CHEE2695 – Lecture 14
Geothermal energy:
- The source of geothermal energy is heat from the original formation of the
earth, 4.5 billion years ago, plus heat from radioactive decay.
- This heat is being lost to space. When we use a geothermal resource deep in
the earth, we speed up this process.
Geothermal heat transfer:
- This is a mixture of convection, conduction, and radiation. Convection
processes drive plate tectonics.
- Geothermal heat replaces the coal combustion step for electricity generation.
Geothermal efficiency:
- Electricity generation from heat is limited by thermodynamics.
- The Carnot efficiency is an example of the maximum possible mechanical
work able to be done by a system based on temperature (in Kelvin) of the
heat source.
TC
η=
TH
Geothermal potential:
- Geothermal energy has had a relatively slow uptake.
- Different regions have different types and grades of heat energy available.
- The three main types of geothermal energy are:
o Water vapour (dry-steam reservoir),
o Liquid water (hot-water reservoir),
o High temperature rocks (hot-dry-rock reservoir).
- The type of reservoir depends on the presence of a fluid, temperature, and
pressure.
- The energy stored in these reservoirs can be used in power cycles, or if T <
100oC, as hot water, it can be used to increase efficiency of power stations,
i.e., as boiler feed water.
Dry-steam reservoir:
- This is the most useful, and least prevalent of the types of geothermal energy.
Geothermal energy:
- The source of geothermal energy is heat from the original formation of the
earth, 4.5 billion years ago, plus heat from radioactive decay.
- This heat is being lost to space. When we use a geothermal resource deep in
the earth, we speed up this process.
Geothermal heat transfer:
- This is a mixture of convection, conduction, and radiation. Convection
processes drive plate tectonics.
- Geothermal heat replaces the coal combustion step for electricity generation.
Geothermal efficiency:
- Electricity generation from heat is limited by thermodynamics.
- The Carnot efficiency is an example of the maximum possible mechanical
work able to be done by a system based on temperature (in Kelvin) of the
heat source.
TC
η=
TH
Geothermal potential:
- Geothermal energy has had a relatively slow uptake.
- Different regions have different types and grades of heat energy available.
- The three main types of geothermal energy are:
o Water vapour (dry-steam reservoir),
o Liquid water (hot-water reservoir),
o High temperature rocks (hot-dry-rock reservoir).
- The type of reservoir depends on the presence of a fluid, temperature, and
pressure.
- The energy stored in these reservoirs can be used in power cycles, or if T <
100oC, as hot water, it can be used to increase efficiency of power stations,
i.e., as boiler feed water.
Dry-steam reservoir:
- This is the most useful, and least prevalent of the types of geothermal energy.
