Open dataset
Across the seven US ISOs (2018-2025), the 100 real-time hours with the largest price deviation from the annual median (about 1% of a year) hold a median 17% of the year's total arbitrage value, and the top 500 hours (about 6% of a year) hold a median 37%. The most concentrated market, ERCOT, reaches a median 55% in its top 500 hours.
How concentrated wholesale value is in a small number of hours, measured as each hour's price deviation from the annual median (the arbitrage a flexible load can capture by shifting out of high-price hours or into low-price ones), by ISO and year, from real-time prices. The core evidence for why shifting load in a handful of hours is worth so much.
Cumulative share of annual energy value vs share of hours, by ISO and year, computed on real-time prices (seven ISOs, SPP for 2025 only).
An earlier real-time run of the same value-concentration curves (six ISOs, CAISO from 2022).
Median, mean, max, min, and standard deviation of LMP by ISO and year.
When the highest-value hours occur, by hour-of-day, month, and day-of-week.
How far the day-ahead price ranking predicts the real-time one: the share of each year's 100 highest real-time hours that were also among the 100 highest day-ahead hours.
Free to use with attribution (CC BY 4.0). These are the derived summary tables, reproducible from the primary sources.
Built from hourly real-time prices across each ISO (the predictability file also compares them with day-ahead prices). Each hour's value is the absolute deviation of its price from that ISO-year's median, |LMP minus median|: the arbitrage a flexible load captures by shifting out of high-price hours or into low-price ones. Hours are ranked by this value and accumulated to trace what share of the year's total deviation sits in the top share of hours. Seven real-time market-years fall below 99% hour coverage: CAISO 2018 (97.6% of hours), CAISO 2020 (96.9%), CAISO 2021 (79.1%), ISO-NE 2018 (76.8%), ISO-NE 2023 (96.1%), MISO 2021 (95.5%), and MISO 2022 (95.3%). Each of those years uses the hours available. For the two MISO years, coverage of the eight hubs is lower than the hour figure (77.1% in 2021 and 82.4% in 2022). For CAISO 2021 most hours from mid-July through September are missing, so that year understates summer real-time price spikes. A backfill of the missing hours is in progress.
Used in Markets: critical-hours value concentration.
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Primary-source grid datasets and the numbers behind them, with the source for each, including a note when this dataset is updated.
Cite this dataset
Corey Balgeman, "Critical-Hours Value Concentration Across US ISOs," Grid Flexibility, 2026. https://gridflexibility.fyi/data/critical-hours-value-concentration
Part of the Grid Flexibility open datasets. Provenance and methodology are published; another researcher can reproduce these tables from the primary sources. Canonical home: https://gridflexibility.fyi/data/critical-hours-value-concentration.