Process may cut cost of coating solar cells - Chemical & Engineering

Silicon solar cells need coatings to improve their efficiency. ... vapor deposition—costly processes, Westinghouse notes, and not well suited to mas...
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something of a threat. Occidental said that should the two companies not be able to agree on terms, "Occidental will not be bound by the terms outlined in this letter in any other action which we may elect to pursue in the future." This seems to leave the way open for an unfriendly tender offer if Occidental believes that it is called for. Mead had earnings in 1977 of about $98 million on sales of $1.8 billion. Sales for second-quarter 1978 were $590.8 million, up 31% from sales of $452.5 million for second-quarter 1977. Income for second-quarter 1978 was $31.3 million, up 11.8% from $28 million in the like period in 1977. •

Fertilizer Industry faces many challenges The U.S. fertilizer industry is losing market share. Fertilizer trade patterns are changing. Today's customers may be tomorrow's competitors. In short, the U.S. fertilizer community—farmers and dealers as well as producers—can no longer take the rest of the world for granted. That's the message from Tennessee Valley Authority economist Edwin A. Harre. It was delivered last week in St. Louis at the TVA Fertilizer Conference, held in conjunction with the Fertilizer Institute's annual trade fair. In 1967, according to a study made by Harre and associate Hazel A. Handley, the U.S. had 26% of the world's ammonia capacity and 46% of the world's phosphoric acid capacity. Since then, the U.S. share has been shrinking. By 1978, although U.S. ammonia and phosphoric acid capacities had both grown about 70%, world capacities had increased more than 200%. The U.S. share is now 20% for ammonia, 31% for phosphoric acid. And whereas current U.S. expansion programs are virtually com-

U.S. lag in fertilizer capacity will continue U.S. capacity as % of world total 60 1

40 B j j ^ HMk L^^5 20 B S S

j i W^Phosphoric Phosphoric acid acid Ammonia Ammonia

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o iHlinilillllHll 1967 69 71 73 75

77 79

Source: Tennessee Valley Authority

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C&EN Aug. 21, 1978

81 83 85

plete, expansions in other countries will, over the next several years, increase world ammonia capacity an additional 35% and phosphoric acid capacity 29%. By 1983, the U.S. share will be only 15% for ammonia, 24% for phosphoric acid. In the past 10 year's, Harre notes, East European countries and the U.S.S.R. have almost tripled ammonia capacity. In the next four years they will increase it another 50%. The fertilizer production capabilities of Asian communist countries have similarly expanded. By 1982, more than half the world's ammonia capacity will be operated by stateowned or -controlled enterprises, compared to about one third in 1967. Publicly owned phosphoric acid capacity has increased 10-fold in 10 years, it now accounts for one third of the world total. Also, a significant amount of the worldwide increase is in developing countries that have been large buyers of U.S. fertilizers. In the next few years, many of these countries will have added enough new capacity to eliminate their needs for fertilizer imports. In fact, Harre points out, some already have capacity beyond their current use level and are actively seeking export markets. Regional trade patterns also have changed markedly in the past 10 years, Harre says. The U.S. is exporting proportionately more fertil-

izer to Europe and South America, proportionately less to Asia. U.S. nitrogen exports are at near-record levels. But the U.S. also imports large tonnages of nitrogen fertilizers; it has been a net importer for three of the past four years. And the U.S.'s two leading customers, Brazil and Mexico, are both embarked on ambitious plant-building programs aimed at reducing their dependency on imports. Mexico already is exporting significant quantities of ammonia to the U.S., Harre notes, and could turn quickly from a net importer to a net exporter. In contrast, U.S. phosphate exports are booming. In the past 15 years, the U.S. export market has grown 16% annually, compared to an annual domestic increase of only 4%. In just the past two years, the U.S. share of world phosphate trade has grown from about a third to more than half. "Is it realistic to expect that we will continue to enjoy this level of export shipments?" Harre asks. He doesn't know. But he warns that the leading markets for U.S. fertilizer exports won't be the same in 1985 as they are today. "If we are to maintain the export tonnage levels that we have today, we must be looking for new market opportunities, rather than expecting them to come to us," he says. "There are too many other potential sources of supply for us to be complacent." •

Process may cut cost of coating solar cells A new process developed at Westinghouse Electric's R&D Center in Pittsburgh could lead to a low-cost method for applying an antireflective coating to silicon solar photovoltaic cells. Westinghouse speculates that the process could lead to a 10- to 20-fold reduction in the cost of coating mass-produced cells. Silicon solar cells need coatings to improve their efficiency. Uncoated, they reflect about 40% of the incident energy. By reducing reflection, the coating can improve efficiency 48%. Existing techniques for coating cells use vacuum sputtering and chemical vapor deposition—costly processes, Westinghouse notes, and not well suited to mass production. The process developed by Westinghouse researcher Bulent E. Yoldas is based, the company says, on a unique method of preparing coating solutions. With the process, cells can be spun or dipped in the solution. After application, the coating is baked for several minutes, leaving a glasslike oxide film on the surface. Yoldas notes that an antireflective coating must be highly transparent,

as well as stable in an outdoor environment. Also, the refractive index and thickness of the coating must meet certain conditions to be antireflective in the desired wave-length range. Minimum reflection from a silicon cell can be achieved, he says, by using an antireflective coating that is a quarter-wave-length thickness, with an index of refraction of about 2.0. With the new process, the index of refraction and thickness of the coating can be controlled precisely by changing the viscosity of the coating solution and varying the drawing or spin rate during coating. Besides lowering the amount of energy needed to make solar cells, the new process reduces waste. But Yoldas stresses that the process's simplicity and inexpensiveness are the most significant aspects. Westinghouse notes that current total costs for producing solar cells are about $11 per watt and that the Department of Energy's goal for 1986 is 50 cents per watt. Existing coating processes cost as much as 20 cents per watt. The new process would cost about 0.5 to 1 cent per watt. •