The standard rail-based mount is popular with sloped rooftop installers, but rail-less systems have their advantages in the right scenario. Both are deployed in residential installs, one using a guiding rail as the panel attachment point, and the other placing module racking directly onto roof mounts.

Installers having trouble deciding which mounting system to use on a rooftop solar project should first consider the roof material, the region’s climate and the worker’s experience with either technology.

A shared-rail rooftop solar installation.

Rail-less mounting systems are installed using fewer components but a lot more precision. Zep Solar, a California mounting solutions developer, pioneered the rail-free system, claiming it could cut install times drastically. Before it was able to fully catch on, the company was bought by SolarCity.

“When SolarCity acquired Zep, they took [rail-less mounts] off the market,” said Andrew Wickham, manager of customer experience with SnapNrack. “You had a bunch of installers out there using that system, but now couldn’t get products, but wanted to install rail-less. That created the surge around other manufacturers creating rail-less systems based on the efficiency benefits with them.”

But Wickham found out install times were comparable between rail-based and rail-less mounts. The big benefit came from hauling fewer components onto a roof.

“On the logistics side of things, not having 14-ft sticks of rail to haul up onto the roof or transport makes a lot of things easier,” he said. “Everything in a rail-less system can come in a box, so then you’re able to get out of jobs and get stuff up on the roof much easier.”

The smaller packaging also makes it easier to warehouse and handle than rail-based mounts.

Training installers to install rail-less systems requires extra focus on alignment. Not all roofs have a completely straight slope, so vertical alignment of roof mounts is important, especially since there isn’t a guiding rail to compensate for an uneven roofing surface. When using traditional L-foot mounts, installers have to adjust at each attachment point. Some mounting manufacturers, like Preformed Line Products (PLP), have release advanced products like its POWER DISK system that allows for quicker and easier vertical adjustments.

Tiled rooftops offer fewer choices for mounting points, with the delicate and time-consuming task of cutting tile, so rail-less mounts make more sense on comp shingle roofs, with the proper flashing. Being able to cut into the covering makes alignment more viable for rail-free mounts. But there are mounting options for tile and standing seam rooftops, like Ecolibrium’s EcoX Residential Rail-Less Racking System.

Preformed Line Products’ POWER DISK Mounting System

“With rail-less systems you have the potential for some efficiency gains as far as your labor time and benefits when you’re in jurisdictions that require rough inspections, but you’re limited as far as your roof types,” Wickham said.

Another factor to consider for rail-less mounts is snow loads. With these mounts, modules take the brunt of the snow load, so that has to be considered in snowy climates.

Rail-free systems can accommodate modules in both landscape and portrait orientations. Since there’s no rail or channel to conceal wiring, it must be clipped to the module frame. Rail-free mounts often come with skirts to conceal hardware and help improve aesthetics.

“On systems that are simple layouts, then rail-free becomes a little easier,” said Johan Alfsen, senior director of product marketing at Everest Solar Systems. “Not to say that it can’t be done on bigger, more complicated arrays, but it tends to lend better toward simple squares and rectangles.”

Rail-based mounts are the more popular choice for sloped roof solar arrays. The residential solar workforce is generally trained in the system, which isn’t limited by roof type or typical weather conditions. A rail-based mount has attachment options for tile, metal and composition shingle rooftops. Panels attach directly to the rail, which is a guide for determining penetration points for system alignment.

“With rail-based systems, you have more flexibility as far as roof types as well as more options as far as attachment points for accessories, utilizing the rail,” Wickham said.

SnapNrack’s RL Roof Mount System

One example of this flexibility is SnapNrack’s Ultra Rail Roof Mount System, which is a snap-in-place L-foot solution that can mount on tile, metal and shingled rooftops with the right hardware.

Unlike rail-less mounts, rail-based systems allow for more options in the angle of installation, rather than just following the slope of the rooftop. With tilt kits, like Quick Mount PV’s QBase, roof arrays can be adjusted between 15 and 45° on low-slope rooftops. Rail-based systems have more options for microinverter and optimizer attachments as well, because the rails provide more space between the panels and the roof.

For installers not wanting two rails per panel row, many mounting manufacturers offer shared-rail options that allow two panel rows to share a middle rail. Certain models, like Everest Solar Systems’ CrossRail Shared Rail System, can switch from dual- to shared-rail on the fly, giving installers more options to fill roof space.

“[Shared-rail] is kind of similar to rail-free in the sense that you’re minimizing penetrations and you’re sharing the middle rail with that penetration row, but you have a standard rail that’s holding up the whole system,” Alfsen said.

Whether using traditional dual- or shared-rail mounting, laying panels atop rails is a quicker task than mounting panels on rail-less systems. However, rails are more cumbersome than rail-free mounts. Carrying 8-ft rails up to roofs puts more strain on installers than the fewer components of rail-free mounts, and shipping rails can be more difficult.

Everest Solar System’s CrossRail Shared Rail System

“We get a lot of damaged rail issues, because we ship longer rails that customers want. They get handled multiple times in and out of trucks, and they can get damaged and bent,” said John Markiewicz, global market manager at Preformed Line Products.

Rail-mounted solar projects can produce more waste too since they’re cut to fit specific roof lengths. But the rail means better weight distribution for panels when it comes to bearing snow loads, not limiting the system to warmer climates.

“From a marketing standpoint, if you have such a discrepancy out in the field about whether [to use] a railed system or a rail-less system, offer both and give the customer [or] the installer the choice based on preferences and their experience,” Markiewicz said. “Don’t necessarily push one over the other, that way you can take advantage of all the market.”

Billy Ludt is associate editor of Solar Power World and currently covers topics on mounting, installation and business for the magazine.

Roof top Solar panels over my GI corrugated sheeting were mounted using die cast aluminium brackets which get screwed on to the sheets. However one flaw was lower air gap below panels of 25 -40 mm. This results in overheating due to summer sun (especially after equinox) and inverter keeps chopping power output. Any solutions? Regards

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