Energy, Power, &
Climate Change
Energy Degradation
Energy Review:
Energy is always conserved – Law of
Conservation of Energy
However, energy becomes less useful
(more entropy) - 2nd Law of
Thermodynamics
Energy Degradation is the process of
energy changing into forms that no
longer can be used to perform
mechanical work.
Sankey diagram
• Visual representation of the energy
flow of a system.
• Width of each arrow is proportional to
amount of the energy that part of the
system carries.
http://the energy carried by that www.bbc.co.uk/schools/gcsebitesize/science/images/ph_energyfuel.gif
http://bioage.typepad.com/photos/uncategorized/energy_path_gasoline_ice.png
http://harvardclimatecollaborative.files.wordpress.com/2008/12/energyflow1.jpg
http://www.celsias.com/media/uploads/admin/sun.jpg
Energy Sources
• Early Civilization – food and sunlight only
energy sources.
– Energy Consumption per person 8MJ/day
• Modern Civilization – energy used for all
aspects of life.
• US 10 kW/day contrasting with
parts of Africa <0.1 kW/day
• If every person on earth (6.7 billion)
used 3 kW/day the total energy
demand for a year would be
6.3x1020J approaching the annual
world production of energy of 1.5x1021 J
http://library.thinkquest.org/06aug/02309/Photosynthesis_2_files/image004.jpg
– Energy Consumption per person 300MJ/day or
3.5 kW / day
GDP vs Energy Consumption
Source: IEA 2006 Key World Energy Statistics
Energy Sources
http://www.sanoypolymer.com/images/sun-animation.gif
Where does all this energy come from?
– Sun
– Gravitational energy of the sun and the
moon
– Nuclear Energy stored within atoms
– Earth’s internal heat energy
Energy Sources
Non-renewable Energy Sources –
Sources of energy that are finite and
are being used up and will eventually
be depleted.
• Coal
• Oil
• Natural Gas
• Nuclear
90% of world’s commercial
energy supplied by fossil fuels.
From the EIA's 2006 World Energy Statistics
Energy Sources
Renewable Energy Sources – Sources
of energy that can not be used up.
• Hydroelectric
• Photovoltaic Cells
• Active Solar Heaters
• Wind
• Biofuels
• Geothermal
Source: IEA Key Stats 2009
http://media3.washingtonpost.com/wp-dyn/content/graphic/2009/11/20/GR2009112003993.jpg
Energy Density
• The energy that can be
obtained from a unit of mass of the
fuel.
http://fti.neep.wisc.edu/~jfs/FuelEnergyDensity.gif
energy  released  from  fuel
Energy  Density 
mass  of  fuel  consumed
– For fossil fuels the energy density is the
heat of combustion.
– Nuclear fuel it is E=mc2
– Hydro-electric Power E=KE=PE
• Major consideration in fuel choice
http://millennium-project.org/millennium/scenarios/table-en-3.jpg
Energy Density
Fossil Fuels:
Historical Development
Coal:
• ~1000 BC: China
• 18th Century: Industrial Revolution
http://www.istp.murdoch.edu.au/ISTP/casestudies/Case_Studies_Asia/urbwater/E12.jpg
– Textile manufacturing machines (spinning jenny)
– Steam engine
– Iron and steel manufacturing
• As industry spread, rate of energy usage
increased
• Industry tended to build in areas where fossil fuel
supplies were already in abundance
• Infrastructure was developed/improved for
transporting fossil fuels (i.e. coal) and the products
made by industry
Fossil Fuels: Historical Development
Oil
• 1960s—became more widely used
than coal for general use, mainly
because of growth in transportation
and gasoline usage
• Coal still more widely use for electrical
power production…
Fossil Fuels
http://www.theviewfromthepeak.net/images/coalform.jpg
Fossil Fuels: Coal
Decaying plant matter, when buried under
sediment, eventually forms peat (very
moist, compact)
• Further compaction, over time, forces the
moisture out of the peat—forms a layer of
lignite
• More compression (compaction), and more
moisture is removed, forming a layer of soft
coal (bituminous)
• Higher pressure and higher temperatures
cause the bituminous coal to
metamorphose into hard coal (anthracite)
Coal
http://faculty.virginia.edu/metals/Images/clip_image004_0002.jpg
lignite
subbituminous
Steam Engine
bituminous
http://www.wsgs.uwyo.edu/coalweb/images/coal-types.gif
anthracite
http://www.edinformatics.com/math_science/alternative_energy/fossil_fuel/GASFORMATION.gif
Fossil Fuels: Oil
http://www.abslpower.com/images/images/oil.jpg
• Derived from the remains of plants and
animals that once lived in ocean
• Organisms died, sank to the ocean bottom,
and were covered with sediment (prevents
rapid decomposition because they are not
exposed to oxygen)
• Decay occurs slowly, forms carbon-rich
compounds that mix with the sediment.
Pressure from more sediment above
causes the compound and sediment
mixture to form shale (“source rock”)
Fossil Fuels: Oil
• More pressure from layers above the
source rock cause the organic matter to
transform into oil.
• Liquid oil finds its way into porous rock
layers (like sandstone and limestone)—
these rocks are known as “Reservoir rocks”
because they store the oil
• A “Cap rock” is a layer of non-porous rock
directly above the reservoir rock that
prevents the oil from leaving that layer.
http://3.bp.blogspot.com/_Eu9SQSvqdYc/SuKbC6S3WvI/AAAAAAAAAjU/qHg9vM46h6Q/s400/reservoir.jpg
Oil Formation
OIL
Fossil Fuels: Oil Reserves
http://lugar.senate.gov/graphics/energy/graphs/Worldwide_Oil_Reserves.gif
Fossil Fuels: Natural Gas
Formed at the same time as oil
• At higher temperatures,
relatively more gas is formed
than oil…at lower temps, more oil
than gas is formed
• Typically gets trapped above the layer of oil and
below the cap rock when there is a “fold” in the
Earth’s rock layers
• Cleaner burning than coal or oil
• Colorless, odorless in its
natural form…power
companies add odor in order
to detect leaks
http://www.georgianaturalgas.com/img/ggHome.jpg
Oil & Natural Gas Issues
http://www.sitevip.net/gifs/oil/
Oil Advantages:

Oil is more concentrated
than coal, burns cleaner,
and is easily transported.

Natural Gas Advantages

Least environmental.
damaging of fossil fuels.

Primary use is heating
Ideal for automobile
use.
Oil Disadvantages

Difficult to extract
 Primary Recovery
removes 1/3 of a
deposit
 Secondary Recovery
force water or steam
into wells

Oil Spills
(22% of US Natural gas used for
domestic heating)
Natural Gas Disadvantages

Drilling requirements
similar to oil.

Hard to transport,
(large amounts often flamed off at
oil fields)

Methane (70-90% natural
gas) contributes to global
warming
http://www.gosolarenergyforlife.com/wp-content/uploads/2009/12/burning-fossil-fuel.jpg
Fossil Fuels
Advantages
• Relatively Cheap
• High energy density
• Used by a wide variety
of engines and
devices
• Extensive distribution
network in place
http://www.treehugger.com/earth-in-oil-fossil-fuels.jpg
http://geothermal.marin.org/GEOpresentation/images/img112.jpg
Disadvantages
• Nonrenewable -will
deplete soon
• Combustion byproducts pollute–acid
rain and contain
greenhouse gases
• Extraction can damage
the environment
• Coal-fired power plants
require large amounts
of fuel
Fossil Fuels – How Long?
Electrical Power Production
Fossil
Fuel
Typical
Efficiency
Max
Efficiency
Coal
35%
42%
Oil
38%
45%
Fossil Fuel Reserves
 Coal Reserves
130 yrs.*
 Oil Reserves –
30 - 40 yrs**
 Natural Gas - 60
yrs***
* http://www.worldcoal.org/coalsociety/coal-energy-security/
Natural 45%
Gas
52%
**The Energy Watch Group
(EWG) 2007 report
***International Energy Outlook 2009
Fossil Fuel - Problem
A 400MW coal powered power plant
operates with an overall efficiency of 35%
a. Calculate the rate at which thermal
energy is provided by the coal.
b. Calculate the rate at which coal is being
burned (coal’s energy density is 30
MJ/kg)
c. The thermal energy not used by the
power plant is removed by cooling water.
The temperature of the water must not
increase by more than 5ºC. Calculate the
rate at which the water must flow.
Nuclear Energy
Nuclear Reactor
• Process - Nuclear fission – splits a large
nucleus into smaller nuclei releasing
energy.
• Fuel – Uranium 235
http://knol.google.com/k/-/-/oml631csgjs7/e4w1oo/fission.jpg
http://www.lanl.gov/science/1663/images/reactor.jpg
– Natural uranium contains only 0.7% of U-235
– Must be enriched typically to about 3% for
commercial power
– Uranium 235 will only absorb thermal (slow )
neutrons requiring a moderator to slow the
neutrons down by colliding with them.
– Critical mass - the minimum amount of U-235
required to absorb neutrons and keep the
reaction going.
Nuclear Reactor
• Induced Fission
1
0
236
140
94
1
n 235
U

U

Xe

Sr

2
92
92
54
38
0n
• Moderator – material surrounding the fuel
rods that slows down the neutrons by
colliding with it.
Types of Reactors
• Pressurized Water Reactor (PWR)
http://oncor.com/images/knowledgecollege/h20.jpg
http://www.succeedingwithscience.com/sellafield/img/agr_reactor_diagram.g
– Water moderator & coolant
• Gas Cooled Reactor
– Graphite moderator & Carbon Dioxide gas
coolant
Nuclear Power
Breeder Reactor
Fast neutrons created from the fissions can
be absorbed by U-238 to produce
Plutonium (P-239).
1
0
239
239
0
n 238
U

U

Np

92
92
93
1 e  v
239
93
Np
239
94
Pu  e  v
0
1
P-239 is a fissionable material
Used as fuel in other reactors or for nuclear
weapons.
http://hyperphysics.phy-astr.gsu.edu/HBASE/NucEne/imgnuk/lmfbr.gif
Nuclear Power
Breeder Reactor
• Core contains uranium and plutonium
about 15-20% plutonium and a greater
amount of U-235 (15-30%).
• Around the core is uranium that will absorb
neutrons and breed plutonium
• Heats up sodium that transfers heat to a
second sodium loop that then heats up
water to make steam
• Can produce 20% more fuel than it uses.
http://www.istockphoto.com/file_thumbview_approve/2853819/2/istockphoto_2853819-warning-nuclear-danger.jpg
Nuclear Power
Nuclear
Power
Advantages
• High power output
• Large reserves of
nuclear fuels
• Nuclear power plants
do not produce
greenhouse gases
Disadvantages
• Radioactive waste products
are difficult to dispose
– Long half-lives requires
nearly indefinite safe
storage.
• Accidents could directly
harm the public and the
environment
• Uranium mining hazardous
– Radon gas
– Radioactive waste material
• Possible produce materials
that could be used for
nuclear weapons
Chernobyl
http://legalplanet.files.wordpress.com/2009/05/smiley-nuclear.jpg
http://www.icjt.org/an/tech/jesvet/amerika_an.gif
http://www.icjt.org/an/tech/jesvet/graf_an.gif
Solar Energy
Source - Sun
• The earth’s upper
atmosphere receives about
1,400 W per square meter of
energy from the sun.
• Some is reflected back into
space. Some is trapped
inside the atmosphere by the
atmosphere’s gases
(greenhouse gases).
• A maximum of 1000 W/m2
hits the surface of the Earth
as direct sunlight on a clear
day
• Averaged over a 24hr time
period gives approximately
340 W/m2
http://www.civilizationsfuture.com/solar_files/image003.gif
http://lakeeffectrunclub.files.wordpress.com/2009/02/how-solar-energy-works-solar-sun-flares.jpg
http://www.asap-highlea.co.uk/solar_power.jpg
http://www.civilizationsfuture.com/solar_files/image003.gif
Physics for the IB Diploma 2nd Edition (Kirk) 2007
Solar Output
Physics for the IB Diploma 5th Edition (Tsokos) 2008
• Sun’s total output power is P=3.9 x 1026 W
(luminosity)
• The average distance between the sun and the
earth is r = 1.50 x 1011m.
• Recall (from sound), the intensity is defined as the
power per area
P
P
I 
A 4r 2
Calculate the intensity of the sun in a path directly
from the sun to the earth
P = 3.9 x 1026 W
P
3.9 x10 26
I

11
2
r = 1.50 x 10 m
4r
4 (1.50 x1011 ) 2
1379 mW2  1400 mW2
Solar Output
Physics for the IB Diploma 5th Edition (Tsokos) 2008
Solar Constant – 1400 W/m2 – the power received by
one square meter placed normally to the path of
the incoming rays of the sun a distance 1.5 x 1011
m from the sun.
• Does not account for
– Variations of ±1.5% in power output of sun.
– Variations of ±4% in the distance due to the elliptical orbit
of the Earth
The solar constant does not entirely reach the
Earth’s surface due to:
– Reflection of radiation
– Latitude, angle of incident
– Average between day & night.
Physics for the IB Diploma 2nd Edition (Kirk) 2007
Solar Output
Albedo(α) - the fraction of solar radiation that
is reflected directly back into space.
Daily Insolation - total amount of energy
received by 1 square meter of the Earth’s
surface throughout one day.
• Greater variation with distance from the
Latitude 30
equator
degrees
Physics for the IB Diploma 5th Edition (Tsokos) 2008
– Energy spread out over a larger area
– Radiation has to penetrate a greater
depth of
Latitude 60
atmosphere.
degrees
Physics for the IB Diploma 5th Edition (Tsokos) 2008
Physics for the IB Diploma 5th Edition (Tsokos) 2008
Physics for the IB Diploma 2nd Edition (Kirk) 2007
Physics for the IB Diploma 2nd Edition (Kirk) 2007
http://www.makeitsolar.com/images/Solar_Panel_03C.GIF
Solar Devices
http://www.pv-mover.com/tl_files/pv_mover/images/solarbaum.gif
Active Solar Devices - Devices that
captures sunlight and directly uses it
to heat water and/or air.
Photovoltaic Cells – Device that
converts sunlight directly into DC
current.
http://isolarit.com/isolarpower%20pics/Types%20of%20Solar%20Power/Men%20installing%20solar%20photovoltaic%20panels.jpg
Active Solar
Devices
• Flat collecting surface
with a coated glass
surface to protect and minimize reflection.
• Blackened surface beneath the glass
collects the sunlight and then transfers it to
pipes circulating water underneath.
• Alternative – pipes are exposed directly to
the sun and are blackened to
increase the absorption.
Physics for the IB Diploma 2nd Edition (Kirk) 2007
Physics for the IB Diploma 2nd Edition (Kirk) 2007
Active Solar Devices – Complex
Concentrator System –
• Incoming light focused then directed
to the collecting surface typically by a
concave mirror.
• With this water can be heated to
between 500ºC and 2000ºC turning
the water into steam which can then
drive a steam turbine and produce
electricity.
http://newenergydirection.com/blog/wp-content/uploads/2008/12/ps10_solar_power_tower_2.jpg
Physics for the IB Diploma 5th Edition (Tsokos) 2008
Photovoltaic Cells
http://buelsolar.com/Photovoltaic-Solar-System-Installation-Los-Angeles.jpg
• Converts sunlight directly into to dc power
due to the physics of semiconductors.
• Developed in 1954 at Bell Labs and used
extensively in the space program.
• Typically, produce low voltages useful in
operating low power electrical devices –
personal electronics, pumps, and other
stand alone devices. – lifetime of ~20 yrs
• Connecting many in series can produce
higher voltages
• Connecting many in
parallel can produce
large currents.
Physics for the IB Diploma 5th Edition (Tsokos) 2008
Semi-conductor Physics
A photovoltaic cell is typically
made of two layers of
semiconducting material
bonded together.
• One layer has excess
electrons (n-layer)
• The other has an excess of
electron vacancies (p-layer)
At the boundary the free
electrons of the n-layer
attempt to cross into the player and fill the electron
holes.
The combining electrons and
holes near the boundary
create a barrier for other
electrons to cross.
• Results in an electric field
forming across the boundary.
http://micro.magnet.fsu.edu/primer/java/solarcell/javasolarcellfigure1.jpg
http://www.ansercenter.org/images/org_photovoltaic.jpg
If light of a specific wavelength
strikes the layer and is
absorbed, the electrons
receive enough energy to
cross the boundary.
However, because of the
electric field they can not
return.
This builds up a charge
imbalance.
If an alternative path is
provided the electrons will
follow this creating a current.
Photovoltaic cells are
constructed with a metal
contact layer providing this
path for the electrons to flow
between the two layers.
http://micro.magnet.fsu.edu/primer/java/solarcell/javasolarcellfigure1.jpg
Source: http://micro.magnet.fsu.edu/primer/java/solarcell/javasolarcellfigure1.jpg
Solar Energy
Advantages:
• Free
• Requires no fuel
(Inexhaustible)
• Produces no waste or
pollution - clean
• In sunny locations
easiest source of
electricity for remote
places
• Handy for low-power
uses – calculators, etc
http://www.renergyb2b.com/kb/Graphics/Solar/world%20solar%20energy%20map-PV.JPG
http://www.solarsam.com/images/Sun_About_Solar.jpg
Disadvantages:
• Only works when the
sun is out – during day
and clear skies
• Unreliable except for
sunny climates.
• Low energy density –
low power output
• Expensive start up
costs to build solar
power stations,
• High cost to output
power.
http://awesome.good.is/transparency/007/images/007_solar_energy.gif
Source of energy –
Hydro-Electric
gravitational potential energy of water.
• Water allowed to flow downhill where the
PEKE
• KE of water  turns turbines generating
energy
• Rapidly expanding with power from
hydroelectric plants doubling every 15
years.
• Dependent on geography and results in
massive changes to the ecology of the area
Physics for the IB Diploma 2nd Edition (Kirk) 2007
http://www.sciencebuddies.org/science-fair-projects/project_ideas/Energy_img045.gif
Hydroelectric
Power
Three Gorges Dam – Yangtze River
Hydroelectric
Hydroelectric Power
http://www.mywindpowersystem.com/wp-content/uploads/2009/08/renewable-energy-tidal-2.gif
Different Schemes
• Reservoir behind dam.
• Water pumped from a
low reservoir to a high
reservoir
– Requires more energy to
pump it than electricity
produced.
– Means of storing energy
for peak needs.
http://www.physics.uiowa.edu/~umallik/adventure/nov_06-04/Grand%20Coulee%20Dam.jpg
• Tidal Power – traps
water at high tide and
releases at low tide
http://www.energex.com.au/switched_on/images/content/power_up_tidal_1.gif
http://www.climateandfuel.com/gifs/green/pumpstorage.jpg
Physics for the IB Diploma 5th Edition (Tsokos) 2008
Hydroelectric
Power
Principle
• Potential Energy (PE) of a mass of water
PE  mgh where h is the height of the water
• Mass (m) is given by m  V
– Where ρ is the density of the water (1000kg/m3)
– And V is the volume occupied
• Recall, the definition of power (P)
P
Energy mgh [ V ]gh
V



gh
t
t
t
t
V
Q
t
• Volume flow rate Q is
• So,
P  Qgh
Physics for the IB Diploma 5th Edition (Ts
Physics for the IB Diploma 5th Edition (Tsokos) 2008
Hydroelectric
Example:
Find the power developed when water
in a stream with a flow rate of 50 L/s
falls from a height of 15m.
• Q=50 L/s 50 Ls 10001LmL 11cmmL  1001mcm  .050 ms
• h = 15 m
• ρ = 1000 kg/m3
3
3
3
1000(.05)(9.8)(15) 
7350W  7.4kW
Hydroelectric Power
Advantages:
• High start-up costs,
but very little cost in
generating energy.
• Clean energy - no
waste or pollution
produced
• Reliable – electricity
can be generated
constantly
• Water can be stored
above the dam ready
to cope with peaks in
demand
Disadvantages:
• Very expensive to
build.
• Drastic changes to the
environment
– Displaces people and
animals
– stops natural flow
• Fish
• Flood cycle
• Water quality and
quantity downstream
can be affected, which
can have an impact on
plant life.
Wave Power
Principle
http://www.inhabitat.com/wp-content/uploads/opillus.JPG
• Utilizes the kinetic energy of waves to
generate electricity.
Challenges
• Wave patterns vary randomly in wave
speed, amplitude, and direction.
• Producing rotary motion to drive a turbine
from the slow motion of the waves.
• Harsh environment – corrosion and marine
life growth
Wave Power - Physics
Physics for the IB Diploma 2nd Edition (Kirk) 2007
• Modeling the wave as a square wave
• The volume of the top of the wave (shaded)
V A

2
L
• The mass of water in that part of the wave
  
m  V    A L 
 2 
• The loss of PE of this water
PE
1
v
• Recall, f   and f  T
• Maximum power available
PEloss
v gA2 Lv
2 
P
 gA L 
t
2 
2
loss
• Maximum power per unit length
  
 mgh   A L  gA
 2 
P gA2v

L
2
Example Problem
A wave in the middle of the Atlantic
Ocean has an amplitude of 2.3 m. The
density of the water is 1000 kg/m3 and
the wave energy transferred speed is 5
m/s. What is the amount of power per
unit length of its wavefront?
P gA v 1000(9.8)( 2.3) (5)
• A = 2.3 m

L
2
2
• ρ = 1000 kg/m3
P
 129605W  .13MW
• v = 5 m/s
L
2
2
Wave Power - Generators
Oscillating Water Column (OWC)
• Captures the energy of the wave without being
exposed to the corrosive environment of the waves.
Process:
Physics for the IB Diploma 5th Edition (Tsokos) 2008
Physics for the IB Diploma 5th Edition (Tsokos) 2008
• As the crest of the wave approaches the
opening of the OWC, it pushes the column
of water in the cavity upward.
• The rising water compresses the air
column above it.
• The air is directed through vents to a
turbine which it turns before being vented to
the atmosphere.
http://pagesperso-orange.fr/prof.danglais/btsindus/alternatives/img/4.jpg
• As the water falls with the trough, air is
drawn into the column again turning the
turbine.
Wave Power - Other Means
Buoys or Pitching Devices Wave Surge Devices
(Tapchan)
• Generate electricity from
• Use a shore-mounted
the bobbing or pitching
structure to channel and
action of a floating
concentrate the waves,
object.
driving them into an
– mounted to a floating
elevated reservoir.
raft or to a device fixed • Water flow out of this
on the ocean floor.
reservoir through a
• Example shown:
piping system to a
turbine.
utilizes the generator
• Hydroelectric system
action of permanent
where PE of reservoir
magnet surrounded by a
water changes to KE that
moveable coil of wire
then turns the turbine.
http://re.emsd.gov.hk/english/other/marine/images/marine_tech_010_2.gif
http://www.forcedgreen.com/wp-content/uploads/2009/06/waveenergy.jpg
Wave Power
Advantages:
Disadvantages:
• Only in areas with large
• Waves are free
waves.
• Reasonable energy
• Difficult to couple lowdensity
frequency water waves
• Produces no waste or
with high-frequency
greenhouse gases
turbines.
• Maintenance and
installation costly.
• Suitable areas for wave
generation are often
remote - far from cities.
• Harsh Environment
http://webecoist.com/wp-content/uploads/2008/11/wave-tidal-and-hydroelectric-power-designs.jpg
– Corrosive & marine life
– Withstand large storms.
Wind Power
Principle:
• Kinetic Energy of the wind turns the blades
of a turbine producing electricity
Source:
• Wind arises from the heating and cooling of
the earth.
• Differences in temperature within the
atmosphere creates pressure differences
due to hot air rising or cold air falling.
Costs:
• Varies from $500 to $5000 per kilowatt of
power
Physics for the IB Diploma 2nd Edition (Kirk) 2007
http://www.physicalgeography.net/fundamentals/images/heatingwind.GIF
Wind Power - Mathematics
Physics for the IB Diploma 2nd Edition (Kirk) 2007
• The area swept out by the turbine blade is
A  r
2
• The volume that passes the turbine in a
period of time is V  vA
t
• So the mass that passes the turbine in a
period of time is m  vA
t
• The kinetic energy available per time is
KE 1
1
 vAv 2  Av 3
t
2
2
Power Available
P
1
Av 3
2
Wind Power - Mathematics
• This relationship shows that the power of the wind
1
P  Av 3
2
– is proportional to the cube of its speed
– directly proportional to the spinning area of the blades.
• Rearranging, the power per area is
P 1 3
 v
A 2
Wind turbine blades do not extract all of the available
power out of the wind.
• Theoretically, their efficiency is between 35% and
45%.
Power coefficient Cp is the efficiency
factor of the turbine blades.
• With this the extracted power of
1
the turbine blades is
P  C p Av 3
http://greenupgrader.com/wp-content/uploads/2008/09/homeenergy-storstartyta.jpg
2
Wind Power - Efficiency
Power derivation assumed that the wind
is completely stopped by the wind
turbine
In addition frictional and other losses
mainly the turbulence of the air lowers
the efficiency.
In reality about 25% of the wind’s energy
is converted to electrical power.
Solar
Energy
Kinetic
Energy
(wind)
Kinetic
Energy of
Rotation
Electrical
Energy
Turbine
Losses in turbine
due to turbulence
Example Problem:
A windmill experiences a wind with a speed
of 12 m/s and an air density of 1.2 kg/m3 .
If the windmill has an efficiency coefficient
of 0.45 and a broad blade area of 50 m2,
what is the power extracted?
• v = 12 m/s
1
P  C p Av 3
2
• ρ = 1.2 kg/m3
1
• Cp = 0.45
P  (0.45)(1.2)(50)(12) 3
2
2
• A = 50 m
P  23328W  23kW
http://www.omafra.gov.on.ca/english/engineer/facts/03-047f7.gif
Historically
• Small wind turbines used for
agriculture use – pump water
• Provide electrical needs for
isolated homes
• Extracts ~ 3 kW of power with wind vanes no larger
than 1m long
Modern
• Wind turbines with vanes larger than 50 m can
extract megawatts of power from the wind
• Blades designed to function similar to airplane
wings utilizing lift created by the wind flowing over
the surface to turn the blades – more efficient
• Turbines mounted on tall towers or at sea can take
advantage of higher winds.
http://blog.ross-mcdonald.com/images/WindTurbine.jpg
http://www.dnrec.delaware.gov/Admin/PublishingImages/08%20Offshore_Wind_Turbine.JPG
Wind Generation
Current
Status
Wind
Myths
http://robinnixon.com/blog/wp-content/uploads/2007/06/bird_death_graph.png
Alternative Designs
Highway wind farms
Wind Towers
• Utilize wind created • Dynamic
by high speed
skyscrapers that
vehicles that create
rotate with the wind
an almost constant
creating their own
wind source.
power.
http://www.inhabitat.com/wp-content/uploads/twirlingtower1.jpg
http://www.popsci.com/files/imagecache/photogallery_image/files/articles/winddam_highway.jpg
Wind
Advantages:
Disadvantages:
• Wind is free
• Wind farms require no
fuel
• Produces no waste or
greenhouse gases
• The land beneath can
usually still be used for
farming,
• It’s a good method of
supplying energy to
remote areas
• The wind is not always
predictable.
• Low power output
• Disrupts the landscape
(ugly) and can disturb
migrating birds.
• Suitable areas for wind
farms are often remote
- far from cities.
• Electrical signal
interference (TV)
• Noise.
http://www.compositesworld.com/uploadedimages/Publications/CW/Articles/Internal/HPC1108_Windbladepart2_a.jpg
Geothermal Energy
Principle:
Utilizes the internal heat of the earth’s core.
Sites of Geothermal Energy
• Tectonic plate boundaries
– ‘Ring of Fire’
• Hot spots
– Area where heat from the earth’s magma
reaches the earth’s surface
• Yellowstone geysers
http://www.geni.org/globalenergy/library/renewable-energy-resources/world/sources_world/geothermalregions_files/img015.j
Geothermal Energy
Direct Geothermal Use
• Drill a well directly into the geothermal
source and the hot water is piped through a
system to provide heat.
• This heat can be used to produce steam
and generate electricity.
Three conventional types of geothermal
power plants
– Dry Steam
– Flash Steam
– Binary Cycle
Geothermal Power – Dry Steam
• Draw from underground resources of steam.
• The steam is piped directly from underground wells
to the power plant
• Directed into a turbine/generator unit.
• Limited -2 known such geothermal reservoirs in US
The Geysers in North California
Yellowstone National Park
http://www.digtheheat.com/geothermal/flash_power_plant.html
http://academic.evergreen.edu/g/grossmaz/geowells.jpeg
Geothermal Power – Flash Steam
• Use geothermal reservoirs with temperatures >360 ºF
• Hot water flows by its own pressure.
• As it rises, it pressure drops causing some of the
water to change into steam.
• The steam is separated from the water and directed
to a steam turbine.
• The condensed steam
and left over water is
piped back into the
reservoir.
More common than dry
steam plant
http://www.digtheheat.com/geothermalpics/flash_steam.gif
Geothermal Power – Binary Cycle
• Operate on lower temperature geothermal sources
(100ºF - 300ºF)
• This hot water is used to heat another secondary
fluid through a heat exchanger.
• This secondary fluid has a low
boiling point and is usually an
organic substance like
isobutane or isopentane.
• This secondary fluid vaporizes
in the heat exchange and then
is directed to a turbine.
• The water is redirected back to
the source.
http://www.digtheheat.com/geothermalpics/flash_steam.gif
Enhanced Geothermal Systems
EGS
Process:
Benefits:
• Drill deep into the earth
No typical
(1-3 miles) to penetrate hot
geothermal
permeable bedrock.
reservoir
• High pressure water is injected
required.
into the well cracking the rock • Large untapped
opening fissures.
energy source
• Water is continually pumped to • A 2006 MIT
assessment of
further extend the fractures.
geothermal power
• A production well is dug to
estimated that the
“technically
intersect the fractures and
extractable portion”
water is circulated through this
of the US
system.
geothermal resource
is “about 2,000
• The water is heated by the
bedrock producing steam that is times the annual
consumption of
used to turn a steam turbine.
primary energy in
• Additional wells are drilled to
the United States.”
expand the capacity.
http://www.pewclimate.org/docUploads/EGS-Fig2.JPG
Geothermal Energy
Advantages:
• Clean energy no
pollution or
greenhouse gases
emitted
• Compact power
stations
• No fuel required
• After initial building
cost, little to no cost in
generating power.
Disadvantages:
• Limited suitable
locations
• Source can be
unreliable and "run
out of steam", perhaps
for decades
• Hazardous gases and
minerals may come up
from underground difficult to safely
dispose of.
Source: www.nrel.gov
Biomass
Organic material made from
plants and animals and their waste
products.
• contains stored energy from the sun.
http://aq48.dnraq.state.ia.us/prairie/images/Biomass2.jpg
– Plants absorb the sun's energy through
photosynthesis and the chemical energy in
plants then gets passed on to animals and
people that eat them.
• Biomass is a renewable energy source
because we can always grow more trees
and crops.
Biofuel and Biomass
• Liquids
Found as solids,
– Biodiesel (vegetable oil)
liquids, and gases
– Ethanol
• Solids:
– Vegetable Oil
http://www.edinformatics.com/math_science/alternative_energy/biomass/BIOMASSTYPES1.gif
– Animal waste,
– bagasse (fiber of
sugarcane after
sugar is removed)
– Trash
– Charcoal
– Wood
– Mixtures
• Gases
– Biogas – produced by
the decaying of plants,
animals, and manure.
– Produced by algae
Possible replacement
for natural gas.
Source: DigTheHeat.com
Biomass
Advantages:
• Utilizes waste
materials
• Cheap fuel
• Lessen demands
on the fossil fuels.
Disadvantages:
• Collecting or growing
the fuel in sufficient
quantities can be
difficult.
• Burning biofuel SO
produces greenhouse
gases
• Some waste materials
used as fuel have
limited periods of
availability
Hydrogen Fuel Cells
Fuel cells harness the chemical energy
of hydrogen to generate electricity
without combustion or pollution
Hydrogen Fuel Cells
Advantages:
• Hydrogen is the
simplest and most
abundant element.
• Wide variety of
production methods
• Pollution free (only
emits water).
• No moving parts
(reliable and quiet).
• More efficient than
internal combustion
engines
Disadvantages:
• More expensive than
other energy sources.
• Little existing
infrastructure to
accommodate
hydrogen fuel.
• The process of
extracting hydrogen
may require fossil
fuels (thus generating
pollution).
• Hydrogen is difficult to
store and distribute