A well-designed solar electric system has clear and unobstructed access to the sun for most of the day throughout the year. Siting a PV system correctly is critical in order to achieve maximum power production and thus maximum energy offset and financial return.
Orientation and Tilt
Optimal orientation for solar panels is true south. As you move away from true south, a system will suffer production losses, up to as much as 15–25% for panels oriented east or west. However with advancements in technology these losses are decreasing as inverter manufacturers learn how to maximize off-of-south orientations. In Seattle, solar panels produce the maximum power annually when mounted at a tilt of roughly 30 degrees.Shading
Avoid shading as much as possible. Even minimal shading can significantly impact power production. You will want to consider potential shading from trees, buildings, power lines, telephone poles, and obstructions like chimneys and vent pipes. Your contractor should include the impact of obstructions on your power production estimate.Sloped Roof
A significant portion of your system cost will be in the installation of the panels, so if you plan on replacing your roof in the next 5–7 years, consider doing that first. Otherwise, your installer will need to come back to remove the panels for the new roofing to be added, and then re-install the panels all at your cost. Overall, you want to be sure your roof is in excellent long-term condition, because PV systems are designed to last a minimum of 20 years and many will last even longer. So, if you are unsure about the structural integrity of your roof, have it professionally inspected to verify its condition and suitability.Flat Roof
Most residential and small commercial PV systems are installed on sloped roofs, yet it is possible to install on a flat roof. Contractors typically avoid penetrating a flat roof and instead use some sort of ballasted (weighted) means of securing the panels against wind. Building code officials will be concerned about the wind sheer and roof loading of such a system. If a flat roof system is in your future, plan to submit a professional engineer (PE) stamped drawing illustrating how the system will be secured to the building.Tracking
Most residential and commercial PV installations are mounted to roofs and are fixed in place. If your system is going to be mounted on a pole or a flat roof, you have the choice of installing a tracking device. The simplest form of tracking is to seasonally adjust the tilt angle of the panels. Automatic tracking devices allow the panels to follow the sun as it moves through the sky, receiving direct light more often than a fixed system. Electrically operated and thermally operated trackers have their own costs, benefits, and drawbacks. Keep in mind that without a tracker, your PV system has no moving parts. While automatic trackers can increase production by 20–40%, they do add moving parts to the system, so there are operation and maintenance concerns to consider. Pole-mounted systems also have the additional cost of the pole installation.