Solar holds midday down; the 8 PM-9 PM net-load ramp is the test

Three developments define this issue: the forecast gross-load peak rose 2,622 MW to 89,424 MW since the prior vintage; the system RT-DA spread flipped from a negative mean to $4.2/MWh across the past 24 joined hours; and constraint activity intensified, with the maximum shadow price reaching $3,500/MWh and binding constraints peaking at 22 on Aug 12, 4 PM CDT. Watch three items into tonight: the 7 PM CDT hour, where MetisCast's divergence from the cleared curve peaks at $12.2/MWh; whether the cross-location median RT-DA spread holds inside its calibrated band through the evening peak; and whether realized load stays within the forecast's error tolerance into the evening peak.

The load-forecast increase and the systemwide swing to a positive real-time premium are already established elsewhere in this issue. What remains open is the price path between now and tonight's peak. The cleared day-ahead curve, the market award known at issuance, peaks across a two-hour window: ERCOT Hub Average $38.5/MWh at 10 PM CDT, North Hub $41/MWh at 8 PM CDT, South Hub $37.2/MWh at 10 PM CDT, West Hub $37.4/MWh at 10 PM CDT, and Houston Hub $39/MWh at 10 PM CDT.

North clears two hours ahead of the other four hubs. MetisCast's ERCOT Hub Average path tracks the cleared curve closely on average, running $2.6/MWh above the award across the 17 joined hours available at issuance. The fit breaks down where it counts: the single-hour gap widens to $12.2/MWh at 7 PM CDT, and the model's own P10-P90 band opens to $39.1/MWh by 8 PM CDT. Direction is settled; level is not.

Over the past 24 joined hours, Houston Hub holds the second-widest hub-level real-time premium over its day-ahead award, at $5.9/MWh. The systemwide common component accounts for $4.2/MWh of that, leaving a $1.65/MWh local residual inside Houston's own historical range. North Hub's premium is $2.2/MWh and South Hub's is $2.7/MWh, both narrower and part of the same system-driven move rather than a location-specific signal. Watch the cross-location median RT-DA spread: it needs to hold between -$9.7/MWh and $8.5/MWh through the evening peak for the cleared curve to be validated. A break below that floor means tonight's premium was overstated across the board.

MetisCast prices ERCOT Hub Average +$2.6/MWh against the cleared day-ahead curve across 17 joined hours. Its P50 tops out at $42.4/MWh at Aug 13, 8 PM CDT while the market cleared $38.5/MWh at Aug 13, 10 PM CDT. The two agree on when the evening matters and disagree on what it pays.

Every priced hub settled real time above its day-ahead award, and a common $4.23/MWh system-wide component drives most of that pattern. West Hub's raw RT-DA spread is widest at $6.13/MWh, but the common piece leaves only a $1.9/MWh local residual, inside West's own historical band. Houston Hub's $5.88/MWh raw spread resolves the same way: a $1.65/MWh residual within its own threshold, even though Houston's $33/MWh real-time mean remains the system's highest hub price. North Hub and South Hub converged in real time, $26.3/MWh versus $23.1/MWh (a $3.2/MWh gap), narrower than their $3.7/MWh day-ahead gap ($24.1/MWh versus $20.4/MWh). No location broke its own residual band; the system moved together, most visibly at the Aug 12, 8:00 PM CDT price peak shared across West, South, Houston, and the ERCOT Hub Average.

Wind's forecast high, 28,707 MW, arrives near 2 AM CDT, and solar's forecast holds near 33,617 MW at 2 PM CDT before falling to zero by evening; neither resource carries the evening transition, the reason the cleared curve and MetisCast diverge most into the 7 PM hour, covered elsewhere in this issue.

Resource outage capacity in effect stands at 9,836 MW as of the Aug 13, 8 AM CDT snapshot, inside the central range of its own trailing 90-day, same-hour history (36th percentile of 64). The published forward curve shows this reading rising to 10,068 MW later in the day, a normal-range outage path rather than an elevated one.

Committed capacity net of load and the ancillary-service requirement reaches 4,982 MW at the Aug 13, 8 PM CDT hour, high versus its own trailing history (93rd percentile of 83, realized daily minimum capacity less load, trailing 90 days). That figure excludes imports and the largest contingency, so it describes a capacity-minus-load margin, not a reserve or scarcity reading.

Since the prior issue, the maximum binding-constraint shadow price rose to $1,110/MWh from $373.4/MWh and the binding constraint count rose to 9.2 from 4.2, both traced to an Aug 12, 4 PM CDT episode that unwound to zero by the latest reading. ERCOT's forecast shows highs in the upper 90s and low 100s across the Aug 12-13 window behind today's load levels. Weather Forecast

The desk's trigger for tonight's ramp is the ERCOT Hub Average RT-DA spread, whose 24-hour mean of $4.2/MWh sits inside the market's convergence band. A break above $8.5/MWh or below -$9.7/MWh across the hub set during the 8 PM-11 PM CDT window moves the call from confirming the cleared curve to repricing it. The parallel gauge is load: 63,206 MW at issuance against the 89,424 MW forecast peak at 5 PM CDT leaves 2,277 MW of room before a demand miss becomes the story instead of the curve.

Houston Hub's $33/MWh real-time mean carries a $5.9/MWh premium over its day-ahead award; the same $4.2/MWh systemwide move leaves a $1.7/MWh local residual, the location worth reopening if either trigger fires. Track both triggers on the Hub detail real-time-versus-day-ahead charts and the MetisCast-versus-cleared-day-ahead chart.

Forecast-vintage policy. Every input in this issue was published at or before the knowledge cutoff. Forecast series are the latest vintage available at that instant and are never revised after the fact; realized history used for percentiles is guarded by the same cutoff. The preceding issue's frozen vintage is stored with the issue, so a revision is measured against what was actually published, not against a later correction. This issue could not close 3 analytical gaps: residual dispatchable demand, reserve, prc and contingency coverage, weather-to-market translation. Each is stated in the analysis rather than filled in by inference.

Source and quality note. 29 of 29 requested issue series were available; 16 longer-lookback series supported deterministic context. 13 event records were known at cutoff and 2 unchanged records were suppressed. Knowledge cutoff: Aug 13, 8:00 AM CDT.