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Part 1
Geothermal Power
Why?
Growing demand for energy
Concern about CO2 from fossil-fuel burning
Recent Report, The Future of Geothermal Energy, gives favorable assessment
Indian Point Power Plants 1 and 2, big energy producers in the NY City area
Electric Power PrimerTypical Big Power Plant generates 1GW
One billion watts … 109 J/s of energy
In a year it generates109 J/s x 3.1x107 s/year = 3.1x1016 J/year
A nice round number is 1018 JThat’s the amount of power a 1GW plantGenerates in its nominal 30-year lifetime
US Electrical Power Production Capacity
906 GW in 2006rate of increase 1% per year
about 1000 big power plantsneed 10 new ones each year
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 …
Geothermal lumped into“Other Renewable” … not much!
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
3.5 km – easy to drill, but not very hotWhat’s that hot spot?
Yellowstone CalderaBiggest Volcano in US
here I amstanding by Old Faithful
above 10,000 cubic kmof magma
6.5 km – expensive but routine, areas of western US are hot
10 km – very hot, but pushing limits of technology
Heat in Rock: Q = Cp V THeat = density * heat capacity * Volume * change
in Temperature
Density = 2500 kg/m3
Heat Capacity = 1000 J/kgKVolume = 1 cubic km = 109 m3
T = 100 KSo 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
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
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
Issues
Drill 2 holes … expense of drilling
Circulate fluid … low permeability of rock
Generate steam … dissolved minerals in water
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
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
60 MW Krafla power plant, Iceland: heat from 33 wells drilled into volcano
Tiny by US standards Lots of wells
Magma
chamber
Power plant
Part 2
Fresh Water
Possibly the most Limiting Resource
How much water do you use in a day?
US Water Usage, %
Irrigation
Domestic SupplyPublic Supply
Livestock & AquacultureIndustrialMining
Thermoelectric Power
34
111
251
48
US Water Usage, billion gallons / day
Irrigation
Domestic SupplyPublic Supply
Livestock & AquacultureIndustrialMining
Thermoelectric Power
80
0.627.3
3.414.91.2
135
Total 262
Ogallala Aquifer
US Water Usage, billion gallons / day
Irrigation
Domestic SupplyPublic Supply
Livestock & AquacultureIndustrialMining
Thermoelectric Power
80
0.627.3
3.414.91.2
135
Total 262
Total 262 billion gallons/day
362 cubic kilometers per year
7 km
H20
Public & Domestic Supply 27.9 billion gallons/day
266 gallons per person per day
drinking
cooking & washing dishes
washing clothes
flushing toilet
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 gallona gallon lights the bulb for an hour
Irrigation 80 billion gallons/day
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
Wheat: 3500 calories/kg
About 750 liters of water to grow a kilogram
Wheat: 4.6 calories/liter
Rice: 3700 calories/kg
About 1550 liters of water to grow a kilogram
Rice: 2.4 calories/liter
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 yearSo how much is available ?
The Hydrologic
Cycle
46,000 km3/yeartransported on shore
108,000 km3/yearprecipitated on land
62,000 km3/yearevaporated fromcontinental reservoirs
46,000 km3/yearrunoff to oceans
Need 14,700 km3
Available 46,000 km3
So superficially about three times as much water is available than is needed.
But consider …
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
Runoff is uneven during the year and may be lost to sea before it can be used
Solution – Reservoirs (“Impoundments”) created by damming rivers
Global impoundments of water8400 km3
Not much growth in last decade, except in Asia-Australia
Regional distribution of large dams
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.
