1. Estimation of the Impact of Drought on Electricity Generation in the Western US Chris Harto - Argonne National Lab Eugene Yan - Argonne National Lab Vince Tidwell – Sandia National Lab

2. Design Drought Scenarios

3. Drought Scenarios Summary Drought scenarios developed based on historical data and through a consensus building process. 2 Primary Scenarios (national lab team) – 10 th 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

4. HUC-2 Basins in WECC and ERCOT

5. Drought Scenario Flows ScenariosDescription HUC-2 Basin MissouriTexasRioGrandeUpper COLower COGreatBasinPacificCalifornia Normal Average historical flow (1901-2009) (acf) 64,011,81020,291,1965,289,68014,348,3844,782,45513,457,301192,154,820101,293,852 Recent Normal* Average historical flow (2000-2009) (acf) 51,309,98321,254,3742,763,4569,015,4342,258,77911,149,388178,925,89574,284,946 10th Percentile Drought Year19551913196319662000195419292009 Flow (acf)34,556,4336,605,4011,921,7328,271,2101,735,7627,265,298132,082,38548,509,010 West-wide Drought1977 flow(acf)41,532,11122,832,5431,364,7088,676,4281,412,1456,729,334127,188,28727,555,014 WECC Low Flow2001 flow (acf)62,459,14329,514,3072,785,1188,700,2642,324,1568,099,021121,128,92744,006,778 Worst Drought** Year193419171964 1904196119261977 Flow (acf)21,785,5773,207,2471,309,0062,550,4881,059,1094,466,372119,089,72027,555,014 **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.

6. Comparison of Normalized Runoff in Selected Drought Years Average Runoff in 2000-2009

7. Hydro Generation Estimation

8. 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

9. HUC-2 Reclamation Bureau of Rec regionBest HUC-2 Equivalent Pacific NW Mid-PacificCalifornia Lower CO Upper CO Great PlainsMissouri Basins Note: Rio Grande, Great Basin and TX Gulf not included due to limited Rec hydro generation in basin

10. Ratios of Hydro Generation and Flow Year200020012002200320042005200620072008R2R2 Pacific NW - G1.100.681.050.950.941.011.08 1.110.846 Pacific NW - F1.090.681.080.950.940.891.201.081.11 Mid Pacific - G1.140.830.901.101.050.921.430.880.750.832 Mid-Pacific - F1.080.590.801.070.951.131.970.690.72 Lower CO - G1.201.12 0.980.940.840.93 0.28 Lower CO - F0.771.030.720.830.722.140.850.821.13 Upper CO - G1.181.050.930.910.870.881.020.981.170.737 Upper CO - F1.090.97 0.980.970.980.990.981.07 Great Plains - G1.181.050.840.870.820.981.100.981.200.126 Great Plains - F0.831.220.910.640.981.050.601.131.64 G = Ratio of annual generation to 9 year average generation F = Ratio of annual flow to 9 year average flow

11. Basins with good correlation between flow and hydro generation

12. Factors potentially leading to poor correlation? Required flows for other needs (fish, water supply) Drawdown or fill up of reservoir storage Flood 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

13. 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

14. Hydro Generation Factors Basin10th percentileWest-wide (1977)WECC Low Flow (2001) Texas 0.311.071.39 RioGrande 0.700.491.01 Upper CO 0.920.960.97 Lower CO 0.770.631.03 GreatBasin 0.650.600.73 Pacific 0.740.710.68 California 0.650.370.59 Missouri 0.670.811.22 Key Assumptions – Hydro generation proportional to flow – Drought flows compared to recent “normal” flows Scenarios – 10 th Percentile = 10 th percentile drought in each basin – West-wide = Single year (1977) drought – WECC Low Flow = Single year (2001) drought

15. Analysis of Impact on Thermoelectric Generation

16. 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.

17. Basin Generation Breakdown Nameplate (MW)Generation (MWh) Regionhydroat risk thermolow riskhydroat risk thermolow risk Missouri0.1250.4940.3800.0730.7060.222 TX Gulf0.0050.6730.3220.0020.7330.264 Rio Grande0.0400.0710.8890.0550.0330.912 Upper CO0.1080.8680.0230.0540.9350.011 Lower CO0.0560.2160.7290.0320.2150.753 Great Basin0.1400.1090.7500.0650.4350.500 Pacific NW0.7060.1490.1450.6830.2020.115 California0.1830.2050.6120.1180.2870.595

18. 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

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

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

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

22. Drought Scenario Summaries

23. 10 th Percentile Drought 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 Missouri0.671.210.0030.0050.0240.0000.024 TX Gulf0.310.660.0140.0450.0020.2520.254 Rio Grande0.700.350.0000.0220.0170.0100.027 Upper CO0.921.310.0250.0180.0040.0000.004 Lower CO0.770.220.0180.0480.0070.0500.057 Great Basin0.651.260.0060.0090.0230.0000.023 Pacific NW0.745.300.000 0.1790.0000.179 California0.651.360.001 0.0410.0000.041

24. West-Wide Drought (1977) Drought flow vs. recent normal flow (2000-2008) Drought flow vs. 2010 water demand Thermoelectric surface 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 Missouri0.811.460.0030.0040.0140.0000.014 TX Gulf1.072.270.0040.0130.000 Rio Grande0.490.250.0010.0310.0280.0170.045 Upper CO0.961.370.0240.0170.0020.0000.002 Lower CO0.630.180.0220.0590.0120.0800.093 Great Basin0.601.170.0060.0100.0260.0000.026 Pacific NW0.715.100.000 0.1970.0000.197 California0.370.770.0020.0030.0740.0660.140

25. WECC Low Flow Hydro (2001) 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 Missouri1.222.190.0020.0030.000 TX Gulf1.392.930.0030.0100.000 Rio Grande1.010.510.0000.0150.000 Upper CO0.971.380.0240.0170.0020.0000.002 Lower CO1.030.300.0130.0360.000 Great Basin0.731.410.0050.0080.0180.0000.018 Pacific NW0.684.860.000 0.2200.0000.220 California0.591.230.0010.0020.0480.0000.048

26. 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.

27. Supplementary Slides