From:
THE PROBLEM OF INCREASING HUMAN ENERGY. WITH SPECIAL REFERENCES
TO THE HARNESSING OF THE SUN'S ENERGY. BY NIKOLA TESLA. ENERGY
FROM THE MEDIUM -- THE WINDMILL AND THE SOLAR ENGINE, --MOTIVE
POWER FROM TERRESTRIAL HEAT -- ELECTRICITY FROM NATURALSOURCES.
Besides fuel, there is abundant material from which we might
eventually derive power. An immense amount of energy is locked
upin limestone, for instance, and machines can be driven by liberating
the carbonic acid through sulphuric acid or otherwise. I once
constructed such an engine, and it operated satisfactorily.
But, whatever our resources of primary energy may be in the
future, we must, to be rational, obtain it without consumption
of any material. Long ago I came to this conclusion, and to arrive
at this result only two ways, as before indicated, appeared possible--either
to turn to use the energy of the sun stored in the ambient medium,
or to transmit, through the medium, the sun's energy to distant
places from some locality where it was obtainable without consumption
of material. At that time I at once rejected the latter method
as entirely impracticable, and turned to examine the possibilities
of the former.
It is difficult to believe, but it is, nevertheless, a fact,
that since time immemorial man has had at his disposal a fairly
good machine which has enabled him to utilize the energy of the
ambient medium. This machine is the windmill. Contrary to popular
belief,the power obtainable from wind is very considerable. Many
a deluded inventor has spent years of his life in endeavoring
to "harness the tides," and some have even proposed
to compress air by tide- or wave-power for supplying energy,
never understanding the signs of the old windmill on the hill,
as it sorrowfully waved its arms about and bade them stop. The
fact is that a wave- or tide-motor would have, as a rule, but
a small chance of competing commercially with the windmill, which
is by far the better machine, allowing a much greater amount
of energy to be obtained in a simpler way. Wind-power has been,
in old times, of inestimable value to man, if for nothing else
but for enabling him, to cross the seas, and it is even now a
very important factor in travel and transportation. But there
are great limitations in this ideally simple method of utilizing
the sun's energy. The machines are large for a given output,
and the power is intermittent, thus necessitating the storage
of energy and increasing the cost of the plant.
A far better way, however, to obtain power would be to avail
ourselves of the sun's rays, which beat the earth incessantly
and supply energy at a maximum rate of over four million horsepower
per square mile. Although the average energy received per square
mile in any locality during the year is only a small fraction
of that amount, yet an inexhaustible source of power would be
opened up by the discovery of some efficient method of utilizing
the energy of the rays. The only rational way known to me at
the time when I began the study of this subject was to employ
some kind of heat- or thermodynamic-engine, driven by a volatile
fluid evaporate in a boiler by the heat of the rays. But closer
investigation of this method, and calculation, showed that, not
withstanding the apparently vast amount of energy received from
the sun's rays, only a small fraction of that energy could be
actually utilized in this manner. Furthermore, the energy supplied
through the sun's radiations is periodical, and the same limitations
as in the use of the windmilI found to exist here also. After
a long study of this mode of obtaining motive power from the
sun, taking into account the necessarily large bulk of the boiler,
the low efficiency of the heat-engine, the additional cost of
storing the energy and other drawbacks, I came to the conclusion
that the "solar engine," a few instances excepted,
could not be industrially exploited with success.
Another way of getting motive power from the medium without
consuming any material would be to utilize the heat contained
in the earth, the water, or the air for driving an engine. It
is a well-known fact that the interior portions of the globe
are very hot, the temperature rising, as observations show, with
the approach to the center at the rate of approximately 1 degree
C. for every hundred feet of depth. The difficulties of sinking
shafts and placing boilers at depths of, say, twelve thousand
feet, corresponding to an increase in temperature of about 120
degrees C., are not insuperable, and we could certainly avail
ourselves in this way ofthe internal heat of the globe. In fact,
it would not be necessary to go to any depth at all in order
to derive energy from the stored terrestrial heat. The superficial
layers of the earth and the airstrata close to the same are at
a temperature sufficiently high to evaporate some extremely volatile
substances, which we might use in our boilers instead of water.
There is no doubt that a vessel might be propelled on the ocean
by an engine driven by such a volatile fluid, no other energy
being used but the heat abstracted from the water. But the amount
of power which could be obtained in this manner would be, without
further provision, very small.
Electricity produced by natural causes is another source ofenergy
which might be rendered available. Lightning discharges involve
great amounts of electrical energy, which we could utilize by
transforming and storing it. Some years ago I made known a method
of electrical transformation which renders the first part of
this task easy, but the storing of the energy of lightning discharges
will be difficult to accomplish. It is well known, furthermore,
that electric currents circulate constantly through the earth,
and that there exists between the earth and any air stratum...
End of excerpt
Nikola Tesla
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