ERCOT’s battery fleet has crossed a threshold this summer. Through the first five days of July, the fleet is pushing enough energy into the evening ramp to visibly shave the top off real-time prices, and that behavior is showing up directly in the arbitrage math. The TB4 and TB2 spreads, the value a 4-hour and a 2-hour battery are respectively built to capture, are running roughly a third to a half below where they sat a year ago at every hub. The fleet is, in effect, competing away the very spread it was built to harvest.

Charging Midday, Capping the Ramp

The daily storage picture over the past week lays out the rhythm. Each morning the fleet charges hard through the midday solar block, with aggregate charge pulling down toward the 9,000 to 10,000 MW range as solar floods the grid and prices sag toward zero. That stored energy then comes back in a sharp evening discharge that peaks alongside the real-time price into the net-load ramp, the same 7 to 9 PM window that used to set the day’s high prints.

Figure 1 | Daily Power Storage – Last 7 Days (Charge / Discharge, MW vs. RT Price, $/MWh)

The key point is where the discharge lands. Across June 29 through July 5, the orange discharge block tracks the climb in the red RT price line and tops out at the same hours the ramp peaks. The fleet is no longer just riding that evening spike; the volume of discharge is now large enough to blunt it. The result is a lower, flatter evening peak than the underlying net-load shape would otherwise produce, which is exactly what keeps the arbitrage spread from widening out.

Spreads Kept in Check

That capping shows up plainly in the TB values. At every hub, the July month-to-date TB2 average has fallen by roughly half versus last July, and TB4 is down on the order of $20 to $24/MWh. Houston’s TB2 has compressed from $62.16 to $26.10, and even West, the richest hub, sits at $38.59 against $70.78 a year ago.

Table 1 | TBNth RT Arbitrage Values by Hub ($/MWh)

This is not simply a soft-2026 versus hot-2025 comparison. The July MTD values also sit below the June 2026 monthly averages at most hubs, so the compression is continuing month over month even as summer heat builds. The step-down is visible across all four hubs when the three periods are placed side by side.

Figure 2 | TB4 RT Arbitrage by Hub, Jul-25 vs. Jun-26 vs. Jul-26 MTD ($/MWh)

The mechanism is a self-limiting loop. A larger fleet discharges more into the evening, which flattens the ramp, which tightens the very spread the fleet is chasing. The batteries are, quite literally, keeping their own arbitrage in check, and the two-hour spread is compressing faster than the four-hour spread because the sharpest part of the peak is the first to get shaved.

Three Summers of Reshaping the Curve

The structural story behind that compression is best seen in the year-on-year hourly profile. Figure 3 plots the average hourly net output of the storage fleet for each month, stacked across 2024, 2025, and 2026, so each monthly block reads as a single daily charge-and-discharge shape.

Figure 3 | Energy Storage Net Output, 12x24 Monthly Hourly Profile by Year (MW)

The three-year progression is striking. In 2024 the profile barely leaves the axis; the fleet was small enough that its aggregate signature was a ripple on the net-load curve. By 2025 a clear daily oscillation has formed. In 2026 the shape is a different animal entirely, with the midday charging trough plunging and the evening discharge peak towering above prior years. July 2026 shows the widest swing on the chart, running from roughly negative 8,000 MW of midday charging to positive 7,500 MW of evening discharge.

Each summer the amplitude of that daily cycle has grown, and the 2026 curve is the first in which the fleet is large enough to bend the shape of the net-load curve rather than merely profit from it. That growing amplitude is the leading indicator; the TB compression in Table 1 is the lagging confirmation. The flatter the fleet makes the evening ramp, the smaller the spread it leaves for the next battery to capture.

Capping the Insight

For the balance of the summer, watch the amplitude, not just the headline price. If the 2026 profile keeps deepening, evening-ramp spreads should stay capped even through peak heat, and the marginal economics for new two-hour builds will keep tightening faster than for four-hour systems. The fleet that was built to arbitrage the ramp is now big enough to erase a meaningful share of it, and that trade-off will define ERCOT’s storage revenue outlook through Q3. For more information regarding the Energy GPS Battery Package we offer as part of the Subscription Product Offering, email us via the Contact Us form on the Energy GPS website or at [email protected]. 

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