Geothermal Power

1
Geothermal Power

• The specification states that you need to be able
  to
• Describe 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.

2
Geothermal Energy

• Fossil fuels such as coal, oil and gas are
  non-renewable resources.
• However, there are renewable resources that can
  be gained from the Earth, namely geothermal
  energy.
• There are three main types of geothermal energy
• 1)    In volcanic areas
• 2)    Hot Rocks such as granites in Cornwall
• 3)    Hydrothermal fluids in sedimentary basins -
  Southampton.

3
Geothermal Energy

• A major advantage is that geothermal power has
  virtually no environmental impact.

4
Volcanic areas

• The simplest form 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.
• Magma is generated and this heats up water that
  has infiltrated down through fractures.

5
Volcanic areas 2

• 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.

6
Volcanic areas 3

• As long as the water is pumped back this form of
  energy is virtually renewable.
• Other examples occur in Italy, New Zealand,
  Mexico, Japan, Russia and Iceland.

• Problems
• In a potentially dangerous area.
• The steam can be corrosive and dangerous.
• Not common.

7
Hot Rocks

• 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.
8
Hot Rocks 2
Water is circulated through 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 trialled in
  Cornwall using the Cornish granites as the heat
  source.

9
Sedimentary basins

• 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.
10
Sedimentary basins

• A pilot scheme has been developed in Southampton
  where water at 70?C has been found at 1.6-km
  depth.
• Other potential areas are in East
  Yorkshire/Lincolnshire and the Midland Valley of
  Scotland.