PV Rack Strategies: Page 3 of 3

By:

Greg McPheeters

Tim Vaughn

Issue Date:

April / May 2011

Last Updated:

12/23/11

Intermediate

Inside this Article

Advance planning, accurate measuring, a good eye, and an extra pair of hands all contribute to a successful PV array installation.

Complex roof angles, obstructions, and shading all affect options for array position. (Note the screen under the array to keep out varmints.)

Laying out the array and rail position with a chalkline and tape measure.

Finding rafter position by tapping with a hammer. This is an acquired skill that professional installers quickly master.

Drilling a pilot hole to verify rafter position. If the drill punches through after going in less than an inch, you didn’t hit a rafter. Size your pilot hole to match the necessary hole size for your lag bolts (1/8 in. is common).

Leveling mounting rails with a string line.

On tile roofs, locating mounting-foot positions becomes trickier. Tile roofs are among the most challenging roof types to work with. Here, the tiles are pried up to allow a tile to be removed in the region where the rafter is believed to be running.

Once the tile is removed and you’ve confirmed your best bet for rafter location, it’s time to probe with a drill to verify.

After a rafter is verified, you can mount the roof attachment hardware (in this case, a standoff) with a lag screw. Even with flashed attachments, roof sealant is used underneath the standoff.

Finish the weatherproofing of the standoff by sliding flashing over it. Some installers take the extra step of trimming the tiles to fit back in tightly around the standoff, which is quick and easy with a cutting wheel, shown here.

Sighting along the edge is often enough to align PV modules accurately.

While two rails might each be straight, they may not lie on the same plane. This can result in an unsightly twist, commonly called “potato chipping.” This is easily avoided by visually checking rail alignment during the leveling process.

It’s often easiest to wire and ground PV modules as you go. Accessing the backs of modules after a full array is installed may be difficult.

This rack allows array wires to be tucked into channels within the mounting rail. This provides protection to the wires and a neat installation.

Some rack manufacturers provide end caps for rails and module clips that attach to the rail underneath the module, so rail ends are flush with the array.

Intermediate

While string lines can be very useful and helpful, they also tend to blow in the wind and sag if they aren’t tight. Most module frames have square edges, which make line of sight an excellent way to confirm alignment. Once a module is roughly in place, one person can sight down the row or string line to position the module, and the other can tighten the hardware.

It is easiest to install and secure module wiring as the installation is progressing. If your rack system has channels for running module leads, put the leads into the rails as you go. If you are using standard lugs and copper wire for grounding, installing as you go will allow you to mount this hardware to the bottom of the modules so that they are hidden under the array.

When you are finished with module installation, double-check all bolt torques. With the modules fully installed, the rails can be trimmed to length. A reciprocating or band saw makes the best cuts. Be careful that you don’t cut into the roof!

Icing the Cake

Several rail systems offer rail end-caps to spruce up the installation. Some manufacturers offer module end-clamps, which allow the rails to be cut flush with the array’s edge. Most of these clamps have the added benefit of being “one size fits all,” working with a variety of module types so long as they have an underside lip on the module frame to clamp to the rail. Finally, to critter-proof your array, consider installing screening around the edges. Racking manufacturers are just beginning to offer simple solutions for this pesky problem.

Access

Greg McPheeters has been designing solar-electric systems and PV mounting solutions since 2001. Greg is the lead design engineer and innovator for SnapNrack Inc.

Tim Vaughn is a 21-year veteran of the solar and PV industry. Tim is currently the program manager for SnapNrack Inc.

Racking Manufacturers:

Conergy • www.conergy.us

Direct Power Solar • www.power-fab.com

EcoFasten Solar • www.ecofastensolar.com

EZ Rack • www.ezrack.net

HatiCon Solar • www.haticonsolar.com

IronRidge • www.ironridge.com

Jac Rack • www.jac-rack.com

Next Generation Energy • www.zillarac.com

Professional Solar Products • www.prosolar.com

Quick Mount PV • www.quickmountpv.com