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Hot Rock Geothermal
Power
In Australia,
there is no potential to use volcanic hot water. Australia has no active volcanoes
or geysers. But Australia has
huge reserves of hot rocks beneath the surface
The temperature of the water produced this way will tend
to be less, and frequently rather than using it to produce power directly, it
is used to heat a secondary generating system using a lower boiling point
liquid like Ammonia.
This requires a fairly high technology to do. Interestingly two of the countries known to
have big reserves of these hot rocks and which have very high energy
requirements are the United States of America
and Australia. Both these countries have the high technology
and the industrial bases needed to utilise this energy.
Not Renewable
Geothermal power is sometimes referred to as being
renewable. I disagree with this
statement. The stored heat of these
rocks was built up over long periods.
Although they would eventually heat up again, it would take a long time
in geological terms. That is, the heat
might take millions of years to build up the energy which could be removed in
thousands of years.
We do not really know how much of usable hot rocks are
available. One estimate suggests that if
one percent of the suitable hot
rocks in Australia were to
be used, it would supply all of Australia’s
electricity requirements at the present rate of demand for the next 26,000 years.
However, different people come up with different
amounts of power available. Another estimate, this time for the United States,
suggests that the total extractable geothermal energy in that country is enough
for about 140,000 years requirement
for all types of energy at the
present rate of demand.
The potential is considerable.
Carbon
Neutral
Although geothermal power generation does not produce
any carbon dioxide, we should recognise that setting up the power plant must
use some, just as all forms of power generation do. However, the initial energy needed to set up
the plant is reasonably low.
Economics
The present estimates suggest that hot rock geothermal
power will be cheaper than coal power generation. In fact in places like South Australia which has no conventional
hydro electric potential and no potential for volcanic geothermal power
generation, geothermal power promises to be the cheapest power source.
Why so Slow?
If hot rock power generation is potentially so profitable, and the
basic technology has been used in France
since the 1970’s, it is a reasonable question to ask why Australia is only up to the stage
of testing a pilot plant.
Perhaps this question is not completely fair, but our
progress does appear a bit slow.
The South Australian Government has put, or planned to
put, enormous amounts of money into such things as a desalination plant, a tram
line extension and an upgraded sports stadium.
A tiny fraction of the Billions of dollars involved in these projects
could have been used to accelerate the testing of the concept in our
conditions.
Basic Idea
The Hot Rocks referred to are typically about 3 to 4
Kilometres below the Earth’s surface.
The best rock is probably Granite.
The heat mostly came from the decay of radioactive elements in the
granite like Uranium and Potassium.
Typically these rocks are around 250 degrees C
A hole is bored down into the rock. Water is pumped down under high pressure
making cracks in the rock. Other holes
are bored and the hot water comes up these holes. The temperature of the water tends to be less
than the water than comes from geysers etc. but it is still hot and contains a
lot of energy.
Hydraulic
Fracturing
Of course the description in the previous paragraph is
an over simplification. Another thing
normally necessary is to break open the rock more using high pressure water.
Sources
Electricity Generation from Geothermal Power in Australia.
http://www.ga.gov.au/image_cache/GA10663.pdf
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