If, while traveling, you keep your eyes on roofs looking for solar arrays, there’s a good chance you’ve been bitten by the solar bug. The low-pitched roof on a ranch house sitting out in the wide-open sun—hey, that’s a good one for solar! How about that 1920s Craftsman bungalow, or the new mini-mansion with the steep, slate-covered trapezoidal roof? What are the PV possibilities for roofs like these? And what innovations are making roof-mounted systems easier to install, more durable, and less expensive?
Any PV system needs sufficient sun access: a steady, unshaded six hours a day (generally, from 9 a.m. to 3 p.m.) is recommended. Several other factors come into play for roof-mounted systems: the roof’s pitch and azimuth, plus the roofing material itself. Standing seam, face-fastened, corrugated or shingled metal, asphalt (a.k.a. composition or “comp”) or wood shingles, slate, concrete, clay or spanish tile—whatever the surface, a manufactured mounting solution is available, although that doesn’t mean every installation will be straightforward or simple.
For nearly a decade, the most common pitched-roof PV racking systems have been based on “top-down mounting.” This method uses compression clips or rails to secure the module frames, rather than bolting through the holes in the back of the module frame. Top-down mounting incorporates roof brackets, rails, and module clips of various designs. The metal frames for most modules are made of anodized aluminum of varying heights and gauge. Accordingly, most racking systems can accommodate hundreds of different makes and models of modules, with only a change of clip height, color, or style.
The goals of the PV industry include reducing system cost, improving efficiency, and increasing safety and longevity. Much research and development has focused on modules and inverters—but there has been only incremental change in racking methods. Top-down racking systems incorporate costly raw materials, including metal attachment brackets and standoffs, rails, clips, and hardware. Those parts and pieces can be time-consuming to install, and grounding the racking system takes extra care and additional materials.
Racking generally accounts for 5% to 10% of an installed system’s materials cost and between 20% and 40% of the labor cost. If installed system cost continues dropping, due to module per watt price decreases, but racking material and labor costs stay the same, those percentages will creep up. Thus, racking has found itself squarely in the sights of innovation.
Pitched-roof racking needs to be lightweight, yet strong enough to withstand at least 25 years on a roof that’s subject to intense physical stresses (including wind, snow, UV exposure, and extreme thermal cycling). Racking systems have traditionally used substantial quantities of expensive and high-embedded-energy materials—mostly anodized aluminum and stainless steel for strength and longevity.
To reduce costs and “energy payback,” racking manufacturers are engineering solutions that use fewer raw materials, while maintaining strength and integrity. One such solution entails eliminating the rails that traditionally attach to roof-mounting brackets and run beneath or between modules. Both Zep Solar and Akeena Solar have introduced PV array systems featuring a slot in the module frame that enables rapid installation and grounding—without rails. Zep-compatible module frame slots couple directly to adjacent modules and to roof-mounting attachments (customized and flashed for a variety of roofing surfaces). Andalay’s slot attaches to roof-mounting brackets, but doesn’t couple to modules. Instead, a splice rod is inserted through holes in the frame.
Zep Solar uses Canadian Solar modules that are factory-modified with a mounting groove. Akeena’s Andalay product uses modified SunTech modules, which can even be purchased with Enphase microinverters pre-installed to save further installation time. (Note: If you’re looking for these products, Andalay is sold directly to dealers/installers, while Zep Solar’s systems will be available through distributors like groSolar.)
Eliminating rails could be a giant leap forward, saving raw materials and installation time, and making lighter-weight systems. Neither system has accumulated lengthy test time in the field, so, as with any new product, more data will accumulate as installs increase.
Another product that can eliminate the need for rails is the S-5! nonpenetrating clamp for standing-seam metal roofs. Installers can purchase S-5! PV kits which include module clips and hardware that attach directly to the roof clamp, or they can purchase the S-5! clamp and separately sourced hardware and rails, which can add flexibility to the installation. S-5! clamps attach with set screws and are available for the differing seam styles found on metal roofs. (The S-5! PV kit clamps come in two different heights to match module frame heights.) Set-screw seam clamps like the S-5! are unique since they are the only nonpenetrating attachment method for PVs on pitched standing-seam metal roofs.
Another product line aimed at reducing raw materials is Unirac’s Clicksys system. Based on an I-beam rail that snaps into a mounting attachment, Clicksys reduces the hardware and time required to bolt rails to mounting feet. Unirac says that Clicksys uses 10% to 50% less material than typical extrusion rail systems, as the I-beam rail has a higher strength-to-weight ratio. While faster to install, the spans between roof-mounting attachments are generally shorter for Clicksys, which means more roof penetrations might be necessary. The Clicksys mounting bracket can be bolted on top of primary flashed brackets, available for each type of roof surface.
The International Building Code requires flashing every roof penetration, a shift away from relying solely on sealants as with the old L-feet method. Flashing is a thin metal or rubber sheet overlapped by the roofing material so that all penetrations are protected from water running down the roof. Flashing can be separate from the mounting attachment, like Oatey flashing, which slides under shingles and wraps tightly around a mounting post, or some manufacturers integrate the flashing into the post itself. If a new roof is being installed prior to a PV installation, then flashing for mounting attachments should be installed by the roofers so the flashing installation is covered by the roofing warranty.
Quick Mount PV, a manufacturer of flashing-integrated mounts, created the “Wheel of Accountability” (available on its Web site; see Access), which summarizes the different authorities that have rules, regulations, and guidelines pertaining to roof penetrations. If planning an installation, perusing the Wheel can clarify where an installer should look for more information on roof mount regulations.
Every major racking manufacturer offers flashed mounting solutions for installers to use, rather than just relying on sealant. Flashing-integrated products include Quick Mount PV, Thompson Technology Industries’ Flat Jack, and EcoFasten Solar’s Quik-Foot and Green-Fasten.
Rooftop PV innovation doesn’t stop with the mounts. Roof-integrated boxes like the SolaDeck enclosure and combiner box are providing flashed solutions for the entry of PV conductors to the building interior. SolaDeck meets UL 1741 requirements for PV combiner boxes, as mandated by the 2008 National Electrical Code. They are low-profile for sleek aesthetics (and can be mounted under an array), while providing multiple functions—transition to interior conduit, flashed penetration, and even PV string combining. But the SolaDeck can be hard to access for troubleshooting, especially if positioned under the array.
Older, tried-and-tested racking systems often use both 1/4- and 3/8-inch hardware, in addition to the stainless steel lag bolts for attaching brackets into rafters. This means multiple tools and multiple nuts and bolts must be managed on the roof.
Newer systems such as AEE Solar’s SnapNrack and Unirac’s Clicksys use only one standard-size hardware besides the lag bolt—one wrench fits every bolt in the system. SnapNrack uses snap-in channel nuts, which eliminate holding, sliding, or dropping bolts, and also allows easy adjustments to keep arrays square and in the same plane regardless of roof irregularities. And to further help installers to fast-track their installations, mount manufacturers provide online code-compliant installation guides, engineering documentation, and training videos.
Making installations easier is important even for less-common roofing materials that often prove difficult to conquer with typical PV racking. Tiles, whether slate or concrete, metal shingles, and face-fastened metal roof (also known as barn tin or 5V tin) all present challenges. Fortunately, attachment methods for each type of roofing material are available to ease the installation. S-5!’s new Versabracket for face-fastened metal roofs and CorruBracket for corrugated metal roofs are versatile solutions for these tricky roof types. While neither uses integrated flashing, there is no easy way to retrofit flashing into these types of metal roofs. DPW Solar’s EZ-Foot, which can be screwed down to the roof sheathing rather than having to be lagged into a rafter, is another practical solution for face-fastened metal roofs. Tile roof installations can use Conergy’s SunTop racking system with tile roof hooks, and Quickmount PV mounts, which replace entire tiles.
The NEC requires that any exposed metal surface be grounded if it could become energized. This includes PV modules’ metal frames, which could become energized in various ways, including ground faults and wire insulation failure.
Traditional module grounding has relied on bare copper equipment-grounding conductors attached to tin-plated copper lay-in lugs (like the Ilsco GBL4 DBT and Burndy CL50-DB-T) at the modules’ grounding points. This procedure is time-consuming, and the materials are fairly expensive. Wiley Electronics, the manufacturer of WEEB clips, has been at the forefront of new module grounding technologies. A WEEB is a stainless steel square that fits around a module racking bolt between the module and rail and “bites” through the anodized non-conductive coating on the module and rail as the bolt is tightened. However, this method is not accepted by all module manufacturers or inspectors—so you’ll need to check with both the module manufacturer and the inspection authority before using them.
The Zep Solar and Akeena Andalay systems are also pushing innovation in module grounding. Both systems have integrated grounding, meaning modules are connected together mechanically and electrically as they are installed on a roof, so no additional grounding hardware is needed for the module frames. The Andalay system uses a threaded stainless steel rod to tighten modules together and create a continuous equipment ground. Zep Solar’s design relies on an “interlock” between modules that provides structural integrity and equipment grounding simultaneously.
Mismanaged PV wiring can allow animals and weather to damage wires, conduit, and connectors, so safer and easier wire management is a target of innovation. Module cables and series string home runs should be adequately secured. Left free, they have the possibility of scraping across the roof surface, which could abrade the cable’s insulation and pose a shock hazard.
Wiley Electronics’ durable, stainless steel Acme cable clips grip one or two module cables and the module frame, more easily securing module interconnection wires to module frames. But that still often leaves the series home run wires to manage. It’s doubtful that nylon cable ties will last 25 years in the extreme roof environment. Some manufacturers are adding channels to the rack where wires can be tucked neatly inside, including AEE’s SnapNrack and NGE’s Zilla Rac system. This is not conduit or raceway, and is not listed as such, but should help to keep the squirrels at bay.
Frameless thin-film modules are starting to hit the marketplace, especially in popular system leasing programs. Pitched-roof racking for frameless thin-film modules require softer plastic- or rubber-gasketed end- and mid-clips that replace the all-metal clips used for framed modules. Both Schletter and HatiCon (established in Europe, though new to the U.S. market) make clips for thin-film modules. Also keep an eye out for monocrystalline frameless modules entering the market soon. Lumos, out of Boulder, Colorado, is in final UL testing for a frameless module that bolts through the module and directly to the rail, without mid- or end-clips. Because it has no metal frame, it won’t require module grounding. The Lumos module will also include a wire raceway with integrated rodent protection to reduce conductor damage.
Rebekah Hren is a licensed electrical contractor and NABCEP-certified PV installer in Durham, North Carolina, where she is implementing large ground-mount solar arrays with O2 Energies. Rebekah co-authored a book on residential energy-efficiency retrofits: The Carbon-Free Home. Her new book, A Solar Buyer’s Guide for Home & Office, a solar-electric and solar thermal buyer’s guide, will be published this fall.
AEE Solar • www.aeesolar.com
Conergy • www.conergy.us
Direct Power Solar • www.power-fab.com
EcoFasten Solar • www.ecofastensolar.com
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
S-5! • www.s-5.com
Schletter Inc. • www.schletter-inc.us
Schüco • www.schuco-usa.com
Sharp • www.sharponenergy.com
Solar Racks • www.solar-racks.com
SunEarth Inc. • www.sunearthinc.com
Thompson Technology Industries • www.ttisolar.com
Unirac • www.unirac.com
Zep Solar • www.zepsolar.com