Basic concepts (I)

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Basic concepts (I)

• How do you define energy?

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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)

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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 earths core

F
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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
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Electric magnetic forces

• Cause electrons to be attracted to nuclei in
  atoms -gt basis for chemistry
• Cause charges (electric current) to flow in
  electric circuits -gt basis for energy used in
  electronics, lights, appliances
• Cause needle of compass to point north

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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 temperaturefor water, heat
  capacity is, 1 calorie per gram per degree
  Celsius or Kelvin
• In a chemical compound
• 2 H2 O2 -gt 2 H2O ,   Enthalpy released -571.6
  kJ/mol

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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?

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SI units for energy

• The SI unit of energy is a Joule 1 kgm2/s2 1
  Newtonm (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
  kgm2/s3
• most commonly used in electricity, but also for
  vehicles in horsepower (acceleration time)

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Other common energy units
http//www.onlineconversion.com/energy.htm
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Prefixes
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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

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Basic concepts (II)

• How do you use energy?

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What is energy for?
How do you use energy?

• Examples of
• Kinetic
• Electro-magnetic
• Electricity
• Radiation (light)
• Chemical
• Potential
• Heat (thermal)
• ?

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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

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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 waterturbine electricity heat

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Basic concepts (III)

• Energy conversion, conversion efficiency

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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

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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

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Efficiencies (2)

• Source Smil 1999

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Efficiencies (3)

• Source Smil 1999

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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)

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Chain of conversion efficienciesLight bulb
Etotal E1 x E2 x E3 35 x 90 x 5 1.6

• Source Tester et al 2005

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Example 2 diesel irrigation
Losses t t t,r t,m
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Example 3 Drive power
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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.

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Efficiency of human-powered motion
kcal/mile
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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

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Importance of consumer behavior/lifestyle

• EU energy label vs. temperature of washing

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USA EnergyGuide label

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

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Basic concepts (IV)

• Thermodynamics and entropy

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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, Avogadros number 61023)
  energy conversion involving heat.

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31 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.

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Paraphrases of 2 laws of thermodynamics

• You cant get something from nothing.
• You cant get something from something.

• You can't get anything without working for it.
  The most you can accomplish is to break even.
• You even can't break even.

• (economics) There is no such thing as a free
  lunch.

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History of thermodynamics (2nd law)

• Nicolas Léonard Sadi Carnot (1796-1832)
• Theory of heat engines, reversibleCarnot
  cycle 2nd law of thermodynamics

• Ludwig Boltzmann (1844-1906)
• Kinetic theory of gases (atomic)
• Mathematical expression of entropyas a function
  of probability

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Entropy

• The entropy function S is defined as
• S kB log (W)
• kB Bolzmanns constant 1.38 10-23  
  Joule/Kelvin
• WWahrscheinlichkeit S possible states
• Increases with increasing disorder
• For instance
• vapor, water, ice
• expanding gas
• burning fuel

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2nd law of thermodynamics
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2nd law of thermodynamics

• Total entropy always increases with time.
• An isolated system can evolve, but only if its
  entropy doesnt decrease.
• A subsystems entropy can increase or decrease,
  but the total entropy (including the subsystems
  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

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Basic concepts (V)

• Applications of thermodynamics heat engines,
  Carnot cycle, maximum and real efficiencies.

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Performance of energy conversion machines (Carnot
cycle)

• Heat engine (cycle)
• Heat, cool engine fluid
• Diesel, internal combustion
• Reversible processes
• Entropy remains constant
• DSc - DSh
• Irreversible processes
• Real world
• Heat losses, no perfect insulator
• Heat leakage
• Pressure losses, friction

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The Carnot Cycle (the physics)
Ideal cycle between isotherms (Tconstant) 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
theoretical maximal for heat engine.
The efficiency is
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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

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Comparison of heat engines
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Coal power plant
Typical generating capacity 500 MW 250 tonnes of
coal per hour
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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

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Wind power

• Power 0.47 x h x D2 x v3 Watts
• h efficiency 30 (59 theoretical maximum)
• D Diameter (40 meters)
• v wind speed (13 m/s)
• P 500 kW

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Hydroelectricity (hydro)

• Uses difference in potential gravitational energy
  of water above and below dam
• E m x g x D h m x D v2 / 2
• P h x r x g x D h x (flow in m3/s)
• r is the density of water 1000 kg /m3
• Efficiency h can be close to 90

D h
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Power plant fuel cell efficiencies
Efficiency
Source Miroslav Havranek, 2007
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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)

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Basic concepts (VI)

• Georgescu-Roegen and entropy applied to the
  economic system.

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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.

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Georgescu-Roegen (1)
Le processus économique nest quune extension
de lévolution biologique et, par conséquent, les
problèmes les plus importants de léconomie
doivent être envisagés sous cet angle
Vision G-R, reprise par H. Daly et l'économie
écologique
Vision Brundtland 1987 du développement durable
Environment
Economy
Society
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Georgescu-Roegen (2)

• la thermodynamique et la biologie sont les
  flambeaux indispensables pour éclairer le
  processus économique (...) la thermodynamique
  parce quelle nous démontre que les ressources
  naturelles sépuisent irrévocablement, la
  biologie parce quelle nous révèle la vraie
  nature du processus économique
• 2 concepts clefs
• les ressources naturelles sépuisent
  irrévocablement (thermodynamique)
• la "vraie nature" du processus économique peut
  être comprise à travers la biologie (surtout
  l'analyse énergétique des écosystèmes)

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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
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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-Rs vision, taken up by H. Daly and ecological
economics
Brundtlands 1987 vision of sustainable
development
Environment
Econo-my
Society
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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

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It is not the suns finite stock of energy
that sets a limit to how long the human species
may survive. Instead it is the meager stock of
the earths 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
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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.

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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)
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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?

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Energy chain
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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.

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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

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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.
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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.

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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).

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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)

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Traditional/commercialaccounting

• 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

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Energy Services
Source Jochem et al 2000
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Energy system services scale
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What is missing?
Source Tester et al. 2005
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Example Driving a car 1 km

• Smart Average Jeep
• Useful energy displacement 0.5 MJ 0.9
  MJ 1.3 MJof car by 1 km
• Final Energy Gasoline/diesel 1.7 MJ 2.9
  MJ 4.5 MJconsumed by car
• Primary Energy Extraction, 2.1 MJ 3.6
  MJ 5.6 MJtransformation,transportation
• (assuming 32 MJ/liter gasoline, 41 MJ/litre
  diesel, engine 1/3 efficient, 25 losses primary
  gt final)