Part 1 Geothermal Power

Why? Growing demand for energy Concern about CO 2 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 Primer Typical Big Power Plant generates 1GW One billion watts … 10 9 J/s of energy In a year it generates 10 9 J/s x 3.1x10 7 s/year = 3.1x10 16 J/year A nice round number is J That’s the amount of power a 1GW plant Generates in its nominal 30-year lifetime

US Electrical Power Production Capacity 906 GW in 2006 rate of increase 1% per year about 1000 big power plants need 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 hot What’s that hot spot?

Yellowstone Caldera Biggest Volcano in US here I am standing by Old Faithful above 10,000 cubic km of 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  T Heat = density * heat capacity * Volume * change in Temperature Density = 2500 kg/m 3 Heat Capacity = 1000 J/kgK Volume = 1 cubic km = 10 9 m 3  T = 100 K So Q = 2.5 x J A 1 GW power plant generates 3.1x10 16 J/year, so this is about tens years of a 1GW power plant

Remember 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 standardsLots 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 Supply Public Supply Livestock & Aquaculture Industrial Mining Thermoelectric Power

US Water Usage, billion gallons / day Irrigation Domestic Supply Public Supply Livestock & Aquaculture Industrial Mining Thermoelectric Power Total 262

Ogallala Aquifer

US Water Usage, billion gallons / day Irrigation Domestic Supply Public Supply Livestock & Aquaculture Industrial Mining Thermoelectric Power Total 262

Total262 billion gallons/day 362 cubic kilometers per year 7 km H20H20

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 gallon a 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  liters/year = cubic kilometers per year So how much is available ?

The Hydrologic Cycle 46,000 km 3 /year transported on shore 108,000 km 3 /year precipitated on land 62,000 km 3 /year evaporated from continental reservoirs 46,000 km 3 /year runoff to oceans

Need 14,700 km 3 Available 46,000 km 3 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 water 8400 km 3 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.