.
Does the roof of your house have good southern exposure?
Are there any trees, power lines, chimneys, neighbors property that shade your roof?
Is your roof structurally sound?
How old is your roof?
Sunlight is the fuel for all solar technologies, and the term ‘solar resource’ refers to identifying how much of it is available to a given collector area. The most rudimentary analysis requires standing on your site with your arms up in a “Y” form and looking to see what obstructions there are in the field of vision between your arms. This basically represents the productive sun hours of 9am to 3pm.
There are professional devices, such as the Solar Pathfinder and Solmetric SunEye, that calculate the Total Solar Resource Fraction (TSRF) which accounts for shading, panel tilt and azimuth (direction relative to south).
The tilt of the earth on its axis and our location north of the equator result in a specific sun path that changes throughout the year. The sun is at its highest point at noon on the Summer Solstice, or June 21st.
Most photovoltaic and solar hot water systems are stationary, and having unobstructed solar access between the hours of 9AM and 3PM is ideal. Tracking systems usually follow the sun path from east to west during the day, and are seasonally adjusted for altitude angle.
Potential Installation Issues
Flat panel collectors weigh about 200-250 lbs. Thermosyphon systems add the weight of the water storage tank. Residential scale evacuated tube arrays weigh about 175 lbs.
More serious considerations, from a structural perspective, are wind-induced loads and concentrated loads. Remember that the snow or ice that used to be spread out evenly over your roof will now be concentrated at the mounting feet. Most of us know what high heels do to a wood floor.
For these reasons, a structural analysis is often required by the building officials who review plans and issue permits for solar systems.
It is a good idea to install solar panels over a roof which has 15 of more years of life in it. Some folks do a partial re-roof under the area of the solar array even if they are not prepared to do a complete roof replacement.
Fire Marshalls are now asserting their authority in the permit/plan review process to make sure they have room to work in the event of a fire in the home/building. A qualified solar contractor will help you work through all of these issues; including working with a structural engineer if that becomes necessary.
With an increasing body of information available, the added assurance of a successful installation that these steps provide adds some expense but not a deal-breaker to your solar system.