Environmental Engineering Reference
In-Depth Information
Strictly speaking, geothermal energy is not renewable.
Almost all of the applications are mining the heat that is
stored below the surface. The average heat
ow to the
surface is very small, only
.
watts per square meter, so
to produce the
MW of power that comes from the
Geysers geothermal
field in northern California would
require collecting the natural heat
flowing up from deep
in the Earth from
square
kilometers) of the surface. The collection area is much
smaller than that so the local high temperature heat res-
ervoir is being depleted slowly. Nevertheless, geothermal
energy is included in the renewables because there is a lot
of it and the total resource will last a very long time,
though individual power plants will become exhausted.
Hydrothermal systems have been in use for as long as
there has been life on Earth. The Rift Valley in Africa,
thought to be the cradle of humanity, has been a refuge
during the periodic ice ages that have punctuated the
evolution of humanity. From the temples of ancient
Greece, to the baths of Rome, to the spas of Europe, to
the National Parks of the United States, hot pools of
water have been important to humankind for relaxation,
medicinal purposes, and the heat that is available (Iceland
gets over
square miles (
% of the energy to heat its residences from its
hot springs). The
first use of geothermal energy for elec-
tricity production was in Italy in the early
s. Today,
the single largest geothermal power plant is the Geysers
in California.
The technology for electricity production is well
developed and new plants are being built wherever there
is a good source of hydrothermal energy. There are envir-
onmental
issues, and some care has to be taken in
