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MIT OpenCourseWare http://ocw.mit.edu 8.21 The Physics of Energy Fall 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms. 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