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Leading the World’s Sustainable Energy Future
OUR VISION
Grid Servicesfrom Solar:Challenges
and Opportunities
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Key Messages
• Utility-scale Solar is now able to provide grid flexibility & essential reliability services
• Leveraging this innovative resource leads to a more efficient power system with lower system costs and reduced emissions
• However, Grid Management Innovations are
needed to leverage solar flexibility given its
inherent variability and uncertainty
Can Solar Provide Essential Reliability Services?
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4• http://www.caiso.com/Documents/TestsShowRenewableP
lantsCanBalanceLow-CarbonGrid.pdf
Solar Can Provide Reliability Services
NERC identified essential reliability services to integrate
higher levels of renewable resources, including:
• Frequency Control
• Ramping capability or flexible capacity
Reduces need for conventional generation
• Goes beyond simple PV energy value
• Enables additional solar
• Reduces need for expensive storage
2018 Intersolar Outstanding
Project Winner
2017 NARUC Award WinnerUtility Industry Innovative Pilots or
Demonstration Projects
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5
170
180
190
200
210
220
230
0 200 400 600 800 1000 1200 1400
RELATIVE TIME (sec)
Available MW Min allowed MW Commanded MW Measured MW
Solar Plant Follows Grid Operator Commands (AGC) Very Accurately
• 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 best
conventional generation
10min
20min
300 MW PV Plant
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Plant Control System Enables Grid Friendly Features
Patent 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)
• 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!
Can Solar Contribute to System Flexibility?
Developments Addressing Grid Integration
Challenges
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Can Solar Contribute to System Flexibility?
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.
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E3/TECO/FS Study Goal
• To quantify value of dispatchable (flexible) solar at an
integrated utility (~5GW peak) adding solar to its generation
portfolio
Key Study Results
• 2019 thermal fleet has adequate flexibility to integrate up to
of 14% penetration of solar (1,200MW ) with nearly zero
solar curtailment
• Solar curtailment rapidly increases to 31% by doubling solar
penetration (at 2,400MW)
• Dispatchable solar reduces curtailment to 12% (i.e. retains
higher value even at 28% potential penetration)
Flexible (“Dispatchable”) Solar Maintains Value with Increased Penetration
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-dispatacbable solar refers to where solar plant is only used to avoid oversupply and not provide any reserves.
31%
12%
~0% Curtailment
at 14% Solar
Penetration
10
Head and Foot Room are Needed to Ensure Operational Control
Forecast accuracy increases
Operational flexibility decreases
Week Ahead
Day AheadHours Ahead
5 Min Ahead
5-min Load
Up
ward
(M
W o
f in
c)
Dow
nw
ard
(M
W o
f d
ec)
Forecast Load
Headroom
Footroom
Forecast Error
Forecast Load
Regulation
Forecast Error
Regulation
Headroom
Footroom
Forecast Error
Regulation
Headroom
Footroom
Forecast Load
Real Time(AGC)
Actual Load
Balancing Interval(5 minutes – 1 hour)
11
Load
Dispatch For Thermal Generation Only
A: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
Generation Dispatch on A Spring Day
12
Load
Dispatch with Must-Run Solar – Infeasible Under Higher Penetration
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
HeadroomOp
era
ble
the
rma
l ra
ng
e
Must-Run Solar
Infeasible:
Minimum thermal
dispatch (PMin) above
footroom -- no feasible
range available
13
Dispatch with Curtailable Solar – Feasible But High Curtailment
Thermal
Gen
PMin
High Solar Penetration
Solar
Thermal
Gen
PMin
Load
Footroom
Headroom
Non-Dispatchable
Solar
Feasible:
Solar does not
contribute to headroom
and footroom range
Load
Footroom
Headroom
SolarCurtailed
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
14
“Dispatchable or Grid Flexible” Solar Contributes to Reserves … Optimizes Value
Thermal
Gen
PMin
Headroom
from
Curtailed
Solar
Thermal
Gen
Reduced
High Solar Penetration
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
So
lar
ran
ge
Th
erm
al
Thermal
Gen
PMinSo
lar
Solar Curtailment
Production Cost Savings
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Flexible Solar Reduces Curtailment – An Illustration (2,400 MW Solar)
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
16
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-dispatacbable solar refers to where solar plant is
only used to avoid oversupply and not provide any reserves.
Comparison of Dispatch Profiles Over The Year (Animated)
Non-Dispatchable Solar Fully Flexible Solar
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Dispatchable Solar Saves System Costs
Flexible dispatch for utility-scale solar resources reduces
solar curtailment, fuel consumption & emissions
Reduces
Curtailment
Reduces
Emissions
Increases Production
Cost Savings
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Utility-scale PV is more flexible and responsive than today’s fossil fleet:
• Operates flexibly from 0 to Available Power (no Pmin)
• Can start up in seconds (when solar resource is available)
• Accurately follows dispatch (AGC – 4 second) signals
PV can operate flexibly from 0 to available power (Pavail)
PVCT
STCC
Pmin PminPmin
Pavail
PV starts up in seconds
< 1 sec 20 min 1-4 hrs 1-2 days
PV
CT
ST
CC
PV follows AGC signal with high accuracy
PV CT STCC
Re
gu
lati
on
E
rro
r
Flexibility = Key Resource Attribute of the Future Grid
Challenges
Developments Addressing Grid Integration
Challenges
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• Uncertainty around resource availability … uncertainty generally reduces closer to real-time dispatch … how do we effectively incorporate uncertainty risk assessment?
• Solar resources are typically prioritized on maximum production over flexibility and services … plant revenue reduction concerns from IPP … how do we reconcile reduced production and delivery with value of flexibility?
• Solar provide services at zero marginal costs (once curtailed) and with superior performance… how do we take advantage of that to reduce costs and emissions?
• While vertically-integrated utilities can optimize dispatch of owned assets for the best benefit to reduce overall system costs …how do we make that possible in markets that balances risks and benefits of VRE?
Key Challenges
Flexible Solar Requires Evolution In Operations (& Procurement)
Summary
Developments Addressing Grid Integration
Challenges
22
Flexible & Dispatchable Solar … Key to Market Expansion & Value Retention
Solar Integration And Scale
Solar Energy
• Solar is part of mid-day load
offsets peak or near-peak
demand
• Energy-Only Value
Grid Flexible Solar
• Adds Grid Reliability Services
& Flexibility Value
Fully Dispatchable Solar
• Storage (hours, not days) time-
shifts solar – fully dispatchable
• Adds Firm Generation Capacity
Value
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Key Messages
• Utility-scale Solar is now able to provide grid flexibility & essential reliability services
• Leveraging this innovative resource leads to a more efficient power system with lower system costs and reduced emissions
• However, Grid Management Innovations are
needed to leverage solar flexibility given its
inherent variability and uncertainty