Your home’s power requirements, roof type, and solar resource will determine the solar electric system type and size.
When purchasing a solar electric system, the right choice will depend on how much sunlight your area receives, your budget, how much conventional power you want to offset with solar power, how much room you have on your roof or in your yard, and where the solar panels will be mounted.
Roof Requirements Before purchasing a solar electric system, homeowners need to determine available roof space and condition. A helpful tool to use when deciding whether to purchase solar for your home or business is Google’s Project Sunroof. With this tool, you can type in your address and see an estimate of how much of your roof is available for a solar installation.
Space and Orientation For maximum performance, your solar electric system needs about 75 to 100 square feet of unshaded south-facing roof or yard space for every kilowatt of electricity produced. If your roof does not face south, you can still use a solar electric system, but the performance will be about 5% less with a southeast- or southwest-facing system. Eastern, western, and northern exposures will show an even greater drop in performance, so be sure you understand how such a system will meet your expectations.
Roof pitch is also important to capture the path of the sun, but the requirements vary with location. Your solar vendor and installer should be able to tell you how the pitch of your roof will affect the performance of your system. When a south-facing roof is not available, some people install solar electric systems on garage roofs or use them as window awnings and porch coverings. If you have a shortage of roof space, panels can be mounted on a pole or in your yard. Ground-mounted systems are great for homes with large yards. Some systems come mounted on a tracker that follows the sun’s movement.
Roof Condition If your roof materials are more than 15 years old, you may want to consider replacing them when you purchase your solar electric system; otherwise you will need to remove your entire solar electric system whenever you update your roofing materials. Most solar vendors recommend using roofing material that will last as long as the system, which is about 25 to 30 years. Make sure the roof can hold the weight of the system, which is estimated at three to five pounds per square foot, depending on the type of technology used and installation methods. In addition, be certain to ask your installer about the structural integrity of your existing roof and its ability to safely support solar panels.
Shading Shading a panel reduces its performance because it blocks sunlight. The most common items that shade solar panels are trees, chimneys, nearby buildings, pipes, skylights, and vents. To determine possible shading problems, consult a solar professional who uses a software program that can estimate site shading. Some people will examine a proposed location throughout the day and year to see how the area shading changes. For example, shading in an area can change from summer to winter because the sun’s path changes.