Set up execs focus on wire administration for rail-less solar on low-slope metallic roofing
The PVKIT 2.0 from S-5! Is one such directly attached solar mounting solution for metal roofs.
Rail-less solar PV systems on the roof have been around for many years and they are still a growing part of the solar market year-on-year. However, there is still hesitation in both technology and learning new methods. One of those hesitations is cable management.
We recently sat down with Doug Claxton, owner of The Solar Revolution and advisor to TSR Energy in Boulder, Colorado. Mark Gies, solar expert and director of solar business at S-5 !; and Shawn Haddock, Senior Field Applications Specialist at S-5 !, to discuss cable management for low-slope, railless PV systems.
Preparing modules on the ground means less work on the roof.
Preparing modules is one of the most critical steps that must be planned, designed and executed to minimize installation time on the roof.
“Every project is unique and there are many different methods of cable management and different product combinations 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 at construction sites, looked at the cable management design and thought this was crazy. Then we land back in the office and spend the day working with the designers to create a better diagram that will now make project days faster. “
“We usually have one or two people on site with a string diagram so they know how to properly prepare the leads,” adds Claxton. “One of the first things we do is figure out how we’re all going to manage optimization leaders because that’s a challenge, but that challenge exists whether or not you have a track.”
Strategic string design
Such a strategic string design minimizes labor and material.
Take the time to strategize your string layouts. This allows you to minimize cable length, reduce the time it takes to clip wires and plug in jumpers, and provide easy access to string ends, optimizers, or microinverters. A few hours at the desk tweaking the string design can save many hours or even days on the roof.
“At the front end, the system designer can complete or cancel the work for installers on the roof and for future O&M activities,” says Claxton. “We have always gone to great lengths to clean up designs through logical string layouts and grouping home runs. I’ve seen layouts that alert the installers to errors and make troubleshooting and diagnosis difficult. I understand that sometimes the goal is to get as many watts on the roof as possible, but I think you end up paying the price for it instead of getting really clean layouts. “
Advantages of attaching solar modules directly to metal roofs
- Far fewer parts
- Huge reduction in freight costs
- Labor reduction
- Reduced handling / logistics
- Reduced dead weight on the roof
- 25 percent better load distribution
- System installation speed
- Better wind resistance
Correction gaps can be as little as 1 inch or large enough to create a narrow aisle for access to all modules.
Although correction gaps (between pairs of modules) are sometimes required to align with metal roof seams, creating a tight walking space (see above) is a clear benefit that speeds access during installation and makes future operations and maintenance much easier and safer. The net loss of module memory is typically less than 3 percent (often zero).
“With fixes, you have easy access to every module in this project without having to go to modules or worry about breaking them,” says Haddock. “You can quickly pull up a module, repair and / or replace connections. These gaps are essentially buffered spaces in which modules can be adjusted, improving the alignment and squareness of the array from the squareness of the roof. The gap can be as little as 1 inch or 8 or 10 inches. In this case it can be used as a walking room. Correction gaps can make the solar system more aesthetic from the ground. “
“This style works particularly well on roofs with a seam spacing two feet down the middle, which is common on low-pitch commercial roofs,” says Claxton. “The gap offers the opportunity to walk between these double modular columns and not over the modules. This also makes cable management and MLPE replacement easier. In my opinion, the fix is worth the small reduction in system size. “
Gies has worked with solar companies who design arrays with a number of rows or columns that match string sizes. “This is the ultimate design because all of the connectors, optimizers, and microinverters are easily accessible from the edge of the array,” he says.
Trunk and Branch Wire Management
The trunk-and-branch method saves installation time. Cable trays minimize the hassle of directing jumpers to home runs.
If sub-arrays grow larger and larger despite careful design of strings and layouts, the string ends can be located deep in the module array. Cable trays can be installed under the modules to save a lot of time that would otherwise be required to tie or attach jumper wires on a direct route from the string ends to the home run (see above).
“Wire bridges can be led to the wire tub, bundled without clips and then taken straight to the home run,” says Gies. “This method can also result in wires being more organized.”
“If you get really big this is a good way to go,” adds Claxton. “But with a 100 kW system and careful planning, you often don’t need that. And even with more than 100 kW, you’re probably doing a multiple of 100 kW blocks. This is certainly a good method when you have no choice but to get a lot of jumpers to the home runs or back to a central point. “
Both types of MLPE, optimizers and micro-inverters, have continued to gain in importance in the solar market and are now more common in roof-top projects of all sizes. MLPE can usually be installed by mounting on the module frame (shown on the right) or directly on the roof. For some there are specific reasons for mounting on the roof, e.g. B. Manufacturer Requirements. In most cases, however, assembly on the module frame is easier and more economical.
“I’ve heard different cases for both, but I’m a big believer in putting MLPE directly on the modules,” says Claxton. “It allows for neat cable management that can be prepared in advance, which makes it easy for the installers who set the mods.
“Microinverters are a different story, but I still think they are great to mount directly onto the modules,” he continues. “You can put a micro-inverter on the module and create something like a real AC module. Then it comes down to managing the trunk cable, which can be achieved with several wire management products designed for this purpose. From there, it’s just plug and go. “
Some installers may prefer to mount microinverters on the roof. Because the AC branch circuit of a microinverter is a cable with a trunk, both the microinverter and the trunk cable cannot be installed together during module preparation. Others may prefer to mount microinverters on the metal roof with brackets and connect all of them to the AC trunk. In this way, the modules are plugged in when they are inserted.
In addition, other logistics such as the weight or size of the MLPE or even local code can hinder or prevent direct attachment to the modules.
Strategically designing module and string layouts, preparing modules in staging areas, and performing repeatable installation procedures overcome all of the hurdles involved in installing railless solar. Even first-time installers of the new S-5 rail-less system have reported time savings of up to 50 percent.
Claxton sums up: “Start with the design; You know all the products that are available to you to achieve good cable management. Use any products to mock it. Make sure your configuration actually works with the module, then run it with robot repetition. “