climate change and seattle city light operations

Climate Change and Seattle City Light Operations

Wing Cheng and Ron Tressler Seattle City Light

September 16, 2009

Presentation Outline• Background on Seattle City Light• Climatic Effects on Hydrology and Operations• Potential Impacts

– Power Generation– Power Delivery– Power Management– Asset Management

• Moving Forward

City of SeattleCity of Seattle

Seattle City Light Facts• Municipal Electric Utility• 376,000 customers• About 90% hydro• Skagit River – 711 MW capacity• Boundary (Pend Oreille River) – 1,047 MW

capacity• Carbon Neutral for last 5 years• Skagit is certified Low Impact Hydro


Power Resources Source Average Megawatts

(2007)

5 SCL-owned Hydroelectric ProjectsSkagit, Boundary, Newhalem, Cedar Falls, Tolt

745

Power Purchase Contracts with Federal Bonneville Power Administration (BPA)

682

Contract with BC Hydro (Canadian) - International Treaty

38

Contracts with other Utilities in Washington, California and Idaho

34

Wind and Small Biomass Plant Contracts

44

TOTAL 1,543

Canada

United States

Ross Dam

Climate Change in the PNW• Temperatures: 1.5°F (1920 and 2003)

• Precipitation: 14% (1930-1995)

• April 1 SWE: 25% in Washington Cascades

• Runoff Timing: Shifted 0-20 Days Earlier

• Following Charts Shows Climate Change in the Skagit Watershed as observed by SCL

• Source: CIG website



Diablo Monthly Average Temperature

30.00

35.00

40.00

45.00

50.00

55.00

60.00

65.00

70.00

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Month

Deg

ree

F

Average (1931-2003)

Average (2000-2008)

Note: More than 1 Deg. F increase in January, February and July


Diablo Monthly Average Precipitation

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

22.00

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Month

Inch

es

Average (1931-1995)Average (2000-2008)10 Percentile (1931-1995)90 Percentile (1931-1995)

Note: An annual decrease of about 1/3 inch

Climate Change Impacts Detected Reduced spring-summer inflow

PDO Positive

PDO Negative

No official PDO Classification


Average Ross Inflow by Month(Cubic Feet/Sec)

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Month of Water Year

Average (1970-1999)

Average (2000-2008)

An 14.5% annual reduction andan 18.2% May-July reduction.


Ross Runoff Starting and Ending Dates

3/1

3/16

3/31

4/15

4/30

5/15

5/30

6/14

6/29

7/14

7/29

8/13

8/28

1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009

Year

Dat

e

Start dayEnd dayLinear (Start day)Linear (End day)

Note: Trends of runoffs shifting to earlier starts and ends

Power Generation

• Skagit Project Managed for “Fish First”– All Pacific salmonid species– Listed Chinook salmon, steelhead, and bull trout

• Intricate annual flow management planning with monthly updates– Protect salmonids during spawning and fry

development– Meet Corps flood control mandates and

recreation pool elevations in Ross Lake City of SeattleCity of Seattle

Power Generation

• Model Skagit Hydrology based on the following:– 3Tier’s DHVSM Water Years 86-03

– Temperature +2.7oF by 2020 and +4.1oF by 2040 over 1990-1999

– Precipitation Unchanged

• Output is Reservoir Inflow

• Optimize Ross Reservoir Outflow based on Inflow Data



Ross Average Monthly Inflow

1000

2000

3000

4000

5000

6000

7000

8000

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug SepMonth in Water Year

CFS

HistoricalCC 2020CC 2040


Ross Average Monthly Outflow

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul

Month in Water Year

CFS

HistoricalYear 2020Year 2040

More power will be generated during winter and less during spring and summer

Skagit River Fisheries

High-flow events scouring redds and rearing habitat

Thermal barriers during low flows

Increased frequency of extreme events


SCL Average Monthly Generation and Load, 2001-2007

400

500

600

700

800

900

1000

1100

1200

1300

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMonth of Year

aMW

SCL Generation

SCL System Load

SCL Owned Generation Only – BPA and Other Power Contracts not Included, e.g. in 2007, SCL Generated 48.3% and Purchased 42.3% from BPA

Power Management

Power Exchange with California

Peak Load in winter (California Summer)Surplus Power in Summer (California

Winter)

Power Management…..continued

• California Load-Resource ChangeCurrently Lacking for Understanding

• SCL Load-Resource ChangeSlight Load Decrease in Winter and Increase in Summer

• SCL Adaptation StrategiesExplore Exchange with Other Regions

Expand Sales and Purchases in Spot Market

Develop Prudent Hedging Strategies

Improve System Load Forecast



Hourly SCL System load on Wednesday

700

800

900

1000

1100

1200

1300

1400

1500

1600

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

MW

Hr

7/22/20097/29/20098/5/20097/24/2006 (Monday)

Daily Average = 69.8 deg and Maximum 82.5 deg

Daily Averae = 85.5 deg and Maximum = 104.8 deg

Daily Average = 64.9 deg and Maximum 75.9 deg

Previous Summer Peak Load Record

Cooling Load on 07/29/09 Heat Wave


Average Monthly SCL System Load, aMW(based on 2.7 and 4.1 degrees adjustment)

950

1000

1050

1100

1150

1200

1250

1300


Dai

ly A

vera

ge M

W

Ave 01_07Ave 2020Ave 20402020 Hourly Peak Load = 1765.5 MW

Monthly Average SCL System Load, aMW(based on MM5 6-Hour Simulation)

1000

1050

1100

1150

1200

1250

1300

1350

1400


aMW

Yr 1990Yr 2020Yr 2050Yr 2090

2020 6-Hours Peak Load = 2175 MW

Uncertainty in System Load Modeling

Power Delivery

• Transmission/Distribution Line Rating+ 5o F on 1000’ span = 2’’ more Sag

Not Significant Now; but Could be at + 10o F

• Transformer Thermal RatingAging Acceleration Factor = 1 with Hottest Spot at 110o F

Insulation Deterioration Rate Doubles every 7o F Increase

Water Spray Now Required During Very Hot Days

De-rate or Replace with Increasing Hot Days?



Healey Fire Protection – Outdoor Transformer Protection with Water Spray System

City of SeattleCity of SeattleSlide 13

Ross Third Quartile Monthly Outflow

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

7000

7500

8000

Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul

Month of Water Year

CFS

HistoricalYear 2020Year 2040

Period Maintenance Works Normally Scheduled

Heavy Glacial Runoff

Downstream

Asset ManagementNormal Period for Plant Maintenance

Possible Loss of a Month

Asset Management…..continued

• Decision on Capital InvestmentsExample of Gorge Second Tunnel

Three 30-MW Units Completed in 1929

A 4th 67-MW Unit Added in 1951

One 20.5’ Diameter, 11000 Feet Long Tunnel

Tunnel Loss at Full Capacity about 60 Feet or 34 MW



New 18 Feet Diameter Tunnel to Supply Water to the Large Unit Only Recover Slightly More Than Half of Tunnel Loss at Full Capacity

Annual Reduction in Tunnel Loss Enough to Power over 7000 Households


Gorge Companion Tunnel Total Energy Gain by Month

0

2000

4000

6000

8000

10000

12000

14000

16000

Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul AugMonth of Water Year

MW

Hrs

Historical (Total = 64,437)CC 2020 (Total = 78,057)CC 2040 (Total = 81,711)

Climate Change May Favor this Project but What About Others?

Moving Forward• Expand Conservation

Program (12 aMW in 2009)• Purchase power to meet I-

937 renewable energy portfolio requirement

• Adapt hydroelectric project operations to changing conditions (cannot solely use historical data)


Research and Next Steps

• Improve River Flow Forecasting• Track Frequency and Timing of Floods• Need Improved Downscaling of Global

Climate Models – Dynamic and Statistical Methods

• Gain Additional Understanding of Glacier Melting Patterns

• Continue to Monitor Impacts on FisheriesCity of SeattleCity of Seattle

climate change and seattle city light operations

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