Combined-cycle gas turbine (CCGT)
A power plant that runs a gas turbine and uses its hot exhaust to raise steam for a second, steam turbine, reaching electrical efficiencies of 55–64%.
A CCGT couples a Brayton cycle (gas turbine) with a Rankine cycle (steam turbine). Gas turbine exhaust at 550–650°C passes through a heat recovery steam generator (HRSG), raising steam at up to three pressure levels.
With a 40% efficient gas turbine and a 35% efficient bottoming cycle, combined efficiency is about 61% (LHV). The latest H- and J-class units exceed 63–64% LHV in combined-cycle mode; older fleets run at 48–55%. A heat rate of 6,000–6,500 kJ/kWh corresponds to these efficiencies, giving direct emissions of about 330–370 g CO2/kWh, against 820–1,000 g for coal.
Typical parameters (NREL ATB, Lazard 2024–2025): unit sizes 250–1,000 MW; overnight capex about USD 900–1,500/kW, rising since 2023 because of turbine backlogs; start-up 30–60 minutes hot, several hours cold; minimum stable load around 40–50%. LCOE is highly sensitive to fuel price and carbon price, generally USD 45–110/MWh. CCGTs can co-fire hydrogen blends of 10–30% by volume today, with 100% hydrogen-capable designs announced, or be fitted with CCS.
Related terms
All terms →- Open-cycle gas turbine (OCGT)
A simple-cycle gas turbine that exhausts hot gas directly to the atmosphere, trading lower efficiency (33–42%) for fast start and low capital cost, used mainly for peaking.
- Natural gas
A fossil fuel composed mainly of methane, used for power generation, industrial and residential heat, and as a chemical feedstock for hydrogen and ammonia.
- Heat rate
The fuel energy a thermal power plant consumes per kWh of electricity generated; the inverse of efficiency, usually in BTU/kWh or kJ/kWh.
- CHP (Combined Heat and Power)
Simultaneous generation of electricity and useful heat from one fuel input, reaching total efficiencies of 75–90% versus about 35–60% for power-only plants.
- Carbon capture and storage (CCS)
Technologies that separate CO2 from flue gas or process streams, compress it, and inject it into deep geological formations for permanent storage.
- Load following
Adjusting a power plant’s output over minutes to hours to track changes in electricity demand or in variable renewable generation.