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).
Using IG rack systems requires paying attention to a couple of important details. One is when the length of the array requires multiple sections of rail. If that’s the case, these sections of rail must be spliced together. Some IG rack systems provide rail-splicing hardware to electrically bond the rail sections; others may require specific grounding straps—in addition to the splicing hardware—between sections of rail to ensure electrical continuity.
Some manufacturers’ IG systems use bonding end-clips, while others only use bonding mid-clips, which bond adjacent module frames. This distinction becomes particularly important in the event that a module adjacent to an end module needs to be removed. If the system uses only bonding mid-clips, removing that module will interrupt the equipment grounding system, leaving that last module frame ungrounded. In this case, a temporary bonding connection must be made to ensure grounding of that end module.
Railless Mounting Systems
Some IG rack systems do not include rails, but use proprietary hardware to physically and electrically bond module frames together. Environmental and practical benefits include less material use (resulting in lower embodied energy); no awkwardly long rails to transport (long distance or to the job site), which decreases shipping costs and hassle; and no rail cutting or splicing kits are required. Additionally, once the learning curve is summited, overall installation time can also be reduced. PMC Industries, Quick Mount PV, S-5!, Spice Solar, Spider-Rax, and Zep Solar offer rail-free mounting systems (see table).
Some railless systems (such as Spice Solar and Zep Solar) require specialized (grooved) module frames. And, in general, railless systems include fewer wire-management options—there is no rail available to support wires or wire-management hardware, and some module frames don’t have appropriate flanges on all sides. Since the module frames are tasked with providing the continuous grounding path, if a module is removed, an alternate grounding path must be implemented to make sure the rest of the array is still adequately grounded.
It’s been gratifying to watch the PV industry evolve over the last decade, and, with it, the equipment and installation innovations that have resulted. While PV racks with IG may not seem earth-shattering, PV installers know how time-consuming the array grounding process can be. It is easy to miss installing a lay-in lug or place a bonding washer on every module—and there’s no visual reminder, as they cannot be seen post-installation. By removing these separate grounding steps, we are not only reducing materials and installation cost, but also helping ensure that PV arrays have a better chance of being appropriately grounded, creating safer installations. This makes a seemingly small evolutionary step in PV mounting a fairly large leap for the solar industry.