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.

2 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: o Loads – Peak demand increased to reflect higher temperatures in drought year (inputs provided by NREL) o Transmission System – None o Generation – Low hydro (2001) data used; increased thermal plant forced outages modeled (inputs provided by Argonne National Laboratory) Results follow… 2022 PC7 WGA Drought Study

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

4 Modeling of Hydro Generation Presented by Chris Harto on Nov 15 DWG callNov 15 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

5 “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 o 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 Impact of Drought on Thermal Plants

6 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 Determining Increased Forced Outage Rates (Down Days)

7 Overview of Lost Thermoelectric Generation BasinLower ColoradoCalifornia Lost Generation (MWh)6,470,0004,670,000 at risk capacity under 50% historical flow (MW)1,9081,791 at risk with WECC equivalent found (MW)1, * Fraction of at risk capacity found in WECC database average down days day/month *Includes 407 MW of CA geothermal at risk

8 Monthly Variability in Lost Generation Lower ColoradoCalifornia Flow Ratio Lost Generation MWhDown DaysFlow Ratio Lost Generation MWhDown Days JAN ,097, , FEB ,220, , MAR , , APR , , MAY , , JUN , , JUL , AUG , , SEP , , OCT , , NOV , DEC0.6691,

9 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 Modifying Forced Outage Rates

10 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 & OutlookHigh Temperatures & Electricity Demand: An Assessment of Supply Adequacy in California, Trends & Outlook o 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) Impact of Drought on Demand

11 1.Match 17 WSCC areas to 2022 TEPPC load bubbles 2.Identify hottest month for each load area in 1977 (Drought year) 3.Increase peak demand for this month only by the 1-in-40 % change value reported for the WSCC area in the CEC study o Monthly energy was increased by ½ of the peak demand change to preserve the demand shape Peak Load Adjustment Method

12 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.)

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

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

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

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

WGA Drought – Changes in Region to Region Transfers

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

Questions or thoughts on this study?