Geothermal Power
A way into the future?
Jonathan Bailey
24th February 2005
Outline
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Introduction
What is geothermal energy?
Utilization of geothermal energy
The Southampton CHP Scheme
Projections
Introduction
• Developments in alternative energy sources
sparked by
– Threats of traditional energy resource exhaustion
– Drive to self-sufficiency
– Growing concern for the environment
• Drive to find alternative energy sources that are
widely available, versatile, renewable, and have
limited impact on the environmental
Traditional Utilization of
Geothermal Energy
• Natural releases of geothermal energy have
been utilized for centuries:
– Balneology
• Healing
• Hygiene
– Domestic services (e.g. Cooking, laundry)
• Native New Zealanders
– Mineral extraction
• geothermal water can contain useful minerals
– Boric acid, sulfur, vitriol or aluminum
• Ex. Etruscans extracted boric acid from boiling springs and
used it for making enamels
What is Geothermal Energy?
• Heat generated by
natural processes
occurring within the earth
• Hot springs and mud pots
are natural phenomena
that result from
geothermal activity
Photo: www.geothermal.marin.org/
Where Can Geothermal Energy
be Harnessed?
• Technology today allows
for small scale
harnessing everywhere
– Heat pumps
• Different areas have
different thermal
gradients and thus
different utilization
potentials
• Higher thermal gradients
correspond to areas
containing more
geothermal energy
•
Photo: www.geothermal.marin.org/
What is Geothermal Energy?
• The centre of the Earth is around 6000 degrees
Celsius - hot enough to melt rock. Even a few
kilometres down, the temperature can be over
250 degrees Celsius. In general, the
temperature rises one degree Celsius for every
36 metres you go down. In volcanic areas,
molten rock can be very close to the surface and
in such areas geothermal energy has been used
for thousands of years for cooking and heating.
Geothermal Fields
• Geothermal field - thermal area where
permeable rock formations below ground
contain a working fluid without which the area
could not be exploited (Armstead, 1978)
• Geothermal field characterizations:
– Semi-thermal field- produces water up to 100oC
from drilling depths of 1-2 km
– Wet hyper-thermal field (water-dominated)produces pressurized water > 100oC
– Dry hyper-thermal field (vapor-dominated)produces dry saturated, or slightly superheated
steam at P > Patm
• By exploiting geothermal fields, particularly
hyper-thermal fields, geothermal energy can
be harnessed on a large scale
Geothermal Fields: Expected
Locations
• Semi-thermal fields typically found in
areas having abnormally high temperature
gradients
• Hyper-thermal fields generally located at
tectonic plate boundaries in seismic zones
Energy Utilization: SemiThermal Fields
• Hot fluid exploited from semi-thermal
fields can be directly transported to
needed areas by intricate systems of
pipes
– District heating – e.g. Southampton
• Uses heat exchanger
– Farming applications
– Industrial usages
Geothermal Usages
• Semi-thermal fields
– District heating
• Building/hot water heating
• Sidewalk clearing
– Farming applications
• Ex. Greenhouses in Iceland
– Industrial usages
• Hyper-thermal fields (supply high grade heat)
– Electric Power Generation
Photo: Sitewalk in Klamath Falls, Oregon (www.geothermal.marin.org/)
Currently…
• Individual power plants operate at capacities
ranging between 100kW and 100MW (World
Bank, 2004)
– Dependent on energy resource and power demand
• Over 8200 megawatts of electricity from
geothermal plants supply energy to 60 million
people in 21 countries (Nemzer, 2001)
– most countries classified as developing nations
Uses of Geothermal Energy
• There are three main
ways of tapping
geothermal energy:
1) Direct use:
Geothermal heat found
near the surface of the
Earth can be used
directly for heating
buildings (CHP), like the
programme in
Southampton
2) Electricity production:
• There are three types of power plant that
can convert geothermal energy to
electricity, depending on the temperature
of the geothermal fluid used. All three use
a turbine that is driven by steam, which
then drives a generator to produce
electricity.
Electricity Generation
– Thermal energy associated with high temperature
fluids extracted from hyper-thermal fields may be
converted into mechanical work and then electricity
(Wahl, 1977)
– Thermal energy is converted into mechanical work by
expanding hot fluid
– Electrical energy generally produced by a generator
powered by an expansion machine producing
mechanical work in the form of a rotating shaft
– Expansion machines
• Steam turbines
• Piston-driven engines
3) Geothermal heat pumps
The relatively constant temperature of the top 15
metres of the Earth's surface (or ground water)
can be used to heat or cool buildings indirectly.
The pump uses a series of pipes to circulate
fluid through the warm ground. When the ground
is warmer than the buildings above, the liquid
absorbs heat from the ground, which is then
concentrated and transferred to the buildings.
This can also be used to heat domestic water.
However, is this solar or geothermal energy?
Solar or Geothermal??
• While geothermal resources are not
spread uniformly, heat pumps can be used
nearly anywhere. This answers the
question that using a heat pump uses
solar energy, as they can be used in
places where no geothermal energy is
available!
Geothermal in the U.K
• The red areas shown in
the figure, are areas of
the United Kingdom that
are available to place
geothermal plants.
However, inside our
island, we would only be
able to introduce
programmes like that of
Southampton. As we are
only a semi-thermal field
zone
The Southampton Scheme 1
The geothermal heat provided by the well is used as part of Southampton's
District Heating scheme , where it works in conjunction with the Combined Heat
and Power scheme. Geothermal energy provides between 15-20% of the total
heat-input into this scheme.
The combined heat and power generators use conventional fuels to make
electricity. "Waste heat" from this process is recovered for distribution through
the 11km mains network. The district heating scheme in Southampton helps
reduce energy bills by 25% and the city's CO2 omissions by 10kt a year. It
closely resembles a huge domestic central heating system, with hot, treated
water circulating underground from the heat station.
The Southampton Scheme 2
• The borehole is non-polluting (at the moment the used
brine is being pumped into the River Test) and costs little
to run. The scheme produces enough electricity from its
own generator to fuel itself, and there is electricity left
over to sell to the electricity board.
The Southampton Scheme 3
• Launched in 1986
• Water is found at a
depth of nearly
1.8km and at a
temperature of
76ºC
• Saved 180kt CO2
going into
atmosphere since
opening!
Sadly we cannot have anything as big as
this in the UK.
The Problems Are?
• As the U.K. is only on a
semi-thermal field we
cannot rely upon its
resource as a way into
the future. The plants we
would open in the coming
years would provide:
• A) A 25% reduction in
CO2 emissions for the
areas in question but for
how long?
• At best guess a plant
opened in the next year
would be open for the
next 25, this would be self
sufficient, but not effect
our overall energy needs,
as the plant would
provide heating/cooling to
around 10-20 large
buildings. This on the
greater scheme of things
would have no effect.
Projections: 0 PJ a fair number?
A Graph to Show Projections for Geothermal
Electricity Generation in the Future
120
GJ value
100
80
60
40
20
0
2000
2005
2010
2015
2020
Time (Year)
2025
2030
2035
Projections Explained
• Values in GJ as PJ values too small to
graphically show.
• The demand value for 2003 was 9914.8PJ so an
input of 0.00008208PJ from a possible
geothermal source proves insignificant and this
source is therefore not worth investing in!
• References
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Books
Armstead, H. C. 1978. Geothermal Energy. John Wiley and Sons: New York, p. 1-12, 39-41,
61-141
Carrington, G. 2002. Basic Thermodynamics. Oxford University Press: New York, p. 31-39.
Collie, M. J. 1978. Geothermal Energy: Recent Developments. Noyas Data Corporation:
New Jersey, p. 35-70, 98-104.
Gupta, H. K. 1980. Geothermal Resources: An Energy Alternative. Elsevier Scientific
Publishing Company: New York, p. 51-98
Veziroglu, T. N. 1977. Alternative Energy Sources: An International Compendium.
Hemisphere Publishing Corporation: New York, p.2577-2598
Veziroglu, T. N. 1980. Alternative Energy Sources III, Volume 4, Indirect Solar/Geothermal
Energy. Hemisphere Publishing Corporation: New York, p. 471-487.
Wahl, E. F. 1977. Geothermal Energy Utilization. John Wiley and Sons: New York, p. 170181.
Websites
The World Bank Group. 2004. Geothermal Energy. Available at
http://www.worldbank.org/html/fpd/energy/geothermal/. Last accessed April 7, 2004.
US Department of Energy. 2004. Geothermal Technologies Program. Available at
http://www.eere.energy.gov/geothermal/. Last accessed April 7, 2004.
Geothermal Education Office. 2001. Introduction to Geothermal Energy Slide Show.
Available at http://geothermal.marin.org/GEOpresentation/. Last accessed April 7, 2004