NJMC Landfill 1A in Kearny, N.J., has been little more than a garbage-filled mound dotted with shrubs for more than 30 years. Officials have long thought 1A and similar landfills could serve a greater purpose. With a view of the New York City skyline, the land would be prime real estate if it weren’t a dump.
Finally, in 2011, municipalities received direction. New Jersey Governor Chris Christie released the Energy Master Plan, which recommends solar projects be constructed on landfills or brownfields instead of open space or farmlands. It also simplified the permitting process for such sites.
The New Jersey Meadowlands Commission, which previously installed a 33-kW solar array on its science education building and operates the 35-acre landfill, took heed. It contracted with the local utility and a construction firm to build a 3-MW solar array, the first on a state-owned landfill. Officials dedicated the project on May 8, 2012.
“What’s the point of having a closed landfill just sitting there, when you could have so much good coming from it?” says Brian Aberback, public information officer at the commission. “This project does a great deal to help the environment and boost the green economy, especially during tough economic times.”
But landfills don’t make for simple installations. Unlike roofs and solid ground, landfills present the problem of settling. As trash decomposes, the ground could shrink under the array. Piling heavy ballast blocks and racking on top of the trash can exacerbate the issue and also endangers the landfill cap, a 1- to 3-inch thick membrane that seals trash into the ground.
While a quick glance at topographic drawings from the Kearny landfill shows settling of more than 20 feet in some areas since its capping decades ago, engineers who surveyed the site for solar found good signs. Methane gas, a by-product of trash decomposition, correlates with settlement. The less gas in the methane monitoring wells, the less settlement is likely to occur. For 1A, the gas had significantly decreased over previous years. Still, engineers had questions to answer: What if settling occurred, and how could they prevent it?
“Our goal in designing the solar array was to minimize the pounds per square feet, including ballast and panels,” says Matthew Skidmore, director of operations at SunDurance Energy, the construction firm that built the array. “We wanted to minimize settling as much as possible, and we used Solar FlexRack to help accomplish that.”
SunDurance chose Youngstown, Ohio-based Solar FlexRack’s Ground Mount for several reasons. First, a three-person crew can build the pre-assembled system in less than five minutes – a claim confirmed by users — which reduces labor costs. It also uses a slide-in rail system that allows for fast panel installation.
Crews worked north to south installing the system. A three-person crew set the rack, which unfolds as it’s hoisted to position on a tilt bracket, and then one person fell back to tighten nuts and bolts. A crew of laborers then installed the panels.
SunDurance also chose FlexRack because the company provided a custom 2×13 rack (two rows of panels, 13 in each row), which SunDurance prefers for string sizing. The rack was 50 feet long and required special shipping, but the oversized load was worth the potential electric savings down the road, Skidmore says. The standard FlexRack is 2×12.
The racking was also non-continuous, a selling point on an irregular landscape. SunDurance hauled more than 200,000 tons of clean fill to the site to make the undulating hills of 1A look like solar panel plateaus. Subarrays allowed the flattened areas to be smaller, requiring less fill.
“Everybody thinks the landfill was covered in stone originally and that it was really flat, but that wasn’t the case,” Skidmore says. “Trash has different compositions so some areas settled 10 feet while others settled 20 feet.”
Construction lasted seven months. The initial months required the removal of vegetation from the site, importing fill and grading it. Then the company allowed a short period of settlement. A survey using GPS confirmed that the site settled no more than a quarter of an inch — within the margins of error for the survey — so construction continued.
Concrete ballast blocks, sized 2 feet by 8 feet, were brought in and workers installed the racking on top of them. Engineers tried to keep the total system under 200 lbs./sq. feet, but it needed to counteract a 105 lbs./sq. feet wind load, a number higher than average because the installation is on a hill not far from the ocean.
Lastly, FlexRack was chosen because, as the name suggests, it’s flexible. Liberal East-West and North-South tolerances are built-in to each Solar FlexRack subarray though slotted connections on the horizontal rail and also the tilt bracket. The tolerances allow for straight lines, providing a nice look for visitors, and some wiggle room when laying down clunky ballast blocks.
“On capped landfills, there’s a limited amount of space,” says Greg Lewis, a regional sales manager for Solar FlexRack. “When SunDurance laid out the site, the row was as tight as you can get without shading. It came down to inches.”
In all, the Solar FlexRack provides several inches of flexibility, but SunDurance — this being their first landfill project — was still concerned.
To be sure that if settling did occur a part of the 13-acre project wouldn’t need rebuilding, the construction company used very conservative approximations in its engineering plans for the site and built additional flexibility into a proprietary post that connects the rack to ballast blocks. Solar FlexRack and SunDurance engineers worked together to develop a sleeved pole system that has up to 24 inches of vertical adjustment.
“There wasn’t a lot of previous research, so we were moving along making relatively safe assumptions,” says Skidmore. “If we did it again, the adjustment in the racking would be enough.”
In other words, the company prepared for the worst. The New Jersey Meadowlands Commission, an organization charged with planning and zoning in an area that was ravaged for decades by indiscriminate dumping, on the other hand, is prepared for the best.
“Part of our mandate is to both protect the environment and provide for orderly development,” says Aberback, the commission’s public information officer. “People might think that’s a conflicting mandate, but here you have a project that accomplishes both.” SPW
PROJECT: New Jersey Meadowlands Commission
LOCATION: Kearny, N.J.
POWER: 3 MW
PV PANELS: 12,506 Kyocera solar panels
SOLAR FLEXRACKS: 481 2×13 ground-mounts, custom-designed to two tilt angles
CONTRACTOR: SunDurance Energy