Solar: A bright future

By Tony Deligio
Published: March 1st, 2010

The amount of solar energy that falls on the planet in one hour is enough to generate sufficient power for every person on earth for one year.

Of all the reasons that solar energy is capturing record levels of investment and spurring frenetic activity, its tremendous potential, laid out by Dan Cunningham of BP Solar (Frederick, MD), is the primary driver for the market. Participating in the Chemical Development & Marketing Assn.’s (CDMA) “Opportunities for Chemicals and Materials: Capitalizing on Wind and Solar” conference held last December at the University of Pennsylvania’s chemistry department, Cunningham addressed a crowd that included the biggest names in plastics supply—BASF, Bayer MaterialScience, Dow, and DuPont to name a few—all of which appreciate the extraordinary opportunity the burgeoning solar energy sector holds for plastics.

DuPont Tedlar polyvinyl fluoride films see use as backsheets for photovoltaic modules.

DuPont’s photovoltaic encapsulants act as a glue for solar modules, sealing them against the elements.

Ascent Solar utilizes DuPont’s Solamet PV metallizations to help enhance the efficiency of thin-film PV modules.

As impressive as the current boom is, Mike Eckhart, president of ACORE (American Council of Renewable Energy), forecasted an even brighter future for solar at the same CDMA event, particularly for the United States, which has only recently thrown the full weight of government subsidies and tax benefits behind the technology. “My prediction is in two years, solar will really take off,” Eckhart said. Admitting that the U.S. is the “laggard” in solar, Eckhart said he believes the country will catch up to the current market leader, Germany, which had 2000 MW of new solar capacity installed in 2009.

Eckhart has stood at the intersection of government and renewable energy before, starting with the Carter administration in the late 1970s, when the U.S., still shell shocked from its impotence during the oil embargoes, found religion with renewable energy. Carter placed solar panels on the White House in 1979, but his successor, Ronald Reagan, had them removed in 1986, and renewable energy symbolically, and in reality, faded into the background once again.

Following the most recent oil shock in 2008 and with growing concern that the emission of carbon dioxide from fossil-fuel-derived energy could be having a deleterious effect on the planet’s climate, the U.S. government has once again taken an interest in renewable energy. The Dept. of Energy’s stated goal is that by 2025, 25% of the energy generated in the U.S. will be from renewable resources. At a state level, 29 local governments have already mandated that local utilities source a certain percentage of the energy they create from those same resources.

In late November, Eckhart and ACORE conducted a policy meeting in the Cannon Caucus room at the U.S. House of Representatives, sketching out the policy framework that could start the country on that energy roadmap. ACORE has determined that the U.S. will need to invest $30 billion-$35 billion to attain that 25% goal. In 2008, $18 billion was invested in energy projects, with 50% in renewable energy.

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 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 films, Kapton polyimide, Teonex PEN, and Teijin Melinex ST polyester are used for substrates.

Arizzi says DuPont’s current research is focused on two areas: improving the performance of existing materials in areas like durability, barrier, and optical clarity; and addressing opportunities for material replacement within the cells. In the latter category, DuPont is working on a polymer substitution for glass.

“Glass is rigid but polymers are flexible,” Arizzi says, “so actually, one of the reasons that we are really excited about this research direction is the fact that we believe that many of the modules of the future will not only be lighter, but also more flexible. Polymers here are actually an enabling technology.” Arizzi says the company is in a piloting phase for glass replacement, utilizing a PVF, with commercialization one to two years away.

Sabic Innovative Plastics began to focus on the PV industry around five years ago, according to Andy Verheijden, global product marketing manager of solar energy at the company. Since that time, it has been able to gain market acceptance for its Noryl family of amorphous blends of PPO polyphenylene ether and polystyrene, as well as some adoption of Lexan copolymer polycarbonate. Noryl has already replaced metal in junction boxes and connectors, and the material was recently chosen by a North American firm for a solar module frame, using an injection molded glass-filled version to replace metal. The company is also at work developing materials for use in backsheets.

Verheijden also describes the market as “booming,” noting that last year, in a down time for the economy, the sector’s demand for Noryl grew by 85%. To support the explosive growth, Sabic IP is in the planning stage of setting up its own testing facility for solar thermal applications in the Netherlands, with the lab set to open this month. Within a year’s time, it would also like to open a test center for the PV industry, which would become a center of excellence for the market. Verheijden says the company hopes to have it operational in the next year.

Jim Bratcher, market segment leader for Honeywell’s Photovoltaic Packaging business, has also seen market demand increase of late, saying prior to 2008, annual growth easily surpassed 30%, with similar gains expected in 2010 after a blip in 2009. “Many analysts are forecasting a return to former growth rates within a few years or even less,” Bratcher says, “driven by anticipated increased demand and new subsidies in North America.”

In 2008, the company began supplying a backing film called PowerShield to the industry. The sandwich structures laminate together barrier, dielectric, and bonding layers. Bratcher says the key enabling component is the ECTFE fluoropolymer barrier film layer that’s made from a proprietary formulation developed and produced by Honeywell.

As the U.S and other nations debate the ongoing role of renewable energy, DuPont’s Arizzi says government programs to spur adoption should be viewed in the proper light. “Incentives are key,” Arizzi explains. “They should be seen as an investment for the future. Looking back at what has happened in countries where solar has developed, incentive mechanisms have been a necessary condition for creating the industry. Some people see it as a cost; in reality it’s an investment. I’m convinced that the U.S. will catch up and become one of the leaders in the solar industry.”

Applications in injection molding
Not all of the money in solar power will be spent on complex film laminates developed by multinational comporations; there are opportunities aplenty even for small to midsized processors. This photo, taken at last fall’s Fakuma trade show in Germany, shows one of the more straightforward potential applications for plastics processors: a console (support) for a solar collector. A cutaway hangs on the wall with a complete solar collector displayed in the foreground.

Dutch injection molder HSV took the part, which was being thermoformed in lower volumes, and now “tens of thousands of these parts will be made per year” on a 2300-tonne machine, according to company officials who spoke with MPW. The 8-kg polypropylene part is formed with just two injection points. Part costs are 30% less than they were when thermoformed. DuPont Tedlar polyvinyl fluoride films see use as backsheets for photovoltaic modules. DuPont’s photovoltaic encapsulants act as a glue for solar modules, sealing them against the elements. Ascent Solar utilizes DuPont’s Solamet PV metallizations to help enhance the efficiency of thin-film PV modules. Tony Deligio

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