Study Results PC8-PC16 System Stress Tests This slide deck contains results from the 2012 TEPPC Study Program related to the various stress tests performed on the 2022 Common Case. The results of the studies are shown along with an indicator to show the robustness of transmission in that area.

2 Description and goal Assumptions Results 10-Year Stress Test Results

Study Description and Goal

4 PC8-PC15 – Add 6,000 GWh Renewables PC16 – RPS Off-Ramp Stress Test Cases – two concepts…

5 Evaluate system’s ability to integrate and deliver added resources to load, subject to transmission constraints “Stress” the system Proxy for o High gas (makes RE more competitive) o High load (requires higher RPS and more RE) o CO 2 Policy (less thermal, more RE) o Increase in RPS (more RE) Studies are designed as indicators Summary “ Examine the Robustness of the Power Grid” Help us to understand how the system may behave under a variety of future conditions. This is robust planning.

6 No additional transmission added Small addition of RE will not solely justify addition of large interregional project Capital cost analysis will not be performed as it is outside the intent of the study Caveats

Study Assumptions

Stress Test: PC8-PC15 Resource Selection Process Calculate ratios of renewables in TEPPC 2022 Common Case Do not include existing resources Do not include DG IRP and LRS data Apply ratio to future build-out of 6,000 GWh Concept: past trends are best the representation of what could be added to each state More recourses available than what is identified in WREZ More granular information from CPUC/CAISO Locate resources using WREZ Extrapolation Method

Resources from CPUC scenario that were originally decremented for Common Case net-short are added Solar GWh Geothermal GWh Evaluated as one 6,000 GWh study. Resource split 50/50 in each Basin state. Per CPUC

10 Stress Test: PC16 Resource Removal Process WECC Class Explanation Class 0Existing Class 1Under active construction. Projected to be in-service within five years. Class 2Additions that were reported to have: 1)Regulatory approval (or in review) 2)Signed Interconnection agreement 3)Expected on-line date within seven years Class 3Meet NERC criteria for Future Planned or Future Other Resources but that do not meet Class 1 or 2 Class 4Meet NERC criteria for Conceptual Resources WECC LRS Data Collection Manual Remove

Common Case Results Refresher

Selection based on → Regional Significance Construction Status Financial Indicators Implementation Indicators

Potential “area of concern” High utilization can be explained or is expected

Flow: BC to NW Flow: NW to BC

IPP generation

Common Trends System seems to be fairly robust given the CCTA and Common Case starting point of system utilization. 1 When more renewable energy is added to the system, gas appears to be the marginal resource in all studies (except Montana), given our current price assumptions. CA gas units are “most marginal.” 2 Heavier utilization, not much congestion (i.e., the transmission system still permits economic transfer). 3

California Stress Test AssumptionsTransmission Results Generation ImpactsKey Finding Robustness Indicator Stress test had only minor impact on transmission utilization. Including additional generation in CA reduces requirement for imports.

Arizona Stress Test AssumptionsTransmission Results Generation ImpactsKey Finding Robustness Indicator Increase in AZ to CA imports. Congestion on P29. More detailed analysis required.

New Mexico Stress Test AssumptionsTransmission Results Generation ImpactsKey Finding Robustness Indicator Increase in P22 (SW of 4- Corners) utilization, but not congested. Other paths are not heavily impacted.

Wyoming Stress Test AssumptionsTransmission Results Generation ImpactsKey Finding Robustness Indicator Some sensitivity observed – P29 and P36. Large change in RMPA to Basin flow.

Montana Stress Test AssumptionsTransmission Results Generation ImpactsKey Finding Robustness Indicator P8 congested as a result. MT system is relatively isolated and is easily stressed.

Washington Stress Test AssumptionsTransmission Results Generation ImpactsKey Finding Robustness Indicator Small impact.

Oregon Stress Test AssumptionsTransmission Results Generation ImpactsKey Finding Robustness Indicator Very little congestion observed.

Basin Stress Test AssumptionsTransmission Results Generation ImpactsKey Finding Robustness Indicator Increased utilization, but not much congestion.

RPS Off-Ramp Stress Test AssumptionsTransmission Results Generation ImpactsKey Finding Robustness Indicator Decrease in congestion outweighs increase. Side bar: Is it apparent that our system designed for “RPS compliance” is highly versatile and can accommodate more “local” generation?

Quick Summary Robustness Indicator NA

Questions or thoughts on this study?