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Report 5 (of 5): Full Steam
Ahead - Italy
Introduction
Natural heat within the Earth, accessible
in many parts of the world, provides a clean, reliable
and underused heat and power source. This is geothermal
energy and the third most widely used form of renewable
energy, after hydroelectricity and biomass (e.g. wood).
Geothermal resources range from hot
water and rock a few miles below Earth's surface,
to the extremely high temperatures of molten rock
called magma which is usually many miles below the
surface. Where shallow high temperatures exist, groundwater
is heated to form steam or hot water. Technologies
that use geothermal energy include heat pumps, direct
use applications such as heating and industrial processes,
and power plants.
In more than 30 countries around the
world geothermal resources provide directly used heat
capacity of 12,000 megawatts (MW) and electric power
generation capacity of over 8,000 MW. Geothermal energy
meets a significant amount of the electrical power
demand in many developed and several developing countries.
Geothermal Resources
Geothermal resources form where rainwater
seeps deep into the Earth through rock below the surface.
As the rock is heated by hot magma from the Earth's
core, the water begins to heat up. Some of this hot
water travels back up to the surface through faults
and cracks and can appear as hot springs or geysers.
The rest stays deep underground, trapped in cracks
and porous rock. This natural collection of hot water
is called a geothermal reservoir.
Geothermal reservoirs can sometimes
be identified by studying the Earth's surface and
by shallow drilling, but a large proportion need to
have the potential energy supply confirmed by drilling
deeper wells.
High temperature geothermal resources,
of 220°C (428°F) and higher, are mainly found in volcanic
regions and on islands. Moderate to low temperature
resources are found on all continents.
Advantages of Geothermal Energy
Geothermal energy has many advantages
over that derived from burning fossil fuels such as
coal, gas, or oil.
- It is a clean source of energy
that can be harnessed without burning a fossil fuel.
Geothermal fields produce only about one-sixth of
the carbon dioxide that a natural-gas-fuelled power
plant produces. It also produces hardly any nitrous
oxide or sulphur gases.
- Geothermal energy is available
every hour of every day. Geothermal power plants
have an average availability of 95 per cent or higher,
compared to 60-70 per cent for coal and nuclear
plants.
- Geothermal power is produced locally,
which reduces dependence on foreign oil.
- It is a renewable source of energy
with a virtually unlimited amount of heat generated
by the Earth's core.
- As the world's largest energy resource,
geothermal energy can be inexhaustible. The resource
is constantly replenished by circulating groundwater.
If the fluids are extracted at a sustainable rate,
the resource will be available for future generations.
- Even in geothermal areas dependent
on a reservoir of hot water, the volume taken out
can be reinjected, making it a sustainable energy
source.
Geothermal technologies offer many
environmental advantages over conventional power generation.
- Power plant emissions are low,
averaging approximately 5 per cent of the emissions
from equivalent fossil fuel power plants
- Salts and dissolved minerals sometimes
contained in geothermal fluids are usually reinjected
with excess water back into the reservoir. This
recycles the geothermal water and replenishes the
reservoir. The system will prolong the life of the
reservoir as it recycles the wastewater and also
maintain aquatic life.
- Some geothermal plants produce
solid materials, or sludges, that require disposal
in approved sites. Some of these solids, such as
zinc and sulphur, are now being extracted for sale,
making the resource more valuable and environmentally
friendly.
- Geothermal plants do not require
extensive land development, nor do they require
storage and transportation of fuels.
Uses of Geothermal Heat
Many countries around the world exploit
geothermal resources to significantly reduce consumption
of imported fossil fuels. In the west of Italy there
is a long belt of land in the Tuscany region and extending
as far south as Campania, near Naples, where very
high temperatures, often exceeding 200°C (392°F),
are located not far below the surface. Geothermal
energy has been used here ever since 1865 when the
first pumps propelled with geothermal steam were installed.
Currently the geothermal energy produced
in Larderello, in Tuscany, provides around two million
households with heating, as well as supplying heat
to greenhouses and fish farms, satisfying a great
part of the energy needs of the Tuscany region.
In Larderello, the local swimming pool
has re-opened after many years of closure and features
a brand-new geothermal heating system. New greenhouses
have been built in the Radicondoli area, and an industrial
plant for the processing of dairy by-products has been
set up in Carboli, in the southernmost part of the Larderello.
The long-term sustainability of geothermal
production has been demonstrated by continuous electrical
power generation in Larderello since 1913, when a
250 kW power station supplied power to the Italian
railway system. Italy is now the fourth largest producer
of geothermal energy in the world. Approximately 2
per cent of its population is provided with energy
from geothermal sources.
Table 1: Summary of geothermal energy
uses
| Reservoir temperature |
Resource type |
Common Use |
Technology commonly chosen
|
High
220°C and above
428°F and above |
Water or Steam |
Power generation
Direct use |
- Flash Steam
- Combined (flash and binary
cycle)
- Direct use
- Heat exchangers
- Heat pumps
|
Moderate
100-220°C
212-430°F |
Water |
Power generation
Direct use |
- Binary cycle
- Direct use
- Heat exchangers
- Heat pumps
|
Low
50-150°C
122-302°F |
Water |
Direct use |
- Direct use
- Heat exchangers
- Heat pumps
|
Heat exchangers are used to extract
the heat from the hot geothermal fluid. As this fluid
often contains chemicals, it cannot be used directly
in drying processes or where clean steam or hot water
is necessary. Heat exchangers transfer the heat either
to clean water or, in the case of drying processes,
to air.
High temperature sources are almost
always used for power production. Individual geothermal
power plants can be as small as 100 kilowatts (kW)
or as large as 100 MW, depending on the energy resource
and power demand. The technology is suitable for rural
electrification and mini-grid applications in addition
to national grid applications.
Most low temperature sources are used
for direct heating purposes or agriculture and aquaculture.
For such direct use technologies, since geothermal
heat is non-transportable (except short distances
by pipeline), any applications must generally be sited
within 10 km (about six miles) of the resource. Pumps
are frequently used to carry the water to the surface.
Low temperature sources can provide
useful energy for heating buildings and for agricultural
and industrial processes. Such heat can also be available
as a by-product of geothermal power generation.
This energy is used for agriculture
and aquaculture. In temperate and colder climates,
greatly improved plant and fish growth can be achieved
by heating soils, greenhouses and fishponds using
geothermal heat. It can also be used for medicinal
purposes and balneology, the practice of using natural
mineral water for the treatment and cure of disease,
such as in spa pools.
Agriculture
Thermal water can be used in open-field
agriculture to irrigate and/or heat the soil and also
to sterilise soil. Geothermal heat can also be used
for crop and timber drying.
The main advantages of temperature
control in open-field agriculture are:
- the prevention of plant damage
from low air temperatures;
- extension of the growing season;
- increased plant growth and production;
and
- soil sterilisation that controls
pests and diseases.
Greenhouses
Greenhouse heating is a common use
of geothermal energy. Glass or plastic film is used
to trap solar radiation and heat, which provides a
controlled environment for plants to grow and increase
yields. Many commercially grown vegetables, flowers,
house plants and tree seedlings are suitable for greenhouse
culture.
Aquaculture
Aquaculture is the farming of aquatic
organisms including fish, molluscs, crustaceans and
aquatic plants. Farming implies some sort of intervention
in the rearing process to enhance production, such
as regular stocking, feeding, and protection from
predators. In geothermal aquaculture the objective
is to heat the water to the optimum temperature for
fish growth. An emerging aquacultural industry is
the cultivation of vegetable species that can be adapted
for human and animal foods. Crops adaptable to geothermal
enhanced growth include duckweed, numerous algae species
and kelp.
Industrial applications
Geothermal energy can be cost effective
and reliable in industrial applications. Some industries
use steam, or superheated water, and starting with
warm water obviously reduces the amount of heat required.
The largest industrial applications are in pulp, paper
and wood processing.
Heating and cooling
Geothermal heat pumps enable the resources
to be used economically. Ground-coupled heat pumps
use earth-temperature soil for heating during winter,
cooling during summer, and supplying hot water year-round.
Water-to-air heat pumps exchange heat with groundwater,
surface water or water passed through cooling towers
for industrial and commercial uses.
Power Generation
Most power plants use steam to generate
electricity. The steam rotates a turbine, which activates
a generator that produces electricity. Many power
plants still use fossil fuels to boil water for steam.
Geothermal power plants as small as 100 kW, but commonly
between 1 and 5 MW, can provide distributed generation
on larger power grids or a major generation source
for smaller power grids. Plants with generation units
up to 100 MW in size are connected to national power
grids and tend to operate on a continuous basis.
There are three types of geothermal
power plants: dry steam, flash steam, and binary cycle.
Dry steam
Dry steam power plants draw from underground
resources of steam. The steam is piped directly from
underground wells to the power plant, where it is
directed into a turbine/generator unit.
Flash steam
Figure 1. A Flash Steam Power Plant © WorldBank
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Flash steam power plants are the most
common. They use geothermal reservoirs of water with
temperatures greater than 182°C (360°F). This very hot
water flows up through wells in the ground under its
own pressure. As it flows upwards, the pressure decreases
and some of the hot water boils into steam. The steam
is then separated from the water and used to power a
turbine/ generator. It is a sustainable resource because
any leftover water and condensed steam are injected
back into the reservoir.
Binary cycle
Figure 2. A Binary Cycle Power Plant © WorldBank
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Binary cycle power plants operate on
water at lower temperatures of around 107°-182°C (225°-360°F).
These plants use the heat from the hot water to boil
a working fluid, usually an organic compound with a
low boiling point. The working fluid is vaporised in
a heat exchanger and used to turn a turbine. The water
is then injected back into the ground to be reheated.
The water and the working fluid are separate during
the whole process, so there are virtually no air emissions.
The Future of Geothermal Energy
Thanks to geothermal energy, millions
of tonnes of fossil fuels are being saved worldwide
and polluting emissions are being greatly reduced.
It is one of the few technologies that significantly
contribute to reducing greenhouse gas emissions. If
geothermal energy continues to be used at the present
rate, it is estimated that the available resources
could last for five million years.
Current geothermal technologies use
only a tiny fraction of total geothermal resources.
Several miles beneath Earth's surface is hot, dry
rock being heated by the molten magma directly below.
Technology is now being developed to drill into this
rock, inject cold water down a well, circulate it
through the hot, fractured rock, and draw off the
heated water from a different well. This has the potential
to supply the energy needs of the entire world for
centuries to come.
For further information about geothermal
energy, please contact:
International Geothermal
Association
IGA Secretariat,
c/o EnelGreenPower
Via A. Pisano 120
56122 Pisa
Italy
Tel: +39-050-535891
Fax: +39-050-535893/533290
E-mail: igasec@enel.it
Website: iga.igg.cnr.it
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Websites
www.worldbank.org/html/fpd/energy/geothermal
The World Bank's Geothermal Energy pages
http://www.crest.org/
The Centre for Renewable Energy and Sustainable Technology
provides research, publication, and dissemination
of timely information regarding sustainable energy,
including geothermal energy.
www.egi.utah.edu/geothermal/geothermal.htm
The University of Utah's Geothermal Energy Unit
rredc.nrel.gov/geothermal
National Renewable Energy Laboratory provides links
to geothermal energy information resources on Internet.
www.geothermie.de/egec-geothernet.htm
Directories of geothermal energy development and research
around Europe, journals, and worldwide conferences
and events. Some internet links. Includes basic information
on geothermal energy technology. English or German.
geothermal.marin.org
Education-related Web site including worldwide geothermal
resources map, an energy scrapbook, and classroom
materials
This document is an output from
a project funded by the UK Department for International
Development (DFID) and the European Commission (EC)
for the benefit of developing countries. The views
expressed are not necessarily those of DFID or the
EC.
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