Why Fuel Diversity Matters
During Winter Storm Uri in February 2021, extreme cold stressed every link between the wellhead and the customer at the same time. The gas system and the electric system failed together, and each failure deepened the other.
- Extreme Cold Hits TexasPolar vortex drives temperatures below design conditions across the system.
- Gas Supply Freezes OffWellheads and processing plants lose output, sharply reducing available gas supply.
- Midstream Capacity Breaks DownCompression and gathering systems lose power or capacity, constraining gas movement.
- Power Plants Lose FuelLow pressure, limited supply and firm-contract constraints reduce deliverable gas.
- Generation Goes OfflineFuel shortages and equipment failures force widespread generator outages and derates.
- Customers Lose PowerERCOT sheds roughly 20,000 MW of load as supply falls below system requirements.
The fuel shortfall was measurable. At the peak on February 17, 6,700 MW across 131 units was outaged or derated for “fuel limitations.” The signs came early: generators reported gas shortages as early as February 10, and 3,500 MW was already fuel-limited before load shed began on February 15. Upstream, throughput across a 27-plant Permian processing sample fell by roughly 85%, with 18 of the 27 plants at zero output on February 17. The failures ran through the whole chain, across production, storage and distribution, and gas equipment sat on the very circuits that load shed cut.
What has changed since 2021
Texas has made cold-weather preparedness mandatory: Senate Bill 3 and subsequent PUCT and RRC rules now require weatherization of generators and critical gas facilities, and more than 7,400 gas-facility weatherization inspections were carried out in FY2025. Texas entered winter 2025–26 with about 525 Bcf of working gas in storage, the highest monthly total in more than 25 years, and during Winter Storm Fern in January 2026, record demand was met without manual load shed.
But the interdependency between the gas and electric systems remains. Extreme weather, compressor failures, pipeline maintenance, force majeure and common electrical dependencies can still interrupt fuel delivery to any single-fed plant. ERCOT continues to procure Firm Fuel Supply Service, reflecting the reliability value of fuel-secure generation, and in extreme conditions residential and human-needs gas service takes priority over industrial load.
02The Pecos design
Layered independence across four system layers
Each layer addresses a different type and duration of disturbance, so that a problem upstream is contained before it reaches the critical load. Generation sits behind the BESS: it recharges the battery bank in all conditions, and the critical load draws only from storage.
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L1
Fuel layer
Dual-fuel flowing + stored fuel
Primary fuel — dual-fuel blend
Generation runs continuously on pipeline natural gas and on-site ethane (~85/15), supplied by multiple Waha-connected pipeline paths and the adjacent Istmo fractionator
Dynamic blend control
With both fuels already flowing, a supply change is a blend-ratio adjustment within OEM envelopes, not a cold fuel switch
Stored propane — reserve
Produced on site and held in storage, available without contemporaneous pipeline delivery
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L2
Generation layer
Recharges the BESS
INNIO Waukesha reciprocating engines
Modular, fast load-following units designed by the OEM for multi-fuel operation
Siemens Energy aeroderivative turbines
Efficient bulk generation on an OEM multi-fuel platform
N+1 on both platforms
Spare units on each fleet, site-rated for West Texas summer conditions
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L3
BESS layer
Always between generation and load
BESS + PCS, always in line
Serves the critical load continuously while generation recharges it; energy reserve sized to the customer’s ride-through specification
Long-duration flow storage
TerraFlow LDUPS™ within the storage layer, in series with the load: hours of reserve, real-time smoothing of AI load swings, harmonic filtering
EPMS controls + boundary isolation
Generation dispatch to recharge the BESS, fuel-supply triggers and a priority load-shed stack; no bulk electrical tie between the IT bus and the fractionator
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L4
Critical load
Customer-facing
The customer sees only this layer.
Served from the BESS at all times, behind the meter, with no grid dependence and no single-fuel dependence.
03Fuel strategy
Different fuels serve different reliability functions
The campus runs on a dual-fuel blend of pipeline natural gas and on-site ethane — all the time, not only during a disruption. Stored propane adds inventory, and stored inventory is what buys time.
Primary fuel · dual-fuel
Natural gas + ethane
- Continuous operation on a ~85/15 natural gas / ethane blend
- Natural gas from multiple Waha-connected pipeline paths
- Ethane produced on site by the adjacent Istmo fractionator
- Fractionator feedstock arrives on a primary Delaware Basin NGL pipeline downstream of multiple cryogenic processing plants — multiple feedstock paths drawing on a large pool of regional NGL supply
Dynamic switching
Blend flexibility
- Because both fuels are already flowing to the units, a change in gas supply is handled by shifting the blend ratio within OEM envelopes
- Historically, most gas curtailments to Texas generators have been partial reductions in delivered volume or pressure, not a complete loss of supply
- The blend leans on more ethane when gas tightens, or runs on pipeline gas alone if the fractionator is offline
Stored resilience fuel
Propane
- Produced on site by the same fractionator
- Held in pressurized sphere storage
- Once stored, independent of contemporaneous pipeline delivery or fractionator operation
- Designed as the longer-duration reserve for prolonged fuel disruption
OEM multi-fuel equipment. Pecos generation runs on INNIO Waukesha and Siemens Energy platforms designed by the OEMs for multi-fuel operation, with OEM-documented performance on the natural gas / ethane blends the campus uses.
Because part of the fuel supply is produced on site through its own supply chain, the campus’s fuel cost is also not tied solely to a single regional gas hub — diversifying exposure to both physical supply risk and gas price volatility.
04Ride-through
Because the load is always served from the BESS, generation events never reach it
Generation’s only job is to keep the BESS charged. The critical load draws from the BESS/PCS in every operating state, so a fuel or generation disturbance shows up as a change in the battery’s state of charge, not as a disturbance at the load.
Critical data center load: served from the BESS/PCS continuously, designed to stay within specification throughout
- T0Fuel disruption detected
- T1Generator fuel transition / unit rebalancing
- T2Stabilization (frequency, voltage, load share)
- T3Recharging resumes on alternate fuel
Blend-ratio adjustment
Gas pressure or volume declines; the dual-fuel blend shifts toward ethane while units keep recharging the BESS. Seconds.
Abrupt gas disruption
Units may trip or reconfigure; the load keeps drawing from the BESS while generation restarts and resumes recharging. Minutes.
Extended event
Pipeline gas stays constrained; stored propane keeps generation recharging the BESS for longer. Hours to days.
Design principle
Usable BESS energy ≥ critical load × (maximum credible generation recovery time + stabilization margin) × safety factor
The BESS carries the load through any interruption in recharging; stored propane keeps generation recharging during long events.
05Long-duration storage
TerraFlow LDUPS™ for Critical-Load Resilience
Pecos pairs its ride-through layer with TerraFlow Energy’s LDUPS™, a long-duration uninterruptible power supply built on flow-battery technology. It sits in series between generation and the critical load, powering the facility continuously rather than switching in only when something fails.
Hours, not minutes
Energy is stored in electrolyte tanks, so duration scales with tank size — extending ride-through from a transition event to a multi-hour reserve.
Built for AI load swings
Absorbs and releases energy in real time, so the rapid, large power swings of AI training loads are absorbed by storage and never reach the generators.
Cleaner power
Filters harmonic distortion at the source and maintains uptime with no switching delay.
Safer chemistry
Water-based flow-battery electrolyte with no thermal-runaway fire mode and minimal degradation over time.
| Layer | What it protects against | What LDUPS™ adds |
|---|---|---|
| Dual-fuel supply | Gas pressure drops and curtailment | More time for blend changes and fuel transitions to complete |
| Multi-fuel generation | Unit trips and fuel-change transients | Generators see a steady recharging load; AI load swings never reach them |
| BESS layer | Interruptions in generator recharging | Duration measured in hours alongside the fast-response battery |
| Critical load | Power-quality excursions | Continuous in-series conditioning and harmonic filtering |
06Failure modes
Responses by Failure Event
Reliability is layered: the architecture assigns each class of event a primary and a secondary response.
| Event | Primary response | Secondary response | Designed outcome at the critical load |
|---|---|---|---|
| Loss of one gas source | Second pipeline sourcing path | Shift blend toward ethane within OEM envelope | No critical-load interruption |
| Gas pressure drop / partial curtailment | Shift blend toward ethane; alternate gas path | Load stays on the BESS throughout | No critical-load interruption |
| Regional gas curtailment | Increased ethane share; alternate gas path | Transition to stored propane reserve | Critical-block continuity for the duration of stored inventory |
| Fractionator interruption | Run on pipeline natural gas alone (OEM baseline fuel) | Stored propane remains available | No interruption while pipeline gas is available |
| Propane storage / vaporizer fault | Dual-fuel gas/ethane operation continues | Alternate gas path | No interruption |
| Single generator trip | Load continues on the BESS | N+1 spare restores full recharging | No critical-load interruption |
| Fleet-wide fuel change | Load continues on the BESS | Staged switching of generator units | No interruption |
| AI load swing | BESS / TerraFlow LDUPS™ absorbs and releases energy in real time | Generators never see the swing; they keep recharging at a steady rate | Stable, conditioned power |
| Fuel-transition transient | Load served from the BESS throughout | Staged generator restart; recharging resumes | Specification-compliant power |
| Grid outage | Not applicable — behind-the-meter, no grid dependence in normal operation | — | No effect |
| Prolonged combined disruption | Stored propane reserve | Priority-load management; critical-block preservation | Critical-load continuity prioritized for the duration of stored inventory |
07Common-mode design
Engineered against shared points of failure
Fuel diversity only adds resilience if the paths are not tied together downstream. The design addresses common-mode exposure directly.
Electrical isolation
No bulk tie between the campus IT bus and the fractionator
Backed auxiliaries
Storage auxiliaries on a dual-fed loop with diesel backstop
Generation isolated from the load
Generation only recharges the BESS; unit trips and governor response stay on the charging side
Distributed generation
Two independent generation platforms, each with N+1 spares
No individual fuel is the product. Resilience is the product.
The Pecos architecture does not assume that any single fuel source will always be available. It is designed around the ability to move between supply, inventory and electrical-reserve layers without passing the disturbance through to the critical load.
Running diligence on Pecos?
Detailed design basis, one-lines, OEM data and the fuel-resilience technical brief are available to qualified parties under NDA.
Request the technical package