PV Rack Innovations: Page 2 of 3

Ballasted Systems for Low-Slope Roofs 

Low-slope roofs are often associated with large commercial buildings, but in many parts of the country, particularly the Southwest, they are common on residences. Because of the rapid growth in commercial installations over the past few years, the choices for low-slope rack systems have expanded dramatically and can be either ballasted or mechanically attached to the roof. 

Ballasted systems use rack and module weight, with additional mass like concrete blocks, to hold down the array and withstand wind uplift. Ballasted arrays frequently have no mechanical attachment to, and thus no penetration through, the roof. The building structure and roofing must be able to handle the additional weight, and the roofing installer and manufacturer should be consulted to ensure that a ballasted system won’t void the roof warranty.

Some new ballasted systems are transitioning from the standard aluminum and steel ballast tray components to heavy-duty plastic, which is nonconductive and doesn’t need to be grounded. Renusol’s CS60 is made from 100% recycled polyethylene. Each PV module is mounted directly on a Renusol base, at a set 10º or 15º tilt. Sollega’s InstaRack is also made from partially recycled polyethylene, and Ecolibrium Solar’s Ecofoot offers another ballasted mounting solution made of a 100% recycled content polymer plastic.

Mechanically attached low-slope roof racks have several roof-penetrating structural attachment points. This, in combination with the rack’s weight and design, ensures the modules can resist uplift forces. PV systems on low-slope roofs in seismically active areas usually require mechanically attached racks. Arrays with steeper tilts experience higher wind loading and may require more ballast. Less ballast may be needed if a combination of mechanical attachments and ballast is used. Nearly every major rack manufacturer has a solution for low-slope roofs, but a few, like PanelClaw’s Polar Bear and SunLink’s RMS, have focused very specifically on this application.

Pole-Mounts, Carports & Awnings

Ground- and pole-mounted PV racks commonly rely on a combination of steel and aluminum support structures—most often using steel poles supporting aluminum rails, although all-steel galvanized racks are becoming common (see “Ground Mounts for PV Arrays” in HP139). 

Pole-Mount Racks

The most common top-of-pole mount uses 4- to 8-inch steel poles embedded in a poured concrete foundation to support standard racks and rails. While pole mounts keep modules cooler, providing plenty of airflow around the array, there is a lot of excavation and concrete work needed to provide wind-loading support. The higher the array is mounted, the longer the buried pole needs to be. 

DPW Solar’s Multi-Pole mount uses 3-inch-diameter (or larger) steel poles to support a column of up to four modules in landscape orientation. 4- by 4-inch (or 5- by 4-inch) steel box tube, set horizontally, supports the module rails. The Multi-Pole mount can be adjusted from horizontal to 55º, making it a flexible solution that can be adapted to various array sizes.