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

The decision window runs Aug 18, 4 PM CDT to 10 PM CDT, closing on the cleared curve's $72.8/MWh peak at 9 PM CDT. Since the prior issue, North Hub's local RT-DA residual widened to $3.3/MWh and South Hub's swung to -$5.3/MWh, while the forecast gross-load peak firmed to 90,821 MW (99th percentile), up 407 MW.

Last night's real-time peaks reached $331.7/MWh (North) and $220.2/MWh (South) at Aug 17, 8 PM CDT, well above the day-ahead awards of $126.8/MWh and $114.9/MWh for the same hour.

Watch the cross-location RT-DA spread against its -$9.8/MWh to $8.3/MWh band, realized load against the 2,206 MW tolerance, and MetisCast's $19.6/MWh gap at 9 PM CDT.

North Hub's real-time price averaged $9.8/MWh above its day-ahead award across 22 joined hours, the widest hub-level gap in the set; South Hub averaged only $1.1/MWh above its award, the narrowest. Most of that gap is systemwide: the common RT-DA convergence spread across hubs sits at $6.5/MWh, the 91st percentile of the trailing 90-day history, so real time is running rich to day-ahead broadly, not at one node. Net of that common move, North's local residual is $3.3/MWh, up $2.8/MWh since the prior issue, and South's is -$5.3/MWh, a $4.7/MWh swing the other way; both sit outside their own calibrated residual bands, while West's $8.6/MWh raw premium and Houston's $6.4/MWh track close to the $6.5/MWh system level and remain inside theirs.

Tonight's cleared day-ahead curve prices the same evening transition: hub highs run from $65.6/MWh (South) to $77.8/MWh (West), both awarded at 9 PM CDT, alongside Houston's $71.6/MWh and the ERCOT Hub Average's $72.8/MWh, also at 9 PM CDT; North's high of $77.7/MWh arrives an hour earlier, at 8 PM CDT. MetisCast prices that same path $2.7/MWh below the cleared curve on average, a gap that sits inside its own wide uncertainty band, so it does not yet argue against the curve.

The number to watch through tonight's peak is the cross-location median RT-DA spread, calibrated to hold between -$9.8/MWh and $8.3/MWh; North and South already sit outside their own bands, so a break in that system-wide median is the signal that today's local frictions have gone system-wide.

MetisCast prices ERCOT Hub Average -$2.7/MWh against the cleared day-ahead curve across 17 joined hours. Its P50 tops out at $68.7/MWh at Aug 18, 8 PM CDT while the market cleared $72.8/MWh at Aug 18, 9 PM CDT. The two agree on when the evening matters and disagree on what it pays.

At the shared realized peak, Aug 17, 8 PM CDT, ERCOT's hubs split rather than moving together. North Hub reached $331.7/MWh and West Hub $329.1/MWh, both clustered near $330/MWh, while the ERCOT Hub Average printed $290.4/MWh, Houston Hub $280.6/MWh, and South Hub trailed at $220.2/MWh, roughly $110/MWh below North and West at the identical hour.

That North-South split reappears in tonight's cleared day-ahead curve, but as a timing offset rather than a level gap. North Hub's award peaks at $77.7/MWh at Aug 18, 8 PM CDT, one hour ahead of South Hub's $65.6/MWh, West Hub's $77.8/MWh, Houston Hub's $71.6/MWh, and the ERCOT Hub Average's $72.8/MWh, all of which clear their highs at 9 PM CDT. Desks holding North exposure into this evening should track the 8 PM CDT hour on its own terms, a full hour before the rest of the system prices its peak.

System demand stood at 61,148 MW at the 8 AM CDT cutoff, the 95th percentile for this hour and weekday type over the trailing 90 days. The forecast gross-load peak firms to 90,821 MW at Aug 18, 5 PM CDT, a 99th-percentile reading against the trailing 90-day range.

Solar is forecast to hold near a 34,718 MW high at Aug 18, 12 PM CDT before falling into the evening, pushing pre-storage net load to 68,295 MW at Aug 18, 9 PM CDT, the 92nd percentile of trailing 90-day peaks, on an 11,979 MW/h climb into 8 PM CDT, the 97th percentile of one-hour ramps. Both sit well above the trailing-90-day range.

Resource outage capacity in effect is 8,992 MW, only the 22nd percentile for this hour, soft against the trailing 90-day range and leaving more capacity available for today's peak. Capacity less load and the ancillary-service requirement reads 865.7 MW, a partial figure excluding imports and the largest contingency, so it marks headroom, not a scarcity finding.

MetisCast's ERCOT Hub Average path, issued Aug 18, 7:45 AM CDT, averages $2.7/MWh below the cleared day-ahead curve across 17 joined hours, widening to a $19.6/MWh gap at Aug 18, 9 PM CDT. The model's P10-P90 band widens to $170.5/MWh at Aug 18, 8 PM CDT, its widest hour in the frozen horizon, against a $33.2/MWh mean width across all 17 hours. The trigger to watch is the cross-location median RT-DA spread breaking below -$9.8/MWh, the invalidation level for tonight's ramp pricing, not the model-to-curve gap itself.

The RT-DA gap across hubs is a common-component story, not a location-specific one: the systemwide convergence spread averaged $6.5/MWh across 22 joined hours. North Hub's $9.8/MWh raw gap and West Hub's $8.6/MWh raw gap leave local residuals of $3.3/MWh and $2.1/MWh, both inside their own thresholds.

South Hub's $1.1/MWh raw gap nets to a -$5.3/MWh residual, and Houston Hub's $6.4/MWh raw gap resolves near zero; neither breaks its own threshold. No hub separates from the system tonight.

The sharper watch item is timing. MetisCast prices the Hub Average $2.7/MWh below the cleared day-ahead curve across 17 joined hours, widening to a $19.6/MWh gap at 9 PM CDT, inside its own $170.5/MWh uncertainty band at 8 PM CDT.

Three triggers govern today's read: the cross-location median RT-DA spread holding between -$9.8/MWh and $8.3/MWh, any hub's absolute residual breaking its own threshold, and realized load staying within 2,206 MW of the cutoff forecast. Open the hub real-time comparison and MetisCast-versus-day-ahead views through the 8 PM-9 PM CDT window.

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. 17 event records were known at cutoff and 2 unchanged records were suppressed. Knowledge cutoff: Aug 18, 8:00 AM CDT.