Environmental Engineering Reference
In-Depth Information
10
10
Geothermal Energy - Power
from the Deep
When planet earth came into being four billion years ago, its form was consider-
ably different from what it is now. At that time earth was in a partially melted
state. It was not until about three billion years ago that the temperature of the
earth's surface dropped to below 100 °C and the earth's crust gradually began to
harden.
It may not seem like it in the depths of a northern winter, but today our planet is
anything but a cold ball. About 99% of the earth is hotter than 1000 °C and 90% of
the rest has temperatures of over 100 °C. Fortunately for us, these high temperatures
are almost exclusively found in the earth's interior. Every so often volcanoes
produce impressive eruptions spewing molten matter from depths of up to 100 km
(Figure 10.1). Different technologies of plutonic geothermal energy enable us to tap
the heat of the earth's interior in a controlled way so that we can satisfy some of
our heat and electricity demands.
10.1 Tapping into the Earth's Heat
Earth itself is made up of concentric (Figure 10.2) bands comprising the core, the
mantle and the crust. The earth's core has a diameter of around 6900 km (4290
miles). A differentiation is made between the outer, liquid core and the inner core,
which is made of solid matter. Maximum temperatures in the earth's core reach
6500 °C, which is hotter than the surface of the sun.
