Recycled plastics enter rooftop solar energy market
The green community likes nothing better than integrating recycled materials into renewable energy and sustainability projects. It’s a
double-down sustainable solution that appeals to solar developers, public utility commissions, community sponsors and, most of all, to commercial and residential buyers.
That’s one reason why more rooftop photovoltaic (PV) panels are being mounted on plastic bases using both 100 percent recycled high density polyethylene (HDPE) and mixes of virgin and recycled resins. These bases, often referred to as mounts, units, pods or tubs are primarily used on flat, membrane commercial rooftops.
Each mount holds a single, standard-size PV panel usually 39” x 64” tilted at the most productive angle to the sun, depending on latitude. In the lower 48 states, the angle can range from 5 to 15 degrees and up to 30 degrees in Canada. On roofs, the mount is placed directly on the membrane. The plastic tub is then filled with loose stone or concrete blocks to hold down the mount. Weight of the ballast is determined by location windload. Over 300 lbs. of ballast are used in severe wind conditions. PV panels are bolted to the mounts. Mounts have weep holes for water and air vents to relieve heat build-up. Rows of mounts can be wired and bolted together side to side, and end to end to form an array.
There are other types of commercial rooftop systems such as SunPower’s solar roof tiles, which are factory assembled units that combine a PV panel in a plastic mount. Tiles are interlocked on a roof to form an array.
Plastic units are relatively new to North America. There are only a handful of manufacturers representing less than 5 percent of installed mounts (the balance being aluminum and stainless steel. In North America, plastic mounts have only begun to be used within the past 10 to 15 years, yet they may come to dominate commercial rooftop solar market due to several advantages besides their recycled content.
John Hudson, director of engineering at Renusol America, the only company using 100 percent recycled material, summed up the benefits of plastic: “Our product is less expensive than aluminum and definitely less than stainless, but the real cost savings comes in speed of installation, prevention of damage to roof membranes and wiring, and improved grounding.”
Renusol is a German company founded in the late 1970s. Over the last 12 years it has sold over 1 million of these units in Europe, primarily in Germany which has the world’s largest per capita solar deployment – 7,400 megawatts generated in 2010 from nearly 250,000 individual systems. Of all German commercial rooftop solar mounts, including aluminum and steel, approximately 10 percent are Renusol plastic units.
“We officially rolled out our plastic mounting system in the United States this July,” said Hudson. “We have limited installations at this point, but a lot of orders.” Renusol is using 100 percent recycled materials sourced domestically from industrial scrap produced by plastic extruders. Based in Atlanta, Renusol takes in the recycled material and thermoforms it into their CS60 mounting unit. Each unit is packed in a box with pre-assembled parts and clamps to accommodate most “standard” PV panels, which vary slightly in size.
Renusol America’s CEO, Bart Leusink, put it this way, “The specifically designed Renusol CS60 system will be a game changer for the United States market. It is a wind-tunnel tested, ballasted system with optional roof fastening for very high wind load or seismic areas. The product further allows for extremely fast and easy planning and assembly and low installation costs. We are among the fastest growing PV mounting systems providers in Europe and we want to be in the top five in the United States by the end of next year.”
“Developers like the fact that it’s 100 percent recycled and use that in sales pitches,” Hudson added. “That message trickles down to the ultimate customer which is typically the building owner. A lot of these owners want to be LEED (Leadership in Energy and Environmental Design) compliant. We are in the green industry and people are concerned about their carbon footprint. We see it as a selling point. It has just as good a performance as 100 percent virgin material without the cost. It’s a good bit less – a noticeable difference in price. We have no problem acquiring supply at this point, but it is a sensitive market and we may have to use some percentage of virgin from time to time.”
Plastic solar mounts do face some challenges, however, both in perceptions about durability and building code compliance. Most PV manufacturers guarantee panels to operate at certain production levels over the life of the panel. For example, 80 percent DC electric output at 20 years, and many solar arrays produce electricity for decades longer.
Kyle Rees, president of Solar Power Products, a Canadian manufacturer of plastic solar panel mounts explained the problem, “In most cases we need virgin plastics in order to ensure longevity. We occasionally use recycled in production but not that often. We have a 20 year warrantee against all of the physical aspects of our supporting a panel, such as for cracking. If we could get a company to supply recycled HDPE and warrantee performance for 20 years we would buy it. Most typical programs in Ontario, for instance, use feed-in tariffs (FIT) for solar systems that require a 20 year lifespan.” (Ontario’s FIT Program is North America’s first comprehensive guaranteed pricing structure for renewable electricity production. It offers stable prices under long-term contracts for energy generated from renewable sources).
Whether virgin or recycled HDPE, Rees observed a major benefit of using plastic rather than metal mounts. “We sell each pod for about $90. Right now we are getting $6 Canadian for a damaged pod that weighs 31 pounds. The recyclers love our product because there’s no processing to recycle it. There’s nothing to take off and they can feed them directly into a shredder. With expected rises in commodity prices, a $90 pod today is probably going to be worth $20 to $25 in basic recycle value in 20 years.” A solid investment with a predictable return.
Renusol currently offers a 10 year warranty on their 100 percent recycled units, but has confidence of performance lasting over 25 years. One reason is their use of a High Molecular Weight Polyethylene (HMWPE) base. “The molecular strands are longer and have higher molecular weight with slightly better rigidity and tensile strength. The materials we are using in this application do not have problem going 25 years and we are expecting a 50 year life. Similar polyethylenes have been used for over 50 years by utilities for above ground water transport and as conduits for above ground electric transmission.” Hudson reported.
Another issue with recycled plastics used to manufacture solar mounts is not meeting two types of UL (Underwriters Laboratories) test certifications conducted on plastic materials to measure flammability and the resistance of the plastic to electrical ignition sources. UL 94 determines the material’s tendency either to extinguish or spread a flame once the specimen has been ignited and UL 746A measures the resistance of the plastic to electrical ignition.
The reason for this non-certification is that UL has no way of assuring exactly how the material is processed or what the recycled content is composed of, or what uncontrolled material such as filler may get into the mix. “This is a sticky technical point in UL’s view. We have yet to encounter a customer request that it be UL 94 or UL 746A compliant. It would pass the test, but you can’t get it certified to that. If requested, we could run a lot of virgin material,” said Hudson.
Sollega is a leading manufacturer of an HDPE ballasted mounting system called InstaRack. The product contains 35 percent recycled content which is sourced internally from trimmings of its own production process. Now installed in over 20 states, the company claims InstaRack is the easiest to install because it has least number of parts of any ballasted system.
Elie Rothschild, Sollega’s CEO commented on sector growth: “Industrial plastic like HDPE will play an increasing role in the solar industry because of its obvious advantages. HDPE is 100 percent recyclable as well as being very robust, flexible, non-conductive and resistant to ultraviolet light. Sollega is the leader in manufacturing solar racking systems using HDPE in the North American market.”
Depending on the project, HDPE mount manufacturers quote labor savings ranging from 20 to 70 percent. Plastic mounts are lighter to transport, easier to handle and require fewer parts and tools than metal mounts.
“Roof membrane manufacturers love it because it’s less abrasive on the membrane than aluminum or stainless steel,” said Hudson. “Our units are lightweight. If an installer drops a heavier aluminum or stainless unit with sharp edges it could penetrate the membrane and cause a leak, which is potentially a huge cost to repair after the array is installed. There’s also less wire chaffing than on metal which has rougher edges. Plastic has nice, soft edges as well as a lot less grounding issues,” said Hudson.
“For sure there’s a great future in plastic mounting systems. It’s the next thing. The aluminum guys are too expensive and there are too many nuts and bolts. If you want to drive down the costs this is the way to do it,” summarized Kyle Rees at Solar Power Products.
Source : americanrecycler.com