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8.21 The Physics of Energy
Fall 2009
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The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
8.21 Lecture 2
Units and the Scales of Energy Use
September 11, 2009
8.21 Lecture 2: Units and the scales of energy use
1
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Outline
•
The basics: SI units
•
The principal players: energy, power, force, pressure
•
The many forms of energy
•
A tour of the energy landscape: From the macroworld to our world
•
CO2 and other greenhouse gases: measurements, units, energy connection
•
Perspectives on energy issues --- common sense
and conversion factors
8.21 Lecture 2: Units and the scales of energy use
2
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
SI ≡ International System
MKSA = Meter, Kilogram, Second, Ampere Units
Not cgs or “English” units!
Electromagnetic units
Derived units
Charge ⇒ Coulombs
Energy ⇒ Joules
Current ⇒ Amperes
Power ⇒ Watts
Electrostatic potential ⇒ Volts
Pressure ⇒ Pascals
Resistance ⇒ Ohms
Force ⇒ Newtons
Thermal units
Temperature ⇒ Kelvin (K )
More about
these next...
8.21 Lecture 2: Units and the scales of energy use
3
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Outline
•
The principal players: energy, power, force, pressure
8.21 Lecture 2: Units and the scales of energy use
4
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Force, Energy, Power and Pressure
[ X ] means “The units of X”
Basics: m ⇔ kilograms, l ⇔meters
t ⇔ seconds, and Q ⇔ coulombs
For example: [ speed ] = l/t = meters/second
We can get the units of any physical
quantity by using a definition or
physical law that relates it to
something we already know...
• Newton’s second law Force = mass × acceleration
[ force ] = [mass][acceleration] = m l/t2 = kilogram meter/second2 = kg m/s2
1 kg m/s2 = 1 Newton
The force of gravity on you:
Fgravity = mg = 80 kg × 9.8 m/s2 = 784 Newtons
• Kinetic energy
Energy =
1
2
2
mass × velocity-squared
[ energy ] = [mass][velocity ] = m l2 /t2 = kilogram meter2 /second2 = kg-m2 /s2
1 kg m2 /s2 = 1 Joule = 1 Newton-meter
Your kinetic energy walking at 3 miles per hour:
meters
Ekinetic = 12 mv 2 = 12 80 kg 3 miles
hour × 1609 mile ×
1 hours 2
3600 second
= 72 Joules
8.21 Lecture 2: Units and the scales of energy use
5
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
• Power
Power = energy per unit time dE /dt
[ power ] = [energy][time−1 ] = ml2 /t2 (1/t) = kilogram meter2 /second3 = kg-m2 /s3
1 kg m2 /s3 = 1 Watt = 1 Joule/second
Power you exert climbing stairs at 0.5 meters per second
ΔE
Pclimbing
= mg Δh = 80 kg × .5 m × 9.8 m/s2 = 390 Joules
= ΔE/Δt = 78 Joules /1 second = 390 Watts
• Pressure
Pressure = force per unit area dF /dA
2
−1
2
1/l = kilogram/meter second2 = kg m−1 s−2
[ pressure ] = [force][area ] = ml/t
1 kg m−1 s−2 = 1 Pascal = 1 Newton/meter2
You, standing on the ground:
pgravity =
Force
784 Newtons
784
=
=
=∼ 34, 000 Pascals
Area
0.023
∼ 36 in2
8.21 Lecture 2: Units and the scales of energy use
6
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Outline
•
The many forms of energy
8.21 Lecture 2: Units and the scales of energy use
7
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Forms of Energy
• A long time to discover energy conservation.
• Energy disappears? No!
Changing form...
kinetic to potential to chemical to thermal to Einstein’s rest energy ...
• In fact it is conservation of energy, a single number characterizing a
system or even each part of a system, that can be traced through time and
as it flows and changes, that makes energy so important in physics.
• Units: All these different forms must have the same units of mass ×
length2 / time2 )
• Review a little 8.01 & 8.02 and see what’s to come
8.21 Lecture 2: Units and the scales of energy use
8
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
K INETIC E NERGY
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
1
2
mv
2
mass × [speed]2
2
l
l2
2
[mass] × [speed] = m ×
=m 2
t
t
Energy manifest in motion
W ORK A ND POTENTIAL ENERGY
Fd
force × distance
l2
ml
[force] × [distance] = 2 × l = m 2
t
t
When a force acts on an object over a distance it does
work that can show up as kinetic energy or be stored
as potential energy
8.21 Lecture 2: Units and the scales of energy use
9
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Units and
conversion
W ORK B Y P RESSURE
orce × volume
pressure × volume = farea
PV
l2
m
3
[pressure] × [volume] = 2 × l = m 2
lt
t
T HERMAL E NERGY
1
2NR T
≡ 12 nkB T
Thermal energy per degree of freedom at temperature T . Alternatively,
• n — number of molecules
• N — number of moles†
• kB — Boltzmann’s Constant 1.381 × 10−23 J K−1
• R — the gas constant R = 8.31447 Joules
mole K
• T — temperature in Kelvins
[NRT] = moles ×
Joules
mole K
• T — temperature in Kelvins
l2
× K=m 2
t
Kinetic energy of all the molecules makes its
appearance as heat
†
Note that the mole departs from
MKS units: It is a gram molecular
weight, the molecular weight of a
compound expressed in grams.
8.21 Lecture 2: Units and the scales of energy use
10
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
T HERMAL E NERGY
N R T ≡ nkB T
Convenient, colloquial unit of
energy: the BTU
1 BTU = energy to heat 1 pound of
H2 O from 60◦ to 61◦ F
)
E LECTRICAL E NERGY
Q×V
Q+
)
++++++++++++++++++++++++++++++
• Q — CHARGE
V
• V — ELECTROSTATIC POTENTIAL
–––––––––––––––––––––––––
Electrostatic potential ⇒ Electric field ⇒ Force
and the force does work on a charge that is moved.
How to measure electrostatic potential in SI Units?
What potential do you have to move one Coulomb of charge through to get (or lose) 1 Joule of
energy:
1 Joule
1 Joule/sec
1 Watt
1 Volt =
=
=
1 Coulomb
1 Coulomb/sec
1 Ampere
8.21 Lecture 2: Units and the scales of energy use
11
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
T WO
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
F O R M S O F E NER G Y T HAT M AY NOT B E A S FAMILIAR .. .
Q UA NTUM E NERGY
E = hν
• h is Planck’s constant
h = 6.626 × 10−34 J s
• ν is the frequency of light.
• Energy of one quantum of light (photon).
[energy] = [h] × [frequency]
ml2
1
=
[
h
]
×
t2
t
[h] = [energy] × [time] = J s
E I N S TEI N ’ S R E S T E N E R G Y: E = mc2
Einstein’s relativity showed that mass itself is a form of
energy with the speed of light as the conversion factor...
E = mc2
[E ] = [mc2 ]
=
ml2
t2
8.21 Lecture 2: Units and the scales of energy use
12
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Outline
•
Translations and scales: units and energy subcultures
8.21 Lecture 2: Units and the scales of energy use
13
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
There’s no other quantity that is described in more
different units than energy.
• exajoules, quads, teraWatt-years
GLOBAL UNITS
• tonnes of coal, tons of TNT, barrels of oil,
INDUSTRIAL STRENGTH UNITS
therms, kiloWatt hours
• BTU, kilocalories
• calories, foot-pounds, Joules
• ergs, electron-Volts
• E NE RGY U NIT S
• P OW E R U NIT S
HUMAN S IZED UNITS
CHILD SIZED UNITS
MICROW ORLD UNITS
Units of Energy and Power
1 electron volt (eV)
1 eV per molecule
1 erg
1 foot pound
1 calorieIT * (calIT)
1 calorieth* (calth)
1 BTUIT *
1 kilocalorieIT * (kcal)
or CalorieIT * (Cal)
1 kilowatt-hour (kWh)
1 cubic meter natural gas
1 therm (U.S.)
1 tonne TNT (tTNT)
1 barrel of oil equivalent
1 ton of coal equivalent
1 ton of oil equivalent
1 quad
1 terawatt-year (TWy)
1 watt (W)
1 foot pound per second
1 horsepower (electric)
1 ton of air conditioning
1.602 x 10-19 J
96.49 kJ mol-1
10-7 J
1.356 J
4.1868 J
4.184 J
1.055 kJ
4.1868 kJ
3.6 MJ
36 MJ
105.5 MJ
4.184 GJ
5.8x106 BTU 6.118 GJ
7 GcalIT 29.3076 GJ
10 GcalIT 41.868 GJ
1015 BTU 1.055 EJ
31.56 EJ
1 joule/sec
1.356 W
746 W
3.517 kW
* th
definition
four significant figures * IT
actual value varies
thermochemical
International Table
8.21 Lecture 2: Units and the scales of energy use
14
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
E NE RGY U NIT S
G LO BA L U NIT S†,
U NIT
SI EQ UIVALENT
E XA J OULE (EJ)
Q UA DRILLION BTU ( QUA D )
T RILLION K ILOWATT- HOURS
T ERAWAT T- YEARS (TW YR )
≡ 10 J
≈ 1.055 × 1018 J
≡ 3.6 × 1018 J
≡ 31.54 × 1018 J
World Total Energy consumption (2005)
World Oil consumption (2006)
World Net Electricity consumption (2005)
U. S. Total Energy consumption (2005)
U. S. Oil consumption (2006)
U. S. Total Electricity consumption (2005)
U. S. Transportation energy consumption
†
18
2005 H UMAN
C ONSUMPTION
488 EJ
463 quads
136 TkWh
14.5 TWyr
I NDUST R IAL S TR EN G T H U NIT S†
U NIT
31.0×10 barrels
15.7 TkWh
101 quads
6.9×109 barrels
2.8 TkWh
28.4 quads
≡
3.6 × 106 J
THERM
≈
1.055 × 108 J
≈
1.055 × 109 J
T ON TNT
≡
4.184 × 109 J
Definition. Approx chemical
energy in 2000 lb of TNT
BARREL OF OIL
∼
6.12 × 109 J
Definition: 5.8×106 BTU
energy of ∼159 liters of oil
T O N N E O F C OA L
∼
2.9 × 1010 J
Definition: 7 GCal
Energy in 1000 kg of coal
MILLION
M ICROW O RL D U NIT S
U NIT
U NIT
SI EQ U I VA LEN T
A PPROX IMAT E
1
≡
4.1868 J
≈
1.356 J
1 BTU
≈
1.055 × 10 J
Energy needed to heat
1 g r a m H2 O 1 ◦ C
Lift one pound 1 foot
against earth’s gravity
Heat 1 lb H2 O from
60◦ to 61◦ at one atm
1 C AL ORIE
OR K IL OCAL ORIE
≡
4.1868 × 103 J
P HYSICAL
SIGNIFI CANCE
1
CAL O RIE
FT- LB
3
BTU
105 BTU
Raise 1000 lb of H2 O 100◦ F
Notice how many units are close to 109 J — not an accident
— close to one human year of work (see later!)
From U. S. DOE Energy Information Administration Website
H UMAN SIZ E D AND C H I LD S I ZED UNIT S†
A PPROX IMAT E PHYSICAL
1 KWH
≡ means it’s a definition
≈ means it’s given to 4 significant figures
∼ means it’s a “nominal” value. Actual value varies, quoted value is often used.
EQ UIVALENT
SIGNIFICANCE
488 EJ
190 EJ
56.5 EJ
106 EJ
42 EJ
10.1 EJ
30.0 EJ
9
SI
ER G
SI EQ U I VA LEN T
≡ 10−7 J
P HYSICAL SIGNIFI CANCE
cgs unit ≡ 1 gm-cm/sec2 ≡ 1 dyne-cm
EV
≈ 1.602 × 10−19 J
Move one electron through one volt
More on the electron volt and erg
• Charge of 1 electron = 1.602176462(63) × 10−19 Coulombs
1 (electron charge) × 1 Volt = 1 “electron-volt” = 1 eV
1 eV = 1.602176462(63) × 10−19 Joules
• Energy of a single quantum (E = hν ) of green light is 2.5 eV
• Present record computer efficiency is ∼ 36 flop/erg†
which is 2.78 kJ/TFlop
†
The “Green 500” website http://www.baselinemag.com/c/b/Projects-Management/ lists a Blue-Gene-L
supercomputer at Daresbury Lab, GB, as the most efficient computer in 2007
8.21 Lecture 2: Units and the scales of energy use
15
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
E NE RGY U NIT S
G LO BA L U NIT S†,
U NIT
SI EQ UIVALENT
E XA J OULE (EJ)
Q UA DRILLION BTU ( QUA D )
T RILLION K ILOWATT- HOURS
T ERAWAT T- YEARS (TW YR )
≡ 1018 J
≈ 1.055 × 1018 J
≡ 3.6 × 1018 J
≡ 31.54 × 1018 J
World Total Energy consumption (2005)
World Oil consumption (2006)
World Net Electricity consumption (2005)
U. S. Total Energy consumption (2005)
U. S. Oil consumption (2006)
U. S. Total Electricity consumption (2005)
U. S. Transportation energy consumption
†
31.0×109 barrels
15.7 TkWh
101 quads
6.9×109 barrels
2.8 TkWh
28.4 quads
2005 H UMAN
C ONSUMPTION
488 EJ
463 quads
136 TkWh
14.5 TWyr
488 EJ
190 EJ
56.5 EJ
106 EJ
42 EJ
10.1 EJ
30.0 EJ
≡ means it’s a definition
≈ means it’s given to 4 significant figures
∼ means it’s a “nominal” value. Actual value varies, quoted value is often used.
From U. S. DOE Energy Information Administration Website
8.21 Lecture 2: Units and the scales of energy use
16
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
I NDUST R IAL S TR EN G T H U NIT S†
U NIT
SI
EQ UIVALENT
A PPROX IMAT E PHYSICAL
SIGNIFICANCE
1 KWH
≡
3.6 × 106 J
THERM
≈
1.055 × 108 J
≈
1.055 × 109 J
T ON TNT
≡
4.184 × 109 J
Definition. Approx chemical
energy in 2000 lb of TNT
BARREL OF OIL
∼
6.12 × 109 J
Definition: 5.8×106 BTU
energy of ∼159 liters of oil
T O N N E O F C OA L
∼
2.9 × 1010 J
Definition: 7 GCal
Energy in 1000 kg of coal
MILLION
BTU
105 BTU
Raise 1000 lb of H2 O 100◦ F
Notice how many units are close to 109 J — not an accident
— close to one human year of work (see later!)
8.21 Lecture 2: Units and the scales of energy use
17
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
H UMAN SIZ E D AND C H I LD S I ZED UNIT S†
U NIT
SI EQUIVALENT
A PPROXIMATE PHYSICAL
SIGNIFICANCE
1 CALORIE
≡
4.1868 J
1 FT- LB
≈
1.356 J
1 BTU
≈
1.055 × 103 J
1 C ALORIE
OR K ILOCALORIE
≡
4.1868 × 103 J
Energy needed to heat
1 gram H2 O 1 ◦ C
Lift one pound 1 foot
against earth’s gravity
Heat 1 lb H2 O from
60◦ to 61◦ at one atm
8.21 Lecture 2: Units and the scales of energy use
18
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
M ICROW O RL D U NIT S
U NIT
ER G
SI EQ U I VA LEN T
≡ 10−7 J
P HYSICAL SIGNIFI CANCE
cgs unit ≡ 1 gm-cm/sec2 ≡ 1 dyne-cm
EV
≈ 1.602 × 10−19 J
Move one electron through one volt
More on the electron volt and erg
• Charge of 1 electron = 1.602176462(63) × 10−19 Coulombs
1 (electron charge) × 1 Volt = 1 “electron-volt” = 1 eV
1 eV = 1.602176462(63) × 10−19 Joules
• Energy of a single quantum (E = hν ) of green light is 2.5 eV
• Present record computer efficiency is ∼ 36 flop/erg†
which is 2.78 kJ/TFlop
†
The “Green 500” website http://www.baselinemag.com/c/b/Projects-Management/ lists a Blue-Gene-L
supercomputer at Daresbury Lab, GB, as the most efficient computer in 2007
8.21 Lecture 2: Units and the scales of energy use
19
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
P OWER U NITS
U NIT
WAT T
SI EQ U I VA LEN T
≡ 1 J/sec (SI Unit)
P HYSICAL SIGNIFI CANCE
One Ampere thru one Ohm
resistance (for example)
FOOT- LB / SE C
≈ 1.356 W
Just what it says!
HOR SE PO WE R
≡ 746 W
Just what it says!
Power back to energy:
1 Watt-second = 1 Joule, or more commonly
1 kilowatt-hour = 1 kWh =
103 × 3600 = 3.6 × 106 Joules = 3.6 MJ
1 MJ = 1 “MegaJoule” ≈ 5-10 hard-working
human beings working for an hour
8.21 Lecture 2: Units and the scales of energy use
20
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Outline
•
A tour of the energy landscape: From the macroworld to our world
8.21 Lecture 2: Units and the scales of energy use
21
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
A guide for our tour: The workingman (or woman).
Although we use Joules for units (as consistently as possible),
it will be helpful to relate to a human scale. 100 Watts is an
average value for power production by a manual laborer...
100 Watts for 8 hours a day, 200 days a year
One
= 100
TH E HUMA N YEA R
= HY R
Joules
days
hours
seconds
× 200
= 580 MegaJoules
× 8
× 3600
hour
year
second
day
• A typical gamma-ray burst — perhaps the
collapse of a neutron star to form a black hole
1044 Joules
1.7 × 1035 hyr
• Solar energy output in a year
3. 8 × 1026 Watts × 3.16 × 107 seconds/year =12 × 1034 Joules
( 12 × 1034 J/year) / (580 MJ/hyr) 2. 1 × 1026 hyr/year
8.21 Lecture 2: Units and the scales of energy use
22
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
• World annual human energy consumption in 2005
490 EJ = 884 × 109 hyr
• Annual energy losses in U. S. (2005)
Efforts of > 100 times
the earth’s population
for a year
Efforts of ~ 15 times
the earth’s population
for a year
56 quads × 1.055 EJ/quad = 59 EJ
59 EJ = 102 ×109 hyr
• Rest energy of a person
Efforts of 2 times
the earth’s population
for a year
80 kg × (3×108 m/sec)2 = 7.2 EJ
7.2 ×1018 J = 12.4 × 109 hyr
• Solar radiation arriving at the top of the earth’s
atmosphere per second
Efforts of ~ U. S.
population for a year
1.7 × 1017 J = 2.93 × 108 hyr
• Annual output of typical nuclear power plant
1 GW ×3.6 × 107 sec/year = 3.6 ×1016 J
.036 EJ = 6.2 ×107 hyr
Efforts of 2 times
California’s population
for a year
8.21 Lecture 2: Units and the scales of energy use
23
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
• U. S. per capita yearly energy consumption in 2005
106 EJ / 300 ×106 people = 350 GJ/person
350 GJ/person = 600 hyr/person
Compare to world: 130
/person
Per day? 1 GJ/(person-day) ≈ 2 hyr/(person-day)
• Average yearly Northeast U. S.
household energy consumption
3 Joule
180 ×106 BTU
year × 1.06 × 10 BTU
= 191 GJ/year
191 GJ/year = 329 hyr/household
http://en.wikipedia.org/wiki/
Energy_use_in_the_United_States
8.21 Lecture 2: Units and the scales of energy use
24
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
• Energy required per person BOS-LAX via Boeing 747
0.01 gallon/mile × 2600 miles = 26 gallons
142 MJ/gallon of Jetfuel ×26 gallons = 3.692 GJ
3.692 GJ ⇒ 6.36 hyr
http://travel.howstuffworks.com/question192.htm
•
http://en.wikipedia.org/wiki/Gasoline#Energy_content
One tank of gasoline
15 gallons × 3.79 liters/gallon = 56.9 liters
56.9 l × 34.8 MJ/l = 1.98 GJ = 3.4 hyr
8.21 Lecture 2: Units and the scales of energy use
25
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
• Recommended U. S. dietary energy intake
2,000 – 2,500 kCal/person-day
2000 kCal/day × 4.187 ×103 J/kCal ×
365 days/year = 3.1 GJ/ (person-year)
Result: One year’s energy intake per
person, 3.1 – 3.9 GJ ⇒
Yearly energy input per person amounts to
5.3 – 6.7 hyr
Or
≈ 10 MJ/(person-day)
• Energy input to produce average Swedish
(where I could find data) diets
Complex definitions of system
boundaries
Include: crop production, processing,
storage, transportation, storage,
preparation, cooking...
Exclude: Capital cost of equipment,
packaging, waste, human labor ...
Result: 6.9 — 21.0 GJ/person-year ⇒
12 – 36 hyr/person
The system boundaries in the study included farm production with production of farm
inputs, drying of crops, processing, storage and transportation up to the retailer. They also
included storage, preparation and cooking in households. The system boundaries excluded
production of capital goods such as machinery and buildings, packaging material, waste
treatment, transportation from the retailer to the consumer and dishwashing. The
economic value of products and by-products was the basis for allocation of energy use
during processes with multiple outputs. The energy use was calculated as process energy
with no inclusion of production and delivery energy, conversion and transmission losses.
Only commercial energy inputs were considered, e.g., inputs derived from electricity, fuel
oil, coal or gasoline. Energy inputs from the sun or from human labour were not
considered
8.21 Lecture 2: Units and the scales of energy use
26
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Outline
•
CO2 and other greenhouse gases: measurements, units, energy connection
8.21 Lecture 2: Units and the scales of energy use
27
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Measurement of CO2 (and other greenhouse gases)
In later lectures we will have much to say about global climate change, its origins
and relation to energy use and to CO2 . Here...
• Properties of CO2 .
• Important measures of CO2 .
• Other greenhouse gases.
Properties of CO2
• Atomic weight 12+16+16=44. Compared to air ≈ 78% N2 and 21% O2 . Atomic weight
28.6. So CO2 has density 44/28.6 = 1.54 × density of air.
• Sublimes (directly from solid to gas) at -70◦ C at atmospheric pressure.
• No liquid state at pressures below 5 atm. At higher pressures CO2 melts at -57◦ C.
8.21 Lecture 2: Units and the scales of energy use
28
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Important measures of CO2
• In the atmosphere — in parts per million (ppm)
• Transfer and production through human activity and in earth’s carbon cycle —
usually in millions of metric tonnes (MMT)
• Emissions in energy processes: kilograms CO2 per Joule of energy produced
(kg/J). (Usually energy produced at the source, not including losses and other
inefficiencies.† )
CO 2 in the atmosphere
Pre-industrial concentration: 280 ± 10 ppm.
Present concentration: ≈ 383 ppm.
Increase due to human activity
†
For example: Find quoted CO2 emission per kWh of coal produced
electricity. Does not include efficiency of power plant (∼ 35%) or
transmission losses, or conversion losses in application.
8.21 Lecture 2: Units and the scales of energy use
29
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
CO 2 produced by human activity (millions of metric tonnes!)
Some U. S. data
• Total CO 2 in the atmosphere: 2,996,000 MMT
• World CO 2 emissions from fossil fuel (2007): 28,190 MMT
• Emissions as a fraction of total: 0.94%
• Leading emitters from fossil fuel (2007):
Region
United States
China
Europe
CO 2 (MMT)
5,957
5,322
4,675
• CO 2 emission in U. S. by sector (2006):
Sector
Residential
Commercial
Industrial
Transportation
Electric Power
CO 2 (MMT)
1,204
1,045
1,650
1,990
2,344
• CO 2 emissions per person in U. S. per year:
6 × 109 tonnes
∼
= 20, 000 kg/person
3 × 108 persons
Staggering!
http://www.eia.doe.gov/oiaf/1605/ggrpt/carbon.html
8.21 Lecture 2: Units and the scales of energy use
30
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
CO 2 emission in energy processes
Different fossil fuels have different carbon and energy content.
Data typically given in standard unit of kilograms of carbon per million BTU of
energy produced at the source. We’ll convert to kilograms of CO 2 per GJ of energy.
Fuel
Coal
Jet fuel, kerosene, gasoline
Liquified petroleum gas
Natural gas
CO 2 emission factor
kg(C)/Million (BTU)
∼ 26
∼ 19
∼ 17
∼ 14.5
kg(CO 2 )/GJ
90
66
59
50
8.21 Lecture 2: Units and the scales of energy use
31
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Units and
conversion
Other greenhouse gases:†
• Methane (CH 4 ), nitrous oxide (N 2 O), and a variety of chloro- and fluorocarbons (collectively
halocarbons) contribute significantly to the greenhouse effect.
Gas
Current
concentration
GWP
Atmospheric
lifetime (years)
Carbon dioxide
Methane
Nitrous oxide
Halocarbons
383 ppm
∼ 1800 ppb
319 ppb
∼ 1 ppb
1
23
296
140 — 10,000
Variable (5 – 200)††
∼ 12
114
5 – 250
Increased
radiative
forcing (W/m 2 )
1.66
0.5
0.16
0.34
• GWP is a measure of “global warming potential” (per unit mass) with CO 2 defined as 1.
• “Increased radiative forcing” is the increase in the rate that energy is made available at the
earth’s surface due to this greenhouse gas, measured in W/m2 and can be compared with the
solar energy input.
• Source: Carbon Dioxide Information Analysis Center, [email protected].
†
††
Water, while an important greenhouse gas, is omitted from the table.
Atmospheric lifetime of CO 2 is hard to estimate because so many different processes affect it.
8.21 Lecture 2: Units and the scales of energy use
32
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Outline
•
Perspectives on energy issues --- common sense
and conversion factors
8.21 Lecture 2: Units and the scales of energy use
33
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
1. The energy content of matter is enormous
Matter equivalent of annual human energy budget:
4.9 × 1020 J
=
M c2
c = 3.0 × 108 m/sec
M
= 4.9 × 1020 /9.0 × 1016
= 5.4 × 103 kg
not even heavy lifting!
What does one gram buy?
10−3 kg × (3 × 108 m/sec)2 = 9 × 1013 J
enough to run a 2.86 megawatt powerplant for a year.
8.21 Lecture 2: Units and the scales of energy use
34
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
2. The solar energy incident on the earth is enormous
Sun’s energy incident at the top of the earth’s atmosphere varies between 1321
and 1412 watts/m2 throughout the year. Average of 1366 watts/m2 . Solar
power incident on the earth
2
1366 W/m2 × πR⊕
≈ 1.74 × 1017 W = 0.174 EJ/sec
so in 488/(.174) seconds = 47 minutes the sun delivers all the energy used by
humanity in a year.
8.21 Lecture 2: Units and the scales of energy use
35
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
3. Estimate what area of solar
would provide U. S. annual
energy budget at 100%
efficiency?
• Find data: National Renewable
Energy Laboratory has solar
radiation atlas.
(www.nrel.gov/gis/solar.html)
• Convert to SI units: Units are
“kWh/m2 /day”, 1 day = 24 hours,
1 kWh/day = 1 kWh÷ 24h/day ≈ 42 W
AV ERAGE P OW ER
So insolation is 42 W/m2 times the factor, I , in the table. Compute area
needed for E = 1.05 × 1020 J/year
• Take I = 6.5 (looks typical for American southwest),
1.05 × 1020 J/year ÷ (3.15 × 107 sec/year) ÷ (6.5 × 42 W/m2 )
= 1.2 × 104 km2
8.21 Lecture 2: Units and the scales of energy use
36
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
Collector area = 1.2 × 104 km2
Looks pretty promising. It’s the
reason why we believe solar energy
is the best long-term energy source.
Warning, big multiplication factor
from inefficiencies (stay tuned).
8.21 Lecture 2: Units and the scales of energy use
37
The Basics: SI Units
Energy, power, force, pressure
The many forms of energy
Units and
conversion
A tour of the energy landscape
CO2 and other greenhouse gases
Common sense and computation
4. What’s the ratio of typical carbon based energy source to typical
nuclear energy source?
• Atomic energy scales are eV — energy necessary to ionize hydrogen is 13.6 eV.
• Nuclear energy scales are MeV — energy necessary to remove a proton from a
typical nucleus is ∼ 8 MeV.
• Energy of reaction for H2 + 12 O2 → H2 O is ∼ 3 eV/reaction.
• Energy of reaction for fission of uranium is ∼ 200 MeV/reaction.
Nuclear fuels have roughly 1 million times the energy density of carbon fuels.
8.21 Lecture 2: Units and the scales of energy use
38