Mounting Structures 101

SnapNrack RL Racking System - RL Installed View PhotoMounting structures are used to fix PV modules to the roof or to the ground so they aren’t moved by wind or snow. Be sure to consult the PV module manufacturer’s installation manual when selecting and configuring a mounting system as not all modules are compatible with all mounting methods. If the manufacturer doesn’t explicitly allow for the type of clamp and mounting locations or grounding method used by the mounting system, it may not pass inspection.

Some ground-mounting systems fasten to the bottom flange using specialized clips, enabling installers to perform virtually all of their work underneath the modules. Top clamps, which clamp the module frame to a mounting rail or roof attachment, are most popular today as the clamps can double as spacers and clamp two modules simultaneously, reducing the total number of fasteners required. Regardless of clamp type, it is also important to clamp the module in the right places.

Most PV modules are designed to be clamped at the quarter-points where the mounting holes typically are. This ensures optimal loading on the module frame and provides maximum static and dynamic load capacity. Some manufacturers also allow for mounting on the short ends of the module, which can allow two rows of modules to share a rail. However, mounting on the ends typically reduces the load ratings of the module, which is why some module manufacturers don’t allow it. Recently, there has been new developments in ‘rail-less’ solar racking solutions, potentially reducing components and cost for roof mounted solar modules.

Early equipment grounding for module frames was accomplished with a bolt or screw with a star washer attached to the grounding wire. AEE Solar later introduced grounding lugs which provided a faster and more secure method for attaching the ground wire and these gave way to WEEB grounding clips or washers which enabled module grounding through the rail. With the advent of the UL 2703 mounting and grounding standard, many mounting systems, such as SnapNrack, accomplish grounding through the mounting components so that the installer only needs to run a grounding wire to the end of each row of modules.

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