Modern Plastics Worldwide - March 2010 - dae uptlax

At the CDMA event, Mark Thirsk, managing partner with
Linx Consulting, forecast that the number of installed photovoltaic
(PV) megawatts will climb from 6000 in 2008 to nearly
16,000 by 2012, with the U.S. and China vying to overtake
Germany as market leader. PV technology comes in two primary
formats at this time, thin film and crystalline silicon, with
both systems heavily reliant on plastics.
Anatomy of a solar cell
Although there are many variations, BP Solar’s Cunningham
says solar cells can largely be separated into four distinct
groups: mono crystalline silicon, multi (poly) crystalline silicon,
amorphous silicon, and cadmium telluride (CdTe) thin film.
Respective efficiencies in converting photons to electrons for
the four are: 14%-18%, 12%-16%, 6%-7%, and 8%-10%.
A typical crystalline silicon system, working from the back
to the front, consists of a polymer backsheet (about 125 μm
thick), EVA (random copolymer of ethylene and vinyl acetate),
solar cell, second EVA layer with 95%-plus light transmission,
and glass. Other elements in the module include encapsulants,
which act as the glue for the whole package; frames and framing
adhesives; tabbing ribbons to connect cells; and junction boxes
and cables. Cunningham says BP Solar uses a polycondensation
polyester for the backsheet because of its performance under
moisture and heat. The backsheet requires good moisture barrier
and must pass a UL fire test with a Class C rating or better.
This structure, and others in the industry, is not immutable,
however. “The PV industry is going through massive growth,
and is constantly looking for new materials,” Cunningham
says. “New materials need to be cost effective and drive the life
of PV products beyond 25 years.” Regardless of the path chosen,
according to Cunningham, in a sunny
climate, a PV cell will generate more than
20 times the electricity used to make it.
Sarah Kurtz, a researcher with the
National Renewable Energy Laboratory
(NREL; Golden, CO), discussed the present
anatomy of thin-film cells at the same
CDMA conference. In addition to CdTe,
common thin-film systems include amorphous
silicon and CuIn(Ga)Se (copper
indium gallium selenium). Both structures
feature layers of EVA, with the cell in
these instances sandwiched on the outside
by glass, and the EVA essentially acting
as an adhesive. It is a fast-changing market,
however, with Kurtz estimating there
are currently 100 companies developing
thin-film products. The industry is pushing
for new substrates to replace glass,
aiming for materials that are flexible,
lightweight, resistant to UV radiation and
moisture, and, in some instances, able to
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withstand process temperatures of 600°C and up.
Thirsk reported that the total annual crystalline silicon
solar capacity in 2008 was roughly 10,500 MW, with thin-film
capacity of 1900 MW. Although there is less of the capacity
installed, thin-film modules have achieved cost-of-energy
rates that drive closer to grid parity. Thirsk believes the total
materials market for PV will climb from $2 billion in 2008 to
around $9 billion by 2015, with backsheet, polyvinyl butyral
(PVB), and EVA accounting for roughly half of all demand.
Within backsheets, there are opportunities for fluoropolymers
and PET, while encapsulant materials can include crosslinkable
elastomers like EVA, polyurethanes, and silicones as well as
thermoplastics like PVB, TPU, olefins, and ionoplast.
Targeting glass
DuPont, which has been a material and technology supplier to
the photovoltaic (PV) industry for more than 25 years, provides
films, resins, encapsulation sheets, flexible substrates, and conductive
pastes for both crystalline silicon and thin-film modules.
Simone Arizzi, global technology director for DuPont photovoltaic
solutions, says the market has consistently expanded at rates ranging
from 20%-40%. “This is a high-growth-rate industry, and
it’s going to stay a high-growth-rate industry for the foreseeable
future,” Arizzi says. “Materials have a very important role to play
in guaranteeing the future success of the photovoltaic market.”
Arizzi says in the last 12 months, DuPont has invested $300
million in new capacity to serve the industry. The company’s
Teflon film is used in front sheets, with Elvax-brand EVA used
as encapsulant, Rynite PET applied in junction boxes and
structural parts, and polyvinyl fluorides (PVF) such as its Tedlar,
Mylar, and Melinex brands found in the backsheet. In thin
DuPont’s photovoltaic encapsulants act as a glue for solar modules, sealing them
against the elements.
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