Battling corrosion to keep
solar panels humming
Sandia National Labs
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| Sandia National Laboratories researchers, left to right, Eric Schindelholz, Olga Lavrova, Rob Sorensen and Erik Spoerke examine points that can corrode on photovoltaic arrays. Sandia researchers collaborate to accelerate corrosion under controlled conditions to help industry develop longer-lasting panels and increase reliability. |
“It’s challenging to predict and even more challenging to design
ways to reduce it because it’s highly dependent on material and environmental
conditions,” said Eric Schindelholz, a Sandia National Laboratories materials
reliability researcher who studies corrosion and how it affects photovoltaic
(PV) system performance.
Sandia researchers from different departments collaborate to
accelerate corrosion under controlled conditions and use what they learn to
help industry develop longer-lasting PV panels and increase reliability.
For example, work by Olga Lavrova of Sandia’s Photovoltaic and
Distributed Systems Integration department demonstrated, for the first time, a
link between corrosion and the risk of arc faults in PV systems’ electrical
connections. Research by Erik Spoerke of Sandia’s Electronic, Optical and Nano
Materials department focuses on developing new nanocomposite films that could
dramatically increase reliability.
“One of our primary goals is to predict how fast corrosion will occur and what damage it does, given certain environments and materials,” Schindelholz said.
“This, in turn, gives us information to select the right
materials for design or to develop materials for corrosion-resistance for a
particular environment. It also allows us to assess the health and operational
risk of systems as they age. This is especially important for solar energy
systems, which are susceptible to corrosion but are expected to last for
decades.”
Corrosion is no small problem. A 2002 study by the National
Association of Corrosion Engineers, backed by the Federal Highway
Administration, estimated corroding metals in various industries,
infrastructure and manufacturing cost $276 billion annually.
Reproducing environmental
conditions to study corrosion
Researchers simplify complex environmental conditions in labs to
study how materials corrode. It’s not easy deciding which environmental
conditions to reproduce.
“Along the coast of Florida, it’s humidity and sea salt in the
air. In Albuquerque, we have high ultraviolet (UV) radiation, so UV might be
one of the important parameters here. The parameters driving corrosion shift
with location and materials,” Schindelholz said. “The challenge lies in
identifying the important parameters — and then tuning the knobs in the lab to get
something that replicates what we see in an outdoor environment.”
Sandia belongs to a new consortium aimed at speeding up
development of new materials for photovoltaic modules, increasing reliability
and lowering the cost of solar power-generated electricity.
The Durable Module
Materials National Lab Consortium (DuraMat) wants to build
bridges between the national laboratories and industry so research at the labs
can benefit the PV community. DuraMat’s importance is underscored by the fact
materials account for about 40 percent of total PV module costs.
DuraMat, led by the National Renewable Energy Laboratory in
partnership with Sandia, Lawrence Berkeley National Laboratory and the SLAC
National Accelerator Laboratory, will receive about $30 million over five years
from the Department of Energy’s (DOE) SunShot Initiative. The consortium is part of
the Energy Materials Network, created by the DOE’s Office of Energy Efficiency
and Renewable Energy.
Using accelerated aging,
forensics to see what’s happening
Lavrova leads projects on the reliability of PV systems,
studying how aging affects solar cells and components and how everything
performs together. Her team works with Schindelholz on two projects under the
SunShot Initiative, a national effort to make solar energy cost-competitive
with other forms of electricity by decade’s end. She also contributes to the
module durability effort under DuraMat.
One project, in collaboration with the Electric Power Research
Institute, studies PV modules from different manufacturers to give the makers
information on what kind of degradation they might expect over 30 years to help
identify ways to slow it down. Sandia applies accelerated aging principles to
speed up studies of slowly developing effects, including corrosion.
The second project, with Case Western Reserve University,
studies corrosion and other degradation from a forensic angle — looking back to
see what’s already occurred. Lavrova’s team takes a big data analysis approach
to study and analyze information from existing installations worldwide.
“Is it
1 percent degradation a year or is it 2 percent? Maybe we’ll see some that are
a half percent, maybe we’ll see some that are 10 percent. Was it a bad original
product or was it installed in Costa Rica where the humidity is 80 percent
every day?” she said.
Spoerke’s team wants to block corrosion altogether.
Collaborating with Texas A&M professor Jaime Grunlan, the team is
developing nanocomposite films made from inexpensive materials as barriers
against water vapor and corrosive gases.
The team hopes such composite
materials, some 100 times thinner than a human hair, will improve ways to
protect solar cells from corrosion.
Inorganic components and organic polymers that make up thin
films must be designed and mixed carefully. “It’s about assembling those
structures in the right way so that you can use inexpensive materials and still
get the benefits you want,” Spoerke said.
“If you build a house, it’s not just
piling together the drywall and two-by-fours and shingles. You’ve got to use
the two-by-fours to make the frame, set the drywall on the two-by-fours, and
assemble the shingles on the roof.”
Thin films aren’t the sole answer, but “I can envision that a
technology like the one that we’re developing could be part of a collaborative
materials system to help replace glass in next-generation PV applications,” he
said.
Systems containing metal
subject to corrosion
Sandia has studied corrosion for decades, analyzing the problem
in all kinds of systems because anything containing metal is susceptible. Solar
cells’ electrical components are protected from corrosion by encapsulating
polymers, sealants and glass, but water vapor and corrosive gases can permeate
as materials and packaging degrade.
Materials, for example, typically corrode faster in the higher
temperatures and humidity of tropical coastal regions than in coastal
Antarctica.
Researchers accelerate these real-world conditions in
environmental chambers to examine corrosion of electronics and other PV system
components. Accelerated tests artificially speed up the corrosion effects of
temperature, humidity, pollutants and salt water.
For example, salt on icy winter
roads or near oceans corrodes cars over time. Since automotive manufacturers
can’t wait decades to see how their products resist that, accelerated
laboratory tests might spray salt continuously on a surface to qualify coatings
and body materials to ensure they’ll be safe and reliable over a product’s
lifetime.
Engineers use corrosion chambers to study different materials in
systems that must meet particular corrosion requirements, or to expose an
electronic component to the environment to see what happens over time.
“Instead of waiting for 30 years of operation outside under the
sun, we bring our PV panels inside to expose them to much higher concentrations
of light or put them in thermal chambers to simulate the equivalent of years of
temperature cycles,” Lavrova said. Accelerated lifetime experiments show in six
months what could happen over decades, she said.
Sandia also studies mechanisms underlying corrosion. “That’s a
greater challenge,” Schindelholz said. “In atmospheric corrosion we have the
chemistry of the atmosphere, the particles landing on surfaces, relative
humidity, temperature and so on. We have to understand the interplay of these
factors and their interaction with the metal surface.”
