East-west solar projects maximize the number of panels on an array
The sun shines from the southern sky in the Northern Hemisphere, and for that reason, in the United States, conventional fixed-tilt solar systems are installed in a south-facing orientation to maximize yield per panel.
Still, there are arguments for installing solar in an east-west or dual-tilt orientation when locations are closer to the equator, have location restrictions, experience high winds, or are in a utility area with longevity.
South facing solar panels have a single face of modules per panel row facing south; east-west arrays lay at least two modules back to back to form a peak, with each panel facing east or west. This orientation is used on both ground-mounted and flat roofs of solar projects.
Interest in east-west solar racks is currently growing internationally, but manufacturers are seeing more east-west projects deployed in southern states and US territories closer to the equator or on projects with location restrictions, such as commercial rooftops.
More solar panels per site
A common feature of east-west racking is the ability to install higher-density solar panels in the same footprint as a south-facing array. Creating an inclined structure by arranging two modules one after the other, there are fewer aisles between panel rows on a site, and in certain racking models, east-west panel rows can be installed one behind the other to form blocks.
Whatever energy loss an east-west array experiences can be recovered by the additional number of modules, especially if it is closer to the equator. The further south a project is, the higher the sun will be in the sky year-round, meaning more exposure for an east-west array.
No two east-west shelving systems are the same, but they all result in a greater panel density per location.
“As panel prices fall and energy storage becomes more common, the ground itself becomes an increasingly expensive part of the system,” said Scott Van Pelt, chief engineer at GameChange Solar. “What do you do to absolutely [ground-coverage ratio]?”
Van Pelt and other manufacturers believe east-west shelving is the answer.
Conventional south-facing, ground-mounted solar panels have rows installed two panels high. With racks like GameChange Solar‘s MaxSpan EastWest, two sets of long span racking structures are placed back to back with a lower slope. Each set of racks contains modules of three or four high, including a minimum of six panels per row.
German manufacturer Jurchen Technologies offers an east-west option through its PEG line of solar foundations. The patented fixings use rebar and accessory plates as foundations and install at a lower profile than conventional solar racks. PEG EW is installed in blocks, with some modules placed in successive fields in the landscape. There are fewer aisles on the overall array, but there is plenty of clearance underneath for panel access and vegetation maintenance. There is also a greater density of panels – Jurchen Technologies claims it has 225% more land yield than conventional arrays.
Austrian scaffolding manufacturer Aerocompact Recently, CompactGROUND G+ debuted, a ground-mounted shelving unit with a design inspired by the CompactFLAT roof racks. Although it does not use the same scaffolding or fastener, G+ does have the same appearance as the CompactFLAT and other east-west scaffolding on flat roofs. With a ground clearance of only 40cm (approximately 8 inches), CompactGROUND offers a low profile option for east-west ground-mounted solar and is secured with scaled-down ground screws and ballast blocks found on rooftop projects.
East-west arrays in the United States are more commonly found on flat roofs. Like ground mounts, double-tilt racks can accommodate more panels on the roof than south-facing arrays. In regions where undeveloped land mass is not abundant, commercial rooftops are viable sites to generate megawatts of solar energy. Any additional output is crucial.
“I think you see it a lot more often when you have a really tight, space-constrained roof and you have to fit as much module wattage on that roof as humanly possible because there’s no space between the rows or it’s very minimal,” said Chris Berg, commercial solutions manager at Unirac. “There’s not a lot of wasted space on a roof when you go to a double-tilt system.”
New Mexico Sun Rack Manufacturer Unirac offers an east-west commercial roof system called RMDT. It is installed using modules instead of guide rails as a spacing template and is secured to the roof with ballast or optional roof fixings.
The CompactFLAT S10+ east-west racks from Aerocompact also use ballast. The system consists of three main components, including a base structure designed to conform to the contours of a commercial roof.
Nils Wollenberg, VP of Product Management and Operations at Aerocompact, said east-west systems are difficult to install on smaller roofs with many obstacles. If one panel fits but the other does not due to an obstruction, both should be removed in a dual module design.
But another advantage that east-west systems have on commercial rooftops is when the building itself is not azimuth.
“When you start dismounting [azimuth] a little more, you start to get the east-west system to cover a much wider range, and they even get some production advantage the more ‘off’ that azimuth gets,” said Tristen Foley, product manager at Unirac. “So when you start seeing those non-traditional buildings, it’s nice to go to these kinds of solutions.”
A wind-resistant, user-friendly rack
These east-west projects—both on the ground and on the roof—are installed at shorter heights than south-facing arrays. The lower angle of the successive modules and shorter height means that wind passes over and through the array. On south-facing arrays, there is greater wind resistance blowing against the back of those modules.
“It makes sense that an east-west system will have slightly lower wind loads than conventional fixed-tilt systems,” said Van Pelt. “With a conventional south-facing fixed tilt system, if you’re in the US, the winds from the north will move behind the panels and increase your negative pressure on the panels. On this system where you have two rows back to back, the wind coming from the bottom of one side of the tent will in fact almost bounce off the other side of the tent. There’s still some suction on the leeward side, but you’ll end up with a significant reduction in your reigning wind pressure.”
East-west systems see a more stable overall output during the day than peak production in the afternoon in south-facing arrays. At the component level, this means avoiding inverter clipping, which is when an inverter receives more electrical input than it is designed to handle.
Some utilities in states such as New York and California have time-of-use (TOU) rates where electricity is more expensive at certain times of the day, such as in the evening. If a south-facing array produces most of its power in the afternoon when a residential customer is away, it will not provide power at critical TOU hours. East-west arrays maintain a constant flow of current throughout the day, including during peak hours.
“Your peak production is less than a south-facing system, but you have a wider window of energy production,” Berg said.
East-west solar arrays may generate less power per panel, but the ability to squeeze more panels into these orientations leads to higher overall output than south-facing arrays. By including more panels on a single shelving structure, it is also cheaper than conventional shelving.
East-west or dual-tilt racks are a viable and economical solar choice for developers when they need to place as many solar panels as possible on a site.