Energy&Sustainability

Lecture9:ElectricPowerGeneration

AndDistribution

February10,2009

Whatfractionofour100Quadsofenergyislosttowasteheat

1.  10%2.  25%3.  40%4.  60%5.  80%

ElectricityFlow

65 % losses

•  4TWh=~13quadsofelectricity(quadrillionBTUs)

•  Thisrequiresnearly40quadsofenergytoproduce–2/3loss

U.S.ElectricityEndUses

ElectricalPowerinUtah

U.S.vsUtah

Compared to Utah:

Coal: 82%

Hydroelectric Power: 1.2%

ElectricalPowerinUtah

USvsUtah

Transportation27%

Residential22%

Industrial33%

Commercial18%

U.S.EnergyEndUsesUtah:

Residential: 88%

Commercial: 11 %

Industrial: 1 %

TheGrid:

Runningthesystem–Thetasksofagrid:

①  technicalcontrol:keepingthegridvoltageandfrequencywithintightspecificlimits

② Keepingsupplyanddemandmatchedatalltimes

③ Keepingthelightsonandcarryingouta‘blackstart’intheeventofagridfailure

④ Optimizingresourcesinthesupplyofelectricity

Whatseasonispeakelectricdemand?

1.  Summer2.  Fall 3.  Winter

4.  Spring

PeakDemandDiscussion•  Uncorrelateddemand•  Correlateddemand

•  Excesscapacity•  Energystorage•  Tradeoffsofgeneratingcosts(forpeakdemand)

ExampleofCorrelatedDemand

Storage:Capacitors

Demand

U.S.AnnualElectricalUsage

TheUSPowerGrid

LossesinPowerTransmission

LossesinPowerTransmission

•  V=IR•  PowertransmittedisP=VI

•  PowerdissipatedP=I2R•  Ploss=I2R=P2/V2R

•  Soforfixedpowertransmittedthehigherthevoltagethelowerthecurrentandthelesstheloss

•  Moderntransmissionrunsat230kVto765kV

Transformer

•  RaisevoltageofA/Ccurrent

EdisonvsTeslaandWestinghouse

Edison–DCPower

Tesla&Westinghouse‐ACPower

•  120VoltsisreallyRMS– Rootmeansquare

– Squarerootoftheaveragesquaredvoltage

•  Peakvoltageis170•  PeaktoPeak340•  RMSis120

TheUSPowerGrid

ElectricalUsage

CapacityFactorThe amount of energy that a power plant actually generates compared to its maximum rated output, expressed as a percentage.!

Whattimeofdayhaspeakelectricdemand?

1.  Morning 2.  LunchTime

3.  Midafternoon

4.  Dinnertime

5.  Night

•  Howmuchcapacityshouldyouown?

–  Doyouneedtohavethecapacitythatexceedspeakdemand

– Whatifyoucouldbuythatextrapoweroccasionally?

•  Howmuchwouldyoubewillingtopayforpeakpower?

•  Whatifyoucontrolledtheavailabilityofpeakpower

–  Howmuchcouldyoumakeifyouhadthiscontrol?

BalancingSupplyandDemand:‘MeritOrder’

•  Baseload:lowestrunningcosts,usuallynuclearorlargecoalfiredstations(>600MW),thermalefficiencyof~40%,buttakes8hourstorampup

•  Middlemeritorderorintermediate:smallercoal‐firedstationswithlowerthermalefficiencies

•  Peakingplants:simplegasturbines,thermalefficiencyunder30%,possiblefuels(naturalgasorkerosene)arelikelytobemoreexpensive,butcanberampedupinthematterofminutes

CanadianLoadDurations•  UShaslesshydroasafractionandmorenuclearinourbaseload