Energy Mechanics · Electricity · Natural-gas generation

The post-coal
swing fuel

GAS · TWh/YR · GW
RELEASE · EIA EPM TABLE 1.1.A & FORM EIA-860 PRIME MOVERS
VINTAGE · —
NEXT EPM · —
CCGT + SCGT + STEAM
STATUS · LOADING
U.S. gas-fired electricity is — TWh/year — the largest single fuel for the power grid (~38% of generation). Combined-cycle gas turbines (CCGT) do most of the work: a Brayton-cycle gas turbine plus a steam bottoming cycle reaches ~60% efficiency and runs near baseload. Simple-cycle gas turbines (SCGT, "peakers") are dispatchable in minutes at lower efficiency (~35%) — they're what keeps the grid up between dusk and the evening solar drop-off. Cheap shale gas drove most of the — TWh of coal displacement since 2010, almost all of it by newly-built CCGTs.
Combined-cycle (CCGT) Simple-cycle (SCGT, peakers) Legacy gas-steam (retiring) bar length ∝ TWh/year · efficiency ≈ MWh out ÷ fuel MWh in (LHV)
TECHNOLOGY · TWh/YEAR CAPACITY (GW) · EFFICIENCY · DISPATCH ROLE Combined-cycle gas turbine (CCGT) BRAYTON GAS TURBINE + STEAM BOTTOMING CYCLE — Capacity — GW · efficiency ~60% CF — · runs near-baseload at low gas prices The single biggest add since 2010 — replaced retiring coal capacity at lower dispatch cost. Modern frames (GE 7HA, Siemens HL): 480 MW each. Simple-cycle gas turbine (SCGT, peakers) AERO-DERIVATIVE + FRAME · MINUTES TO FULL OUTPUT — Capacity — GW · efficiency ~35% CF — · runs <15% of hours, on demand spikes CAISO & ERCOT call SCGTs as the sun sets. As batteries scale, they take over the <4h peak; SCGTs stay for the longer-duration tails. TOP GENERATING STATES · TWh/YEAR Texas — ERCOT · ~25% of U.S. gas-fired · Permian gas at the wellhead Florida — FPL + Duke · summer A/C demand · pipeline from FGT Pennsylvania — PJM · Marcellus Shale at the doorstep · large new-build CCGT California — CAISO peakers fire at dusk · once-through cooling retirements ongoing Ohio — PJM · Utica + Marcellus on the doorstep · post-coal pivot TOP 5 STATES = — OF U.S. GAS-FIRED · TX ALONE ≈ —
Total gas-fired generation
—
vs 5 yrs ago
—
Total gas-fired capacity
—
GW · CCGT + SCGT
Avg fleet capacity factor
—
CCGT pulls average up; peakers pull it down
Share of U.S. generation
—
largest single fuel for U.S. power
SOURCE · U.S. Energy Information Administration, Electric Power Monthly (Table 1.1.A net generation by source; NG fueltype, broken out by prime mover where Form EIA-860 reporting allows). Per-state numbers are EIA EPM Table 1.6.B. Combined cycle pairs a Brayton-cycle gas turbine with a heat-recovery steam generator (HRSG) and steam Rankine cycle; modern frames reach ~60% LHV efficiency, vs ~35% for simple cycle. Coal displacement from 2010 onward (~900 TWh of coal generation gone) was overwhelmingly CCGT-led: shale gas brought Henry Hub from ~$8/MMBtu pre-2008 to $2–4/MMBtu through the 2010s, flipping the dispatch merit order so CCGT energy out-cleared coal even before counting MATS compliance costs. Peakers (SCGT) increasingly compete with battery storage on sub-4-hour evening demand spikes, but still dominate longer-duration tails and cold-snap reliability events. Texas alone is ~25% of U.S. gas-fired generation — Permian gas, wellhead-priced, with ERCOT's energy-only market structure rewarding both baseload CCGTs and scarcity-cleared peakers.
SECOND·ORDER·EDGE