Transcript Geothermal Power

Geothermal Power
The specification states that you need
to be able to:
 Explain about geothermal energy from
volcanic sources around the world and
potential 'hot' rock sources in the British
Isles.
 Understand that geothermal energy is
an example of a renewable energy
resource.







Fossil fuels such as coal, oil and gas are
essentially non-renewable resources.
However, there are renewable resources that can
be gained from the Earth, namely geothermal
energy.
There are three main varieties of geothermal
energy:
1) In volcanic areas
2) Hot Rocks – such as granites in Cornwall
3) Hydrothermal fluids in sedimentary basins Southampton.
This energy has the most potential and is the
most plentiful resource today.
A major advantage is that geothermal power
has virtually no environmental impact. 
 From where does the Earth’s heat come?
 Engineers estimate that 32 million quads of
energy are available only 10 km. below the
surface of the U. S. A.
 Most of this cannot be accessed but land is
now being set aside for exploration of this
resource.





The simplest manifestation of
geothermal energy is just hot
water or steam.
For example the Geysers of
California could produce enough
electricity to supply half of San
Francisco.
Another example is in Western
Canada above a subduction zone.
Magma is generated and this heats
up water that has infiltrated down
through fractures.




The water may reach 200C.
This water either reaches the
surface as geysers or is tapped
into via boreholes.
In this example 100, 000 Kg/h
of steam at 8 atmospheres
pressure turns 255 mega watt
turbines to produce 110 mega
watts of power.
Once the steam has cooled and
condensed the water is
pumped back underground.



As long as the water is
pumped back this form of
energy is virtually
renewable.
Other examples occur in
Italy, New Zealand, Mexico,
Japan, U. S. S. R. and
Iceland.
Problems:



In a potentially dangerous
area.
The steam can be corrosive
and dangerous.
Not common.




These are hot dry rock formations
where there is no naturally
occurring hot water brought to the
surface.
In particular such hot rocks are
associated with granites that
contain a higher proportion of
radioactive elements than an
average rock.
They therefore produce more heat
and have a steeper geothermal
gradient 40C/km.
Therefore it gets hotter quicker with
depth.



Water is circulated through at
least 2 drill holes which are
joined by man made fractures
in the hot rock.
Pumping cold water down into
the hot granite makes the
fractures.
In the U. K. a hot rock scheme
has been developed in
Cornwall using the Cornish
granites as the heat source.


In some deep sedimentary
basins the water that the
sedimentary rocks contain
can be abundant enough
and hot enough to form
convection currents of
hydrothermal fluids.
These fluids can then be
pumped up closer to the
surface and tapped as
steam.


A pilot scheme has
been developed in
Southampton where
water at 70C has
been found at 1.6km depth.
Other potential
areas are in East
Yorkshire/Lincolnsh
ire and the Midland
Valley of Scotland.