2. Source of Geothermal Energy
• Geothermal energy is a renewable and sustainable power source that comes from the heat
generated by magma from the earth’s core. "Geo" means earth and "thermal" means heat.
• The Earth has four main layers, where each layer has different compositions, functions and
temperatures, as is illustrated in the two figures below. Sometimes magma reaches the surface of
the crust and is then called lava. The magma reaches the crust and heats nearby rocks and water.
The heated water can reach the surface and form hot springs and geysers.
• In volcanic areas, magma heats reservoir of water available beneath the surface and forms steam.
Large amount of steam with relatively high pressure is formed in the reservoir, and this is the source
of geothermal energy.
3. Geothermal Power Plant
• Geothermal power plants are used all over the world, but can not be located just
anywhere. They are located in the areas of volcanic activity, where large amount of
steam is available from heated ground water reservoir. .
• Geothermal energy is produced by drilling a well into the ground where thermal activity is occuring.
The steam from the ground flows to the surface by it’s pressure. The steam is the separated from
the water and other impurities (sulfur, dirt, etc), before it is used to drive a turbine engine which turns
a generator. Usually the water is injected back into the ground to maintain the water availability in
the reservoir. The picture below illustrates how the set-up of a geothermal power plant
4. • Geothermal power plants use thermodynamics Rankine Cycle, to convert thermal energy from the
steam into mechanical energy which then converted into electrical energy by the generator.
• Typical installation diagram and Rankine Cycle for a geothermal power plant is shown in the figures
below.
Steam
Purification
Steam
from the
Well
Water
back to
the Well
Water and
Steam Well 0 2 4 6 8 10 1212
0
100
200
300
400
500
s [kJ/kg-K]
T[C]
6000 kPa
10 kPa
Rankine Vapor Power Cycle
1
2
3
4
23
Steam
Purification
Plant
5. Types of Geothermal Power Plant.
There are three types of Geothermal Power Plant technology.
1. Dry Steam Power Plants
2. Binary Cycle Power Plants
3. Flash Steam Power Plants
Dry Steam Power Plant
The characteristics of Dry Steam Power Plant are,
• Vapor dominated resources where steam
production is not contaminated
• Steam is 500°C - 650°C
• Steam directly passes through turbine
• Need water to inject down into rock
• Well is deep
6. Binary Cycle Power Plants
The characteristics of Binary Cycle Power Plant are,
• Uses lower-temperatures, usually hot water resources (40° C – 160° C).
• Hot water is passed through a heat exchanger in conjunction with a secondary fluid with a lower boiling point (usually
a hydrocarbon such as isobutane or isopentane).
• Secondary fluid vaporizes, which
turns the turbines and drive the generators.
• Remaining secondary fluid is simply
recycled through the heat exchanger.
• Geothermal fluid is condensed and
returned to the reservoir.
• Lower-temperature reservoirs are
far more common, which makes
binary plants more prevalent.
7. Flash Steam Power Plants
The characteristics of Dry Steam Power Plant are,
• Use very hot (more than 150° C) steam and hot water resources
• Steam either comes directly from the resource, or the very hot, high-pressure water is depressurized
("flashed") to produce steam.
• Steam then turns turbines, which drive generators that generate electricity.
