Harnessing sun's energy for industrial purposes

While most current uses for nuclear energy have been centered on supplying power for industry and the military, those for the applications of solar energy have been directed more toward the home or generating a modest electric power.

Yet for the last few years, Arthur Braundmeier, professor of physics at Southern Illinois University here, has been bucking the trend by doing basic research on the potential application of solar energy to industry.

Professor Braundmeier, in short, is seeking answers to some fundamental questions about ''high-temperature, photo-thermal solar energy absorbers.''

Until recently, his research was funded by both the Department of Energy and Southern Illinois, but now the DOE has pulled out.

''No one can deny,'' the professor says, ''that solar energy has two inherent advantages over both coal and nuclear energy: Its supply is virtually unlimited, and it has no attendant pollution or waste-disposal hazard.''

''The only absolutely safe way to dispose of nuclear waste,'' he asserted with a wry smile, ''would be to send it to the sun. But it would be a long and expensive garbage run - about 93 million miles.

''The Reagan administration wants to put most of its chips on nuclear energy, especially the breeder reactor, which I do not support. But I will continue my work even without DOE because I think I'm close enough to solving the materials problem for solar absorbers.''

Braundmeier notes with some satisfaction that Congress has been nudging the administration about its lax pursuit of solar energy, particularly that used by the photovoltaic cell, rather than by the absorbers that Braundmeier is working on.

In the past, Energy Department support enabled him to buy such things as a sophisticated vacuum-evaporator system with built-in computer in which intense heat and an almost total vacuum allow minute particles of copper or aluminum to move from a source to a target without colliding with any of the components of air.

Why that is important brings up the nature of Braundmeier's research.

Put in the most elementary terms, the professor is seeking materials that will collect or absorb the sun's energy and retain it; in other words, without immediately radiating it off again.

The catch is that such materials, to be feasible for industrial uses, must be able to withstand temperatures of 1,000 degrees F. over a period of 20 to 25 years. The 1,000-degree temperature derives from the generally established temperature at which steam is supplied to run the generators of industry.

Braundmeier envisions large collecting surfaces coated with some material that will both absorb and reflect solar energy. His particular search, therefore , has been for the proper material.

After trying many possibilities, he decided the best hope was a combination of two substances: copper oxide and either aluminum or copper, each having a characteristic complementary to the other; that is, where one transmits or absorbs while the other reflects or re-radiates. But at temperatures as high as 1,000 degrees F., adjacent metals tend to corrupt or diffuse into one another.

At this point the search became one for some third substance that could be placed between the two others to prevent high-temperature diffusion.

Braundmeier finally settled on aluminum oxide, or ''corundum,'' better known in its more exotic form as the semiprecious sapphire. (It may depress amateur gemologists to learn that the sapphire is mere aluminum oxide.)

''Quartz would also work as the insulator,'' the professor said, ''as would gold or platinum, but of course the latter two are ruinously expensive.''

Having isolated these optimum materials from many others, Braundmeier can now project how his solar collector would be built to operate.

Large panels would be coated with very thin layers of, first, aluminum, then sapphire, and finally with the copper oxide on top. Here, by ''thin'' he is talking in terms of microns, one-millionth part of a meter - or 0.0000039 inch. The aluminum on the bottom must be one micron thick; the sapphire, 0.10 micron thick; and the copper oxide, 0.5 micron thick. By way of comparison, a human hair is about 60 microns thick.

Coatings of such minute thinness can be laid down only by the use of the vacuum-evaporator system.

In a vacuum and under intense heat, minute particles of both copper oxide and aluminum will migrate or stream to another surface and be deposited there in thicknesses that can be monitored by a computer to the order of 0.10 to 1.0 micron. Thus the coatings of the solar collectors are prepared.

The sun's rays are then focused on the coated collectors by curved mirrors.

''The principle here,'' Braundmeier said, ''is the same one applied by any enterprising schoolboy when he learns he can burn a hole in his trousers by focusing the sun's rays through a magnifying glass. Simply, it gets hot. In such heat, the outer surface of copper oxide then becomes transparent, allowing the very short wavelength of the sun's rays to pass through the sapphire layer to the aluminum layer, which then re-radiates the sun's energy, not as light, but as the longer wavelength known as heat.

''You need to remember,'' the professor explained, ''that light and heat are merely different wavelengths of the same energy.''

The storing or transmitting of re-radiated heat for subsequent use is a phase of solar energy application that Braundmeier has not yet tackled. At the moment, he says, he will be content if his devising of suitable coatings for solar collectors proves a workable and efficient means of helping use the sun's energy to run the generators of industry.

As he pointed out, ''Oil is running out - at around $35 a barrel - and nuclear energy has yet to be produced in a manner that inspires widespread confidence in its safety.''

Before coming to Southern Illinois, Professor Braundmeier was a researcher for five years at the Oak Ridge Laboratory. There, he sat at the desk of Enrico Fermi, preserved exactly as the physicist left it in 1954.

''I was disappointed,'' Braundmeier said with a smile, ''that there wasn't some kind of chain reaction.''

The pun would have pleased Enrico Fermi.

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