Power from Earth's Heat

Dr. Nikola Tesla, whose series of inventions have proved of such importance to mankind that he has always to be taken seriously, makes announcement through the December issue of Everyday Science and Mechanics that he has designed two new power plants, one to utilize the heat below the surface of the earth, the other to take advantage of the difference in temperature between the upper and lower levels of the ocean in tropical regions.

It will be recalled that down in Cuba last year Professor Georges Claude of Paris constructed on Matanzas Bay a power plant that actually operated by means of pumping up the cold water from below the warm. He termed it purely an experiment, and conceded that it would have to be developed greatly before it could be commercially practical. Dr. Tesla now expresses the belief that the Claude plan cannot be made commercially profitable, and he has devised a radically different plan to meet the main objections. Primarily, this seems to be the construction of a tunnel to meet the cold water at the bottom, instead of pumping it up to ground level. However, as in the Claude plan, the scheme will be useful only in tropical regions.

Thus it is with the Tesla scheme for getting power out of the bowels of the earth that we have chief concern, for right here in Rome we may have it in operation within a few years — providing the machinery works as well in practice as in theory. As is well known, even in cold climates the lower one goes below the surface the hotter the temperature, until a very great heat is obtained. Comparing his land machinery with his water plant, Tesla writes:

Instead of placing the boiler at the bottom of the shaft, and so limiting the influx of heat, I utilize the heat flowing into the whole shaft which is many times greater, of course, to generate steam. The arrangement is of ideal simplicity. The steam is drawn from the bottom of the shaft through a heavily insulated pipe to a turbine on level ground. From the turbine the steam is discharged into the condenser and the condensed water flows by gravity through another insulated pipe reaching to a depth at which the temperature of the ground exceeds that of the condensate.

By circulating the steam in great volume through the turbine and condenser I am able to maintain a considerable temperature difference between the ground and the interior of the shaft, so that a very great quantity of heat flows into the same continually to be transformed into mechanical work. The only requisite is a sufficient volume of condensing water, and this problem is the more easily satisfied the colder the climate.

Instead of water, of course, I may use a volatile fluid, such as ether, for a working medium, and in this case the difficulties of condensation are greatly reduced.

By his method, Tesla declares it practicable to supply all the power which a small community may require from a shaft of moderate depth, "certainly less than a mile." And for isolated dwellings a "few hundred feet" would be ample. He has been engaged for some time in making estimates of costs of installation and finds that "it would not be prohibitive by comparison with other sources of power."

For many a year engineers and amateurs have sought to make use of the sea as power after some other manner than the tide mills which used to be so familiar upon our coasts. Usually it has been the resistless power of the waves that has inspired experiments; but both Claude and Tesla depart from that. In a certain California county a few years ago small geysers were harnessed for power; but that is not Tesla's plan either. It is the combination of high and low temperatures in connection with a vacuum.