Renewable Energy Sources

In the last 100 years, the Earth warmed up by ~1° C
100 years is nothing by geological time scales!

Climate change due to natural causes (solar variations, volcanoes, etc.)
Can we predict the past?

CO2 Concentration, Temperature, and Sea Level
Continue to Rise Long after Emissions are Reduced
100 years
1,000 years
Sea-level rise due to ice melting: several millennia
Sea-level rise due to thermal expansion:
centuries to millennia
Temperature stabilization:
a few centuries
CO2 stabilization:
100 to 300 years
CO2 emissions
CO2 emissions peak
0 to 100 years
Today

The possibility / likelihood of global warming is disturbing …
… but there may be a bigger problem!
Chu

Consumption of Energy Increased by 85%
Between 1970 and 1999
By 2020, Consumption will Triple

World production of oil and gas is predicted to peak within 10 - 40 years

Energy conservation and
efficiency can buy time
(a factor of ~2)
but the fundamental problem remains

Electrical generation
Switch from petroleum to coal and natural gas
Why has hydroelectric declined?
When did nuclear go up?

Numbers = how long it would last if all energy came from one source
Resource recoverable recoverable and hoped for
Coal 125 1300
Petroleum 5 50?
Natural gas 5 50?
Oil shale 0 2500
Conventional reactors 3 15
Breeder reactors 115 750
Fusion 106 to 109
Geothermal surface 0.2 60
deep rock 0 600
Estimates of depletable energy resources in the U.S.

Numbers = proportion of current U.S. energy needs that could be supplied for an indefinite period.
Tidal energy 0.1
Organic Waste 0.1
Photosynthesis 0.23
Hydropower 0.14
Wind Power 5
Solar radiation 740
Estimates of renewable energy

(in the U.S. in 2002)
1-4 ¢
2.3-5.0 ¢
6-8 ¢
5-7 ¢
Today: Production Cost of Electricity
6-7 ¢
25-50 ¢
Cost, ¢/kW-hr
Courtesy Nate Lewis

Energy Costs
Brazil
Europe
$0.05/kW-hr
www.undp.org/seed/eap/activities/wea
Courtesy Nate Lewis

Potential Sources of Energy when
Fossil Fuels Run Out
Nuclear Fission
Magnetic Plasma Confinement,
Inertial Fusion
Waste &
Nuclear Proliferation
Nuclear Fusion
10 TW = 10,000 new 1 GW reactors: i.e., a new reactor every other day for the next 50 years

Solar, Wind and Water
We do not know how to store electrical energy on a massive scale

Geothermal
Heat near surface of the earth = geysers, volcanoes, hot springs

Photosynthesis
Photovoltaic and
electricity to chemical
H O
O
H
2
2
2
sc
M
e
sc
e
M
CO
Sugar
H O
O
2
2
2
Solar to Chemical Energy
Semiconductor/
liquid junctions

Energy gained in corn ethanol production

Total CO2 emissions

From Summary of Renewable Fuel Options (NCEP)
“Unlike corn ethanol, cellulosic ethanol has potential to achieve near-zero net carbon emissions.
Cultivation of cellulosic feedstocks requires very low energy inputs and, if sustainably managed, the carbon released during fuel combustion is reabsorbed by the growth of new feedstocks.”

Use heat to make steam to turn turbine for electrical generation
Note: deep hot waters are corrosive to best to inject clean water in a closed system and bring it back to the surface as steam.
Geothermal Energy in More Details

In U.S., much done on public land = cheap
Very little potential in east and mid west

World wide distribution of volcanos, hot springs, etc.
Japan, Iceland,New Zealand big users of geothermal.

Although hot areas near surface are limited, the earth is hot everywhere if you go down far enough.

Bright idea!? – drill deep enough to find heat. Since rock is a poor conductor of heat, set off a big bomb to crack the rock and allow heat to move – then pump down water to make steam.

Hydropower in More Details

Hydropower = dams
Not much used in world, why??

Norway, Zambia, Ghana big users

Most unused hydropower in U.S. = Alaska,
In World = Canada, Russia

Problems with hydroelectric
Location = unused rivers are in extreme north or low population areas
Competition with recreational uses (U.S.) and environmental concerns
Hard to build dams in populated river valleys
Siltation of dams – limited life.

Tidal Power
In areas of large tides
Anywhere – build offshore dam

Highest tides in the world = Bay of Fundy 16 meters = 48+ feet!

Tidal power anywhere
No dam – but a turbine.
Problems:
Corrosion
Navigation
Appearance
Amount of energy available is low
Best tides are near poles – away from people.

Banning Pass
Wind Power in More Details

Wind Power Generation

Best wind location = Aleutian Islands, why no wind development there?

Best U.S. localities
Midwest, mountains
And coastal areas.

Netherlands = coastal development

England = off shore

Wind energy problems
Location – near population center
Bird migration –
Visual
Must be coupled with other sources of electricity (intermittent supply)

Solar Energy in More Details
1. Solar Thermal

At focal point = heat liquid – steam to turn turbine

Solar Resource for a Concentrating Collector

Big Plants

2. Solar Photovoltaics

‘hard’ vs ‘soft’ energy paths
Hard =
Big plants
Centralized production
Soft =
Decentralized
units per household

Big Plants

Energy efficient house; wind power on roof. Solar panels for heat and electricity.
Decentralized

Solar electricity generation

Solar water heating solar air heating

Solar house problems
The Los Angeles air = smog
Retrofitting- very expensive
Hard for big hotels, Walmarts, etc.