“How large a system will satisfy a signifi cant portion of the occupant’s power demand without waste and payback his investment in the shortest time possible? We have seen high-energy-use commercial facili- ties where every square foot of usable roof space was employed, and other cases where only 20 or 30 percent of available space was used.” PV installation and preparation is easier for large,
fl at, unadorned roof areas. Roof vents, antennas, sat- ellite dishes or any other roof fi tting may need to be relocated. “If the roof area is cut up, there is typically more installation time needed,” says Alan E. Burnett, PE, associate at Gales Associates Inc. in Mountain View, Calif. “Open roofs with low slopes and simple shapes like a rectangular outline provide more ef- fi cient installation. Access and staging are typically easier for lowslope roofs.” High-sloped roofs will typically require a pene-
trating PV racking system that meets wind and snow requirements of the loads for its region. To determine wind loads, Hanis recommends checking local build- ing and safety departments for specifi c requirements. International building code wind speed charts can determine basic wind speeds for U.S. locations.
Determining the angle of the PV array is an important part of a solar PV installation. (Image courtesy of Tecta America Corp.)
Solar prep: new versus existing roofs Solar panel installation preparation is different for existing building roofs than it is for new building roofs. For existing roofs, the contractor should inspect the roof to confi rm that existing features will not be affected by the new photovolta- ics. Also, the contractor should verify that the remaining roof service life is similar to the PV service life. “If the PV system will be mounted to the roof structure, the penetrations should be fl ashed in a watertight manner and the roof warranty should not be compromised, if the roof is under warranty,” says Alan E. Burnett, PE, associate, Gales Associates Inc., Mountain View, Calif. “If under warranty, the contractor should ensure the roof manufacturer is notifi ed and approves of the roof repairs for warranty compliance.” For new building roofs, the PV layout needs
to be coordinated with other roofmounted items such as mechanical units and electrical conduits. If the PV will be connected to the roof structure, the curbs or stanchions should be installed prior to the roof installation to avoid having to repair the recently installed roof. “These PV support items will need to be 8-inch minimum above the fi nished roof surface and should not obstruct drainage,” Burnett says. “For some projects, the PV system can be a separate design build item and the contractor will need to coordinate his work with the PV designer and contractor.”
Installed safety rails and ballast blocks with a slip sheet are part of a successful and safe solar PV installation. (Image courtesy of Tecta America Corp.)