Skip to Main Content

Cover Story

November 20, 2006
Volume 84, Number 47
pp. 25-28

Solar Revolution

The market for photovoltaics is expanding rapidly, and chemical companies are taking notice

Alexander H. Tullo

Earlier this year, DuPont installed a 40-kW solar panel array at its Chestnut Run research and office complex in Wilmington, Del. The panels are more than a ploy to impress passing motorists. To DuPont, and to a growing number of companies in the chemical enterprise, solar power is becoming big business.

DuPont
Southern Exposure DuPont recently installed solar panels at its Chestnut Run facility in Wilmington, Del., sufficient to power eight homes.

For now, solar energy is both the smallest and one of the most expensive sources of energy. According to the Department of Energy's Energy Information Administration (EIA), solar contributed a mere 0.063 quadrillion Btu of the roughly 100 quadrillion Btu of energy consumed in the U.S. in 2004. Moreover, it comprised only about 400 MW out of the 970,000 MW of summer electric capacity of the U.S. in 2004.

But the business is taking off. According to the Solar Energy Industries Association (SEIA), the global voltaic market was worth about $15 billion in 2005 and has been growing at a 30% annual clip over the past five years. According to EIA, the U.S. market grew by 72% in 2005, hitting 134,000 of what the industry calls peak kilowatts-the output of photovoltaic cells under ideal conditions.

Rhone Resch, SEIA's president, expects global growth to slow down to about 15% in 2006. He attributes the slowdown in growth to a shortage of polycrystalline silicon used for photovoltaic cells and points out that, this year, photovoltaics will surpass semiconductor manufacturing as the top user of silicon. He expects photovoltaic growth to get back on track as silicon manufacturers install new capacity dedicated to the solar market (C&EN, Oct. 2, page 30).

Resch credits government incentives around the world for fostering demand that is gobbling up solar panels as quickly as possible. The U.S. Energy Policy Act of 2005, for example, allows for a tax credit of 30% of the photovoltaic system cost. The California public utilities commission recently allocated $3.2 billion for incentives for home and business owners to install solar panels over the next 11 years.

These incentives can help make the technology economical for certain users, Resch points out. For example, in San Francisco, electricity for commercial users can cost about 33 cents/kWh in the peak afternoon power-use period. With the federal and California subsidies, the cost of solar power can be driven down from above 30 cents/kWh to the midteens.

Mark Conroy, general manager for solar at GE Energy, notes a similar situation in Hawaii. "There are pockets around the world where solar is already competitive," he says.

Andrew M. Weber, global business director for DuPont Fluoropolymer Solutions, says solar power is becoming a viable source of alternative energy rather than a novelty. "The industry is really ramping up, and we are now seeing strong growth rates and more and more interest in photovoltaics," he says.

At the heart of the most common photovoltaic cells is a polycrystalline silicon semiconductor. The doped silicon is sensitive to photons, which knock electrons loose, thereby creating a current.

But silicon alone does not a solar panel make. To work properly over warrantee periods of 25 years, photovoltaic panels need other materials that protect them from the elements, draw current from the silicon, and provide insulation and mechanical strength, according to Weber. "Silicon creates the electricity, but to get that electricity out into a workable product requires other materials," he says.

Among the chemical companies supplying these materials, DuPont is the most prominent. Different DuPont businesses, such as fluoropolymers and industrial polymers, had been selling materials for silicon-based photovoltaic cells for about 30 years. Two years ago, the company formed DuPont Photovoltaic Solutions to coordinate efforts throughout the company targeting the solar power industry, says Thomas R. Earnest Jr., venture manager for the new business.

One of DuPont's key materials for the solar energy market is Elvax ethylene vinyl acetate resins. These are extruded by customers into a film used to encapsulate the silicon wafer, which lies under a tempered glass housing. According to Stanley D. Merritt, global business planning manager for DuPont Photovoltaic Solutions, EVA provides optical clarity while matching the refractive index of the glass and silicon, thereby cutting down on reflections. It also holds together the components inside the cell and provides physical strength to the photovoltaic panel.

Other materials companies have become interested in this encapsulation market. Mitsui Chemicals recently built a plant in Nagoya, Japan, with capacity for 4,000 metric tons per year of EVA film, enough to accommodate 570 MW of photovoltaic cells. In 2005, Bridgestone expanded its EVA films plant in Iwata, Japan, to up to 12,000 metric tons per year.

Another important part of DuPont's offering for photovoltaics is Tedlar polyvinyl fluoride film, which is coextruded with polyester film and applied to the bottom of silicon-based photovoltaic cells as a backplane that provides electrical insulation and protects against weathering.

In August, DuPont announced that it was investing $50 million to expand production of Tedlar in Fayetteville, N.C. The company says demand for the material—also used in aerospace, construction, and graphic arts applications—is growing at 30% per year. The expansion is the largest part of the $100 million that DuPont says it is spending in the photovoltaic field.

Other companies are active in the area of backplane materials. Arkema, for example, supplies its Kynar polyvinylidene fluoride film, which has similar properties to Tedlar. Kevin Hanrahan, business development manager, says the company has been enjoying growth in the sector of up to 30% annually.

But Hanrahan compliments DuPont and sees Kynar as a way for solar panel manufacturers to differentiate their supply base. "It is not necessarily our strategy to tackle Tedlar and put them out of business," he says. "They have a good product."

Another important part of DuPont's photovoltaics offering is its Solamet silver metallization pastes. Lines of this paste are drawn onto the silicon wafers to conduct the electrons generated by the cell. These lines must be drawn thin—about 100 µm wide—so as not to block the sunlight from hitting the silicon wafer. Earnest says the goal is to shrink the lines down to as small as 75 ??m.

DuPont isn't alone in supplying a wide range of materials to the photovoltaics sector. Dow Corning, through its Hemlock Semiconductor joint venture with Shin-Etsu Handotai and Mitsubishi Materials, is a major polycrystalline silicon producer. Dow Corning also offers a broad range of ancillary materials for photovoltaics, including silicone-based encapsulants, photovoltaic cell and substrate coatings, and materials for sealing junction boxes and photovoltaic frames.

Further solar panel cost reductions will make photovoltaic power more competitive with conventional power. One approach has been greater manufacturing economies of scale, SEIA's Resch says. He estimates that solar panel costs drop 18% for every doubling of industry manufacturing capacity. Costs, he adds, have decreased by an average of 6% per year for the past 20 years.

Santa Clara, Calif.-based Applied Materials, a leader in chemical application equipment for the semiconductor and display industries, announced in September that it is entering the photovoltaics industry. The company's strategy is to apply technologies developed in integrated circuits and displays to photovoltaic manufacturing on a large scale.

Charles Gay, vice president of Applied Materials' solar business group, notes that photovoltaic and integrated circuit manufacturing are both largely a matter of laying materials onto silicon wafers. "The chemistry and formation of various kinds of layers to serve as semiconductors, transparent conductors, metallic current-carrying layers, and packaging materials are all up the alley of a company like Applied Materials," he says.

Moreover, the company has expertise in handling the kinds of materials used in photovoltaics at high throughput. For example, in integrated circuit manufacturing, silicon nitride is used as a dielectric material. In photovoltaics, the firm uses reactive-sputtering techniques to apply a layer of silicon nitride to help the silicon trap more light.

Such technologies, Gay says, can help the photovoltaics industry transition from plants that today produce about 50 MW worth of photovoltaic cells per year to those with output of 100 MW and even gigawatt quantities. "With the economies of scale we can achieve, we can accelerate the cost reduction of solar modules, which moves us from competing with peak-power to bulk-power electricity," he says.

Another way to drive down photovoltaic costs is to tackle the silicon shortage that is driving up costs and limiting availability. According to GE's Conroy, silicon represents more than 50% of the cost of making the solar panel. "The trend has been to maximize the wafer so you get the same amount of power out of a thinner wafer," he says.

To reduce silicon costs, the industry is slicing the wafers used in photovoltaic cells thinner and thinner. DuPont's Merritt says the thickness of silicon wafers once averaged about 300 µm. This thickness is now down to about 180 µm, he says, and the industry is trying to get it even lower.

Applied Materials' Gay compares the thinning of wafers in the photovoltaics industry with the narrowing of circuit lines in the semiconductor industry. "To some extent, as every decade has gone by that solar wafers have been manufactured, the thickness of the solar wafer has been cut in half," he says.

Rather than trying to thin wafers, GE is developing a technology to cast wafers from silicon powder. Conroy says the cast wafers turn out to be thicker and less efficient than traditional wafers, but they are made faster and avoid the 30% waste produced in the conventional wafer-sawing process.

Thinner wafers bring other changes. For example, thinner wafers must be encapsulated with more advanced materials to be effectively incorporated into solar panels, says DuPont's Weber. "When you are going to thinner silicon, it ripples throughout the system," he says.

Nonpolycrystalline silicon technologies are also poised to take advantage of the shortage. United Solar Ovonic, the photovoltaic power arm of Rochester Hills, Mich.-based Energy Conversion Devices, operates a plant in Auburn Hills, Mich., that makes about 25 MW per year of photovoltaic cells based on thin-film amorphous-silicon technology.

Subhendu Guha, United Solar's president and chief operating officer, says the technology has two cost advantages. First, the raw material is silane gas, not the polycrystalline silicon that is in short supply. "Our raw material cost is much lower than polycrystalline silicon wafer, and we are not affected by the polycrystalline silicon shortage," he says. And second, United Solar's cells are made on a flexible stainless steel substrate in a roll-to-roll process, further reducing costs.

The material doesn't offer the 15-20% efficiency in converting sunlight into electricity that polycrystalline silicon-based cells do. But it does not need direct sunlight to start producing electricity. As a result, Guha says, it can produce more kilowatt hours of electricity over a long period of time given the same power rating.

United Solar is currently starting up another 25-MW manufacturing line in Auburn Hills. And the company is setting up two 60-MW lines in Greenville, Mich.; one is expected to start up in 2007 and the other in 2008. The company wants to have 300 MW of capacity by 2010.

Lowell, Mass.-based Konarka is developing nonpolycrystalline technology based on organic semiconductors. Daniel P. McGahn, Konarka's chief marketing officer, will not disclose what materials and companies it is working with, but he does point out that polythiophenes are the focus of much attention in organic semiconductors.

Like Guha at United Solar, McGahn admits that the efficiencies of the alternative photovoltaics are now less than that of polycrystalline silicon-based cells, but he also notes that they can scavenge light over a wider range of intensity than can traditional cells.

An advantage of Konarka's technology, McGahn says, is the potential for continuous roll-to-roll manufacturing, which can translate "a product like photovoltaics out of the world of fabs and silicon and into the chemical world of coating and printing." The company is working with partners on the commercial scale-up of the technology.

The attention being given to thin-film photovoltaics is more than just hype, says SEIA's Resch. Although polycrystalline silicon-based cells now command about 95% of the solar energy marketplace, he maintains that thin-film cells could grow to as much as 20% of the market as early as 2010.

DuPont's Earnest predicts that there will be enough growth in photovoltaics to go around if, as some predict, solar panels put out 1% of the power produced in the U.S. by 2020. "It is still a niche," he says. "Out of the total electric power consumption in this country, photovoltaics put out less than one-tenth of 1%. Getting to 1% is going to be huge for this industry."

Cover Story

  • Better Energy Through Chemistry
  • By supporting new energy creation techniques, specialty chemical companies are turning the oil and gas price run-up into a business opportunity.
  • Solar Revolution
  • The market for photovoltaics is expanding rapidly, and chemical companies are taking notice.
  • Fuels Of The Future
  • Chemistry and agriculture join to make a new generation of renewable fuels.
  • Start-up Firms Pursue Biofuels
  • Entrepreneurs invigorate search for economical biomass-based fuels.
  • Back To The Well
  • Chemistry targets cost-efficient extraction of oil and gas from mature reserves.
  • Microbial Methane Farming
  • With a boost from BASF, Luca is testing production of 'real-time' gas in mature wells.

Cover Story

  • Better Energy Through Chemistry
  • By supporting new energy creation techniques, specialty chemical companies are turning the oil and gas price run-up into a business opportunity.
  • Solar Revolution
  • The market for photovoltaics is expanding rapidly, and chemical companies are taking notice.
  • Fuels Of The Future
  • Chemistry and agriculture join to make a new generation of renewable fuels.
  • Start-up Firms Pursue Biofuels
  • Entrepreneurs invigorate search for economical biomass-based fuels.
  • Back To The Well
  • Chemistry targets cost-efficient extraction of oil and gas from mature reserves.
  • Microbial Methane Farming
  • With a boost from BASF, Luca is testing production of 'real-time' gas in mature wells.

Related Stories

Adjust text size:

A- A+

Articles By Topic