2026 Common Case Development Byron Woertz, Manager—System Adequacy Planning W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Overview 2026 Common Case development process Enhancing the Common Case with Round Trip functionality What we have achieved What remains to be done Next steps 2 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Context This has been a learning process WECC and stakeholders have used a new approach: simultaneous development of a usable Common Case and implementation of Round Trip functionality This is an extremely challenging process The timeline has been very aggressive We have accomplished a lot and learned a lot 3 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

2026 Common Case Components LoadsResourcesTransmission Expected loads in 2026 Based on 2015 Loads and Resources submittals Presented by TEPPC Load Area Load distribution to buses Current resources plus resources expected by 2026 New resources used in both power flow and PCM models Generator characteristics Generator locations by bus # Current transmission topology… Plus new transmission expected by 2016 Common Case Transmission Assumptions (CCTA) represent new transmission in W ESTERN E LECTRICITY C OORDINATING C OUNCIL

AugSepOctNovDec Jan 2016 FebMarAprMayJun 2016 Today Release Version 1.0 of 2026 Common Case (tentative) 6/30/2016 Release pre-release review version of 2026 Common Case 3/31/2016 Solved 2026CC Power Flow delivered to WECC 12/7/2015 Begin work on 2026 Common Case3 8/3/2015 WECC staff and regional development of 2026 CC 8/3/ /31/2016 Regional review of Common Case resources 8/3/ /30/2015 Data Work Group review of CC inputs 9/1/ /22/2016 Stakeholder review of pre-release CC 4/1/ /29/2016 Revision of 2026 CC resource set 4/1/ /31/2016 Final review and revision of 2026 CC 6/1/ /24/2016 Common Case Development Process

Connecting the Common Case with Round Trip Functionality Effort led by Northern Tier Transmission Group (NTTG) Goal: enable users to solve an hour of Production Cost Model output in power flow with minimal changes Approach: use power flow model to develop Common Case – Produce output compatible with solving in power flow 6 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

The Good News—What We Have Load information is complete Transmission information is complete Development of Round Trip capability is underway 7 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

…But There Are Some Challenges PCM model doesn’t provide solvable power flow Significant resources from PCM were omitted from the solved 2026CC power flow – RPS assumptions were developed on incomplete resource set (2024 Common Case) Updated renewable profiles not yet received – Renewable Portfolio Standard (RPS), Resource Adequacy (RA) and Flexibility Reserve Margin (FRM) compliance checks contingent on complete resource set DR profiles not yet received 8 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

2026 Common Case Challenges 2026 Common Case – Build process – Power flow case import – Generator match-up and reconciliation – Comparison to 2024 common case – Managing expectations – Examples – Other considerations 9 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

2026 Common Case – Build Process Common Case V TSS Base Case HS1 NTTG 2024 RT Dataset Regional Updates Generator Bus Mappings Generator Updates Bus Area Assignments 2026 Updates Load Forecasts Load Changes – Pmp, EE, DG Hourly Load Shapes CCTA Projects Generator Retirements Hourly Profiles – Hydro Wind Solar Wheeling Rates Generator Cost Parameters Fuel Prices & Emission Rates Nomograms Reserves GHG Policies RPS & Resource Adequacy Demand Response Outages Other 2026 Common Case Validation & Studies

Power Flow Import to PCM Builds or updates system network – Buses, branches, components Reconciles generator buses to PCM generators by bus number and id – Builds exception lists Reconciles network buses to PCM load areas – Builds exception lists 11 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Power Flow Case Guidelines 12 W ESTERN E LECTRICITY C OORDINATING C OUNCIL Loads – By type, may be composite loads Generation – Unit level threshold is 10 MVA – Aggregate level threshold is 20 MVA – No rule on multi-unit plants – Some generation netted with load – Low priority for renewable generation Transmission and Equipment – Generally 69 kV, but 13 kV for generators

Same.. Bus # and ID Gen type, size Generation Match-up 13 W ESTERN E LECTRICITY C OORDINATING C OUNCIL 2025 HS1 Base Case Generators 2024 TEPPC Common Case Generators Exact Match? Yes 2026 Data Set No Add to dataset as and status off Reconcile? Find by Name, type, size Reconcile? NoYes Keep status off Keep Add Discard or Add to PF Match? Keep No Yes No Yes Status on Change Name

Final NTTG Generator Reconciliation 14 W ESTERN E LECTRICITY C OORDINATING C OUNCIL 2025 HS1 power flow  2024 NTTG PCM Power flow has 4,346 generator buses Goal to deliver Round-trip capability Initial import produced ̴1200 units 584 units not resolved (26 GW) NTTG process impacted several generators from 2024 common case (see next slide)

Filtered Comparison 2024 CC vs. NTTG RT 2024 > 0 MWh NTTG = 0 MWh 2024 = 0 MWh NTTG > 0 MWh Number of Units1,06581 Capacity (MW)32,4404,558 Energy (GWh)82,49710,635 Match, no dispatch W ESTERN E LECTRICITY C OORDINATING C OUNCIL Possibly 30 – 40 units where names were changed. Process: Combine generator names from both datasets and lookup the energy produced for each generator from both result files.

NTTG vs Common Case 16 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

NTTG vs Common Case 17 W ESTERN E LECTRICITY C OORDINATING C OUNCIL Load Reduction Renewable Decrease

Generator Definitions Also Changed It appears that the generation types for several generators were changed Net reduction of 14,969 GWh Based on example of Milford Wind 2 (see next slide), this impacts the modeling of these units – Milford Wind 2 output reduced from 237 GWh to 0 Need to know why these changed so can avoid this in future 18 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Milford Wind 2 19 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Springerville 3 20 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Managing Expectations Difficult to reconcile generation and maintain Round-trip capability NTTG led effort in 4Q2015 to reconcile 2024CC and 2025HSPF resource data – Goals: build on extensive efforts to reconcile generators for the 2024 common case – Take advantage of expertise of the regional participants to “true-up” generation Misunderstanding on limitations of resulting dataset 21 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Example – Cimarron Solar (1) 30 MW solar farm in NM located at bus in 2024 common case – online in 2010 The Cimarron PCM unit was removed from the NTTG dataset due to no matching generator bus in 2025HS1 power flow Not resolved by NTTG regional effort 22 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Example – Cimarron Solar (2) HS1 PF Case

Example – Cimarron Solar (3) HS1 PF Case

Example – Cimarron Solar (4) HS1 PF Case

Example – Cimarron Solar (5) 26 W ESTERN E LECTRICITY C OORDINATING C OUNCIL New 2025 power flow added more detail, moved Cimarron from bus to bus How to resolve – Cannot simply fix bus number in PCM since generator was removed – Now must work with new unit Change name Specify solar profile and other parameters Enter commission date Change status to ON Ensure that round-trip maintained

Another Example Desert Sunlight Solar Farm – 550 MW solar farm in Southern California – Completed in 2014 and 2015 in two phases – Had in 2024 common case, removed by NTTG – Not in 2025 HS1 power flow case and not in NTTG PCM dataset – Ties at Red Bluff substation – Produced 1,286,745 MWh in W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Other Large Generators Gone Missing Agua Caliente (290) Arlington Vly (254) Carlsbad (600) Energia S Juarez (250) Genesis (250) Mojave Solar (250) Solar Star (579) DG units Gap units OTC units Planned RPS CPUC SONGS repl. units 28 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Questions 29 W ESTERN E LECTRICITY C OORDINATING C OUNCIL How many missing generators? Does power flow case have complete representation of generation? – Existing – Under construction and planned – Renewable Resolution – If unmatched need to reconcile, but be careful of duplicates – If not in power flow, need to add to PCM and power flow – Need to maintain Round-trip capability

Other Considerations TEPPC has always recognized that the power flow representation of generation is incomplete. It is obvious that an update of the generation is required to capture additions, retirements and other changes; and to re-add the applicable units that were removed by NTTG. Note that Tom Carr is finding several units that are not in either dataset (mostly renewable). 30 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Questions or Comments 31 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Round-Trip Functionality Challenges Dump Energy Evaluate power flow export Modify to represent load/gen balance Voltage Profile Corrections Reflect system voltage components for specified export hour Case Data Assessment Correct transformer nominal voltages, bus types, etc. Solution Automation Not intuitive 8,760 potential export cases Fixing GridView export by each user not realistic Automate: “fix files?” 32 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

What Do We Have? A very rough Common Case that needs significant work – Loads are in pretty good shape – Transmission is in pretty good shape Clearer understanding of Round Trip functionality needs 33 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

What Remains to Be Done? Reconcile resources – Resources from solved 2026CC power flow – Renewable resource additions from PCM Add revised renewable resource profiles Complete RPS, RA and FRM compliance checks on complete resource set Update DR profiles 34 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

What Remains to Be Done? When 2026 Common Case is complete, continue round trip basic functionality development – GridView output does not solve in power flow – WECC plans to focus on producing a solid Common Case before additional work on round trip functionality – Developing the Common Case based on power flow iterations did not work because… (I need some help here) 35 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Next Steps March 31 Post pre- release 2026 Common Case Week of April 11 Develop specific tasks to complete 2026 Common Case version 1.0 Week of April 18 Finalize schedule for completing Version 1.0 April - June Complete tasks for Version 1.0 TBD Publish version 1.0 of 2026 Common Case 36 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

Action Items 37 W ESTERN E LECTRICITY C OORDINATING C OUNCIL By April 11 Review posted version of 2026 Common Case Review Pre-Release Notes Submit recommended actions, suggested timelines and suggested participants April 14(?) Webinar to review draft project plan