Sustainable Energy Systems: Energy, Power, and Conversions

1. Sustainable Energy Systems: Energy, Power, and Conversions Lecture 2 - Elks ENGR 1559 Dr. Carl Elks

2. Sustainable Energy Systems: Review of the Why • Energy consuming population will go up – reducing energy poverty for emerging middle class in developing countries. Need sustainable means to generate energy and lessen the demand of energy/person. • Energy Security - It seems possible that cheap oil and cheap gas will be very difficult to obtain in our lifetime. Dependence. • Climate Change - Third, using fossil fuels changes the climate. Climate change is blamed on several human activities, but the biggest contributor to climate change is the increase in greenhouse effect produced by (Co2) • Today we start building our toolboxes for analyzing energy systems.

3. MissionofthisLecture • Introducetheimportanceandchallengesof Energy, Power, Conversions with respect to Sustainable Energy supply • Work, Energy, and Power • Energy Flows • Energy and Power density • Heat and Work 2

4. The Basics of Energy and Power • Most discussions of energy consumption and production are confusing because of the proliferation of units in which energy and power are measured. ( Dozens) • For most of practical analyses, we just need a few simple concepts and measures to build on. • People use the two terms energy and power interchangeably, but we will stick to their scientific/engineeringdefinitions. • Energy is a fundamental entity of nature that is transferred between parts of a system in the production of physical change within the system and usually regarded as the capacity for doing work. • Power is the rate at which something “uses or consumes” energy.

5. Energy and Power • A good analogy for understanding energy production and consumption is the water faucet analogy. • If you want a drink of water, you want a volume of water – one pint. You create a flow of water – one liter per minute when the faucet is on. • We say that a flow is a rate at which volume is delivered. If you know the volume delivered in a particular time, you get the flow by dividing the volume by the time: • flow = • Here’s the connection to energy and power • Energy is like water volume • power is like water flow

6. Work It…Review of Physics • Work is done whenever a force acting on a system results in a displacement of that system. (External Work) • W = F̅Δs cos θ • Pretty meaningless equation without some explanations. • For work to occur, we need motion (that is displacement). That is, Δs. • Can be displacement of a car, electrons, water, turbine blades, etc… • F̅ Force may be thought of as any influence which tends to change the motion of an object. • Magnetic Force (from Jackass) • Θ is the angle at which the force is applied to the system. If the force is perpendicular to the object – no work. Ds F

7. Work: Illustrations W = F̅Δs cos θ Forces at work transfer Energy - which is what we are interested in. http://www.physics.classroom

8. Energy Review • A system possesses energy if it has the ability to do work. • The more energy the better? • Most of the time, but you have to turn that energy into useful work…Can get tricky… • Work shifts energy from one system to another. • Pith Balls – Electric Force  Pith Balls Move  Work is produced • Energy can exist in many different forms. All forms of energy are either kinetic or potential. • The energy associated with motion is called kinetic energy. • The energy associated with position is called potential energy • Energy is measured in Joules (SI) - kg m2/S2 • KE = 1/2mv2- kinetic energy of an object is the energy it possesses because of its motion • PE =U = is equal to the work you must do to move an object from the U=0 reference point to the position r.

9. Potential Energy http://hyperphysics.phy-astr.gsu.edu

10. Kinetic Energy http://hyperphysics.phy-astr.gsu.edu

11. Power • Power is the rate of doing work. It is equivalent to an amount of energy consumed per unit time. • Rates at which we use or produce energy • The units of power are watts. 1 joule per second.

12. Units of Energy

13. All Together Now… http://hyperphysics.phy-astr.gsu.edu

14. Energy and Power • In Energy Systems, numerous measures for Energy and Power.. • We can convert between them, but let’s standardize on a few that make since for this class. • Energy = 1KWhr (remember a watt is 1 joule per second) so a Kilowatt is 1000 joules per second. KWhr is what the power company measures for your energy demands. • Power - rates at which we use or produce energy - Let’s get the terminology straight: atoaster uses one kilowatt. It doesn’t use “one kilowatt per second.” The “per second” is already built in to the definition of the kilowatt. • Power = KWhr/day or KWhr/year or MegaWatts/day. • Examples: (40W ≃ 1 kWh/d) – if you leave a 40 watt light bulb on all day – it consumes 1KW. • Another useful measure for comparison needs is KWhr/day/person  KWhr/d/person. • Why this strange measure? – we can compare the average power use per person for different regions and countries. • As you will see this will help us form several nice metrics for comparing various renewable energy source production to current and project energy needs.

15. EnergyConversion • EnergyConversionistheprocessof changingenergyfromoneformtoanother Useful Energy Energy Source Energy Conversion 3

16. Historic Energy ConversionSequences • Biomass →heat (esp. cooking) • Solar→heat, dryclothes,dryfood • Solarisstillmainlightsource,noneedforconversion • Solarissourceofbiomass,wind,hydro,etc. • Biomass →farmanimals→horsepower, food • Later,peoplealso did theseconversions: • Coal→heat • Hydro→millingflour, runningmachinery • Wind→pumpwater 4

17. ModernEnergyConversion Sequences • Heatingof Buildings: • Gas,oil,biomass → heat • Solar→ heat ElectricityGeneration: • Coal,gas, nuclear→ heat→ mechanical→ electricity • Hydro→ mechanical→ electricity • Wind → mechanical→ electricity • Solar→ Electricity Transportation: • Oil→ gasoline,diesel,jetfuel → heat→ mechanical • Biomass → ethanol→ heat→ mechanical • Fuelcellcars:Gas → hydrogen→ electricity→ mechanical • Hybridcars:Gasoline→ mechanical→ electricity→ • battery→ electricity→ mechanical • 5

18. EnergySources

19. Our Energy System Model Conversions Take place here..

20. Scales of energy flows

21. OrderofMagnitudeofEnergyResources 10 Source:http://www.worldenergy.org/publications/

22. Important Metrics Related to Energy and Power • Energy density -is simply the amount of energy per unit weight (gravimetric energy density) or per unit volume (volumetric energy density). With energy expressed in joules. • Energy density is often expressed as joules per gram (J/g) or joules per cubic centimeter (J/cm3) or, more commonly, mega-joules per kilogram (MJ/kg) and mega-joules per liter (MJ/L) or gigajoules per ton (GJ/t) and gigajoules per cubic meter (GJ/m3). • Power density – Not so simple. But for now, we will define as W/m2 of horizontal area of land or water surface or a square area. 12 SustainableEnergy– Fall2010– Conversion

23. TypicalEnergy Density Values Bituminouscoal 310 13 Channiwala,etal. 2002andNISTChemistryWebBook

24. KeyMetric:ConversionEfficiency Conversion Process EnergyInput UsefulEnergyOutput Energy Loss • When producingwork(mechanicalorelectricity): • = WorkOutput/ EnergyInput • When producing energycarriers(diesel,hydrogen): • = EnergyContentofProduct/ EnergyInput

25. ConversionEfficiencies Source:SustainableEnergy 17

26. Overall EnergyConversionEfficiency

27. EnergyConversion • LawsofThermodynamicsprovidelimits • First law: Energy is conserved; it can be neither created nor destroyed. • Second law: In an isolated system, natural processes are spontaneous when they lead to an increase in disorder, or entropy. • Work < Heat(1-Tlow/Thigh) …more on this latter slides… • Heatandwork are notthe same theyare both energy,but…cannotconvertallheattowork • Eachconversionstepreducesefficiency • Maximumwork outputonlyoccursinidealized reversibleprocesses…talk about this later • Allrealprocessesareirreversible • Lossesalwaysoccurtodegradetheefficiency of energyconversionand reduce work/powerproducingpotential Inotherwords– Youcan’twinoreven breakevenor win in the real world....

28. Example: Incandescent Light Bulb Non- reversible process – can’t take light and turn it into steam Chemical  Steam  Mechanical  Electrical  Light

29. Fluxesofheat,material,electronsmustbedriven bygradientsinfreeenergy Consequence:the heat arrivesatlowerT,themassarrives atlowerP,the electronsarrive atlowerV,etc.:“Losses” 21

30. Heat Engine model • Conceptual device – Allows us to reason (thru Physics of Thermodynamics) about real engines – steam turbines, gasoline motors, etc… • Efficiency and capacity of work are the key parameters. • If it’s 60% efficient, but can only produce 1 joule of work…not very practical…

31. HeatTransfer • Forheatto betransferredatan appreciablerate in a energy system,atemperature difference(DT)is required. • –Q = U A DT • Q = Energy added to system • U = Change in Internal Energy • A = Area • DT = Temperature difference between external and internal… • Thenon-zeroDTguarantees irreversibility… • AsDTgoesto zero,areaand cost goestoinfinity to maintain same Q… Heat Exchanger for producing Steam or hot water.. Image by Mbeychok on Wikimedia Commons.

32. Humanity’s MainEnergySource:Chemicalreactions • Virtuallyallfossil fuels andbiofuelsareconvertedto usefulenergyviachemicalreactions • Energyreleasedby conversionreactionscanbe converted tomechanicalenergyor electricity • Some reactionsareusedto convertaprimaryenergy sourcestomoreuseful formsof chemicallystoredenergy • Solidfossilfuels (coal) Liquidfuels (Coal liquefaction – oil)) • NaturalGas Hydrogen • Biomass Liquidfuels (Biodiesel)

33. ChemicalReactions • Chemicalreactionseither requireor releaseheat. • H = Enthalpy = The sum of the internal energy of the system plus the product of the pressure of the gas in the system and its volume. • H= SEsys+ PV • Combustion is always exothermic, the enthalpy change for the reaction is negative, ΔH is negative. • By definition, the heat of combustion (Q) is a positive value • CH4+2O2→ CO2+2 H2O (Natural gas) : H=-890kJ/mol

34. ExamplesofEnergyConversionReactions Fuelcombustion C8H12+11 O2=8 CO2+6 H2O– gasoline C6H12O6+6O2=6 CO2+6H2O– cellulosicbiomass CH4+2O2= CO2+2 H2O–naturalgas Hydrogenfuelcell H2+½O2= H2O+ electricity+heat Theseoverallreactionsoccurthrough multiplesteps.. Can be represented by the Heat Transfer and/or Heat Engine model..

35. Energy Transport • Recall, from Professor Beans lecture, that current (or flow of electrons) in a conductor is governed by the conductivity of the material.. • Good conductor – free association of electrons between atoms – electrons move down the voltage gradient without much impedance. • Moving that electrical energy efficiently is important. • We already loose a lot of our energy at the chemical Mechanical energy conversion stage (50% or more). • When we talk about large amounts of energy, then small changes in efficiency matter…

36. Energy Transport • A 750KVA transmission line. • If losses are just 5%, we lose 37,500 KVA. • KVA = Kilo Volt-Amperes = essentially the same thing as power = watts. • That’s enough energy to power several houses.

37. CommonConversionEfficiencyChallenges,Part1 • ThermoLimitonConversionofheattowork: • Work < Heat(1-Tlow/Thigh) • Material(boiler,turbine)&emission(NOX)limitsThigh …Hard to Find a material that does not degrade at high temperatures… • Coolingtower(rateofevaporation,Low Heat Value of fuel (LHV) )limiton Tlow • Difficulttopreciselycontrolchemicalreactions • Commonenergyconversionstrategy:justmix a fuel withair,andletthereactionruntocompletion. • Thenextractworkfromthehotexhaustgases. • Usuallytheconversionofchemicalenergytoheatis irreversible:largeincreaseinentropy.

38. CommonConversionEfficiencyChallenges,Part2 • EnergyResourcesFarFrom Users • Real security,global economyissues • Takesenergyandmoneytomovetheresourceorelectricitytotheusers • Convenience,Reliability,Emissions Matter • SolidFuelsDifficulttohandle(sowedon’t usecoalforshipsanymore) • Coalonly1/10thepriceofoil • EnergyDensityandSpecificEnergyMatters • Lots oflandneededtocollectdiffuseresourceslikesolar,wind,biomass,hydro • Transportcostsandtransportenergysignificantforlow-energy-densityfuels(e.g. naturalgas,hydrogen) • PowerDensityMatters • Energyconversionequipmentisexpensive,wanttodo alotofconversionwith smallequipment:LargeFluxesrequired,soLargeFreeEnergyGradients • For transportation,needtocarrytheenergyconversionequipmentwithyou! Remember,each conversion reducesefficiency andcosts money.

39. Assignment for Next Thursday • Pick one of the following and answer: • The developed world tends to blame unsustainability on population growth in developing countries. The developing countries, on the other hand, point to the high levels of energy consumption in the developed world. The US per capita energy use is double that of most European countries and Japan. What are the reasons that US energy use is so high? Write at least ½ page explaining the reasons in your opinion.. • Consider things like our transportation infrastructure, lifestyle habits, housing, etc… • Taking the recent World Energy Council and United Nations resource base figures for the total amount of fossil energy in the ground worldwide as 356,000 quads, how long will it take to exhaust our fossil resources, assuming that we can recover ½ of the resource base and that usage grows at 3% per year? The world currently consumes about 400 quads of primary energy per year, of which 85% is from fossil sources. (hint – you will need to account for the compounding, exponential growth effect of the 3% per year increase in consumption). • Let T = Total recoverable fossil resources • Co = Current rate of fossil fuel consumption • r = Annual rate of increase in consumption rate • n = Number of years to deplete resource • T = Co [ 1 + R + … +Rn-1 ] = Co { [ 1 – Rn ] / [1 – R ] } (this formula is to get you thinking about compounding) • Hint: A geometric series for compounding is the right choice. Can find the formula online…