3/28/2019 1 Renewable Energy Resources The big picture: Energy (power) reaching the Earth’s surface Solar: Radiated energy at land surface 84,000 TW (TW = Terawatt = 10 12 W) Tides: Gravitational interaction of Earth, Moon, and Sun 3 TW Geothermal: Heat from radioactive decay of long-lived isotopes within the Earth 44 TW ~99.95% ~0.05% ~0.003% This power is ~ half that at the ‘top’ of the atmosphere 1 2
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3/28/2019
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Renewable Energy Resources
The big picture: Energy (power) reaching the Earth’s surface
Solar: Radiated energy at land surface
84,000 TW (TW = Terawatt = 1012 W)
Tides: Gravitational interaction
of Earth, Moon, and Sun
3 TW
Geothermal: Heat from radioactive decay
of long-lived isotopes within the Earth
44 TW
~99.95%
~0.05%
~0.003%
This power is ~ half that at the ‘top’ of the atmosphere
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Energy fluxes (Power per unit area)
Energy flux = Energy / (Area*Time)
Space- and time-averaged
Solar: 160 W/m2
Geothermal: 0.09 W/m2
Tide: 0.006 W/m2
We use these fluxes directly when
developing alternative / renewable
energy resources
Your text makes use of fluxes
The big picture: Energy use
2008 Global energy use ~ 500 exajoules
(5001018 J)
Equivalent to 15 TW power consumption
The breakdown:
13 TW Fossil fuels (85+%)
1 TW Nuclear
1 TW Renewable / Alternative
Mostly hydroelectric
Wee bits everything else
Po
we
r co
nsu
mp
tio
n (
TW
)
EIA 2008 data
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Review Problem: What was the per capita power consumption in 2008?
Given: Total power consumption of 15 TW in 2008
Global population ~ 7 billion
Globally, how many 100 W light bulbs are ‘you’ using at all times?
?
Time out
In kicking our ‘fossil sunshine’ habit, what
are the major challenges we face?
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46 coal-fired plants in Minnesota:
XCEL Energy (MSP):
30 plants @ 8961 MW total
ALLETE (DLH):
9 plants @ 1441 MW total
Great River Energy (Maple Grove):
3 plants @ 1400 MW total
Excelsior (Minnetonka):
4 plants @ 1035 MW total
Average MN fossil plant ~ 300 MW output
Typical fossil plant output ~ 200 – 500 MW
Typical nuclear plant output ~ 500 MW – 2 GW
Always keep in mind the ‘economies of scale’
Gut check: A useful measuring stick, perhaps?
Outline
• Geothermal
• Tides
• Solar
• Hydroelectric
• Wind
• Waves
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Sources of energy (heat) on Earth:
Solar input from above (~160 W / m2)
Geothermal heat from below (~90 mW / m2)
Wide range depending on geology / tectonics
~ 20 mW / m2 in subduction zones
~ 200 mW / m2 in volcanic provinces
Source for geothermal is radioactive decay of elements