lecture 2 - PHES.pdf (energy storage systems)

Pumped-storage hydroelectricity

1. EnergyStorageSystems
PUMPED-HYDRO ENERGY
STORAGE

2. Introduction2

3. 3
PotentialEnergyStorage
Energycanbestoredaspotentialenergy
Consideramass,melevatedtoaheight,ℎ
Itspotentialenergyincreaseis:
E = mgh
Liftingthemassrequiresaninputof
work equalto(atleast)theenergy
increaseof themass
Weputenergyintoliftthemass
Thatenergyisstoredinthemassas
potentialenergy

4. 4
PotentialEnergyStorage
Ifweallowthemasstofallbacktoits
originalheight,wecancapturethe
storedpotentialenergy
Potentialenergyconvertedto
kinetic energyasthemassfalls
Kineticenergycanbecapturedto
perform work
Perhapsconvertedtorotational
energy, andthentoelectricalenergy

5. 5
Pumped-HydroEnergyStorage
Potentialenergy
storagein
elevatedmassis
thebasisfor
pumped-hydro
energystorage
(PHES)
Energyusedto
pumpwaterfrom
alowerreservoirtoanupperreservoir
Electricalenergyinputtomotorsis convertedto
rotational mechanicalenergy
Pumpstransferenergytothewateraskinetic,then
potentialenergy

6. 6
Pumped-HydroEnergyStorage
Energystoredin
thewaterofthe
upperreservoiris
releasedaswater
flowstothelower
reservoir
Potential
energyis
convertedto
kineticenergy
Kineticenergyoffallingwaterturnsaturbine
Turbineturnsagenerator
Generatorconvertsmechanicalenergytoelectrical
energy

7. 7
HistoryofPHES
PHESwas firstintroducedinItalyandSwitzerland
inthe 1890’s
FavorabletopographyintheAlps
Four-unitsystems
◼Turbine
◼Generator
◼Motor
◼Pump

8. 8
HistoryofPHES
FirstPHESplantintheUS:
RockyRiverhydro
plant, NewMilford,CT
Waterfromthe
Housatonic Riverpumped
upinto CandlewoodLake
230feetofhead
6billionft
3
ofwater
Two-unit(binary)system
◼Reversiblepump/turbine–
oneofthefirst
29MWofgenerating
power

9. 9
Pumped-HydroStorageToday
PHESaccountsfor99%ofworldwideenergystorage
Totalpower:~127GW
Totalenergy:~740TWh
Powerofindividualplants:10sofMW–3GW
IntheUS:
~40operationalPHESplants
75%are>500MW–strongeconomiesofscale
Totalpower:~23GW
◼Currentplansforanadditional~6GW
Totalenergy:~220TWh

10. PHESFundamentals10

11. 11
PHESFundamentals
Twostorage
reservoirs
Upperandlower
Lowerreservoir
may beariveror
even thesea
Separatedbyaheight,ℎ
Thehydraulichead
Assumeℎ≫depthoftheupperreservoir
◼ℎremainsconstantthroughoutcharge/dischargecycle
Upperreservoircanstoreavolumeofwater,V
u

12. 12
PHESFundamentals-Energy
Totalstoredenergy(assumingitisallataheight,h)
Theenergydensity–energyperunitvolume–ofthestoredwateris
therefore

13. 13
PHESFundamentals–HydrostaticPressure
Theenergydensityofthestoredwaterisalsothe
hydrostaticpressureatthelevelofthelower
reservoir
Thisistheenergydensityofthewateratthe
turbine

14. 14
PHESFundamentals-Power
Therateatwhichenergyistransferredtothe
turbine(fromthepump)isthepowerextracted
from(deliveredto)thewater
Thisisthetotalpoweravailableattheturbine
Lessthanthepoweractuallydeliveredto theturbine
(fromthepump),duetoinefficiencies

15. 15
AGeneralizedPowerRelation
Notethatpowerisgivenbytheproductofadriving
potential,oreffort,??????,andaflow,??????

16. 16
AGeneralizedPowerRelation
Alsosimilartoanelectricalsystem

17. 17
Energy&Powervs.Head
Thetotalstoredenergyandavailablepowerare
Bothareproportionaltohead,ℎ
Largeverticalseparationbetweenlowerandupperreservoirs is
desirable
Limitedbytopography
Limitedbyequipment–pumpandturbine
Specificenergyisalsoproportionaltohead:
Asisenergydensity:

18. 18
SpecificEnergy&EnergyDensityvs.Head
MostPHESplantshaveheadintherangeof100–1000m
Using300masarepresentativehead,gives:
Energydensityforh = 300 m
Specificenergyforh = 300 m

19. 19
SpecificEnergy&EnergyDensity
ComparisonofPHESenergydensityandspecificenergy
withotherenergystorage/sources
PHES
h=100m
PHES
h=500m
PHES
h=1000m
Li-ion
Battery
Natural
Gas GasolineUnits
Energy
Density
0.273 1.36 2.73 400 10.1 9,500Wh/L
Specific
Energy
0.273 1.36 2.73 15015,40013,000Wh/kg
Evenathighheads,PHEShasverylowenergydensity
Largereservoirsarerequired

20. 20
PHESApplications
Pumpedhydroplantscansupplylargeamountsof
bothpowerandenergy
Canquicklyrespondtolargeloadvariations
UsesforPHES:
Peakshaving/loadleveling
Helpmeetloadsduringpeakhours
◼Generatingwhilereleasingwaterfromupperreservoir
◼Supplyingexpensiveenergy
Storeenergyduringoff-peakhours
◼Pumpingwatertotheupperreservoir
◼Consuminginexpensiveenergy

21. 21
PHESApplications
Frequencyregulation
Powervariationtotrackshort-termloadvariations
Helpsmaintaingridfrequencyat60Hz(50Hz)
Voltagesupport
Reactivepowerflowcontroltohelpmaintain
desired gridvoltage
◼Varyingthefieldexcitationvoltageofthegenerator/motor

22. 22
PHESApplications
Blackstartcapability
Abilitytostartgeneratingwithoutanexternal
power supply
Bringthegridbackonlineafterablackout
Spinningreserve
Capableofrespondingquickly–withinseconds
to minutes–totheneedforadditionalgeneration

23. ComponentsofaPHESPlant23

24. 24
ComponentsofaPHESPlant
K. Webb ESE471

25. 25
PHESComponents–Reservoirs
Upperandlower
reservoirsseparatedby
anelevationdifference
Twoconfigurations:
Open-loop:
◼Atleastoneofthe
reservoirsconnectedtoa
sourceofnaturalinflow
◼Naturallake,river,river-fedreservoir,thesea
Closed-loop:
◼Neitherreservoirhasanaturalsourceofinflow
◼Initialfillingandcompensationofleakageandevaporation
providedbygroundwaterwells
◼Lesscommonthanopen-loop

26. 26
PHESComponents–Penstock
Penstock
Conduitforwaterflowing
betweenreservoirsandtothe
pump/generator
Above-groundpipesor below
groundshafts/tunnels
◼5-10mdiameteriscommon
◼Oneplantmayhaveseveralpenstocks
◼Typically,steel-orconcrete-lined,thoughmaybeunlined
Flowvelocityrangeof1–5m/siscommon
Tradeoffbetweencostandefficiencyforagivenflowrate,Q
Largercross-sectionalarea:
◼Slowerflow
◼Lowerloss
◼Highercost

27. 27
PHESComponents
Tailracetunnel
Typically, larger
diameter thanpenstocks
Lowerpressure
Lowerflowrate
Downwardslopefrom
lower reservoirto
pump/turbine
◼Inletheadhelpsprevent
cavitationinpumpingmode
Surgetanks
Accumulatortankstoabsorbhighpressuretransients
during startupandmodechangeover
Maybelocatedonpenstockortailrace
Especiallyimportantforlongertunnels
Hydraulicbypasscapacitors

28. 28
PHESComponents–PowerHouse
Powerhouse
Contains
pump/turbines and
motor/generators
Oftenunderground
Typicallybelowthe
level ofthelower
reservoirto provide
requiredpump inlet
head
Threepossibleconfigurations
◼Binaryset:onepump/turbineandonemotor/generator
◼Ternaryset:onepump,oneturbine,andonemotor/generator
◼Quaternaryset:separatepump,turbine,motor,andgenerator

29. PowerPlantConfigurations29

30. 30
PowerPlantConfigurations–QuaternarySet
Quaternaryset
Pumpdrivenbyamotor
Generatordrivenbyaturbine
Pumpandturbineare
completelydecoupled
Possiblyseparate
penstocks/tailracetunnels
Mostcommonconfiguration
priorto1920
Highequipment/infrastructure
costs
Highefficiency
◼Pumpandturbinedesignedto optimize
individualperformance

31. 31
PowerPlantConfigurations–TernarySet
Ternaryset
Pump,turbine,and
motor/generatorallon asingle
shaft
◼Pumpandturbinerotate inthe
samedirection
Turbinerigidlycoupledto
the motor/generator
Pumpcoupledtoshaft
witha clutch
Populardesign1920–1960s
Nowadays,usedwhenheadexceeds theusablerangeofa
single-stagepump/turbine
◼High-headturbines(e.g.,Pelton)canbeused
Pumpandturbinedesignscanbeindividuallyoptimized

32. 32
PowerPlantConfigurations–TernarySet
Ternaryset
Generatingmode:
◼Turbinespinsgenerator
◼Pumpdecoupledfromtheshaft
andisolatedwithvalves
Pumpingmode:
◼Motorturnsthepump
◼Turbinespinsinair,isolatedwith
valves
Bothturbineandpump
can operatesimultaneously
Turbinecanbeusedforpumpstartup
◼Bothspininthesamedirection
◼Turbinebringspumpuptospeedandsynchronizedwithgrid,then
shutsdown
◼Changeovertimereduced

33. 33
PowerPlantConfigurations–BinarySet
Binaryset
Singlereversible
pump/turbinecoupledtoa
singlemotor/generator
Mostpopular
configuration formodern
PHES
Lowestcostconfiguration
◼Lessequipment
◼Simplifiedhydraulicpathways
◼Fewervalves,gates,controls,etc.
Lowerefficiencythanforternaryorquaternarysets
◼Pump/turbinerunnerdesignisacompromisebetweenpumpand
turbineperformance

34. 34
PowerPlantConfigurations–BinarySet
Binaryset
Rotationisinopposite
directionsforpumpingand
generating
Shaftand
motor/generator must
changedirections when
changingmodes
◼Slowerchangeoverthanforternaryorquaternaryunits
Pumpstartup:
◼Pump/turbinerunnerdewateredandspinninginair
◼Motorbringspumpuptospeedandinsynchronismwiththe
gridbeforepumpingofwaterbegins

35. Turbines35

36. 36
Turbines
Hydroturbinedesignselectionbasedon
Head
Flowrate
PHESplantsaretypicallysitedtohavelargehead
Energydensityisproportionaltohead
Typically100sofmeters
ReversibleFrancispump/turbine
MostcommonturbineforPHESapplications
Single-stagepump/turbinesoperatewithheadsupto700m
Forhigherhead:
Multi-stagepump/turbines
TernaryunitswithPeltonturbines

37. 37
TurbineSelection

38. 38
FrancisTurbine–Components
Volutecasing(scrollcasing)
Spiralcasingthat
feeds waterfromthe
penstock totheturbine
runner
 Cross-sectional
area decreases
alongthelengthof
thecasing
◼Constantflowrate
maintainedalongthe
length
Francisturbinecasing–GrandCoulee:

39. 39
FrancisTurbine–Components
Guidevanesandstayvanes
Directwaterflowfromthecasingintotherunner
Stayvanesarefixed
Guidevanes,orwicketgates,areadjustable
◼Openandclosetocontrolflowrate
◼Poweroutputmodulatedbycontrollingflowrate
◼Setfullyopenforpumpingmode
Source:Stahlkocher Source:Stahlkocher

40. 40
FrancisTurbine–Components
Turbinerunner
Reactionturbine
◼Pressureenergyisextractedfrom theflow
◼Pressuredropsasflowpasses throughthe
runner
Flowentersradially
Flowexitsaxially
Typicallyorientedwitha vertical
shaft
Drafttube
Diffuserthatguidesexitingflow tothe
tailrace
Source:VoithSiemensHydroPower

41. 41
High-HeadPHES
Optionsforheadsin excessof
700m:
Two-stageFrancis
pump/turbines
◼Typically,nowicketgatesin two-stage
configuration
◼Nomechanismforvarying generating
power
TernaryunitwithPelton turbine
Two-stagepump/turbine:
Source:Alstom

42. 42
PeltonTurbines
PeltonTurbine
Suitableforheadsupto1000m
Impulseturbine
◼Nozzlesconvertpressureenergytokinetic
energy
Source:Alstom
◼High-velocityjetsimpingeontherunnerat
atmosphericpressure
◼Kineticenergy
transferredtothe
runner
◼Waterexitstheturbine
atlowvelocity
Cannotbeused
for pumping
◼Usedaspartofa
ternaryset
Source:BFLHydroPower

43. Motor/Generator43

44. 44
Motor/Generator–Fixed-Speed
Pump/turbineshaftconnectstoamotor/generatorunit
Abovetheturbinerunnerintypicalverticalconfiguration
Motor/generatortypedependsPHEScategory:
Fixed-speed pump/turbine
Variable-speedpump/turbine
Fixed-speedpump/turbine
Motor/generatoroperatesatafixedspeedinboth
pumping andgeneratingmodes
Synchronousmotor/generator
◼RotationissynchronouswiththeACgridfrequency
◼Statorwindingsconnecttothree-phaseACatgridfrequency
◼RotorwindingsfedwithDCexcitationcurrentviasliprings

45. 45
Motor/Generator
Variable-speed(adjustable-speed)pump/turbine
Rotationalspeedofmotor/generatorisadjustable
Thepreferredconfigurationforlarge(>100MW)PHES
plants nowadays
Advantagesofvariable-speedplants
Pumpandturbinespeedscanbeindependentlyvaried
to optimizeefficiencyoverrangeofflowrateandhead
Pumpingpowercanbevariedinadditiontogenerating
power

46. 46
PHESforFrequencyRegulation
Frequencyregulation
 Trackingshort-termload
variationstomaintaingrid
frequencyat60Hz(or50Hz)
PHESplantscanprovidefrequency
regulation
Differentforfixed-orvariable-speedplants
Fixed-speedplants
Generatingmode
◼Frequencyregulationprovidedbyrapidlyvaryingpoweroutput
◼Powervariedbyusingwicketgatestomodulateflowrate
◼Sameasinconventionalhydroplants
Pumpingmode
◼Pumpoperatesatratedpoweronly–powerinputcannotbevaried
◼Nofrequencyregulationinpumpingmode

47. 47
FrequencyRegulation–Variable-Speed
Variable-speedplants
Pumpspeedcanbevaried
over somerange,e.g.±10%
Pumppowerisproportional
to pumpspeedcubed
◼For±10%speedvariation,powerisadjustableover±30%
Powervariationinpumpingmodecantrackrapid
load variations
Frequencyregulationcanbeprovidedinboth
modes ofoperation

48. 48
FrequencyRegulation–TernarySets
Fixed-speedternarysets
Generatingmode
◼Wicketgatesinturbinecontrolflowratetovarypower
output
◼Pumpdisconnectedfromshaft
Pumpingmode
◼Hydraulicshortcircuitprovidespowermodulation
◼Pumpandgeneratorbothturnontheshaft
◼Pumpoperatesatfullload
◼Generatoroperatesatvariablepartialload

49. 49
HydraulicShortCircuit
KopsIIPHESplantinAustrianAlps:
Source:VorarlbergerIllvwerkeAG

50. PHESEfficiency50

51. 51
PHESSystemEfficiency
Round-tripefficiency:
Typicalround-tripefficiencyforPHESplantsintherangeof70%–80%
PHESlossmechanisms
Transformer
Motor/generator
Pump/turbine
Water conduit

52. 52
PHESLosses
Transformers
PumpedhydroplantsconnecttotheACelectricalgrid
◼Transformersstepvoltagebetweenhighvoltageonthegridside
tolowervoltageatthemotor/generator
Transformerlossmechanisms:
◼Windingresistance
◼Leakageflux
◼Hysteresisandeddycurrentsinthecore
◼Magnetizingcurrent–finitecorepermeability
Powerflowsthroughtransformersonthewayinto
the storageplantandagainonthewayout
Typicalloss:~0.5%

53. 53
PHESLosses
Motor/generatorlosses
Electricalresistance
Mechanicalfriction
Typicalloss:~2%
Pump/turbine
Singlerunnerinbinarysets
◼Typically,lowerefficiency,particularlyforfixed-
speed operation–designofbothcompromised
Separaterunnersinternary,quaternarysets
◼Higherefficiency
Typicalloss:~7%-10%

54. PHESLosses
Penstock
Frictionallossofwaterflowingthroughthe
conduit
◼Majorlossesalongpenstock
◼Minorlossesfrombends,penstockinlet,turbineinlet,etc.
Dependenton
◼Flowvelocity
◼Penstockdiameter
◼Penstocklength
◼Penstocklining–steel,concrete,etc.
Highheadisdesirable,butlongpenstocksarenot
◼Steeperpenstocksreducefrictionallossesforagivenhead
◼Typicallength-to-headratio:4:1–12:1
Typicalloss:~1%

55. PHESLosses
TypicallossesforPHES:

56. Pumping-ModeEfficiency
Efficiencyofthepumpingoperationisgivenby

57. Pumping-ModeEfficiency
Thevolumeofwaterpumpedtotheupperreservoiris

58. Generating-ModeEfficiency
Efficiencyofthegeneratingoperationisgivenby

59. Generating-ModeEfficiency
Generatingmodeefficiencyis

60. PumpingandGeneratingTimes
Duetolosses,charging/dischargingtimes differ,evenforequalgrid-side
powerinput/output
Energyflowsinfromthegridfasterthanitisstoredintheupperreservoir
Energyflowsoutofstoragefasterthanitisdeliveredtothegrid

61. PumpingandGeneratingTimes
Ratioofgenerationtopumpingtime:
Thatis,theratioofdischargingtochargingtimeisequalto
the round-tripefficiency

62. RailEnergyStorage62

63. DisadvantagesofPHES
DisadvantagesofPHES
Environmentalissues
◼Waterusage
◼River/habitatdisruption
Headvariation
◼Pressuredropsasupperreservoirdrains
◼Efficiencymayvarythroughoutcharge/dischargecycle
◼Particularlyanissueforlower-headplantswithsteep,narrowupper
reservoirs
Sitingoptionsarelimited
◼Availablewater
◼Favorable topography
◼Largelandarea
Possiblealternativepotentialenergystorage:
Railenergystorage

64. RailEnergyStorage
Railenergystorage
Electric-motor-drivenrailcars
Weightsareshuttledupanddownaninclinebetweenupper
and lowerstorageyards
Powerinputdrivesmotorstomoveweightsupthetrack
Regenerative
brakingontheway
downsupplies
powertothegrid
Weightsare
loaded and
unloadedat
storageyards
◼Largequantitiesof
energycanbe
storedwithfew
trains

65. AdvantagesofRailEnergyStorage
MoresitingoptionsthanforPHES
Openspace
Elevationchange
Noneedforwateror
topographyconduciveto
reservoirs
LowercapitalcostthanPHES
Easilyscalable
Efficient
RTefficiency:78%-86%
Constant
efficiency,
independent ofSoC
Nostandbylosses
Noevaporation/leakage

66. RailEnergyStorage
Threecategoriesofrailenergystorageplantsproposed
byARES:
Small
◼20–50MW
◼Ancillaryservicesonly
Intermediate
◼50–200MW
◼Ancillaryservices,
integrationof
renewables
Grid-scale
◼200MW–3GW
◼4–16hoursofstorageatfullpower