Solar Engine

Coincident with his 47th birthday last week, Professor Robert Hutchings Goddard, Clark University rocket inventor (TIME, July 29), disclosed his invention of a sun engine. His laboratory model consists of a parabolic mirror one foot in diameter, which focuses sunlight upon a hollow glass sphere five-eighths of an inch in diameter. The sphere contains water and finely divided carbon. The focused light passes through the clear water without heating it. But when the light strikes the opaque carbon, the carbon heats almost instantly and in turn heats the water, which turns to steam. The steam escapes through a hole in the top of the sphere, whence it could be piped to operate a steam piston, and so an engine.

For practical operation Professor Goddard suggested last week a mirror 20 feet in diameter focusing on a boiler with a fused quartz base. The boiler would contain, instead of pulverized carbon, mercury sprayed continuously at the focus point of the reflected light. The mercury spray would turn instantly to mercury vapor and in turn vaporize the water which would operate a steam turbine. The turbine would operate an electric generator. Efficiency of such a sun engine would be 50% of the sun energy fused.* Professor Goddard calculates that such an engine would produce 30 h.p. while operated under a clear sky between 10:00 a.m. and 3:00 p.m., when sunlight is strongest in the U. S. If storage batteries were used, the owner could get an average of 4 h.p. per hour day & night, all year around.

Director Dr. Charles Greeley Abbott of the Smithsonian Institution has worked on sun engines. There is one, the Eaneas, working at low efficiency at Pasadena, Calif. At Meadi, near Cairo, Egypt, the Shumann engine produces 60 h.p. Its reflectors cover an acre. If an efficient and practical sun engine can be built, its sun source of energy is not only free but stupendous in quantity. The energy falling on a square mile of earth on a bright sunny day with a clear atmosphere is equivalent to two or three million horsepower. According to Dr. Abbott the sun energy reaching the whole earth each day equals the caloric value of 507 billion tons of coal.

* The best steam turbine now operating is only 25% efficient.