Power Plant Engineering

86 POWER PLANT ENGINEERING

For a given pair of elements,

L

m

dW

d

&

= 0 which gives m = 1.

∴ W&L =

1

4

22

α−,10()

+

pn

pn

TT

RR

Maximum efficiency corresponding to max power,

ηmax, power =^10

1

TT

T

−

.

10

11

1

2 14

2

TT

TZT

−

−+

2.20 Geo Thermal Energy

We live between two great sources of energy, the hot rocks beneath the surface of the earth and
the sun in the sky. Our ancestors knew the value of geothermal energy; they bathed and cooked in hot
springs. Today we have recognized that this resource has potential for much broader application.
The term geothermal comes geo meaning earth and thermal meaning heat. Heat from the Earth,
or geothermal from the Greek — Geo (Earth) + thermal (heat) — energy can be and already is accessed
by drilling water or steam wells in a process similar to drilling for oil.
The core of the earth is very hot and it is possible to make use of this geothermal energy (in
Greek it means heat from the earth). These are areas where there are volcanoes, hot springs, and gey-
sers, and methane under the water in the oceans and seas. In some countries, such as in the USA water
is pumped from underground hot water deposits and used to heat people’s houses.
Geothermal energy is an enormous, underused heat and power resource that is clean (emits little
or no greenhouse gases), reliable (average system availability of 95%), and homegrown (making us
less dependent on foreign oil). The geothermal fields were first discovered in 1847 by William Bell
Elliot, an explorer surveyor who was hiking in the mountains between Cloverdale and Calistoga, Cali-
fornia, in search of grizzly bears. He discovered steam seeping out of the ground along a quarter of a
mile on the steep slope of a canyon near colb Mountain, an extinct volcano, now known as the Geysers.
The first application of geothermal energy was for space heating, cooking, and medicinal purposes.
The center of the earth is estimated at temperature up to 10,000 K due to decay process of
radioactive isotopes. The total steady geothermal energy flow towards earth's surface is 4.2 × 10^10 kW.
But the average flow energy is only 0.063 W/m^2.

The utilization of geothermal energy for the production of electricity dates back to the early part
of the twentieth century. For 50 years the generation of electricity from geothermal energy was con-
fined to Italy and interest in this technology was slow to spread elsewhere. In 1943 the use of geothermal
hot water was pioneered in Iceland.

The following general objectives of geothermal energy:
(1) Reduction of dependence on nonrenewable energy and stimulation of the state’s economy
through development of geothermal energy.