The sun shines from southern skies in the Northern Hemisphere, and for that reason, fixed-tilt solar systems are conventionally installed in a south-facing orientation in the United States to receive maximum yield per panel.
Yet, there are arguments for installing solar in an east-west, or dual-tilt, orientation when sites are closer to the equator, have location constraints, experience high winds or are in a utility territory with time-of-use rates.
South-facing solar arrays have a single plane of modules per panel row that are pointed south; east-west arrays lay at least two modules back-to-back to form a peak, with each panel pointing east or west. This orientation is used on both ground-mounted and flat rooftop solar projects.
Interest in east-west solar racking is currently greater internationally, but manufacturers are seeing more east-west projects being deployed in southern states and U.S. territories closer to the equator or on projects with site constraints, like commercial rooftops.
More solar panels per site
A common feature among east-west racking is the ability to install a higher density of solar modules in the same footprint as a south-facing array. By creating a pitched structure by laying two modules in succession, there are fewer aisles between panel rows on a site, and in certain racking models, east-west panel rows can be installed consecutively to form blocks.
Whatever energy loss an east-west array experiences can be recovered by its extra module count, especially if it’s located closer to the equator. The further south a project is, the higher the sun will be in the sky throughout the year, meaning more exposure for an east-west array.
No two east-west racking systems are the same, but they all result in greater panel density per site.
“As panel prices drop and as energy storage becomes more common, the ground itself is going to be an increasingly expensive part of the system,” said Scott Van Pelt, chief engineer at GameChange Solar. “What do you do to absolutely maximize your [ground-coverage ratio]?”
Van Pelt and other manufacturers believe east-west racking is the answer.
Conventional south-facing ground-mounted solar arrays have rows that are installed two panels high. With racking like GameChange Solar‘s MaxSpan EastWest, two sets of long-span racking structures are installed back-to-back with a lower slope. Each set of racking holds modules three or four high, including at least six panels per row.
German manufacturer Jurchen Technologies offers an east-west option through its PEG line of solar foundations. The proprietary mounts use rebar and accessory plates as foundations and install at a lower profile than conventional solar racking. PEG EW is installed in blocks, with single modules placed in landscape in consecutive pitches. There are fewer aisles on the overall array but enough headspace underneath for panel access and vegetation maintenance. There’s also a greater density of panels — Jurchen Technologies claims it has 225% more land yield than conventional arrays.
Austrian racking manufacturer Aerocompact recently debuted CompactGROUND G+, a ground-mount racking with a design informed by its CompactFLAT rooftop racking. While it doesn’t use the same racking or fastener, G+ does have a similar appearance to the CompactFLAT and other east-west racking found on flat rooftops. With a ground clearance of just 40 cm (about 8 in.), CompactGROUND offers a low-profile option for east-west ground-mounted solar and attaches using scaled-down ground screws and ballast blocks that are found on rooftop projects.
East-west arrays in the United States are more commonly found on flat rooftops. Like ground mounts, dual-tilt racking can put more panels on the roof than south-facing arrays. In regions where undeveloped land mass isn’t plentiful, commercial rooftops are viable sites to generate megawatts of solar. Any additional output is crucial.
“I think you see it way more often when you have a really tight, space-constrained roof and you need to fit as much module wattage on that roof as humanly possible because there’s no inter-row space or it’s very minimal,” said Chris Berg, commercial solutions manager at Unirac. “There’s not a lot of wasted area on a roof when you go to a dual-tilt system.”
New Mexico solar racking manufacturer Unirac offers an east-west system for commercial rooftops called RMDT. It’s installed using modules instead of guiding rails as a spacing template and secures to the roof with ballast or optional roof attachments.
Aerocompact’s CompactFLAT S10+ east-west racking also uses ballast. The system is composed of three main components, including a base structure designed to adapt to the contours of a commercial rooftop.
Nils Wollenberg, VP of product management and operations at Aerocompact, said east-west systems are difficult to install on smaller rooftops with many obstructions. If one panel can fit but the other cannot because of an obstruction, both would have to be removed in a double-module design.
But another advantage east-west systems have on commercial rooftops is when the building itself is off azimuth.
“As you start getting off [azimuth] a bit more, you start getting the east-west system to cover a much wider range, and they actually get some production benefit the larger ‘off’ that azimuth it gets,” said Tristen Foley, product manager at Unirac. “So, when you start seeing those nontraditional buildings, it’s nice to pivot to this type of solution.”
A wind-resistant, utility-friendly racking
These east-west projects — both on the ground and roof — are installed at shorter heights than south-facing arrays. The lower angling of the consecutive modules and shorter height means wind passes over and through the array. On south-facing arrays, there is greater wind resistance blowing against the backside of those modules.
“Logically it makes sense that an east-west system is going to have slightly lower wind loads than conventional fixed-tilt systems,” Van Pelt said. “A conventional fixed-tilt system facing south, if you’re in the U.S., winds from the north are going to stall behind the panels and increase your negative pressures on the panels. On this system where you have two arrays back-to-back, wind coming from the underside of one side of the tent will basically almost skip off the opposite side of the tent. There’s still some suction on the leeward side, but you end up with a meaningful reduction in your governing wind pressures.”
East-west systems see steadier overall output throughout the day rather than the spike in production at midday found in south-facing arrays. At a component level, this means avoiding inverter clipping, which is when an inverter receives more electrical input than it’s designed to process.
Some utilities in states like New York and California have time-of-use (TOU) rates where electricity costs more during certain times of the day, like in the evening. If a south-facing array is producing most of its power at noon when a residential customer isn’t home, then it’s not providing power at critical TOU hours. East-west arrays maintain a steady current of power throughout the day, including during peak hours.
“Your peak production is less than a south-facing system, but you have a broader window of power-producing time,” Berg said.
East-west solar layouts may generate less power per panel, but the ability to squeeze more panels into these orientations leads to higher overall production than south-facing arrays. Incorporating more panels on a single racking structure means it’s cheaper than conventional racking, too.
East-west or dual-tilt racking is a viable and economic solar structure choice for developers when they need to fit as many solar panels on a site as possible.