Science: Sun Power in the Pyrenees

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Far too huge to follow the sun itself, the parabolic reflector depends on the help of 63 smaller mirrors set in eight rows on a terraced slope in front of it. Called heliostats (from the Greek helios, sun; statos, to cause to stand still), they track the solar disk across the sky, capture its light and bounce it in parallel beams into the big mirror. The system involves some ingenious engineering. Each heliostat is controlled by its own photoelectric cells. Whenever one of the hehostats (each of which is made 180 individual mirrors) loses its lock on the sun, these tiny electric eyes inform a minicomputer, which in turn controls a pair of hydraulic pumps that can rotate and tilt the heliostat into th proper position. Only one manual ad justment is needed to operate the heliostats. It is made at the end of the day, when they must be reset to face the position of the next day's sunrise.

Rotating Vats. The crucible of the furnace is located inside a smaller f-shaped building near the base of the big mirror. It is set behind large stainless-steel doors at the focal point of the parabola—where the sun's scorching rays are concentrated into a blazing circle only twelve inches wide. Target material, hoisted into place by a ten-ton lift, is placed into an inclined trough-as the target melts, it runs off into catch pans. Another, more sophisticated technique is to load the material into two aluminum vats whose outer walls are water-cooled to prevent melting. Placed with their open ends at the focal point and rotated like washing machines to distribute the heat evenly, these containers can hold up to 21 tons of molten material at one time.

Is all this elaborate effort worth the French government's $2,000,000 investment in the furnace? Trombe says yes.

For one thing, the power is almost entirely free (only 13 kilowatts of electricity are needed to operate the mirrors). More important, the furnace gives off what he calls "aristocratic" or uncontaminating heat; there is, for example, none of the adulterating carbon that is produced by the hot electrodes in ordinary high-intensity electric arc furnaces. Thus the solar oven is ideal for the production of chemically pure materials.

French industry is beginning to agree In a recent test for an electronics manufacturer, the furnace fused several tons of bauxite and ceramics to produce high-voltage insulators of unmatched purity The oven could easily fuse other highly heat-resistant materials: quartz crystals for radio transmitters, corundum for industrial grinding stones and zircon parts for nuclear reactors. It could also be used in experiments to develop new space-age alloys, such as special tungsten or cobalt steels, and even materials to withstand the searing heat of a nuclear blast.