ERCOT's own day-ahead settlement price minus its natural-gas-fired generation cost (heat-rate-adjusted Henry Hub price), tested against the spread's own forward mean reversion - the same hypothesis that made the WTI/Brent spread our first Tier 1 factor, now confirmed independently across all 15 real ERCOT hubs and load zones.
-0.60x to -0.89x realized volatility at 20 trading days, depending on hub/zone - LZ_WEST the single largest, most nodes below it.
GET /v1/factors?factor=ercot_spark_spread&subject=HB_HOUSTON/RNGWHHD
Subject ids follow the pattern {settlement_point}/RNGWHHD - e.g. HB_HOUSTON, HB_NORTH, LZ_WEST, across all 7 trading hubs and 8 load zones ERCOT publishes.
Full validation methodology and every real number behind these verdicts: FACTOR_CATALOGUE.md.
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