Houston Import Evaluation Cross Texas Transmission & Garland Power & Light ERCOT RPG Meeting August 27th, 2013

Agenda Houston Import Needs Discussion GP&L/TMPA Affected Facilities – Existing N-H corridor Impact of N-H import/solution on Gibbons Creek Additional Considerations Transmission Options Studied Preferred Options

Houston Import Needs Discussion Base case reliability need observed for Houston import for 2018 Thermal overloads under N-1 + G-1 conditions observed to be key drivers for the reliability need N-H transfer levels modeled at 3100 MW for the 2018 study case Houston Import reliability needs and long-term effectiveness of proposed solutions sensitive to the following N-H transfer levels Generation availability within Houston and along the N-H import path Long term Houston load deliverability may require significant re-conductor and/or upgrades of existing N-H corridors Important consideration when evaluating feasibility of import options

GP&L/TMPA Affected Facilities – Existing N-H Corridor Significant history of anticipated congestion on existing N-H corridors across various ERCOT Houston Import study efforts ERCOT Houston Import Study Update (April 2010) – “2014 benchmark case showed heavy congestion on Singleton-Zenith 345-kV line for the contingency loss of Roans Prairie-Kuykendahl/ Singleton-Tomball 345-kV double circuit. Congestion also observed on Jewett-Singleton and Twin Oak-Jack Creek 345-kV lines” ERCOT 2012 Long Term Study (LTS) – Scenarios of Interest from Houston Import standpoint Scenario #2: Base with All Tech and Retirements (retirement of legacy natural gas-fired generators) Scenario #3: Base with All Tech and Incremental Wind

GP&L/TMPA Affected Facilities – Existing N-H Corridor Significant history of anticipated congestion on existing N-H corridors across various ERCOT Houston Import study efforts (Contd.) ERCOT 2012 Long Term Study (LTS) – Scenarios of Interest from Houston Import standpoint Scenario #5-a: Drought Scenario Summer capabilities of existing water – consuming resources de-rated Increased peak load Scenario #7: BAU – Hi Natural Gas Characterized by a high natural gas price ($9.55 by 2016, $13.7 by 2022) Resources retire in 2018 and 2022 for competitive reasons

GP&L/TMPA Affected Facilities – Existing N-H Corridor Estimated Congestion Costs, N-H Constraints, ERCOT LTS Effort Source: ERCOT DOE Long Term Study (ERCOT POI Site)

GP&L/TMPA Affected Facilities – Existing N-H Corridor Houston Import, Congested Elements, ERCOT LTS Effort

GP&L/TMPA Affected Facilities – Existing N-H Corridor 2015 & 2017 Projected Economic Constraints, ERCOT C&N Report 2012 (Source: ERCOT 2012 Constraints & Needs Report)

GP&L/TMPA Affected Facilities – Existing N-H Corridor All ERCOT Houston Import evaluations indicative of significant anticipated congestion on existing N-H corridor Two key GP&L/TMPA facilities part of the congestion constraints 345kV Gibbons Creek – Twin Oak 345kV Gibbons Creek - Singleton Avoiding congestion (and overloads) on existing N-H corridors will provide significant cost savings to Houston region Provides significant economic benefits to any Houston reliability project Prevent the need to take additional outages to re-conductor 345kV lines along an already congested N-H corridor Critical aspect to be taken into account when evaluating import project options

Houston Import – Impact on TMPA/GP&L Facilities Need to alleviate congestion/potential overloads on TMPA/GP&L transmission facilities in existing N-H corridor as part of Houston Import Need to ensure that potential Houston import solutions divert enough power from existing N-H corridors Looping N-H projects via intermediate stations South – Houston projects with large enough transfer capability to offset flows from the north Direct solutions with series compensation Transmission solutions looped through existing TMPA facilities may exacerbate over-voltage issues under light load conditions TMPA RPG approved project for 130-150 MVAR reactor on 345kV Gibbons Creek expected to address this issue

Additional Considerations Recent history of Gibbons Creek unit being requested to provide VAR support during high N-H transfer levels (at the cost of active power to TMPA member cities) Gibbons Creek unit exempt from PRR830 requirements Gibbons location significantly strong with little ability of external reactive equipment impacting voltage downstream Optimal approach would be to reduce impedance between Gibbons & Houston thereby improving voltage conditions in the region Ability to reduce the “N-1” impact created by the proposed solution itself Important to ensure that the proposed solution does not become the single largest contingency for Houston import Utilize existing infrastructure and expansion capability to reduce the reliability impact for the outage of the proposed option

Transmission Options Studied (Source: CTT/GP&L Houston Import RPG Submission)

Preferred Options Preferred Options, Houston Import Study (Source: CTT/GP&L Houston Import RPG Submission)

Preferred Options Test Project 2022 capital cost ($M) Reliability benefit of test project ($M) Capital Cost Adjusted for Reliability Benefit ($M) Production Cost Savings ($M) 1/6 of Capital Cost ($M) 1/6 of Adjusted Capital Cost ($M) Meet ERCOT Economic Criteria ? Limestone-Gibbons Creek-Zenith 268.4 120.6 147.8 36.6 44.7 24.6 Yes Watermill-Big Brown 208.2 23.1 185.1 0.1 34.7 30.9 No Lake Creek – Navarro 104.1 42.1 62.0 1.7 17.3 10.3 Lake Creek – Watermill 297.4 19.0 278.4 0.4 49.6 46.4 Clear Spring - Hill County 0.0 4.1 17.4 Hays - Kendall second 345kV circuit 41.8 3.2 7.0 Sandow - Garfield 133.8 4.0 22.3 ERCOT LTS Scenario 3, 2022 Economic Project Assessment

Preferred Options 345kV Limestone – Gibbons Creek - Zenith Most optimal performing option in terms of incremental Houston import capability vs project cost (across options providing greater than 2500 MW Houston import capability) Houston import capability observed to be as high as 3000 MW with MLSE upgrades on TMPA N-H facilities Virtually no need to upgrade existing N-H corridor to achieve import capability Flexibility to achieve close to 3500 MW Houston import capability with upgrades on N-H corridor in long term Deemed economic via the ERCOT LTS Study for 2022 (S3) with significant reliability benefits ($121M) Provide all the benefits stemming from Gibbons Creek – Zenith Limestone provides access to significant generation in the North

Preferred Options 345kV Gibbons Creek – Zenith Provides close to 2000 MW of Houston import capability at significantly high MW/$M Requires comparatively less upgrades on existing N-H corridor to achieve Houston import capability level 345kV Gibbons Creek – Tomball Provides close to 2200 MW of Houston import capability at significantly high MW/$M May require reactive equipment enforcements in the long term to result in Houston import levels greater than 3000 MW

Questions/Discussion