Rooftop solar panels are a smart move for today's homeowners and business owners. Financial and environmental benefits have increased even as prices have dropped, and modern solar panels are efficient and attractive. Although it is possible to place solar panels on any type of roof, there are specific procedures that must be followed to assure maximum solar collection and minimize roof damage. Photovoltaic (PV) systems must be properly sized, sited and installed whether or not they are connected to the grid.
Installation is a job for professionals. The installer must assure that sufficient roof surface is available; a thorough examination of the existing roof and its underlying structure is the next step. Age, condition and type of roof and underlayment will all help determine the type of installation method or system to be used—a roof that is not in good condition will not be a suitable foundation for solar panels. Considerations include roof slope, shingle type, drainage, access, and safety issues. Any visible damage must first be assessed, and then repaired. An installer should also identify potential concerns; overhanging tree limbs, excessive dirt buildup, obvious rooftop intrusion by squirrels or other pests, and unfavorable roof orientation.
Types of Mountings
In order to mount panels permanently, roof penetrations are required; they must be safe and sealed prior to setting the panels. Improper penetrations can damage roof rafters and cause leaks. Flashing is essential; and proper mounts and connections are required to prevent panel slippage and damage.
Two basic types of mounting systems exist: racks that include rails and fasteners and newer rackless systems that rely on panel frames to provide mounting structure. In either case, it is essential that all fittings are properly aligned and tightened, and that the PV system is sited in a way that produces maximum gain as well as assuring maximum protection from weather and other types of damage. Specialty mounting systems have been developed for some roof types.
Types of Roofs
In general, it is best that installers check with owners and manufacturers regarding a specific roof type.
Composition shingles have specific requirements. Primary concerns are waterproofing, proper flashing installation, and use of sealants that match and won't react with the roofing material. Although few wood shingle roofs still exist, installing a solar array atop wood shingles would represent an added challenge.
Barry Cinnamon, CEO of Spice Solar, notes that the biggest concern is locating rafters that are not visible from the topside of the roof, and then attempting to make a secure connection in the center of the rafter. He adds that it's "trial and error" and that installers should be trained to patch the penetrations when they miss!
Tile is sensitive, cannot be penetrated and requires a different installation method. Some type of hook system is the best option; there are various types available to accommodate PV installation on both curved and flat tiles; most have preformed flashing to assure code compliance. Working on a tile roof requires extra care because cracks and broken tiles can result even from walking on the surface.
Another option, however, is to remove a section of tile, replacing the area underneath a planned solar array with asphalt shingles. It involves another step for the owner, but can simplify panel installation.
Another specialty roofing material, slate presents a real challenge because it is expensive and brittle. Drilling through a slate roof is not an option and because slate lies flat there is no way to attach a lift or a hook. Basically, the only solution is to remove pieces of slate -- either an entire section to accommodate the solar array, or individual tiles so that standoff pipes and flashing can be installed. The tiles must then be reinstalled individually.
Mounts on standing seam metal roofs are relatively simple and straightforward, and should attach to the seam. For corrugated roofs, the mounts should attach to panel sides rather than in the valley where moisture can accumulate. Installers should avoid making holes in the roofing material, and confirm that PV installation will not void a manufacturer's warranty.
In some sunny areas such as the Southwestern United States, flat roofs are common and local installers know the best and most economical ways to orient and install PV panels on those roofs. In other parts of the country, flat roof panel installation may entail a learning curve. Penetrations are not typically required; instead, a code-compliant and safe ballast system uses gravity to keep panels in place. Specially angled mounts are, however, normally required to assure the best panel angle.
No matter what type of roof, there is an efficient and effective way to gain the benefits of solar energy. Professional PV installers should have the knowledge and resources to find the best method for every installation.