9.5 Gigawatts Signed, One Substation in the Middle: Why "Chalybe" Is Brownsville's Power Story for 2026 and 2027

9.5 gigawatts. That is how much new electric load AEP Texas told the state's grid operator in July 2026 it has signed agreements to serve in the Rio Grande Valley. Every bit of it is in Cameron County.

For scale: the entire Valley uses about 2.5 to 2.6 gigawatts today, according to the same AEP presentation to ERCOT. The signed new load is nearly four times that.

Much of the power story for 2026 and 2027 comes back to one place: a substation just south of Highway 48 in Brownsville called Chalybe.

WHAT CHANGED IN 2026

On July 21, 2026, AEP presented its "Rio Grande Valley System Improvement" to ERCOT's Regional Planning Group. ERCOT tracks it as project 26RPG009. According to that presentation:

- AEP has signed agreements for about 9.5 GW of large load in the Valley. That is up from about 6.8 GW when AEP first filed the project, after AEP signed about 3 GW more.

- All of the signed large load is in Cameron County.

- The recommended plan costs about $4.98 billion in 2026 dollars, with an estimated in-service date of May 2031.

- It calls for about 400+ miles of new 765-kilovolt lines, the highest voltage on the Texas grid, plus about 50 miles of 345-kV work. That includes new 765-kV stations named Puma and Cruce.

- AEP says nearly 6 GW of the signed load sits near the proposed Puma station.

The presentation does not name any customer and does not say what kind of facilities the load is. It refers only to "large load" and "contracted loads." Its one-line diagrams show connections to existing and planned stations, including "AEP Chalybe," "S.U Palmito," and Sharyland's Kingfisher.

Even with those upgrades, AEP's presentation projects the Valley's grid could serve about 8.5 GW at peak, well short of nearly 12 GW of peak demand if all signed load arrives. AEP calls that a large gap.

WHAT CHALYBE IS

Chalybe is not new on paper. It is the rebuilt version of AEP Texas' existing Union Carbide 138-kV station, which AEP describes in a November 26, 2025 filing at the Public Utility Commission as "just south of Highway 48 in Brownsville."

In December 2024, ERCOT endorsed a $423.8 million AEP plan built around it, according to ERCOT's board memo. That plan:

- Adds a 345-kV yard at Chalybe with two large transformers.

- Builds a new Chalybe-to-Kingfisher 345-kV double-circuit line, about 22 miles, on new right-of-way.

- Builds new short lines from Chalybe to Palmito and Stillman.

- Rebuilds about 44.5 miles of existing 138-kV lines in Cameron County.

ERCOT said that project was needed to serve 650 MW of new load in the Brownsville area. AEP's original target was May 2027. ERCOT's endorsed version now targets May 2029.

That 650 MW looked large in 2024. Measured against 9.5 GW of signed load in 2026, it now looks like a down payment.

THREE PROJECTS, ONE SUBSTATION

Chalybe is now tied to several separate filings from 2025 and 2026:

- South Texas Electric Cooperative's Southeast Brownsville large load project. ERCOT recommended it in May 2026 at about $96.6 million. It rebuilds lines from Chalybe and runs about 19 miles of new line to a new "Boca Chica" substation for 250 MW of confirmed load. According to a July 2026 ERCOT filing at the PUC, an alternative that would have run directly out of Chalybe was ruled out because of the planned substation's limited room to expand.

- Battery storage. Three "Ouroboros Grid BESS" units of about 200 MW each entered ERCOT's queue in July 2025 listing a Chalybe 345-kV connection and June 2028 start dates, according to queue trackers that publish ERCOT data. That is about a year before Chalybe's 345-kV yard is due.

- A state legal fight. In July 2025, Sharyland Utilities asked the PUC for a declaratory order in Docket 58408, a request for a ruling on a legal question. The record shows AEP and Sharyland disagree over facilities at Chalybe. The case carries a State Office of Administrative Hearings number, a sign it went to a contested hearing. The record also includes Cameron County Regional Mobility Authority correspondence on a Chalybe "draft siting study."

THE ROUTE NOBODY HAS SEEN

The Chalybe-to-Kingfisher line needs about 22 miles of new right-of-way. Kingfisher sits on the west side of Casey Road, County Road 315, about 0.8 miles south of FM 510, southeast of San Benito, according to a 2022 PUC order.

Before that line can be built, AEP must win a Certificate of Convenience and Necessity from the PUC. In that case, the utility proposes several routes, directly affected landowners receive mailed notice and can intervene, and the PUC picks the final path. In the records The 956 Report reviewed, no route for the Chalybe-to-Kingfisher line has been made public.

Once a route is approved, a utility can use eminent domain if a landowner will not sell an easement. Under the Texas Landowner's Bill of Rights, owners get a written offer and an appraisal, can hire their own appraiser and attorney, and can take a dispute to court-appointed special commissioners. On the nearby La Palma-to-Kingfisher line, AEP reported in January 2025 that "several tracts" were "proceeding to condemnation."

A 345-kV line runs on steel poles about 155 feet tall, on a right-of-way about 150 feet wide, according to AEP's fact sheet for that nearby line. AEP's 2026 plan would add 765-kV lines, which are larger still.

WHY IT MATTERS TO YOU

If you own land between Brownsville and San Benito, a 22-mile line has to go somewhere, and the route maps have not come out yet. If you pay an electric bill in Texas, transmission costs in ERCOT are generally spread across customers statewide, and AEP's Valley plan alone is estimated at $4.87 billion. And if 9.5 GW of new demand arrives, Cameron County's landscape, water use and economy will change, from customers no public document names.

QUESTIONS THAT REMAIN (ANALYSIS)

Who signed agreements for 9.5 GW in Cameron County? Where will the Puma station go? When will the Chalybe-to-Kingfisher route be filed? How will the PUC rule in Docket 58408? Can Chalybe be finished in time for the projects already lining up behind it? The documents reviewed do not answer these questions.

WHAT TO WATCH NEXT

- ERCOT's decision on AEP's $4.87 billion Rio Grande Valley plan. As a Tier 1 project, it needs a vote by ERCOT's board.

- Route applications, mailed landowner notices and open houses for Chalybe-to-Kingfisher and for the new 765-kV lines.

- A ruling in Docket 58408.

- ERCOT's large-load verification report, due to the PUC by December 10, 2026, under Gov. Greg Abbott's August 2026 directive on data center grid connections.

SOURCES

1. "AEPSC RGV System Improvements (26RPG009) Overview," AEP Service Corp. presentation to ERCOT Regional Planning Group, July 21, 2026. https://www.ercot.com/files/docs/2026/07/20/14.-AEPSC-RGV-System-Improvements-26RPG009-OVERVIEW.pdf

2. Item 10.3.1: AEPSC Brownsville Area Improvements Transmission Project (revised board memo), ERCOT, December 2, 2024. https://www.ercot.com/files/docs/2024/12/02/10-3-1-aepsc-brownsville-area-improvements-transmission-project-revised.pdf

3. Item 6.1: AEPSC Brownsville Area Improvements Transmission Project, ERCOT Independent Review, November 21, 2024. https://www.ercot.com/files/docs/2024/11/21/6-1-aepsc-brownsville-area-improvements-transmission-project.pdf

4. PUC Docket 58408, Item 77, AEP Texas supplemental response, filed November 26, 2025. https://interchange.puc.texas.gov/Documents/58408_77_1561326.PDF

5. PUC Docket 58408 filings list, "Petition of Sharyland Utilities, L.L.C. for a Declaratory Order." https://interchange.puc.texas.gov/Search/Filings?ControlNumber=58408

6. ERCOT Independent Review Status Update, STEC Southeast Brownsville Large Load Project (25RPG039), April 13, 2026. https://www.ercot.com/files/docs/2026/04/09/7.-EIR-Status-Update-STEC-Southeast-Brownsville-Large-Load-Project-RPG_April_2026_Final.pdf

7. ERCOT Independent Review report, STEC Southeast Brownsville Large Load Project, filed at PUC Project 55999, July 10, 2026. https://interchange.puc.texas.gov/Documents/55999_254_1664903.PDF

8. Ouroboros Grid BESS 1 to 3 queue entries (28INR0397, 28INR0398, 28INR0403), via InfraSure. https://www.infrasure.ai/project/ercot-28inr0398-ouroboros-grid-bess-2

9. Item 14: Batch Zero Update, ERCOT Board of Directors, September 14-15, 2026. https://www.ercot.com/files/docs/2026/09/11/14-Batch-Zero-Update.pdf

10. Final Order, PUC Docket 53727 (La Palma to Kingfisher 345-kV line), December 2022, hosted by AEP. https://aeptransmission.com/Texas/LaPalma-Kingfisher/docs/Kingfisher-La%20Palma_Final%20Order_1-18-2023.pdf

11. Project No. 52682 Quarterly Report (1Q 2025), AEP Texas, filed January 31, 2025. https://interchange.puc.texas.gov/Documents/52682_74_1464886.PDF

12. La Palma-Kingfisher Fact Sheet V16, AEP Transmission. https://www.aeptransmission.com/cmsuploads/Kingfisher-LaPalma_Factsheet_V16.pdf

13. Texas Landowner's Bill of Rights summary, LCRA. https://www.lcra.org/energy/electric-transmission/transmission-line-routing/texas-landowners-bill-of-rights/

14. White & Case, "PUCT sets financial commitments for data center interconnection as governor pauses permit approvals," 2026. https://www.whitecase.com/insight-alert/puct-sets-financial-commitments-data-center-interconnection-governor-pauses-permit