Estimation of the Impact of Drought on Electricity Generation in the Western US Chris Harto -...

Estimation of the Impact of Drought on Electricity Generation in the Western US

Chris Harto - Argonne National LabEugene Yan - Argonne National LabVince Tidwell – Sandia National Lab

Design Drought Scenarios

Drought Scenarios Summary

• Drought scenarios developed based on historical data and through a consensus building process.

• 2 Primary Scenarios (national lab team)– 10th percentile drought year assumed in each

individual basin – Assume 1977 drought conditions

• WECC low flow hydro scenario (WECC)– Assume 2001 drought conditions

• Drought Scenarios defined by HUC-2 Basins

HUC-2 Basins in WECC and ERCOT

Drought Scenario Flows

Scenarios Description HUC-2 BasinMissouri Texas RioGrande Upper CO Lower CO GreatBasin Pacific California

Normal Average historical flow (1901-2009) (acf) 64,011,810 20,291,196 5,289,680 14,348,384 4,782,455 13,457,301 192,154,820 101,293,852

Recent Normal* Average historical flow (2000-2009) (acf) 51,309,983 21,254,374 2,763,456 9,015,434 2,258,779 11,149,388 178,925,895 74,284,946

10th Percentile Drought Year 1955 1913 1963 1966 2000 1954 1929 2009Flow (acf) 34,556,433 6,605,401 1,921,732 8,271,210 1,735,762 7,265,298 132,082,385 48,509,010

West-wide Drought 1977 flow(acf) 41,532,111 22,832,543 1,364,708 8,676,428 1,412,145 6,729,334 127,188,287 27,555,014WECC Low Flow 2001 flow (acf) 62,459,143 29,514,307 2,785,118 8,700,264 2,324,156 8,099,021 121,128,927 44,006,778

Worst Drought** Year 1934 1917 1964 1964 1904 1961 1926 1977Flow (acf) 21,785,577 3,207,247 1,309,006 2,550,488 1,059,109 4,466,372 119,089,720 27,555,014

**Worst Drought year shown for comparison

*Recent Normal flows used for comparison and analysis of drought impact due to the fact that operations and expectations are most likely to be calibrated towards recent experience

Note: Runoff was estimated using gauge data from the USGS stream gauge network. Runoff per area for each gauge based on its drainage area are combined to derive the runoff per area for the entire HUC-2 basin using a weighted factor estimated from the drainage area percentage of the HUC-2 basin for each gauge. The total runoff of HUC-2 basin is estimated by runoff per area time the area of the basin.

Comparison of Normalized Runoff in Selected Drought Years

Texas-Gulf Rio Grande U Colorado L Colorado Great Basin California Pacific Northwest

Missouri0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Worst10th percentile19772001

Average Runoff in 2000-2009

Hydro Generation Estimation

Approach

• Hypothesis: Hydro Generation Proportional to Basin Flow• Validation:

– Correlate annual flow volume to annual hydro generation within each basin for years 2000-2008 (years I could get good hydro generation data)

– Use USGS stream guage data– Use Bureau of Reclamation power generation data

• Assumes Bureau of Reclamation generation proportional to all hydro generation

– Compare ratios of annual values (both generation and flow) to 9-year average of values

– Challenge• Matching Bureau of Rec regions with HUC-2 basins

HUC-2Reclamation

Bureau of Rec region Best HUC-2 EquivalentPacific NW Pacific NWMid-Pacific CaliforniaLower CO Lower COUpper CO Upper CO Great Plains Missouri

Basins

Note: Rio Grande, Great Basin and TX Gulf not included due to limited Rec hydro generation in basin

Ratios of Hydro Generation and FlowYear 2000 2001 2002 2003 2004 2005 2006 2007 2008 R2

Pacific NW - G 1.10 0.68 1.05 0.95 0.94 1.01 1.08 1.08 1.11 0.846Pacific NW - F 1.09 0.68 1.08 0.95 0.94 0.89 1.20 1.08 1.11

Mid Pacific - G 1.14 0.83 0.90 1.10 1.05 0.92 1.43 0.88 0.75 0.832Mid-Pacific - F 1.08 0.59 0.80 1.07 0.95 1.13 1.97 0.69 0.72

Lower CO - G 1.20 1.12 1.12 0.98 0.94 0.84 0.93 0.93 0.93 0.28Lower CO - F 0.77 1.03 0.72 0.83 0.72 2.14 0.85 0.82 1.13

Upper CO - G 1.18 1.05 0.93 0.91 0.87 0.88 1.02 0.98 1.17 0.737Upper CO - F 1.09 0.97 0.97 0.98 0.97 0.98 0.99 0.98 1.07

Great Plains - G 1.18 1.05 0.84 0.87 0.82 0.98 1.10 0.98 1.20 0.126Great Plains - F 0.83 1.22 0.91 0.64 0.98 1.05 0.60 1.13 1.64

G = Ratio of annual generation to 9 year average generationF = Ratio of annual flow to 9 year average flow

2000 2001 2002 2003 2004 2005 2006 2007 20080.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

Pacific NW

GenerationFlow

2000 2001 2002 2003 2004 2005 2006 2007 20080.00

0.50

1.00

1.50

2.00

2.50

Mid Pacific/California

GenerationFlow

2000 2001 2002 2003 2004 2005 2006 2007 20080.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

Upper CO

GenerationFlow

Basins with good correlation between flow and hydro generation

2000 2001 2002 2003 2004 2005 2006 2007 20080.00

0.50

1.00

1.50

2.00

2.50

Lower CO

GenerationFlow

2000 2001 2002 2003 2004 2005 2006 2007 20080.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

Great Plains/Missouri

GenerationFlowFactors potentially leading to poor

correlation?Required flows for other needs (fish, water supply)

Drawdown or fill up of reservoir storageFlood control Electricity demand

Alternative to flow correlation?

Overall variability in flow is greater than variability in generation. Likely due to buffering effect of reservoir storage. Assuming correlation would represent a “worst case” for these basins.

Basins with poor correlation between flow and hydro generation

0.50 0.75 1.00 1.25 1.50 1.75 2.000.50

0.75

1.00

1.25

1.50

1.75

2.00

Correlation of Hydro Generation to Basin Flow

Pacific NWCaliforniaLower COUpper COMissouri

Basin Flow Ratio

Hydr

o Ge

nera

tion

Ratio

0.50 0.60 0.70 0.80 0.90 1.000.50

0.75

1.00

1.25

Correlation of Hydro Generation to Basin Flow

Basin Flow Ratio

Hydr

o Ge

nera

tion

Ratio

Area of interest

While correlation between basin flow and hydro generation is far from perfect, it represents a reasonable minimum or “worst case” estimate

For flow ratio below 0.9, hydro generation always equal or greater

Hydro Generation Factors

Basin 10th percentile West-wide (1977) WECC Low Flow (2001)Texas 0.31 1.07 1.39

RioGrande 0.70 0.49 1.01Upper CO 0.92 0.96 0.97Lower CO 0.77 0.63 1.03

GreatBasin 0.65 0.60 0.73Pacific 0.74 0.71 0.68

California 0.65 0.37 0.59Missouri 0.67 0.81 1.22

• Key Assumptions– Hydro generation proportional to flow– Drought flows compared to recent “normal” flows

• Scenarios– 10th Percentile = 10th percentile drought in each basin– West-wide = Single year (1977) drought– WECC Low Flow = Single year (2001) drought

Analysis of Impact on Thermoelectric Generation

Determining Generation Risk

• Using data on individual generating units compiled by NREL and UT, total electricity generation for each basin was categorized into one of three categories– Hydro – thus at risk to reduced flow– Low Risk – generation that either required no cooling

water (solar, wind, combustion turbine) or utilized non surface water (wells, ocean, treated wastewater)

– At Risk Thermoelectric – Thermoelectric generation that relies on surface water or unspecified water sources.

Basin Generation Breakdown Nameplate (MW) Generation (MWh)Region hydro at risk thermo low risk hydro at risk thermo low riskMissouri 0.125 0.494 0.380 0.073 0.706 0.222TX Gulf 0.005 0.673 0.322 0.002 0.733 0.264Rio Grande 0.040 0.071 0.889 0.055 0.033 0.912Upper CO 0.108 0.868 0.023 0.054 0.935 0.011Lower CO 0.056 0.216 0.729 0.032 0.215 0.753Great Basin 0.140 0.109 0.750 0.065 0.435 0.500Pacific NW 0.706 0.149 0.145 0.683 0.202 0.115California 0.183 0.205 0.612 0.118 0.287 0.595

Missouri

TX Gulf

Rio Grande

Upper CO

Lower

Co

Great B

asin

Pacific N

W

Californ

ia0%

10%20%30%40%50%60%70%80%90%

100%

Generation Breakdown by Basin (MWh basis)

Low Risk

At Risk Thermo

Hydro

Thermoelectric “Worst Case Scenarios”

• Fraction of thermoelectric generation “at risk” has been identified• Determining how much of the “at risk” generation will actually have to

be derated is more challenging• Potential reasons for derating or forced outages

– Junior water rights– Water levels dropping below intake structures– Discharge water temperatures exceeding permitted limits

• Operators generally have plans and strategies for mitigating these risks– Quote from AZ utility representative - “We have never experienced a water

related outage”– Documents obtained from utilities indicate they have been thinking about

these issues and have a range of mitigation options • Alternative water supplies• Demand Response• Power Purchases/Exchange Agreements

Worst Case 1• Assume loss of “at risk”

thermoelectric generation is proportional to the loss of flow from normal levels in drought scenario

• Poor assumptions– Assumes no excess flow in basin– Assumes no prioritization of water

usage– Assumes no mitigation activities

Missouri

TX Gulf

Rio Grande

Upper CO

Lower

Co

Great B

asin

Pacific N

W

Californ

ia0.000

0.100

0.200

0.300

0.400

0.500

0.600

Worst Case 1 - loss of total generation from thermo

10th Percentile Drought

West-wide Drought (1977)

WECC Low Flow (2001)

MWh Basis

Worst Case 1 = at risk thermo * (1-(drought flow/recent normal flow))

Worst Case 2• Assume loss of “at risk”

thermoelectric generation is proportional to the shortfall of flow relative to total basin water demand in 2010

• Poor assumptions– Assumes all water demand supplied

by surface flows (not good assumption for dryer basins)

– Assumes no prioritization of water useage

– Assumes no mitigation activities

Missouri

TX Gulf

Rio Grande

Upper CO

Lower

Co

Great B

asin

Pacific N

W

Californ

ia0.000

0.050

0.100

0.150

0.200

0.250

0.300





Worst Case 2 = at risk thermo * (1-(drought flow/2010 water demand))

Worst Case 3• Assumes minimum value from Worst

Case 1 and Worst Case 2. • Taking minimum of the two values

eliminates the following errors– Cases where normal flow in the basin does

not meet 2010 demand (indicating water supplied from other sources)

– Cases where reductions in flows are still sufficient to meet total water demand.

• Still assumes:– No mitigation – No prioritization of water consumption – Potential for localized water shortages are

ignored

• This is the best guess at the worst case loss of thermoelectric generation

Missouri

TX Gulf

Rio Grande

Upper CO

Lower

Co

Great B

asin

Pacific N

W

Californ

ia0.000

0.050

0.100

0.150

0.200

0.250

0.300





Worst Case 3 = min(Worst Case 1, Worst Case 2)

Drought Scenario Summaries


Drought flow vs. recent normal flow (2000-2008)

Drought flow vs. 2010 water demand

Thermoelectric water demand (based on NREL and UT estimates)vs. drought flow

Thermoelectric water demand (Sandia 2010 consumption data)vs. drought flow

Worst case loss of generation from hydro

Worst case loss of total generation from thermoelectric

Total Worst Case Loss of Generation

Missouri 0.67 1.21 0.003 0.005 0.024 0.000 0.024TX Gulf 0.31 0.66 0.014 0.045 0.002 0.252 0.254Rio Grande 0.70 0.35 0.000 0.022 0.017 0.010 0.027Upper CO 0.92 1.31 0.025 0.018 0.004 0.000 0.004Lower CO 0.77 0.22 0.018 0.048 0.007 0.050 0.057Great Basin 0.65 1.26 0.006 0.009 0.023 0.000 0.023Pacific NW 0.74 5.30 0.000 0.000 0.179 0.000 0.179California 0.65 1.36 0.001 0.001 0.041 0.000 0.041

Missouri

TX Gulf

Rio Grande

Upper CO

Lower

Co

Great B

asin

Pacific N

W

Californ

ia0.000

0.050

0.100

0.150

0.200

0.250

0.300

Worst Case Loss of Generation, 10th Percentile Scenario

Thermo

Hydro

Frac

tion

of to

tal g

ener

ation

lost

(MW

h ba

sis)

West-Wide Drought (1977)



Thermoelectric surface water demand (based on NREL and UT estimates)vs. drought flow






Missouri

TX Gulf

Rio Grande

Upper CO

Lower

Co

Great B

asin

Pacific N

W

Californ

ia0.000

0.050

0.100

0.150

0.200

0.250

Worst Case Loss of Generation 1977 Scenario

Thermo

Hydro

Frac

tion

of to

tal g

ener

ation

lost

(MW

h ba

sis)

WECC Low Flow Hydro (2001)



Thermoelectric water demand (based on NREL and UT estimates)vs. drought flow






Missouri

TX Gulf

Rio Grande

Upper CO

Lower

Co

Great B

asin

Pacific N

W

Californ

ia0.000

0.050

0.100

0.150

0.200

0.250

Worst Case Loss of Generation 2001 Scenario

Thermo

Hydro

Frac

tion

of to

tal g

ener

ation

lost

(MW

h ba

sis)

Final thoughts

• Estimates of lost electricity generation should be viewed as the worst case for the given scenario

• A number of basins appear to have relatively low risk from lost generation in all scenarios

• Greatest risk appears to be from hydro generation in the Pacific NW

• Better understanding of the true risk to thermoelectric generation is still needed.

Supplementary Slides

Estimation of the Impact of Drought on Electricity Generation in the Western US Chris Harto -...

Documents

Transcript of Estimation of the Impact of Drought on Electricity Generation in the Western US Chris Harto -...