Copper was one of the first metals that mankind learned to refine and fashion. Thus, it should not be surprising that copper smelting may be one of the first major industrial uses of solar power.
While there are no immediate plans to use the sun's energy to refine ore into this soft, reddish, and vital metal, a study of a proposed major solar addition to an existing New Mexico smelter found that not only was this possible, but surprisingly cost-effective.
''I believe this is the first study of a major industrial application of solar energy with favorable enough economics to be of interest to private enterprise,'' announced Paul Curto of Gibb cf11& Hill Inc., a New York architect-engineering firm, at the annual meeting of the Solar Energy Industries Association being held here this week.
Gibb & Hill, which has designed a number of innovative industrial facilities, including a number of nuclear reactors, performed the study for the US Department of Energy . It involved the ''solarization'' of the Hidalgo copper smelter of Phelps-Dodge, one of the largest US producers of the metal.
At an estimated cost in 1986 of $400 million to $560 million, the proposed installation would involve the construction of a mile square array of mirrors which would focus the bright, New Mexico sun on a central tower. This would produce enough 1,000-degree-F. air to smelt copper ''365 days per year, 24 hours per day,'' Mr. Curto says.
At present, the Hidalgo smelter produces 106 million metric tons of copper a year, but takes 500,000 barrels of oil and 112 million kilowatt-hours of electricity to do so. With the addition of solar power, the refinery could produce twice as much copper while consuming only 81,000 barrels of oil and producing an excess 58 million killowatt-hours, which could be sold to a utility.
''We estimate that such an addition would pay for itself in less than two years,'' Mr. Curto says, adding, ''Even if the cost is twice what we calculate, the rate of return on the investment is a respectable 25-30 percent.''
The reason the economics looks so good, he admits, is in part because a number of efficiency measures not directly tied to solar also have been incorporated.
For instance, the process allows use of a different and more efficient ''flash'' type furnace. This could also be used in a coal-fired operation, but the rate of return looks substantially lower than when used with solar, Curto says.
To cut costs but allow solar power to provide year-around heat for the smelter, Gibbs & Hill hit on the idea of using slag from the smelter, covered by earth, to store enough heat to keep the plant operating for two to four sunless days.
Reliability, repair, and maintenance for the solarized smelter look about the same as those for a conventional operation, he estimates.
Unfortunately, Phelps-Dodge does not now have the money to build the world's first solar smelter, Curto reports. And it will not for another five years, when improvements on another smelter are finished. Also, budget cuts in the government's solar program mean that no follow-up studies of this promising application are possible.
Still, Curto says he believes that such an installation is just a matter of time. ''In this business, you don't see an innovative design built until you have gray hair,'' he observes wrily. He believes there are literally thousands of industrial applications where solar energy can be used economically.