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.
An open-cycle gas turbine compresses air, burns fuel in it, and expands the hot gas through a turbine without recovering exhaust heat. Exhaust leaves at 450–600°C, which is why efficiency is well below a CCGT.
Two families dominate. Aeroderivative units (e.g. 30–140 MW, derived from jet engines) reach 38–44% efficiency and start in 5–10 minutes. Heavy-duty frame units (100–400 MW) run at 33–40% and take 10–30 minutes. Direct emissions are about 500–650 g CO2/kWh. Reciprocating gas engines (40–48% efficient) compete in the same role.
OCGTs serve peak load, reserves and black start. Capex is lower than CCGT, roughly USD 700–1,200/kW in 2024–2025, but with capacity factors often below 10% their LCOE is high, USD 110–230/MWh (Lazard). Their revenue usually depends on capacity markets and scarcity pricing. Battery storage increasingly competes with OCGTs for durations up to four hours.
Related terms
All terms →- 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%.
- Peak load
The highest electricity demand recorded on a grid during a given period, which sets the capacity the system must be able to supply.
- Capacity market
A mechanism that pays resources for being available to supply power or reduce demand at times of system stress, alongside payments for energy.
- Black start
The process of restoring a power system after a total or partial blackout using units that can start without power from the grid.
- 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.