advances in utility- scale pv plants - key lessons learned · a central control system, inverters...
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Advances in Utility-Scale PV Plants - Key Lessons Learned
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Utility-scale PV
Solar Contributes
to Grid Stability
& Reliability
Combined with
Storage, Solar
provides Clean &
Competitive Firm
Capacity
Utility-scale PV
Solar provides
Essential
Reliability
Services &
Grid Flexibility
Solar Power Provides Energy, Flexibility and Capacity
Solar Supports GridStability & Reliability
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PV Solar Supports Grid Reliability & Stability
Sources: (1) NERC: 2012 Special Assessment Interconnection Requirements for Variable Generation (2) M. Morjaria, D. Anichkov, V. Chadliev, and S. Soni. “A Grid-Friendly Plant.” IEEE Power and Energy Magazine May/June (2014)
Features Required by NERC to be a Good Grid Citizen:
Voltage regulation
Active power control (ramping. curtailment)
Grid disturbance ride through (voltage and frequency excursions)
Primary frequency droop response
Short circuit duty control
Power Control
dP
dt
Voltage Support
P
Q
Frequency DroopRide Through
Base Capability
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5Patent No. 8,774,974. Real-time photovoltaic power plant control system
POWER GRIDSUBSTATION
DC
•••
Sunlight to DC Power DC Power to AC Power AC Power to Grid
SWITCHGEAR
AC
SOLAR ARRAYS COMBINERBOX
DC
POWER CONVERSION STATION
Typical DC Voltage 1kV or 1.5kV Typical AC Collection Voltage 34.5kV
(Alternatives 4.16kV to 27.6kV)
69 to 765kV (AC)
Operator EntersSet Points Plant SCADA System
PPCPower Plant Controller
Set Points
Grid Parameters
• Checks grid’s actual conditions and required set points
• Sends individual instructions to each inverter based on location, losses, and performance
• Controls quality of power coming out of the PV plant
Closed-loop controls at 100 milliseconds!
Smart Plant Control System Enables Grid Friendly Features
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Dynamic Power Factor Regulation
• Source: Agua Caliente PV Plant in Yuma, Arizona, USA May 23, 2012. ~212MW on-line.
Command Power Factor
Power Factor Set Point Changed from 0.98 to 1.0
Reaches 90% Steady State Value in ~ 3.2 seconds
Inverters Change VAr Output
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Agua Caliente 290MW (AC)
California
Arizona
Palo Verde Nuclear
Generating Station
North Gila
Substation
Hoodoo Wash
Substation
Agua Caliente
500kV Palo Verde-Hassayampa
Transmission Line
Hassayampa
Substation
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Typical Plant Operation (Unity Power Factor)
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March 21st 2014 Event
Palo Verde Nuclear
Generating Station
North Gila
Substation
Hoodoo Wash
Substation
Agua Caliente
500kV Palo Verde-Hassayampa
Transmission Line
Hassayampa
SubstationO
Line Taken Out of Service
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Voltage Support from PV Plant During Abnormal Condition
90%
95%
100%
105%
110%
-0.3
0.0
0.3
0.6
0.9
1.2
4:00 8:00 12:00 16:00 20:00
Vo
lta
ge
(P
U)
an
d P
ow
er
Fa
cto
r
Po
we
r (P
U)
an
d R
ea
cti
ve P
ow
er
(PU
)
Time of Day
Plant Operating Under Voltage Control
<- Power (PU)
<- Reactive Power (PU)
Voltage (PU) -><- Power (PU)
Voltage (PU) ->
Voltage (PU) ->
<- Power (PU)
Night
Shutdown
Voltage Control
Started
Grid Operator
Seeks Voltage
Support
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• Power Curtailment at Different Levels
• Source: Agua Caliente PV Plant in Yuma, Arizona, USA March 13, 2012. ~90MW on-line.
Plant Curtailment Test
Set PointReduced
Set PointIncreased
Ramp rates between set point changes are controlled
Inverters are Turned Down/ OFF to curtail
output
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a central control system, inverters are individually controlled when needed to meet the plant limit …
Benefit of Plant Level Control System
Plant Output Limit
0
50
100
150
200
250
300
13:00 13:15 13:30 13:45 14:00
0
50
100
150
200
250
300
13:00 13:15 13:30 13:45 14:00
Plant Output Limit
Inverter Curtailed Locally
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Geographic Dispersion Attenuates Short-Term Intermittency
~20 minutes
Large Plant Size Attenuates Impact
of Cloud Passages on Power Output
Intermittency
Solar Provides Essential Reliability Services
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170
180
190
200
210
220
230
0 200 400 600 800 1000 1200 1400
TIME
Available MW Min allowed MW Commanded MW Measured MW
Solar Plant Provides Essential Reliability Services
• Source: http://www.caiso.com/Documents/TestsShowRenewablePlantsCanBalanceLow-CarbonGrid.pdf.AGC: Automated Generator Control
PO
WE
R (M
W)
MORNING
30MW Headroom
Available MW
Measured Power
CommandedPower (4 s)
Regulation is ~27 %points more accurate than bestconventional generation
10min
20min
300 MW PV Plant
Power Regulation • AGC
• Up-Regulation
• Down-Regulation
• Frequency Regulation
• Flexibility
Grid Reliability Services
NERC: Essential reliability services
• Frequency Control
• Ramping capability or flexible capacity
2018 Intersolar
Outstanding
Project Winner
2017 NARUC
Award Winner
Solar Contributes to System Flexibility
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0%
5%
10%
15%
20%
25%
30%
35%
0% 5% 10% 15% 20% 25% 30%
Sola
r C
urt
ailm
en
t (%
of
Pro
du
ctio
n P
ote
nti
al)
Annual Solar Penetration Potential (%)
2000 MW Solar
17%
Curtailed
1200 MW Solar
~1%
Curtailed
2400 MW Solar
31%
Curtailed
1600 MW Solar
6%
Curtailed
Source: E3,TECO, First Solar Report “Investigating the Economic Value of Flexible
Solar Power Plant Operation”, https://www.ethree.com/wp-
content/uploads/2018/10/Investigating-the-Economic-Value-of-Flexible-Solar-Power-
Plant-Operation.pdf
.
~5 GW Peak Load
Solar Curtailment Increases with Solar Penetration
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As real time approaches…
Load
(MW)
Load
Forecast
X Time Ahead
Headroom:
Resources
increase output
Actual Load
could increase...
Footroom:
Resources
decrease output
Actual Load
could decrease...
Time = 0
Lower Solar
Generation...
Headroom
Required
Higher Solar
Generation
Footroom
Required
Solar
Forecast
Operational Flexibility Needed to Balance System While Managing Variability &
Forecast Uncertainty
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Head and Foot Room are Needed to Ensure Operational Control
Forecast accuracy increases
Operational flexibility decreases
Week Ahead Day Ahead Hours Ahead 5 Min Ahead
5-min Load
Up
wa
rd(M
W o
f in
c)
Do
wn
wa
rd
(MW
of
de
c)
Headroom
Footroom
Forecast Error
Forecast Load
Regulation
Forecast Error
Regulation
Headroom
Footroom
Headroom
Forecast Error
Regulation
Footroom
Forecast Load
Real Time
(AGC)
Actual Load
Balancing Interval(5 minutes – 1 hour)
Forecast Load
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Load
“Dispatchable or Grid Flexible” Solar Contributes to Reserves
Thermal
Gen
PMin
Headroom
from
Curtailed
Solar
Thermal
Gen
Reduced
High Solar PenetrationA:Thermal
Generation OnlyO
pe
rab
le
the
rma
l ra
nge
PMin
Thermal
Gen
Ava
ila
ble
Ra
nge
Un
ava
ila
ble
Ra
nge
MW
0
Footroom
Headroom
Required
Headroom and
Footroom fit within
generation fleet
available range
Solar
Thermal
Gen
PMin
Load
Solar increases
balancing needs
Footroom
Headroom
Non-Dispatchable
Solar
Feasible:
Solar does not
contribute to headroom
and footroom range
Dispatchable Solar
Optimal:
Solar contributes to
footroom to headroom
range
Load
Footroom
Headroom
SolarCurtailed
Solar
Solar
Op
era
ble
the
rma
l ra
ng
e
Must-Run Solar
Infeasible:
Minimum thermal
dispatch (PMin) above
footroom -- no feasible
range available
Op
era
ble
the
rma
l ra
ng
e
So
lar
ran
ge
Th
erm
al
Thermal
Gen
PMinSo
lar
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Solar Provides Flexibility
Solar Provides No Regulation Reserves Flexible Solar: Provides regulation reserves.
“Inflexible” Solar Flexible Solar
Source: E3,TECO, First Solar Report “Investigating the Economic Value of
Flexible Solar Power Plant Operation”, https://www.ethree.com/wp-
content/uploads/2018/10/Investigating-the-Economic-Value-of-Flexible-Solar-
Power-Plant-Operation.pdf
.
60% Lower
curtailment
Reduced
Thermal Gen
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Source: E3,TECO, First Solar Report “Dispatchable Solar: The Key to Unlocking the Clean Energy Grid of the Future”, under review. Dispatchable or Grid Flexible Solar: operating solar plants at an optimal point which may be lower than available resource and providing regulation reserves. Non-dispatacbablesolar refers to where solar plant is only used to avoid oversupply and not provide any reserves.
Non-Dispatchable Solar Fully Flexible Solar
Comparison of Dispatch Profiles Over The Year — Animated
00
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-25%
-20%
-15%
-10%
-5%
0%
0% 5% 10% 15% 20% 25% 30%
An
nu
al
Pro
du
cti
on
Co
st
Re
du
cti
on
(%
)
Annual Solar Penetration Potential (%)
Curtailable
Fully Flexible
Flexible Solar Reduces Production Costs
Assumes Solar $0 Variable Cost
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PV can start up in seconds
(when solar resource is available)
< 1 sec 20 min 1-4 hrs 1-2 days
PV
CT
ST
CC
PV follows AGC (4-sec)
signal with high accuracy
PV CT STCC
Re
gu
lati
on
Err
or
Utility-scale PV is more flexible and responsive than today’s fossil fleet:
Combustion TurbineCT CC Combined Cycle ST Steam Turbine
Flexibility = Key Resource Attribute of the Future Grid
PV can operate flexibly from
0 to available power (Pavail)
PV
CT
Pmin
CC
Pmin
ST
Pmin
Pavail
Solar Provides Firm Capacity
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Solar + Storage Provide Clean Dispatchable Generation
INTERMITTENCY
GRID RELIABILITY& STABILITY
FLEXIBLEGENERATION
DISPATCHABLE GENERATION
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Drivers of Energy Storage
- Benefits of Energy Storage on the
Utility Grid
- Flexible generation resource
performing multiple
applications
- Simpler siting and permitting
vs. fossil generation
- Beneficiary of continued cost
improvement from EV market
drivers
Transportation electrification demand is driving Li-Ion price declines
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Can Solar Provide Firm Capacity?
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Solar and Storage Provide Firm Capacity
Hour of the Day1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
January
February
March
April
May
June
July
August
September
October
November
December
25%No
Storage
Summer Evening Peak Period
Hour of the Day1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
January
February
March
April
May
June
July
August
September
October
November
December
48%1 hr
Storage
Summer Evening Peak Period
Hour of the Day1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
January
February
March
April
May
June
July
August
September
October
November
December
72%2 hr
Storage
Summer Evening Peak Period
Hour of the Day1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
January
February
March
April
May
June
July
August
September
October
November
December
98%4 hr
Storage
Summer Evening Peak Period
+
Game Changer: Clean Energy PlantMore Cost-effective Than Conventional Generation
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Storage Enhances Grid Capability of PV Plant
Power RegulationRamp Control
dP
dt
Voltage Support
P
Q
Solar Grid Capabilities Enhanced with Storage
• AGC
• Up-Regulation
• Down-Regulation
• Frequency Regulation
FlexibilityCapacity Firming Energy Shifting
Grid Reliability ServicesBase Solar Capability
Summary
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Regulatory, Market and Policy Recommendations
http://www.solarpowereurope.org/wp-content/uploads/2018/12/4018_SPE_Grid_Intelligent_Solar_report_05_hr.pdf
https://windsolaralliance.org/wp-content/uploads/2018/11/WSA_Market_Reform_report_online.pdf
• Attract flexible solar (VRE) through open
participation and efficient market pricing
• Allow flexible solar to participate in all
reliability services markets
• Ensure capacity markets reflect true
capacity contribution of solar
• Favor lowest cost resources with the most
flexible capabilities
Lower system costs and reduce emissions
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Utility-scale PV
Solar Contributes
to Grid Stability
& Reliability
Combined with
Storage, Solar
provides Clean &
Competitive Firm
Capacity
Utility-scale PV
Solar provides
Essential
Reliability
Services &
Grid Flexibility
Solar Power Provides Energy, Flexibility and Capacity
