Endurance Park leads ERCOT performance

In August 2025, ERCOT's published performance data revealed two standouts: Endurance Park and Cross Trails systems, optimized by Gridmatic, topped the leaderboard with 115% and 99% Real-Time TBx capture rates, as reported by Modo Energy.

"Two two-hour batteries of note this month however were Endurance Park and Cross Trails Storage, with higher than average capture rates of 115% and 99%. These batteries took discharging positions in the Day-Ahead Market more often to earn revenues much higher than the 30–55% median."

Such performance shows that TBx is not a ceiling but a reference point—and in real market conditions, well-optimized assets can surpass it. To understand why, we need to unpack the gap between TBx's simplified assumptions and the true operational flexibility of modern storage systems.

Understanding TBx

ERCOT's TBx metric serves as a simplified benchmark for assessing storage arbitrage performance.

Definition: TBx measures the difference between the average of the top x hourly prices and the bottom x hourly prices in the Real-Time market each day.
Purpose: It estimates the theoretical maximum energy-only arbitrage revenue a perfectly foresighted battery could earn from one full daily cycle with no efficiency losses.

While useful as a reference, TBx reflects a stylized model of market participation rather than actual operational behavior.

How a battery can exceed 100% of TBx

A capture rate above 100% may seem counterintuitive, but it reflects how real-world systems operate beyond TBx's simplifying assumptions. Several factors make this possible:

Granularity: TBx uses hourly averages, while actual Real Time prices change every 5 minutes — which creates opportunities for intervals where price spreads can be substantially larger.
Cycling Frequency: TBx assumes a single charge–discharge cycle per day, but in practice, assets can perform multiple cycles when market signals justify it.
Revenue Sources: TBx in ERCOT accounts for Real-Time energy arbitrage only. Real assets can also generate ancillary-service revenues from regulation, reserves, Day Ahead energy, and other ERCOT products.
Market Dynamics: TBx is static and backward-looking, while real optimization is dynamic, guided by forecasting, probabilistic models, and responsive control systems that capture transient price patterns such as ramping events, reserve shortages, and negative pricing.

Together, these realities explain how operationally agile batteries can legitimately surpass the theoretical 100% benchmark.

Broader implications

Differentiation through Capability: As ERCOT's storage fleet expands, the dispersion in financial performance is widening. Assets that incorporate sophisticated forecasting and automated optimization are better positioned to deliver stable, superior returns.
TBx as a Reference, Not a Ceiling: The benchmark remains a useful comparative tool, but it is no longer the upper bound of achievable performance.
Operational Proof Points: Capture rates above 100% signal systems that are technically robust, commercially agile, and capable of translating volatility into predictable cash flow — qualities that reduce downside risk for investors.

Conclusion

Endurance Park's August performance — 115% of TB2 and revenues well above the ERCOT median — illustrates how modern energy storage assets can outperform traditional benchmarks. For investors, it offers a clear proof point: optimization expertise can materially enhance BESS economics.

As ERCOT's market design continues to evolve, including the introduction of RTC+B reforms, the ability to respond with the speed and precision that AI-powered optimization affords will become even more critical. In this increasingly dynamic environment, operational agility will distinguish assets that merely participate from those that lead in capturing value. Gridmatic will share additional insights on these developments in forthcoming analyses. In addition, we will expand our analysis beyond ERCOT within our upcoming CAISO Storage Performance Report.