Physics 100 Lecture 23Physics 100 Lecture 23 Geothermal Energy ... Geysers • Hot springs 4. Hot...
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Physics 100 Lecture 23 Geothermal Energy April 23, 2018 1
Transcript of Physics 100 Lecture 23Physics 100 Lecture 23 Geothermal Energy ... Geysers • Hot springs 4. Hot...
Physics 100
Lecture 23
Geothermal Energy
April 23, 2018
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The Interior of the Earth
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Plate Tectonics
Earth’s crust is divided into moving tectonic
plates. The intersections of these plates are
the focus of geologic activity.
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Subduction Zone
Friction between the
plates brings hot material
near the surface:
• Volcanoes
• Geysers
• Hot springs
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Hot Water
Geothermal
System
One of 21 geothermal power plants called The Geysers in northern California
Heat from the Earth
produces steam that
can be used to
generate electricity.
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Types of Geothermal Resources
Hydrothermal Systems (shallow, small, localized)• Wet steam – superheated water flashes into
one part steam and four parts hot water.
• Dry steam – the water boils far underground and the steam is brought to the surface to drive a generator.
Hot Dry Rock Systems – water from surface is circulated through cracks in hot subsurface rocks
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Types of Geothermal Resources
Geopressurized reservoirs – hot, liquid brines in large, very deep (3 km to 6 km below the surface) areas and are under very high pressure. We currently lack the technology to fully exploit this resource.
Low-Temperature Geothermal Resources – hot water can be brought to the surface and used for space heating, greenhouses, fish farming, etc.
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Geothermal Energy in the US
Geopressured resources
o
Temperature <90C
Temperature >90C
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Which state has the most
geothermal energy?
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A. Florida
B. Wisconsin
C. Utah
D. Vermont
Geopressured
resources
o
Temperature <90C
Temperature >90C
Which state has the most
geothermal energy?
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A. Florida
B. Wisconsin
C. Utah
D. Vermont
What makes geothermal energy
unique from other renewable
energies (solar, wind, biomass, etc.)?
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A. It produces no gaseous emissions
at all.
B. It works both day and night.
C. It is not derived from the Sun.
D. It can be harnessed anywhere in
the U.S.
At what rate is energy conducted
through each square meter of
300-m-thick rock (R = 275 m2·°C/W) if
DT is 205°C?
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A. 0.275 W
B. 0.745 W
C. 2.24 W
D. 275 W
At what rate is energy conducted
through each square meter of
300-m-thick rock (R = 275 m2·°C/W) if
DT is 205°C?
A. 0.275 W
B. 0.745 W
C. 2.24 W
D. 275 W
2
2
1 m 205°C
275 m °C W
0.745 W
cQ A T
t R
D
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Suppose a geothermal system
generates steam at 227°C when the
outside temperature is 27°C. What is
the maximum efficiency of the power
plant?
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A. 20%
B. 40 %
C. 50%
D. 60%
Suppose a geothermal system
generates steam at 227°C when the
outside temperature is 27°C. What is
the maximum efficiency of the power
plant?
A. 20%
B. 40 %
C. 50%
D. 60% max
227 273 500 K
27 273 300 K
300 K1 1 40%
500 K
H
C
C
H
T
T
Te
T
The steam temperature in a coal-fired plant is often 825 K,
for a max efficiency of 64%. In either case we can achieve
about half of the maximum efficiency, and geothermal
plants are less efficient than fossil fuel plants.
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Problems with Geothermal
Energy
Many geothermal facilities vent smelly H2S
from the ground. High concentrations of
H2S are hazardous to human health.
Many minerals are contained in the
wastewater, affecting stream or lake
chemistry, corroding equipment, clogging
pipes.
Removing lots of water can cause the land
above to settle.
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Residential Geothermal Energy:
Earth-Sheltered Homes
Subsurface
temperature is a
steady 52°F (11°C)
Underground areas of
the home are cooled
in the summer and
warmed in the winter
relative to
surrounding air
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Earth-sheltered homes
De Soto, WI
Umbricht Haus,
Schweiz, Germany
Honingham, UK
Cumbria, UK
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Geothermal heat pumps
(Ch. 5 pp. 142-146)
A heat pump draws energy from outside
a home to heat it, or from inside a home
to cool it.
It is a heat engine
operated in reverse.
See Chapter 5,
pages 142-146
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Heat engine Heat pump
Geothermal heat pumps
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COLD HOT HOT COLD
Figure 5.18 p. 143
Coefficient of Performance
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Hheat transferredCOP
electricity input
Q
W
How much heat can a 2.0-kW heat
pump add to a house in one day of
continuous operation if it has a COP
of 3.6?
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A. 590,000 BTU
B. 360,000 BTU
C. 200,000 BTU
D. 184,000 BTU
How much heat can a 2.0-kW heat
pump add to a house in one day of
continuous operation if it has a COP
of 3.6?
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A. 590,000 BTU
B. 360,000 BTU
C. 200,000 BTU
D. 180,000 BTU
HH
H
6
8
H
COP
COP
3.6 2.0 kW 24 h
3.6 10 J172.8 kWh
kWh
1 BTU6.22 10 J
1055 J
590,000 BTU
QCOP Q W
W
Q Pt
Q
Geothermal heat pump
economics
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Average WI
2017 rates
Electric
9.97¢
Nat. gas
42.40¢Fig. 5.20
p.145
X
X
