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Created by Andy Darvill,
Science teacher at
Broadoak Community School,
Weston-super-Mare, England
Web site www.darvill.clara.net
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Geothermal
Energy is energy from heat inside the Earth.
Introduction How it works More details Advantages
Disadvantages Is it renewable?
Introduction
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.
Geothermal
energy has been used for thousands of years in some countries
for cooking and heating.
The name
"geothermal" comes from two Greek words: "geo"
means "Earth" and "thermal" means "heat".
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How
it works
Hot rocks
underground heat water to produce steam.
We drill holes down to the hot region, steam comes up, is purified
and used to drive turbines, which drive electric generators.
There may
be natural "groundwater" in the hot rocks anyway,
or we may need to drill more holes and pump water down to them.
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The
first geothermal power station was built at Landrello, in Italy,
and the second was at Wairekei in New Zealand. Others are in
Iceland, Japan, the Philippines and the United States.
In
Iceland, geothermal heat is used to heat houses as well as for
generating electricity.
If
the rocks aren't hot enough to produce steam we can sometimes
still use the energy - the Town Hall in Southampton, England,
is partly heated this way.
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More
details
Geothermal
energy is an important resource in volcanically active places such as
Iceland and New Zealand.
How useful it is depends on how hot the water gets. This depends on
how hot the rocks were to start with, and how much water we pump down
to them.
Water
is pumped down an "injection well", filters through the cracks
in the rocks in the hot region, and comes back up the "recovery
well" under pressure. It "flashes" into steam when it
reaches the surface.
The
steam may be used to drive a turbogenerator, or passed through a heat
exchanger to heat water to warm houses. A town in Iceland is heated
this way.
The
steam must be purified before it is used to drive a turbine, or the
turbine blades will get "furred up" like your kettle and be
ruined.
See
Also:
A geothermal
project in Hawaii http://www.geothermalhawaii.com/
A diagram
showing a geothermal project http://www.geothermal.marin.org/GEOpresentation/sld037.htm
Advantages
- Geothermal
energy does not produce any pollution, and does not contribute to
the greenhouse effect.
- The power stations
do not take up much room, so there is not much impact on the environment.
- No fuel is
needed.
- Once you've
built a geothermal power station, the energy is almost free.
It may need a little energy to run a pump, but this can be taken
from the energy being generated.
Disadvantages
- The big problem
is that there are not many places where you can build a geothermal
power station.
You need hot rocks of a suitable type, at a depth where we can drill
down to them.
The type of rock above is also important, it must be of a type that
we can easily drill through.
- Sometimes a
geothermal site may "run out of steam", perhaps for decades.
- Hazardous gases
and minerals may come up from underground, and can be difficult
to safely dispose of.
Is
it renewable?
Geothermal
energy is renewable.
The energy
keeps on coming, as long as we don't pump too much cold water down and
cool the rocks too much.
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