Aside from harvesting landfill gas, closed landfill acreage
is largely wasteland. And where are these vast tracks
of vacant land located? They are usually close to the
metropolitan centers that filled them up or close to
cities where large utilities are scrambling to meet
renewable energy portfolio targets. This relative geography
opens up large potential for the installation of plastic
geomembrane caps covered with thin-film photovoltaics
(PV). Very importantly, and unlike many solar or wind
farms, this largely unproductive wasteland is usually
sited next to power lines standing ready to deliver
electricity into urban areas, which avoids building
costly transmission infrastructure.
Traditional ground-mounted PV does not work for landfills
because of prohibitions against drilling into soil
caps to build the foundations necessary for steel racks
to support conventional PV arrays, and the land is
far too unstable to support other heavy structures
like wind towers. After long term settlement these
lands may serve as green space, golf courses or parklands,
but usage is often problematic because of the underlying
decomposition.
Exposed geomembrane caps are well established for closing
landfills. A main advantage is that durable plastic
covering is an environmentally safe and economical
alternative that circumvents the high expense of buying,
carting and spreading the required clay-content capping
soils. Geomembranes are highly efficient in preventing
rainwater from percolating through the waste and becoming
troublesome leachate. And better than soil caps, they
contain landfill gas for recovery while masking unpleasant
odor.
Take the inherent benefits of modern geomembrane durability
and combine it with the latest developments in thin-film
solar technology, and many people are convinced that
this is a hybrid solution with great potential. Combine
a solar-geomembrane with gas recovery, and suddenly,
what were once wastelands can become productive energy
farms. At least, that’s the theory.
An expert appraisal of solar-geomembrane technology
Dr. Jean-Pierre Giroud has been a pioneer in the
field of geosynthetics for 40 years and is recognized
throughout the world as a leading expert in geosynthetics
engineering. In 1977, he coined the words “geotextile”
and “geomembrane” and was instrumental in the formation
of the International Geosynthetics Society. In 2009,
he was elected to the National Academy of Engineering.
Following are his thoughts on solar-geomembrane technology,
collected via interview by American Recycler writer
Mike Breslin:
What is the significance solar-geomembrane technology
for landfill operators?
Of course, solar-geomembrane technology can generate
revenue for landfill operators. However, I would
like to point out an additional benefit. Landfills
are sometimes said to have bad reputation, which
is undeserved in my opinion, because modern landfills
built with state-of-the-art technology protect the
environment very effectively. Nevertheless, we have
to recognize that, in many circumstances, landfills
are not well accepted by the public. The fact that,
thanks to solar-geomembrane technology, landfills
can generate clean energy can only contribute to
improving landfill acceptance by the public.
Is there interest outside of the States for this
technology?
I do not know if, at the present time, there is interest
outside the United States in solar-geomembrane technology.
However, I can say that, historically, the United
States has been at the forefront of the use of geomembranes
in landfills, and the domestic state of practice
regarding geomembranes in landfills has inspired
landfill owners, designers and regulators in many
countries. Therefore, it can be expected that the
United States solar-geomembrane technology will generate
a lot of interest when it becomes better known abroad.
Accordingly, it is important to describe the State’s
solar-geomembrane technology in articles published
in highly respected journals and magazines.
If you were advising a government agency, would you
recommend they consider this technology?
Yes, I would. And I would recommend that research
is encouraged by government agencies to develop the
solar-geomembrane technology.
Are you optimistic about the widespread deployment?
The landfill industry is highly competitive. Therefore,
I think that the growth of the solar-geomembrane
technology will depend on economic considerations.
Costs associated with the solar-geomembrane technology
can be reduced if appropriate research and development
effort is undertaken.
We should recognize that the technology is currently
in its infancy. Progress can be made in at least
two areas. First, the method used to attach the photovoltaic
cells to the geomembrane and the method used to collect
the electric power generated by the cells could probably
be simplified. Second, inexpensive ways to secure
the geomembrane against the risk of uplift by wind
should be developed. Clearly, research and development
work should be done by both the scientists who develop
the photovoltaic cells and the civil engineers who
design landfills. These are the conditions for the
widespread deployment of the solar-geomembrane technology
in the future.
Where do you think this technology will be in 10
years?
Predictions of this kind are generally incorrect.
I can only say that the solar-geomembrane technology
should be very successful in less than ten years
if appropriate means are devoted to research and
development.
And the theory is being deployed in a few large-scale
commercial applications with early indications of success.
United Solar Ovonic (known as Uni-Solar), a wholly owned
subsidiary of Energy Conversion Devices, has been the
pioneer in developing its amorphous silicon thin-film
technology for landfill geomembranes. Energy Conversion
Devices has been manufacturing thin-film panels for over
20 years and has approximately 250 megawatts in operation
worldwide, primarily mounted on roofs.
No other solar manufacturer is doing geomembranes at
this time, although others are interested because of
the potential size of the global market.
Different than the heavy crystalline-silicon solar panels
with aluminum frames and glass surfaces that must be
bolted down, these thin-film panels are less than a quarter-inch
thick and adhesive-applied to geomembranes. Built on
a flexible, stainless steel substrate, the layers of
photovoltaics are encapsulated in polymers.
While having lower energy output per square foot than
conventional panels, thin films cost less to manufacture
and are much lighter weight. Despite requiring a larger
footprint than conventional panels for equivalent electric
production, Uni-Solar claims that the payback time on
investment is better than conventional panels.
In late 2007, the Malagrotta landfill outside of Rome,
Italy became the world’s first to use thin-film solar
to cover a landfill, but the panels were not affixed
to a geomembrane. Rather, a 226,000 square foot sloping
area of a closed portion was graded and covered with
a thin concrete cap. On top, a two-foot high metal roof
was built and covered with solar panels – essentially
a roofed-over landfill. Installed by SolarIntegrated
and using Uni-Solar panels, the nearly one megawatt system
produces approximately 1,421,000 kWh per year.
The next evolution in the technology happened last spring
when Republic Services became the first in the world
to inaugurate a solar-geomembrane cap at the Tessman
Road Landfill in San Antonio, Texas. This 134.4 kW DC
system also uses Uni-Solar collection strips, but they
are glued directly to a geomembrane made by Firestone
and cover 5.6 acres of the 680 acre site.
“The system has been working great. But keep in mind
it’s only been online since April. We’re averaging about
750 kWh per day. It’s not a big system, but very reliable
and low maintenance. We have done no maintenance since
we installed it. We get quite a bit of rain so it washes
down the panels for us,” said Tony Walker, Republic’s
project manager, who also pioneered the concept.
This geomembrane was installed by the traditional method
of anchor-trenching the perimeter edges, and Tessman
Road was specified to withstand winds up to 90 mph. The
Firestone material was selected for its durability. It’s
a 60-mil polyolefin thermoplastic that has been used
in roofing, is warranted for 20 years and green to look
like a lawn from a distance.
Large sections of 60’x60’ geomembrane were used to mount
the flexible solar panels. Trench depressions between
sections were used to carry wires in weather resistant
chases to inverters that convert solar DC to AC, at which
point the power goes to CPS Energy.
Each solar panel affixed to the geomembrane measures
18’ long, 15” wide and has a power output rating of 128
watts. 1,050 panels were installed on graded slopes for
a total of 134.4 kW DC output. “It’s interesting that
the modules start producing early in the morning and
go to late evening. They work in very low light and we
will probably be over our estimate in projected kilowatt
hours by the one year anniversary date,” Walker said.
Like other types of solar panels, Republic’s are performance
warranted – 92 percent of minimum power output for 10
years, 84 percent for 20 years and 80 percent for 25
years.
Republic reported only one outage of less than 24 hours
since the system became operational. That was caused
by a major electrical storm. Lightning struck the inverter
unit, but as the unit was designed to handle lightning,
it only required changing a blown fuse.
Walker, who is based in Phoenix, is able to remotely
monitor the Tessman Road system on a web-based monitoring
system by Fat Spaniel, a provider of monitoring and control
systems to the solar industry. In addition to monitoring
real-time energy production, the system archives daily,
monthly and annual production.
Republic’s monitoring is for company tracking only, but
many solar generators publish information on websites
to show the public how much renewable energy is being
generated and the amount of emissions being prevented
by the system.
“We’ve had several world experts on geomembranes visit
our site, people who advise the EPA. All endorsed it
highly. We’ve had other solid waste companies visit us
that are interested in the concept. We also have a lot
of solar manufacturers calling and touting that they
have the same type of product, but don’t have the manufacturing
capability that we need. It will be interesting to see
how the competition develops,” Walker noted.
Meanwhile, solar geomembrane capping has been capturing
the interest of landfill operators across the country
and from several foreign countries. Republic was recently
awarded a permit to construct a solar geomembrane project
in Illinois of 140 kW that will generate approximately
180,000 kWh per year. “There’s not as much sun as in
Texas, but we want to test this system there because
it’s a different climate, colder with ice and snow. We
want to see how the geomembranes and solar cells perform
under those conditions,” said Walker. “The State of Illinois
has voiced interest in this type of solar for the redevelopment
of brownfields.”
Republic is also applying for a permit for a one megawatt
system for a 48-acre closed landfill just outside downtown
Atlanta. “That will be a good project because of the
magnitude. When you fly over, it will bring wide public
exposure to the technology,” said Walker. “Municipal
landfills and project developers around the country,
particularly in Florida, New York, New Jersey, Massachusetts
and California have inquired. The market potential is
huge.”
The flexible solar landfill cover approach is just that:
flexible. By helping prevent erosion, sediment buildup
and the growth of vegetation, it makes inspections easier
and more thorough. To accommodate settling, sections
of the solar-geomembrane can be removed, the ground remediated
and then retrenched.
There is a lot of government and media hype about the
“new green economy” and how it will create millions of
new green jobs. However, many people do not know that
the vast majority of conventional solar panels and wind
turbines installed in the United States are manufactured
overseas. Uni-Solar’s thin-film panels are manufactured
domestically at four factories in Michigan, and they
have broken ground on a fifth factory there. It’s just
one more reason why flexible solar systems make sense.
