Study Results Drought Scenario Study This slide deck contains results from the 2011 TEPPC Study Program. This study shows the impact in the interconection of increased thermal plant forced outages and decreased hydro caused by drought conditions.

2022 PC7 WGA Drought Study Change to starting input assumptions: Central Question: What impact do changes in thermal plant operation and hydro generation availability have on transmission utilization, production cost, and the ability of the Western Interconnection to continue serving its load obligation? Change to starting input assumptions: Loads – Peak demand increased to reflect higher temperatures in drought year (inputs provided by NREL) Transmission System – None Generation – Low hydro (2001) data used; increased thermal plant forced outages modeled (inputs provided by Argonne National Laboratory) Results follow…

Drought Condition Selected for Study 1977 western drought Selected due to severity and coincidence within multiple basins Defined by USGS HUC-2 Basin flows Presented by Chris Harto (ANL) on Nov 15 DWG call

Modeling of Hydro Generation Hydroelectric Generation : Same as TEPPC low flow hydro case (2001) Differences: Slight overestimation of impact to Pacific NW and CA Slight underestimation for Great Basin and Lower CO Presented by Chris Harto on Nov 15 DWG call

Impact of Drought on Thermal Plants “At-risk” thermal plants identified based on their dependence upon surface water for cooling Impacted plants identified in sub-basins where flow under drought was less than 50% of normal flow List of impacted plants in WECC will not be reported since no plant-specific analysis of drought mitigation plans was conducted Impact to “at-risk” plants modeled as increased forced outage rates

Determining Increased Forced Outage Rates (Down Days) Based on estimate of lost generation Calculated using EIA data for impacted plants Lost generation proportional to the loss of flow relative to the minimum of the average basin flow or 2010 water demand Lost generation was allocated monthly based on deviation from normal flow in that month relative to other months

Overview of Lost Thermoelectric Generation Basin Lower Colorado California Lost Generation (MWh) 6,470,000 4,670,000 at risk capacity under 50% historical flow (MW) 1,908 1,791 at risk with WECC equivalent found (MW) 1,837 1460* Fraction of at risk capacity found in WECC database 0.96 0.82 average down days 147 133 day/month 12.2 11.1 *Includes 407 MW of CA geothermal at risk

Monthly Variability in Lost Generation   Lower Colorado California Flow Ratio Lost Generation MWh Down Days JAN 0.3649 1,097,515 24.9 0.2632 652,592 18.6 FEB 0.2935 1,220,901 27.7 0.2538 660,918 18.9 MAR 0.5556 767,967 17.4 0.2783 639,218 18.2 APR 0.6923 531,736 12.1 0.292 627,083 17.9 MAY 0.6667 575,975 13.1 0.3013 618,846 17.7 JUN 0.8182 314,168 7.1 0.4333 501,932 14.3 JUL 1.125 0.0 0.6183 338,076 9.6 AUG 0.931 119,239 2.7 0.6788 284,490 8.1 SEP 0.8571 246,945 5.6 0.6592 301,850 8.6 OCT 0.878 210,828 4.8 0.6438 315,490 9.0 NOV 0.4737 909,498 20.6 1.2627 DEC 0.6 691,239 15.7 1.0427

Modifying Forced Outage Rates Forced outage rates modified to reflect increased “down days” for all impacted plants within a basin All impacted plants assumed to be down the same number of days in a given month Overlap allowed with scheduled maintenance

Impact of Drought on Demand Developed by NREL Basis for demand changes: ‘99 California Energy Commission Study titled High Temperatures & Electricity Demand: An Assessment of Supply Adequacy in California, Trends & Outlook Study provided an estimate for the change in peak demand for 17 areas in the WSCC for two high temperature scenarios (1-in-5 and 1-in-40 probability)

Peak Load Adjustment Method Match 17 WSCC areas to 2022 TEPPC load bubbles Identify hottest month for each load area in 1977 (Drought year) Increase peak demand for this month only by the 1-in-40 % change value reported for the WSCC area in the CEC study Monthly energy was increased by ½ of the peak demand change to preserve the demand shape

Peak Load Adjustments Summary 2022 PC1 WECC-Wide Coincident Peak Demand: 172,082 MW 2022 PC7 Adjusted Coincident Peak Demand: 176,080 MW (2.3% inc.)

2022 WGA Drought – Changes in Total Annual Generation vs. Common Case Only an increase in areas with emergency in the Common Case (CFE, AESO) GWh Low Hydro Results

2022 WGA Drought – Changes in Total Annual Generation vs. Low Hydro GWh

2022 WGA Drought – Changes in Generation by State vs. Common Case Low Hydro Results

2022 WGA Drought – Changes in Generation by State vs. Low Hydro Result of increased forced outages applied to plants in the California water basin Result of increased forced outages applied to plants in the Lower Colorado water basin

2022 WGA Drought – Changes in Region to Region Transfers

2022 WGA Drought – Changes in Transmission Utilization Most Heavily Utilized Paths Increases in U90 Relative to Common >5% Case Indicated in Red P01 Alberta-British Columbia P03 Northwest-British Columbia P08 Montana to Northwest P11 West of Crossover P10 West of Colstrip Similar to Low Hydro results P29 Intermountain-Gonder P27 IPP DC Line P60 Inyo-Control P26 Northern-Southern California P47 – Southern New Mexico P45 SDG&E-CFE

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