Commercial rooftop solar projects in the United States tend to use racking that places photovoltaic panels in landscape orientation. It’s the popular option for maximizing a solar project’s power density within the parapets of a commercial rooftop. Installing modules in landscape minimizes the height of an array and reduces inter-row shading and spacing between solar panel rows.
Installing modules in portrait isn’t as common in the United States, but it is useful in certain climates and on certain styles of flat roofs. Many portrait-oriented solar projects can be found in Latin America, where homes have flat concrete roofs with obstructions that aren’t conducive to laying out long spans of landscape panel rows — especially if the roof can’t handle the weight of ballast.
Credit: SunModo
Installing portrait-oriented solar modules is essentially the same as landscape, with the largest difference being the racking system. Installation will vary by model, but the steps remain the same: racking is secured to the roof by mounting to a structural support, weighing down with ballasts, or a combination of both. In portrait, modules are laid on the racking and secured with clamps on the long side of the panel frame.
“Short-side clamping [in portrait] just doesn’t allow for the same load ratings that clamping in the proper long-side zones would, especially in these northern regions where there’s snow load or excessive wind load,” said Mike O’Brien, engineering manager at TerraGen Solar.
TerraGen Solar is a racking manufacturer based in New Tecumseth, Ontario, Canada, that produces racking optimized for portrait module orientation. TerraGen was founded in 2009 as a commercial EPC and eventually developed its own commercial roof racking. In 2017, it ceased installation and now strictly sells its mounting structures.
O’Brien recommends against using clamps on the short side of modules on landscape-oriented projects in climates with high winds and snow loads for risk of developing microcracks. Over time, these can cause drastic failures of systems not tested for extreme environmental loads.
TerraGen’s racking rails supporting the panels can be installed onto or elevated from the base rail, and the racking also supports dual-tilt or east-west panel layouts.
“There was a transition in the racking industry to move away from rail-based systems. The industry trend toward foot-based systems, which for us, as an installer at the time, we felt led to higher install costs through increased ballast requirements, because there was less structural rigidity within the mounting systems as well as increased labor time to put the systems in,” said Darren Jones, general manager of TerraGen Solar.
SunModo, a solar mounting manufacturer from Vancouver, Washington, produces racking for several different applications, including one that orients panels in portrait for smaller flat roofs. The SMR Tilt Up System is also rail-based and resembles railed racking found on pitched-roof solar projects. It uses two mounting rails per panel row and each rail is lifted off the roof with a set of legs, shorter in the front and longer in the back, to tilt the panels. Tilt Up is built to work on roofs with low weight-bearing, so its legs are fastened to the roof with SunModo’s proprietary NanoMount attachments.
“I’d say it’s definitely a niche. You’re really only going to see them on pretty small commercial, flat-roof projects, or maybe — rarely — on a residential roof,” said Steve Mumma, CEO of SunModo. “But for the most part, it’s on smaller commercial flat roofs, probably in the 100-kW or less range.”
Portrait-oriented projects depend on location
The further north a state is located, the more likely it is to experience regular snowfall in winter months. That doesn’t prevent solar installers from putting panels on rooftops, but accumulated snow can prevent modules from producing power. One installer has found that installing panels in portrait solves the issue of snowshed and has some other advantages over landscape.
Arch Solar C&I, the commercial and industrial installation arm of Wisconsin-based Arch Electric, strictly installs commercial rooftop solar projects in portrait orientation, largely because of the state’s climate. In its early days, Arch Solar installed some projects in landscape and found that snow did not slide off the panels, affecting their wintertime production.
“I got really sick of people taking pictures and sending, ‘Ope, here’s another Wisconsin solar system working well again,’” said Dan Steinhardt, project developer at Arch Electric. “It was just killing the argument I had that solar could be working all the time.”
The company sought other racking options and was introduced to TerraGen. Although Arch and TerraGen are separated by the U.S.-Canada border, two Great Lakes and the entire state of Michigan, the companies are based in similar latitudes and climates. TerraGen was once a solar contractor and knew what it was like to install commercial roof projects with consideration for snowfall. Since their first meeting, Arch has installed every commercial roof project in portrait with TerraGen racking.
Credit: TerraGen
“Our competitors will probably harp a bit against that. ‘There’s not a lot of sunlight in winter, why would you change the orientation, you’re losing power density,’ stuff like that,” Steinhardt said. “Some of the arguments can hold water depending upon the surface area of the roof, but in a lot of cases it doesn’t really, and it’s almost better to shoot for higher efficiency vs. power density.”
Arch achieves that efficiency by using bifacial modules on flat-roof projects. The company tracked production from two solar arrays it installed — one in landscape and another in portrait. A 199.9-kW landscape solar project installed in 2019 for the city of Whitefish Bay has produced 1,151 kWh per kilowatt on average since coming online. The array uses monofacial modules and was installed at a 10° tilt. Compare that to a 340-kW portrait solar project installed in 2021 in Oregon, Wisconsin, which has produced 1,290 kWh per kilowatt on average. The bifacial modules were installed at a 23° tilt to keep snow from gathering on the glass.
The longer span and potential higher tilt of portrait modules also means there’s likely more space between panel rows. With larger walkways, crews will have easier access underneath panels for maintenance.
“You can get back there without disassembling. If an optimizer goes bad, you can just go back there, cut a couple zip ties and swap it out,” said Andrew Holmstrom, head of project development, Arch Solar C&I. “You’re not unfastening all the bolts, lifting up the modules and disconnecting.”
Even with the longer plane of a portrait module, these systems have been deployed in areas with high wind and precipitation. The taller profile of flat-roof arrays with portrait modules doesn’t necessarily prevent them from meeting standards for wind loads.
“Generally speaking, the codes and standards for flat-roof solar and the building codes for the U.S. and Canada have their limitation of how high you can be off the roof deck,” TerraGen’s O’Brien said. “As long as you’re below that, you’re operating within their guidelines. While I’m sure there’s some different wind dynamics involved with being a little bit higher off the roof deck, it doesn’t show up in the actual calculations.”
It’s unlikely that portrait panel orientation will overtake landscape in U.S. commercial rooftop solar installation. But there will be roofs with obstructions and low weight-bearing capabilities where a scaled portrait project makes sense, especially in snowier climates.
Arch Solar C&I installs all of its commercial roof solar projects with modules in portrait orientation. The company has found it helps with snow shed. Arch Solar C&I
