Solar Energy Systems - Array Mounting Racks - Solar Ray - Solar Panel - PV Racks and Mounts
Arrays are most commonly mounted on roofs or on steel poles set in concrete. In certain applications, they may be mounted at ground level or on building walls. Solar modules can also be mounted to serve as part or all of a shade structure such as a patio cover. On roof-mounted systems, the PV array is typically mounted on fixed racks, parallel to the roof for aesthetic reasons and stood off several inches above the roof surface to allow airflow that will keep them as cool as practical.
Adjustability – The tilt of sloped rooftop arrays is usually not changed, since this is inconvenient in many cases and sometimes dangerous. However, many mounting racks are adjustable, allowing resetting of the angle of the PV modules seasonally.
Tracking – Pole-mounted PV arrays can incorporate tracking devices that allow the array to automatically follow the sun. Tracked PV arrays can increase the system’s daily energy output by 25 percent to 40 percent. Despite the increased power output, tracking systems usually are not justified by the increased cost and complexity of the system.
General Installation Notes – Proper roof mounting can be labor intensive, depending largely on the type of roof and how the mounting brackets are installed and sealed. It is best to follow the recommendations of the roofing contractor, racking system suppliers and module manufacturers. Module manufacturers will provide details of support requirements for their modules. A good racking supplier will provide code-compliant engineering specifications with their product. As a general rule for bidding purposes, however, it is typical to have one support bracket for every 100 watts of PV modules. Particular attention must be given to securing the array directly to the structural members of the roof and to weather sealing of roof penetrations. All details regarding attaching the mounting brackets to the roof and sealing around them are best approved and carried out by the roofing contractor so that the roof warranty will not be voided.
Asphalt Composition Roofs – For asphalt composition roofs, all mounts need to be secured to the roof with stainless steel lag bolts, bolted into the rafters. Mount types include support posts and L-brackets. Support posts are preferred because they are designed to give a good seal on boots. Support posts are best mounted after the roof decking is applied and before the roof material is installed. Support posts and roof jacks may be installed by either the roofing contractor or the crew in charge of laying out the array mounting system. The roofing contractor then flashes around the posts as they install the roof.
It is very common to install mounts after the roof is installed, drilling through the asphalt composition roofing to install the bolts. Sealant is then applied around the bolts without flashing. As well, the top layer of roofing should be carefully lifted back to inject sealant under the roofing. While this is much less labor intensive than when flashed, unless performed by the roofing contractor, this method may void the warranty on the roof.
Metal Roofs – There are several types of standing seam metal roof products, including vertical seam, horizontal seam and delta seam products. Currently, special clamps, referred to as S-5 clamps, are available to attach arrays without any penetrations to vertical and horizontal seam roofs and certain other standing seam roof profiles. These clamps make installation of the solar array a relatively easy matter compared to any other roof type. In contrast, clamps for delta seam metal roofs are not available. For these roofs, it is necessary to cut into the roofing, install boots around the mounting posts, and then seal the penetration. This being undesirable and labor intensive, it is best to clearly specify in advance a vertical or horizontal seam metal roof or other roof type compatible with S-5 clamps.
Other Roof Types – While it is possible to install a PV array on shake, tile and slate roofs, these roof types pose certain problems. Contact the racking system supplier for information on products and installation methods for these roof types. Work directly with the roofing contractor before ordering the racking system. Also look for roofintegrated modules that can be used with tile or slate roofs.
Roof Vents and Fans – We suggest installing roof vents, plumbing vents, and fans on the north side of the roof to avoid interference with the solar array. This will also reduce the potential for inadvertent shading of the array.
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