Electrical Systems and Services, Inc is always looking at new and improved solar PV installation techniques. These improvements not only allow for better and longer lasting solar systems, but in most cases decrease the overall cost of the system, with quicker installation times.
No
two solar sites are precisely alike; both the built and natural environments
affect an installation’s specifics. A thorough site survey quantifies these
factors, and a quality system requires tailoring the design to the site
specifics. Working with PV rack companies can take much of the guesswork out of
the process, as they will provide engineered designs to meet wind uplift
forces, snow load, and soil or roofing material types.
Roof-Mounted PV Arrays
Because
of space limitations, ground-level shading, and the excavating and trenching
required for pole and ground mounts, the least expensive and most frequent
location for PV arrays is on a roof.
Roofs
can be classified as either low- or steep-sloped—low slope generally means a
roof with a pitch of less than 3:12 (less than 14°). Low-sloped roofs are often
mistakenly referred to as flat roofs, but no roof is ever really flat, as a
pitch is needed for shedding water. Even a roof that appears flat will have a
pitch of at least 0.5:12.
Top-Down Innovations
On
steep-sloped roofs, modules are almost always flush-mounted—mounted parallel to
the roof plane. The most common technique for flush-mounting steep roof arrays
is “top-down mounting.” Anodized aluminum rails are used to support modules,
and stainless steel or aluminum compression clips hold the modules onto the rails,
usually with a bolt and nut captured by slots in the rails. This speeds up
installation, eliminating bolting through the mounting holes on the back of
module frames as was once common. Now, installation is easily accomplished with
the modules in position on the rails from above—thus, the description “top-down”.
Recent
design improvements in top-down mounting decrease materials and reduce labor.
They include automatic grounding and one-tool installation, all of the bolts
have the same size head, so one wrench fits all bolts. Snap-in nuts attach
standoffs and top-down clips, the rails are height-adjustable, and there’s a
built-in channel for wire management. In addition, both the mid- and end-clips
have a universal design, meaning that regardless of module-frame dimensions, a
single clip works with any module and the clips don’t have to be specified in
advance.
Structural Attachments
Structural
attachments from the array to the roof are a critical part of the installation.
The attachment type and method will vary based on the roofing type (shingle,
metal, tile, etc.) and with the roof’s structural design (wood trusses,
structural insulated panels, metal, etc.).
Preventing
roof leaks and meeting building codes for live and dead loads (including wind
uplift, rack and array weight, and snow loads) are primary concerns. A properly
installed array will meet these concerns and maintain the roof warranty. In
nearly all installations, every roof penetration needs to be flashed for
waterproofing. On a composition (asphalt) shingle roof, the metal flashing fits
underneath higher rows of shingles, so water runs over the top of the flashing
and around the roof penetration. For years, many installers relied solely on
sealant for penetrations, but new structural attachments make installing
flashed penetrations simple and quick.
