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