Geothermal Power

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Part 1

• Geothermal Power

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Why?

• Growing demand for energy
• Concern about CO2 from fossil-fuel burning
• Recent Report, The Future of Geothermal Energy,
  gives favorable assessment

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Indian Point Power Plants 1 and 2, big energy
producers in the NY City area
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Electric Power Primer

• Typical Big Power Plant generates 1GW
• One billion watts 109 J/s of energy
• In a year it generates
• 109 J/s x 3.1x107 s/year 3.1x1016 J/year
• A nice round number is 1018 J
• Thats the amount of power a 1GW plant
• Generates in its nominal 30-year lifetime

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US Electrical Power Production Capacity906 GW
in 2006rate of increase 1 per yearabout 1000
big power plantsneed 10 new ones each year
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An aside controversial Cape Wind project
offshore Cape Cod would generated 0.4 GW by 120
turbines
Offsets growth of New England power demand for
about a year or two
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Geothermal lumped into Other Renewable not
much!
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Where is the Heat?

• Typical Geothermal Gradient
• typical region 20 K/km
• volcanic region 100 K/km
• Power production needs temperatures well above
  100 deg-C
• So drilling needed to access heat

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3.5 km easy to drill, but not very hot
Whats that hot spot?
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Yellowstone CalderaBiggest Volcano in UShere I
amstanding by Old Faithfulabove 10,000 cubic
kmof magma
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6.5 km expensive but routine, areas of western
US are hot
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10 km very hot, but pushing limits of technology
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• Heat in Rock Q r Cp V DT
• Heat density heat capacity Volume change
  in Temperature
• Density 2500 kg/m3
• Heat Capacity 1000 J/kgK
• Volume 1 cubic km 109 m3
• DT 100 K
• So Q 2.5 x 1017 J
• A 1 GW power plant generates 3.1x1016 J/year,
• so this is about tens years of a 1GW power plant

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Remember 1018 J is roughly the amount of energy
produced by a power plant in its nominal 30 year
lifetime, so these estimates indicate a huge
supply of heat energy
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How to access heat?

• Drill 2 holes, one to inject cold water, another
  to extract hot water
• Circulate fluid
• Use hot water to generate steam that turns
  turbine of more-or-less standard design

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Issues

• Drill 2 holes expense of drilling
• Circulate fluid low permeability of rock
• Generate steam dissolved minerals in water

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Money Counts!

• Any sort of mining or extraction is an
• Economic Activity
• that competes by price against alternatives
• If the economics are not right
• It will not be done
• even if it is in theoretically possible to do

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Solution to low permeabiliy

• Artificially increase permeability by creating
  fractures
• Hydrofracture pressurize well until you
  crack the surrounding rock, routinely used in oil
  extraction, at least for small volumes of rock

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60 MW Krafla power plant, Iceland heat from 33
wells drilled into volcano
Tiny by US standards
Lots of wells
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Power plant
Magma chamber
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Part 2

• Fresh Water
• Possibly the most Limiting Resource

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How much water do you use in a day?
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US Water Usage,
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1
34
2
5
1
48
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US Water Usage, billion gallons / day
Public Supply
27.3
Domestic Supply
0.6
Irrigation
80
Livestock Aquaculture
3.4
Industrial
14.9
Mining
1.2
Thermoelectric Power
135
Total 262
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Ogallala Aquifer
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US Water Usage, billion gallons / day
Public Supply
27.3
Domestic Supply
0.6
Irrigation
80
Livestock Aquaculture
3.4
Industrial
14.9
Mining
1.2
Thermoelectric Power
135
Total 262
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Total
262 billion gallons/day
362 cubic kilometers per year
H20
7 km
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27.9 billion gallons/day
Public Domestic Supply
266 gallons per person per day drinking cookin
g washing dishes washing clothes flushing
toilet
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Cooling water for power plants
135 billion gallons/day
450 gallons per person per day 40 kWh average
daily electrical consumption per person in US So
0.08 kWh per gallon
a gallon lights the bulb for an hour
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80 billion gallons/day
Irrigation
266 gallons per person per day 2750 calories
average daily food consumption per person in
US So 10.3 calories per gallon 2.7
calories per liter
a gallon gets you a chip
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Wheat 3500 calories/kg
Wheat 4.6 calories/liter
About 750 liters of water to grow a kilogram
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Rice 3700 calories/kg
Rice 2.4 calories/liter
About 1550 liters of water to grow a kilogram
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How much irrigation water does the world
need? 2000 calories/day minimum At 3
cal/liter 670 liters/day ? 6 billion people ? 365
days/year 1.46 ? 1015 liters/year 14700 cubic
kilometers per year
So how much is available ?
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The Hydrologic Cycle
108,000 km3/year precipitated on land
46,000 km3/year transported on shore
62,000 km3/year evaporated from continental
reservoirs
46,000 km3/year runoff to oceans
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Need 14,700 km3 Available 46,000 km3 So
superficially about three times as much water is
available than is needed.
But consider
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Some runoff is in uninhabited regions Runoff is
uneven during the year and may be lost to sea
before it can be used The rest of the biosphere
uses water, too Human populations are growing
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Runoff is uneven during the year and may be lost
to sea before it can be used Solution
Reservoirs (Impoundments) created by damming
rivers
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Global impoundments of water 8400 km3
Not much growth in last decade, except in
Asia-Australia
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Regional distribution of large dams
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Dams in the US. Note that the red symbols
indicate high hazard potential. Dam maintenance
has not been a high priority for many
municipalities and other dam owners.