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Except over time
scales of hundreds of years, geothermal energy
cannot strictly be regarded as a renewable energy
sources since though heat is being continuously
generated within the earth, the rate of its
build-up is much slower than any economical
extraction rate. On the other hand the scale of
the resources is vast.
Geothermal energy is the natural heat generated
from within the earth. Undemeath the earth’s
relatively thin crust, temperatures range from
1000 to 4000 C and in some areas, pressure exceeds
20,000 pounds per square inch (Psl). Geothermal
energy is most likely generated from radioactive
thorium, pot assium and uranium dispersed evenly
throughout the earth’s interior which produce heat
as part of the decaying process. Volcances, hot
springs, geysers and fumaroles are natural clues
as to the presence of geothermal resources near
the surface and perhaps where economic drilling
operations can tap their heat and pressure. About
10 percent of the worlds land mass contains
accessible geothermal resources and could provide
several million quads of energy annually.
Geothermal energy is derived using the earth’s
natural fluids to extract thermal energy that can
be sent through turbines to generate electricity
or be used directly e.g. direct heating and
industrial process heat. Conventional oil and gas
drilling methods are primarily used to extract
ge0thermal resources using harder drill bills to
combal corrosion and high temperature. As it is
uneconomical to transport the thermal energy over
long distances, the end use is often located near
the source.
Geothermal manifestations are widespread in India,
in the form of 340 hot springs sites. Large tracks
of hol ground waters with 15-20 excess
temperatures over mean ambient values, and high
bottom hole temperatures (140-200-C) recorded in
many of the boreholes drilled in various
sedimentary basins for hydrocarbons are known to
exist. These manifestations are localised in the
Himalayan Valley, Cambay. Fault Talta Pani (M.P.)
and many other places in Gujarat, Cambay Fault is
one of the promising areas. ONGC is formulating a
programme for hamessing Geothermal energy. |
