A square and level array begins with a good layout on the roof. Taking the time to do this in the beginning will make the entire process go more smoothly.
Sketch the basic layout on the roof with either a nonpermanent marker (for metal roofs) or chalk (for rough surfaces), starting with the array outline from your design. In addition to the array outline, mark where the rails will be located. To avoid confusing your lines, use one color for the array outline and another for rail lines. With the system lined out, then install your roof attachments, which may be L-brackets or standoff posts—just be certain to use flashing to meet building codes and prevent leaks.
First, determine that the array lies in a single plane. This process is easiest when you work with at least one other person—and with a rack system that has quick and easy leveling features. Otherwise, this step can be a huge time sink.
Install your rails onto the previously installed roof attachments. Leave the rail hardware loose to allow the rails to rest low on their mounts.
The rails are fairly rigid and tend to lay straight, but from rail to rail there is no connectivity. To line up the installed rails, place an extra rail or other straight-edge perpendicular to the installed rails. Another option is to use a string line or laser level—although the laser level may be difficult to see in the sunlight.
Tighten the bolts on the top and bottom rails; then use the straight-edge to level the rails in between. If the middle of the roof sags, the rails in between will be adjusted higher. If the middle of the roof is raised, then the top and bottom rows will need to be raised.
Watch for “potato chipping,” which is caused by the top rail not sitting in the same plane as the bottom rail. This is easily observed, so get your eye down to the plane of the rail tops to look for any variations. Check that the top and bottom rails are in the same plane before working on the rails in between. Site from both ends of the array. It is often helpful to also inspect the rails from ground level, where they’ll be seen the most.
It is tempting to use a bubble level to check that the rails are plumb. But roofs aren’t necessarily level. If you want the array to look good, it’s more important that it match the roof lines.
Next, square the rails as preparation for installing and squaring the modules. To verify that a rectangle is square, measure diagonally—from the top corner of each side to the opposite bottom corner. The two lengths of the “X” should be equal. (Note: On most installations, the rails do not need to be perfectly square. It is more important that they look square when comparing them to the roof and building.)
When you are done squaring and leveling the rails, tighten every fastener to its torque specification before access is limited by the modules.
Roofs are rarely square, so as you install the modules, make them square to the lines of the structure that will be most visible from the ground. As a result, modules may not be perfectly lined up to the rails, which is usually fine. It’s difficult to spot minor discrepancies in rail alignment relative to module alignment, but if the modules are not aligned to the prominent edges of the structure, it will be very visible.
A common practice is to start with the bottom row of modules, since the bottom roof edge is often the most critical visually. A string line can help with lining up the bottom row and will help you catch “module creep” early. Make sure any string lines used are taut, so they won’t blow in the wind or sag.
Generally, PV modules have very square edges, which make line-of-sight an excellent way to confirm alignment as the installation progresses. However, don’t assume that all PV modules are perfectly square—the module frame itself can get slightly out of square during shipping and handling.
Once the first row of modules is in place, the other rows usually install quickly as they are spaced uniformly adjacent to the first row. Occasionally, one side of the array may be more visible from the ground or even from a second-story window—so you may want to do visual inspections from various vantage points as you attach the PV modules to the rails. Continue using your tape measure, string line, and a discerning pair of eyes to make certain the array looks good from every angle.
Finally, verify that all of the module clip bolts are tightened to their recommended specifications.
—Greg McPheeters & Tim Vaughn