NERC Sees US Grid Adding 20 GW This Winter as Data Centres Outrun Transmission Build
The reliability regulator forecasts a 2.5% capacity gain into winter 2026-27, but coal economics and stalled grid upgrades leave PJM, MISO and ERCOT exposed.
The North American Electric Reliability Corporation expects bulk power system capacity to rise by 20.2 GW, or 2.5%, over last winter's forecast, according to its Winter Reliability Assessment published on 2 June (2026-06-02).5
That number sets the baseline for how much margin the US grid carries into peak winter demand, and it lands as regional operators warn they cannot upgrade transmission fast enough to absorb the load already queued. In late 2021 the Federal Energy Regulatory Commission directed all six major regional operators outside Texas to establish programs to lift transmission capacity. Those operators have now asked FERC for an extension on the deadline, DatacenterDynamics reported on 19 May (2026-05-19).5,4
The demand pressure is concentrated. Data centres now account for about half of incremental US electricity demand growth, according to the IEA's global energy assessment.3 EIA projects server electricity use alone will climb from 7% of commercial-sector consumption in 2025 to between 22% and 33% by 2050, reaching 446 to 818 billion kWh across its cases.2 The load is arriving faster than the wires to serve it, with grid engineers and regulators describing permitting, supply chains and interconnection queues that cannot match data-centre growth.3
The consensus in the signal data leans bullish on real-time power across PJM, MISO and ERCOT, driven by six converging signals against a lighter bearish weight.1 The clearest evidence sits in MISO's fuel economics. EIA data show the average MISO electricity price rose 44% from 2024 to 2025, while coal prices increased just 3%.1 That gap widened the coal dark spread from $11/MWh to $23/MWh, a 111% jump, as power prices climbed faster than coal generation costs.1
Gas did not keep pace. The MISO spark spread rose only 18% over the same period, held back by a 63% increase in natural gas prices that offset rising power revenue.1 In dollar terms the spark spread moved from $12/MWh to $14/MWh, a $2/MWh gain against the dark spread's $12/MWh advance.1 For MISO dispatch this winter, coal stays economically favoured wherever units remain available, which cuts against the assumption that gas has permanently displaced it in the Midcontinent stack.
Yet the bullish read is not unanimous. Contrarian signals flag MISO real-time and API2 coal front-month as bearish, both driven by supply, each carrying a contrarian score above 0.30.1 The supply case is straightforward: NERC's 20.2 GW capacity addition, if it materialises on schedule, loosens the margin that would otherwise push real-time prices higher during cold snaps.5
MISO's own seasonal readiness modelling shows how thin the margin can get under stress. In one three-day January scenario, the operator modelled a 108 GW peak against 6.5°F temperatures, 19 GW of renewable output and 9 GW of incremental outages, with unit commitment uplift costs running to millions of dollars.6 Those are the conditions under which forecast capacity and delivered capacity diverge, and the winter assessment's headline gain says little about performance in the coldest 72 hours.
ERCOT sits apart from the transmission mandate but faces the same demand curve. EIA expects ERCOT solar generation to reach 78 billion kWh in 2026, against 60 billion kWh for coal, a crossover that reshapes the intraday shape even as winter peaks still lean on thermal and gas.2 Texas has added generation quickly, but its winter risk has always been a cold-morning ramp when solar is absent and gas and wind must carry the load.
The structural point is that capacity additions and transmission build are moving at different speeds. NERC counts the 20.2 GW as available supply.5 The grid operators asking FERC for more time are telling regulators the wires to move that supply to load are not ready.4 For a data-centre cluster in PJM or MISO, nameplate capacity elsewhere on the system is not the same as deliverable power at the meter.
For traders, the near-term signal is fuel-switching in MISO, where a $23/MWh coal dark spread against a $14/MWh spark spread favours coal in the merit order this winter.1 The medium-term risk is a cold-snap event that exposes the gap between NERC's forecast margin and the outage-adjusted reality MISO models internally.6 Watch whether FERC grants the transmission extension, and whether the 20.2 GW of new capacity clears interconnection in time to count when demand peaks.4,5