1. Basic concepts (I)
How do you define energy?

2. Energy: definition related to physical forces
• Definition of energy: in physics, energy is the
work that a force can or could do.
• Forces are:
– gravitational (due to interaction between mass and
energy concentrations)
– electric (attraction and repulsion of charged particles)
– magnetic (attraction and repulsion of magnetic objects)
– chemical (driving chemical reactions: electro-magnetic)
– nuclear (binding nuclei together or breaking unstable
apart)
– mechanic (impact of one moving object on another)

3. Force of Gravity
• On earth, we are constantly under the force
of gravity. What types of energy does gravity
produce?
– Acceleration of falling objects
– Altitude and depth pressure gradients of the
atmosphere and the seas
– Part of the fusion of the earth’s core
F

4. Mechanical Force
• Mechanic forces are when one object hits
another. What type of energy does this
produce?
– Acceleration / deceleration of interacting objects
– Heat dissipation within the objects
– Change of shape of objects
v v
v v

5. Electric & magnetic forces
• Cause electrons to be attracted to nuclei in
atoms -> basis for chemistry
• Cause charges (electric current) to flow in
electric circuits -> basis for energy used in
electronics, lights, appliances
• Cause needle of compass to point north

6. Energy: definition, continued
• Energy is can also be inherent in a system,
without any forces acting on it.
• Types of inherent energy are:
– In a steadily moving particle: ½ mass x velocity2
– In a mass: mass x (speed of light)2 = mc2
– In a body at a certain temperature:
(heat capacity of body) x temperature
for water, heat capacity is, 1 calorie per gram per
degree Celsius or Kelvin
– In a chemical compound:
2 H2 + O2 -> 2 H2O , Enthalpy released = -571.6 kJ/mol

7. Forms of energy
• Energy can take many forms
– kinetic (movement of a mass)
– electric, magnetic (movement of charges or electromagnetic
fields radiating)
• Electricity
• Radiation (light)
– chemical (molecules with internal energy)
– heat (thermal) (statistical expression of kinetic energy of
many objects in a gas, liquid or solid - or even radiation)
– potential (water above a dam, a charge in an electric
potential or a battery)
Other examples?

8. SI units for energy
• The SI unit of energy is a Joule: 1 kg*m2/s2 =
1 Newton*m (Newton is the unit of Force)
– mass * velocity 2
– mass * g * height (on earth, g = 9.81 m/s2 )
– for an ideal gas = cvkBT (cv =3/2 for a monatomic
gas)
• Power is energy per time: 1 Watt = 1 Joule/s
= 1 kg*m2/s3
– most commonly used in electricity, but also for
vehicles in horsepower (acceleration time)

9. Other common energy units
http://www.onlineconversion.com/energy.htm
Energy conversion
Unit Quantity to Note
1 calorie = 4.1868000 Joule
1 kiloWatt hour = kWh = 3600000 Joule A power of 1 kW for a duration of 1 hour.
It is a is a unit of energy used in North
1 British Thermal Unit = btu 1055.06 Joule
America.
It is the rounded-off amount of energy that
1 ton oil equivalent = 1 toe 4.19E+010 Joule would be produced by burning one
metric ton of crude oil.
1 ton coal equivalent 2.93E+10 Joule
Barrel
1 ton oil equivalent = 1 toe 1 / 7.33 or 1 / 7.1 or 1 / 7.4 ...
of oil
1 cubic meter of natural gas 3.70E+07 Joule or roughly 1000 btu/ft3
1000 Watts for one year 3.16E+010 Joule for the 2000 Watt society
1000 Watts for one year 8.77E+006 kWh for the 2000 Watt society
1 horsepower 7.46E+002 Watts

10. Prefixes
Orders of magnitude
Name Quantity Prefix
thousand 1E+03 kilo
million 1E+06 mega
billion 1E+09 giga
trillion 1E+12 tera
quadrillion 1E+15 peta
quintillion 1E+18 exa
sextillion 1E+21 zetta
septillion 1E+24 yotta

11. How to do energy conversions
(quick reminder)
• Given E = 5 kWh, what is value in MJ?
• From table, 1 kWh = 3.6 MJ
• 5 kWh x (3.6 MJ / kWh) = 18 MJ
• In other direction: 5 MJ = ? kWh
• 1 MJ = 0.28 kWh
• 5 MJ x (0.28 kWh / MJ) = 1.4 kWh

12. Basic concepts (II)
How do you use energy?

13. What is energy for?
How do you use energy?
Examples of:
• Kinetic
• Electro-magnetic
– Electricity
– Radiation (light)
• Chemical
• Potential
• Heat (thermal)
?

14. Practical energy: what is it for?
Energy in daily life: we use it to ...
– stay alive (food, oxygen: chemical)
– move faster (transportation fuel: chemical)
– keep warm (heating fuel: chemical)
– almost everything else (keep cold, preserve food,
light and ventilate spaces, cook, run machines,
communicate, measure, store data, compute,...):
electricity
In industrial processes: we use it to …
– Extract (mechanical), refine (chemical),
synthesize (chemical), shape (heat, mechanical),
assemble (mechanical): produce

15. Properties of energy
• In any process, energy can be
transformed but is always
conserved
–Fuel + oxygen: heat, light + new
compounds
–Moving objects collide: heat + work
on objects
–Falling water+turbine: electricity +
heat

16. Basic concepts (III)
Energy conversion, conversion efficiency

17. Energy conversion
• Energy conversion: from one type to another
• Examples:
– Chemical to kinetic
– Chemical to electric
– Potential to electric
– Thermal to electric
– Chemical to thermal
– Radiation to chemical
– Radiation to electric
– Radiation to thermal
– Electric to thermal
– Electric to chemical

18. Why is this important? Efficiency
• What is efficiency?
Output / Input
Energy out / energy in for an energy
conversion process?
Energy out = energy in , so not very
useful
Useful energy out / energy in
Physical work / Heat content of fuel
Electricity / physical work
Food / Inputs to agriculture

20. Efficiencies (2)
Source: Smil 1999

21. Efficiencies (3)
Source: Smil 1999

22. More than one conversion process
• The total efficiency is the product of all
conversion efficiencies:
Etotal = E1 x E2 x E3 x E4 x E5 x E6 x …
• Total losses can be (and are) tremendous
• Most losses are in the form of radiated heat,
heat exhaust
• But can also be non-edible biomass or non-
work bodily functions (depending on final
goal of energy)

23. Chain of conversion efficiencies:
Light bulb
t
r
t
c e e r
Etotal = E1 x E2 x E3 = 35% x 90% x 5% = 1.6%
Source: Tester et al 2005

24. Example 2: diesel irrigation
Losses: t t t,r t,m

25. Example 3: Drive power

26. Example 4: living and eating
• Need 2500 kcal/day = 10 MJ/day or 2kcal/min.
• 2200 for a woman, not pregnant or lactating,
2800 for a man (FAO). EU: 3200 kcal/day.
• Equivalent to 4.75 GJ/year vegetable calories
in a vegetarian diet (including 1/3 loss of food
between field and stomach)
• Equivalent to 26.12 GJ/year vegetable calories
in a carnivorous diet (1/2 calories from meat)
• Vegetarians are 5.5 times more efficient in
terms of vegetable calories.

27. Efficiency of human-powered motion
kcal/mile

28. EU Energy Label
• A, B, C … ratings for
many common appliances
• Based on EU standard
metrics for each appliance
– kWh / kg for laundry
– % of reference appliance
for refrigerators

29. Importance of consumer
behavior/lifestyle
• EU energy label vs. temperature of washing
kWh per cycle/Energy
Rating A B C D E F
90°C wash 1.22 1.46 1.59 1.72 1.85 1.98
60°C wash 0.94 1.12 1.23 1.34 1.47 1.6
40°C wash 0.56 0.67 0.74 0.79 0.85 0.91

30. USA EnergyGuide label
• EnergyStar ratings
exist, but are not
A,B,C grades
• Instead, appliances
have EnergyGuide
labels (usually
without EnergyStar
ratings)

31. Basic concepts (IV)
Thermodynamics and entropy

32. Conservation, but …
• Energy is ALWAYS conserved
• However, energy is not always useful:
dissipated heat is usually not recoverable.
• Useful energy is an anthropocentric concept
in physics: from study of thermodynamics
• Thermodynamics investigates statistical
phenomena (many particles, Avogadro’s
number = 6×1023): energy conversion
involving heat.

33. 3+1 laws of thermodynamics
• If systems A and B are in thermal
equilibrium with system C, A and B are in
thermal equilibrium with each other
(definition of temperature).
• Energy is always conserved.
• The entropy of an isolated system not at
equilibrium will tend to increase over time.
• As temperature approaches absolute zero,
the entropy of a system approaches a
constant.

34. Paraphrases of 2 laws of
thermodynamics
• You can’t get something from nothing.
• You can’t get something from something.
1. You can't get anything without working for it.
The most you can accomplish is to break even.
2. You even can't break even.
• (economics)
There is no such thing as a free lunch.

35. History of thermodynamics (2nd law)
Nicolas Léonard Sadi Carnot
(1796-1832)
– Theory of heat engines, “reversible”
Carnot cycle: 2nd law of thermodynamics
Ludwig Boltzmann (1844-1906)
Kinetic theory of gases (atomic)
– Mathematical expression of entropy
as a function of probability

36. Entropy
The entropy function S is defined as
S = kB log (W)
– kB = Bolzmann’s constant = 1.38× 10 −23
=Joule/Kelvin
– W=Wahrscheinlichkeit
= Σ possible states
– Increases with increasing disorder
For instance:
• vapor, water, ice
• expanding gas
• burning fuel

37. 2nd law of thermodynamics
dS
≥ 0 entropy increases over time (definition of time)
dt
For a system undergoing a change,
∆S system ≥ 0 for an isolated system
∆S system + ∆S environment ≥ 0 for an non - isolated system

38. 2nd law of thermodynamics
Total entropy always increases with time.
An isolated system can evolve, but only if its entropy
doesn’t decrease.
A subsystem’s entropy can increase or decrease, but the
total entropy (including the subsystem’s environment)
cannot decrease.
R. Clausius (1865):
“Die Energie der Welt ist konstant.
Die Entropie der Welt strebt einem Maximum zu.”
Notion of “heat death of the universe”

39. Basic concepts (V)
Applications of thermodynamics: heat engines,
Carnot cycle, maximum and real efficiencies.

40. Performance of energy conversion
machines (Carnot cycle)
• Heat engine (cycle)
– Heat, cool engine fluid
– Diesel, internal combustion
• Reversible processes:
– Entropy remains constant
– ∆Sc = - ∆Sh
• Irreversible processes
– Real world
– Heat losses, no perfect insulator
– Heat leakage
– Pressure losses, friction

41. The Carnot Cycle (the physics)
Ideal cycle between
isotherms (T=constant)
and adiabats (S =
constant).
dE = dW - dQ
where dW = PdV
dQ = TdS
Loop integral over dE = 0.
The total work from one cycle of the engine is
The heat taken from the warm reservoir is
The efficiency is : theoretical maximal for heat engine.

42. Common types of heat engines
• Rankine cycle: stationary power system (power plant
for generating electricity from fossil fuels or nuclear
fission), efficiency around 30%
• Brayton cycle: improvement on Rankine to reduce
degradation of materials at high temperature (natural
gas and oil power plants), efficiencies of 28%
• Combined Rankine-Brayton cycle: for natural gas
only, efficiencies of 60%!
• Otto cycle: internal combustion engine, electric
spark ignition, efficiency around 30%
• Diesel cycle: internal combustion engine,
compression ignition (more efficient than Otto if
compression ratio is higher), efficiency around 30%

43. Comparison of heat engines

44. Coal power plant
Typical generating capacity: 500 MW
250 tonnes of coal per hour

45. Other types of power generation
• Not based on heat (fossil combustibles or
nuclear)
• Use various types of energy (guess which?)
– Hydraulic power: gravitational energy of water
– Wind power: kinetic energy of air
– Solar power: radiation from sun

46. Wind power
• Power = 0.47 x η x D2 x v3 Watts
– η = efficiency ~ 30% (59%
theoretical maximum)
– D = Diameter (40 meters)
– v = wind speed (13 m/s)
– P = 500 kW

47. Hydroelectricity (hydro)
Uses difference in potential gravitational energy of
water above and below dam
• E = m x g x ∆ h + m x ∆ v2 / 2
• P = η x ρ x g x ∆ h x (flow in m3/s)
• ρ is the density of water = 1000 kg /m3
• Efficiency η can be close to 90%
∆ h

48. Power plant & fuel cell efficiencies
% Efficiency
Source: Miroslav Havranek, 2007

49. Energy, entropy and economy:
some history
• Austrian Eduard Sacher (1834-1903) Grundzüge
einer Mechanik des Gesellschaft : economies try to
win energy from nature, correlates stages of cultural
progress with energy consumption.
• Wilhelm Ostwald (1853-1932) “Vergeute keine
Energie, verwerte Sie!” concerns due to rising fuel
demands and realization of thermodynamic losses
• Frederick Soddy (1877-1956) “how long the natural
resources of energy of the globe will hold out”,
distinguishes between energy flows in nature and
fossil fuels (“spending interest” vs. “spending
capital”)

50. Basic concepts (VI)
Georgescu-Roegen and entropy applied to the
economic system.

51. Implications of entropy for economics
• Geogescu-Roegen (1906-1994),
Romanian economist, wrote The
Entropy Law and the Economic
Process in 1971.
• Points out that economic processes
are not circular, but take low entropy
(high quality resources) as inputs
and produce high entropy emissions
(degraded wastes).
• Worries about CO2 emissions from
fossil fuel burning
• Concludes that current entropy
production is too high, advocates
solar input scale for global
economy.

52. Georgescu-Roegen (1)
« Le processus économique n’est qu’une extension
de l’évolution biologique et, par conséquent, les
problèmes les plus importants de l’économie
doivent être envisagés sous cet angle »
Vision G-R, reprise par H. Daly
et l'économie écologique
Vision Brundtland 1987 du
développement durable Environment
Society
Econom Environ
y ment Econo
my
Society

53. Georgescu-Roegen (2)
« la thermodynamique et la biologie sont les flambeaux
indispensables pour éclairer le processus économique (...) la
thermodynamique parce qu’elle nous démontre que les
ressources naturelles s’épuisent irrévocablement, la biologie
parce qu’elle nous révèle la vraie nature du processus
économique »
2 concepts clefs:
• les ressources naturelles s’épuisent irrévocablement
(thermodynamique)
• la "vraie nature" du processus économique peut être
comprise à travers la biologie (surtout l'analyse énergétique
des écosystèmes)

54. Georgescu-Roegen (3)
" Chaque fois que nous produisons une voiture, nous
détruisons irrévocablement une quantité de basse entropie qui
autrement, pourrait être utilisée pour fabriquer une charrue ou
une bêche. Autrement dit, chaque fois que nous produisons
une voiture, nous le faisons au prix d'une baisse du nombre de
vies à venir."
concepts clefs:
le patrimoine limité de l'humanité en ressources naturelles
et donc la responsabilité envers les générations suivantes
The entropy law and the economic process

55. Georgescu-Roegen (1)
“The economic process is nothing but an extension
of biological evolution. Therefore the most important
problems of the economy must be considered
through this lens.”
G-R’s vision, taken up by H. Daly
and ecological economics
Brundtland’s 1987 vision of
sustainable development Environment
Society
Econo- Environ
my ment Econo
my
Society

56. Georgescu-Roegen (2)
“(…) our whole economic life feeds on low entropy, to wit,
cloth, lumber, china, copper, etc., all of which are highly
ordered structures. (…) production represents a deficit in
entropy terms: it increases total entropy (…). (…) After the
copper sheet has entered into the consumption sector the
automatic shuffling takes over the job of gradually spreading
its molecules to the four winds. So the popular economic
maxim “you cannot get something for nothing” should be
replaced by “you cannot get anything but at a far greater cost
in low entropy”.”
The entropy law and the economic process, p. 277-279
key concepts:
Economic processes feed on low entropy, produce high
entropy
• Concentrated natural resources are gradually dispersed

57. “[…] It is not the sun’s finite stock of energy that sets a limit to how long
the human species may survive. Instead it is the meager stock of the
earth’s resources that constitutes the crucial scarcity. […] First, the
population may increase. Second, for the same size of population we
may speed up the decumulation of natural resources for satisfying
man-made wants, usually extravagant wants. The conclusion is
straightforward. If we stampede over details, we can say that every
baby born now means one human life less in the future. But also every
Cadillac produced at any time means fewer lives in the future. ”
Key concepts:
Solar energy will still be available in the future, however
the quantity (STOCK) of low entropy natural resources is
limited
thus the responsibility to future generations.
The entropy law and the economic process, p. 304

58. Global entropy – global population
• Meadows (1971): There are limits to
economic and physical growth of human
societies.
• Daly (1973): steady-state economy and
population is a goal, but at levels supported
by organic agriculture alone: population
probably lower than today. Advocate of
managed decline in population, economic
growth.

59. Basic concepts (VII)
Origin of energy
How do we get energy?
Where does it all come from?
(not so simple...)
Energy system
(primary, final, useful, energy services)

60. Origin of energy on earth
• Food? Solar (via photosynthesis)
• Oxygen? Solar (via photosynthesis)
• Wood for burning? Solar (via photosynthesis)
• Fossil fuels? Solar (via photosynthesis and
geological processes: geothermal heating, pressure)
• Hydraulic or wind? Combination of solar and earth's
rotation (Coriolis effect)
• Geothermal? Combination of nuclear fission and
gravitation.
• Nuclear fission? Fossil supernova explosion energy.
How do we compare such different sources?

61. Energy chain

62. Origin of nuclear energy: supernova
Nuclear fusion,
powered by
gravity, is the fuel
of stars. Fusion is
only efficient up to
iron creation
(nothing heavier).
Some heavy stars
burn to iron, then
implode under the
force of gravity.
The shock wave is
so strong it creates
heavier atoms.

64. Comparing energy types
• Primary energy: energy initially extracted from nature
• Final energy: transported, transformed, converted,
ready to use (electricity, gasoline, bioethanol)
• Useful energy: used by final consumer (light, heat,
motion)
These concepts are mainly applicable to fossil energy
systems.
Three main types of primary energy: fossil, solar-based
(renewable) and nuclear

65. Including
biomass
Source: Haberl 2001
Also advocates an
approach to energy
accounting similar to
material flow analysis:
energy density of all
materials (and wastes)
should be included.

66. Emergy
• H. T. Odum
• Embodied (and/or Emergent) Energy
• “Emergy is the available energy of one kind
previously used up directly and indirectly to
make a product or service.”
• Solar emergy for ecological systems.

67. Exergy
• Refers to a process analysis in which the material
and energy flows are measured with respect to a
“reference state”
• Can be done at a large regional or global level, if
“reference state” of materials is calculated relative to
their earth averages.
• Exergy studied and concept promoted by Robert
and Leslie Ayres (many references).

68. Calorific content: gross & net
• Gross calorific value: include heat from exhaust
water (C + H both burn with O, creating CO2 + H2O)
• Net calorific value: exclude latent heat of water
vapor.
• Difference:
– Gross is 5-6% larger than net for solid + liquid fuels
– Gross is 10% larger than net for natural gas.
– Worse if fuel is damp (has water trapped inside it)

69. Traditional/commercial
accounting
• International Energy Agency compiles
national statistics (since 1960s for OECD
and 1970s non-OECD)
• Available online at
– http://www.iea.org/Textbase/stats/index.asp

70. Source: Jochem et al 2000
Energy Services

71. Energy system: services & scale
Lifestyle
But where does
Building envelope infrastructure like rail/
Technology highway or urban
solutions at different Shared heat/cold facilities density/diversity
geographic scales: belong? Topography
the larger the scale, the bigger the potential savings. of energy stream.

72. What is missing?
Source: Tester et al. 2005

73. Example: Driving a car 1 km
Smart Average Jeep
Useful energy
displacement 0.5 MJ 0.9 MJ 1.3 MJ
of car by 1 km
Final Energy
Gasoline/diesel 1.7 MJ 2.9 MJ 4.5 MJ
consumed by car
Primary Energy
Extraction, 2.1 MJ 3.6 MJ 5.6 MJ
transformation,
transportation
(assuming 32 MJ/liter gasoline, 41 MJ/litre diesel,
engine 1/3 efficient, 25% losses primary => final)