Racking & Mounting

Mounting structures are used to fix solar panels (PV modules) to the roof or to the ground so they aren’t moved by wind or snow. Be sure to consult the solar panel 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.

Most modules can be fastened via holes in the bottom flange of the frame but this can be awkward and time consuming. 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 most manufacturers don’t allow it.

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 have since given way to WEEB clips 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.

Note that specialized PV products like frameless or flexible modules typically require their own proprietary mounting and grounding components.

Grid-Interactive Inverters for Backup Power Applications

Grid-interactive inverters, also called dual-function or hybrid inverters, can export power to the utility grid, but can also supply backup power to protected loads during a grid outage. These inverters use a battery bank for energy storage, will not operate without batteries, and include an automatic transfer switch that enables them to safely operate off-grid during a blackout.

The grid-interactive inverter is connected to the battery bank (usually 24 or 48 VDC), an AC sub-panel for protected loads, and the building’s utility entrance load center. The battery bank is charged by the PV array connected through a charge controller or through the battery inverter via AC coupling. Under normal conditions, it will export surplus power produced by the PV array. During a grid outage, the inverter will automatically disconnect from the grid and supply AC power to the protected load subpanel by drawing energy from the battery bank and solar array. When the outage is over, the inverter will automatically switch back to grid-tie operation and recharge the batteries.

It is important to note that a significant amount of energy is used to maintain the battery bank. For this reason, systems with battery backup typically provide 5 to 10% less energy (kWh) per kW of PV array than equivalent grid-tie systems that don’t include batteries.