Install pros discuss wire management for rail-less solar on low-slope metal roofing
Linear rooftop PV systems have been around for many years and are still a growing part of the solar market year after year. Nevertheless, doubts remain both with the technology and with the teaching of new methodologies. One such hesitation is thread management.
We recently had a conversation with Doug Claxton, owner of The solar revolution and advisor at TSR energy based in Boulder, Colo .; Mark Gies, solar expert and director of solar business at S-5! and Shawn Haddock, senior field application specialist at S-5!, to discuss wire management on low slope railless PV systems.
Preparing modules is one of the very critical steps that must be planned, designed and executed to minimize installation time on the roof.
“Each project is unique, and there are many different wire management methods and different combinations of products when it comes to home runs – but it can always be figured out before you get on the roof. That’s what I’ve seen helps installers the most, ”says Haddock. “I showed up on job boards, looked at their wire management design and thought, ‘this is crazy’. Then we end up back in the office and spend the day working with the designers to come up with a better diagram that will now speed up the project days. “
“We usually have one or two people on the ground with a string diagram on site, so they know how to properly prepare the leads,” adds Claxton. “One of the first things we do is figure out how we’re going to manage all the optimization leaders because that’s a challenge, but that challenge exists whether you have a trail or not.”
Strategic string design
Take the time to strategically design your string layouts. This allows you to minimize cable length, shorten the time it takes to clip wires and connect jumpers, and also provide easy access to string ends, optimizers or microinverters. A few hours at the desk to optimize the string design can save many hours or even days on the roof.
“Up front, the system designer can make or break the job for rooftop installers as well as for future O&M activities,” says Claxton. “We’ve always been great at cleaning up designs through logical string layouts and grouping home runs. I’ve seen layouts that notify installers for failure and make troubleshooting and diagnostics more difficult. I understand that sometimes the goal is to get as much watts on the roof as possible, but I think you end up paying the price for that rather than getting really clean layouts. “
Advantages of direct mounting of solar panels on metal roofs
- Much fewer parts
- Enormous reduction in freight costs
- Reduction of labor
- Less handling / logistics
- Less own load on the roof
- 25 percent better load distribution
- Speed of system installation
- Better wind resistance
While correction holes are sometimes required (between pairs of modules) to align with metal roof joints, there is a clear benefit of creating a narrow walking space (shown above), which speeds access during installation and makes future O&M much easier and safer. The net loss of module space is usually less than 3 percent (often zero).
“With correction holes, you can easily access every module in that project without having to walk over modules or worry about damaging them,” says Haddock. “You can quickly pull up a module, repair and / or replace connections. These openings are essentially buffered spaces that allow modules to be adjusted, improving the alignment and squareness of the array to the squareness of the roof. The opening can be as small as 1 inch or as large as 8 or 10 inches, in which case it can be used as a walking space. Correction holes can make the solar panels more aesthetically pleasing from the ground up. “
“This style works especially well if you have roofs spaced two feet apart in the middle, which is common on low-slope commercial roofs,” says Claxton. “The opening offers the possibility to walk between those double module columns and not on top of the modules. This also facilitates thread management and MLPE replacement. In my opinion, the correction gap is well worth the small reduction in system size. “
Gies has worked with solar companies who design arrays with the number of rows or columns equal to the string sizes. “That’s the ultimate design, as all connectors, optimizers, and microinverters are easily accessible from the edge of the array,” he says.
Trunk and branch wire management
As sub-arrays get bigger and bigger, even with careful string and layout design, the ends of the string can be deep in the module array. Wire trays can be installed under the modules to save much of the time that would otherwise be required to tie or snap jumper wires on a direct path from the string ends to the home page (shown above).
“Wire bridges can be routed to the wire mesh tray, bundled into it without the need for clips, and then routed straight to the home run,” says Gies. “This method also allows the wires to be better organized.”
“If you are really growing up, this is a good choice,” adds Claxton. “But often with a 100 kW system, with careful planning, you probably don’t need this. And, even with over 100 kW, you probably do multiples of 100 kW blocks. This is certainly a good method if you have no choice but to take many jumpers to home runs or back to one central point. “
Both types of MLPE, optimizers and microinverters, have become increasingly popular in the solar market and are now more common in roof projects of all sizes. MLPE can usually be installed by mounting on the module frame (shown right) or directly on the roof. For some there are specific reasons for mounting on the roof, such as the manufacturer’s requirements, but in most cases mounting on the module frame is easier and more economical.
“I’ve heard different cases for both, but I’m a big believer in mounting MLPE directly onto the modules,” says Claxton. “It provides a clean wire management that can be prepared in advance, making it easy for the installers setting up the mods.
“Now microinverters are a different story, but I still think they are great for mounting directly on the modules,” he continues. “You can place a micro-inverter on top of the module to create something that resembles a real AC module. Then it is a matter of managing the trunk cable, which can be achieved with various wire management products intended for this purpose. From there, just plug in and go. “
Some installers prefer to mount microinverters on the roof. Since the AC circuit of a microinverter is a single trunk cable, both the microinverter and the trunk cable cannot be installed together during the module preparation process. Others may prefer to mount microinverters with clamps on the metal roof and connect them all to the AC trunk. In this way, the modules are plugged in while they are in place.
In addition, other logistics, such as the weight or size of the MLPE, or even local codes, can prevent or prevent direct attachment to the modules.
Binding it together
Strategically designing module and string layouts, preparing modules in staging areas, and performing repeatable installation procedures overcomes all hurdles to install railless solar. Even novice installers of the S-5’s new railless system have reported time savings of up to 50 percent.
Claxton concludes: “Start with the design; know all the products that are available to you to achieve good wire management; use any products to mock it; make sure your configuration is really what will work with the module, then run it with robotic iteration. “