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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.
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