ISO Confidential

August 21, 2017 Solar Eclipse Review

Nancy Traweek

Executive Director, System Operations

ISO Confidential

CAISO solar eclipse overview

• Installed solar capacity at BES level ~ 10,000 MW– Peak solar output of 9,914 MW on June 17, 2017

• Installed wind capacity of ~ 6,500 MW– Peak wind output of 4,985 MW on May 16, 2017

• Rooftop solar ~ 5,800 MW– Approximately 31% or 1855 MW are commercial or industrial installations with

the remainder being residential

• Expected obscuration – 76% at the higher latitudes of Northern California to approximately 62% in the

lower latitudes of Southern California

• ISO all-time peak load of 50,270 MW July 24, 2006– Forecast peak load for August 21 - 36,339 MW

– Actual load on August 21 - 36,046 MW

Slide 2

ISO Confidential

CAISO preparation for the solar eclipse

• Performed studies using high, medium, and low load level days

• Adjusted load forecast in studies and day ahead market to compensate for

reduction in behind-the-meter solar

• Adjust solar ramp as follows for both the studies and day ahead market*– HE10 max solar, HE 11 min solar, HE12 max solar

• Increased regulation up & down procurement for the eclipse period

• Tightened AGC bands (close to L10) for the eclipse period

• Restricted Maintenance Operations (no TTC derate)– Actual RMO was set 2 weeks in advance

• Solar resources– Requested to follow Dispatch Operating Target (DOT) during return from eclipse

• Hydro generation

– Requested hydro resources be ready for rapid response during loss and return

of solar

• ISO RT Ops staff– Crew training – used simulator and table top

– Created guide for on-shift crew

Slide 3

* The CAISO Day Ahead Market normally uses hourly averages for load and resource values. This would have dampened the impact of the eclipse.

ISO Confidential

Coordination in preparation for the solar eclipse

Slide 4

Entity Items

Peak RC • Shared Operational Plan

• Discussed eclipse impact on BES & rooftop resources

• Shared market simulation results

• Peak RC solar eclipse readiness call

Adjacent BA’s • Reviewed anticipated eclipse impact & Operational

Plans

EIM Participants • Discussed consistent policy for ETSR’s during eclipse

• Accounted for eclipse in energy schedule submittals

Gas companies • Shared gas burn calculations from market simulations

• Discussed any planned gas line work

CAISO TO’s • Anticipated eclipse impact & Operational plan

• Sent “Peak Day” messaging before and during the

eclipse

Market Participants • Shared anticipated eclipse impact & Operational Plan

• Verified resources had adequate fuel

• Requested bids to keep resources flexible

• Requested they follow their DOT (dispatch target)

ISO Confidential

Anticipated and actual impact on CAISO solar

resources

Slide 5

Actual solar at start of

eclipse = 6,392 MW

Lower than forecast

due to some cloud

cover

Actual solar at

maximum obscuration

= 2,845 MW

Estimated actual solar

loss of 6,000 MW

Blue line is similar day solar output. Yellow is forecast of the solar eclipse impact on solar production.

ISO Confidential

Solar production during the eclipse compared to

adjacent days

Slide 6

ISO Confidential

Comparison of solar forecast and actual generation

Slide 7

Due to excessive energy all

resources, including solar,

were economically

decremented using

supplied bids

ISO Confidential

CAISO load and solar eclipse impact on behind the

meter solar

Slide 8

Red is actual load, yellow is day ahead forecast, blue is Monday August 14, 2017

Increase in load

due to loss of roof

top solar

Load was lower

than forecast as the

sun reappeared

ISO Confidential

CAISO resource mix for August 21, 2017

Slide 9

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Ge

ne

ratio

n (

MW

)

Nuclear Other Renewable Large Hydro Thermal

Net Imports Wind Solar Total Load

ISO Confidential

Downward and Upward ramps during the eclipse were

about 50MW/min and 150MW/min

Page 10

2,000

2,500

3,000

3,500

4,000

4,500

5,000

5,500

6,000

6,500

7,000

7,500

8,000

8,500

9,000

9,500

10,000

08

:45

09

:00

09

:15

09

:30

09

:45

10

:00

10

:15

10

:30

10

:45

11

:00

11

:15

11

:30

11

:45

12

:00

12

:15

12

:30

12

:45

So

lar

Pro

ductio

n (M

W) 9:11:24

6,392 MW

10:24:422,845 MW 11:55:32

6,413 MW

12:13:099,055 MW11:17:16

6,909 MW

ISO Confidential

CAISO performance indices

Slide 11

Last 30 minutes

10 sec ago

Current

ISO Confidential

Wrap-up

• Replacement energy came from the following– Interties (~3,200 MW)

– Hydro (~800 MW)

– Thermal (~1,600 MW)

– EIM transfers (~350 MW)

• No manual intervention was required during the eclipse– No manual curtailment of solar resources

– No manual/verbal dispatch of resources

Key points• Extensive preparation by all teams was key to making this a success

• Accurate forecasts for load and variable resources are crucial

• A flexible resource fleet is important– Decremental bid on solar was very useful during return from eclipse

– Variability of resources types helped manage the ramp up and down due to

limitations on configuration transitions.

– Giving hydro resources enough heads up to adjust water for maximum

flexibility

Slide 12