Innovations in PV module rack systems offer more streamlined, straightforward installation, reducing materials and labor.
It seems that each year the photovoltaic (PV) industry makes strides to become more cost-competitive with conventional power sources. From simpler module wiring to combining functions within inverters, equipment manufacturers have found ways to reduce material use (and thus cost). With multiple functions in one piece of equipment, an added benefit is streamlined installation. Module rack systems have likewise evolved, with the result of decreasing installation time. One of the most notable recent innovations in racking is “integrated grounding (IG),” now offered by several rack manufacturers.
To understand what integrated grounding is—and why it is getting much attention in the industry—you need to understand how time-consuming and detailed the grounding process once was. In the past, an equipment-grounding conductor (EGC) was secured to each module by a lay-in lug. This was attached to the module grounding point with a stainless steel thread-forming screw—after the surface was properly prepared by sanding off the module frame anodization at the point of lug contact. The grounding wire continued in this way from module to module, then to another lay-in lug bonded to the rack, then to any other metallic electrical box, and so on—to connect to the rest of the equipment grounding system (see “Code Corner” in HP102).
Top-Down Shows Up
Soon, “top-down” module mounting—with two rails under each row of modules and the modules secured to the rails by clips accessible from above the modules—became commonplace. End-clips are used to secure modules at the end of each row, and mid-clips are used between adjacent modules. The clips are bolted to the rail; their edges overlap the module frames to secure the module against the rails. Bonding washers placed between the module frame and the rail replaced the lay-in lug and wire. When the clips are tightened, the teeth of the washer pierce both the module frame and the rail to electrically connect the rack and modules.
This method sped up the equipment-grounding process since no surface preparation is required. It also reduced expense—the bonding washers are less expensive than lay-in lugs and the EGC that had to span all the module frames (see “Code Corner” in HP152.)
On to Integration—With or Without Rails
The logical next step in top-down mounting and module grounding is bonding clips that, when bolted down, simultaneously secure the module to the rail, and electrically bond adjacent modules and the underlying rail. It eliminates the need for separate bonding hardware (bonding washers or lay-in lugs). While bonding clips vary in shape and dimensions, all have a method—usually sharp, serrated surfaces—to pierce the frames’ and rails’ anodized coating when the clip is secured.
Integrated grounding is still an innovation, so at this time, each manufacturer typically offers only one rack system with this feature—note the specific rack model(s) in the “Integrated Grounding” table (and don’t assume that all of the other products the manufacturer makes have IG capability).