The mounting rails add cost in raw materials, shipping, embodied energy, and installation labor. Zep Solar, Westinghouse Solar, and Silicon Energy offer rack systems without aluminum rails. Instead, these use PV modules with special frames that connect directly to structural attachment points. Zep Solar and Westinghouse Solar have partnered with module manufacturers to add proprietary grooved frames—providing connection points that lock onto mounting attachments. Zep systems are designed so that microinverters or DC converters can be included. Westinghouse provides an AC module option. Silicon Energy’s Cascade modules are also designed to bolt directly to mounting feet and adjacent modules. They are framed only on the two long edges. Since there isn’t a frame and lip on the modules’ lower edges, water and dirt are more easily shed.
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.
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).
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.
With electric cars entering the mainstream market, more systems are being installed on carports. Lumos Solar’s LSX freestanding two-car canopy comes in a 5,760 W engineered package, featuring frameless glass-on-glass modules that allow some light through the array. Silicon Energy’s Cascade Series module is another double-glass, transparent module that can be installed in carport and awning structures for dappled sunlight.
General Motors, maker of the Chevy Volt electric vehicle (EV), has partnered with Sunlogics to make the Green Zone, a four- or eight-stall solar parking canopy and EV-charging station. SunPartner is another manufacturer of solar carports, offering a steel-supported 2,300 W single-stall model and a two-car, 4,600 W model, with array tilts from horizontal to 15°. Schletter makes custom carports, and their structures have even been used for solar-double cropping—for farms growing crops under and between rows of PV cover (see “Solar Double-Cropping” in HP147). DPW Solar’s Multi-Pole mount has been installed with the bottom module edge as high as 14 feet above the ground, making it another option for a solar carport or patio cover, and DPW offers custom-designed awning mounts as well.