Gas turbines and combined cycle: Engineering methods

Combined cycle, fast peakers and jet engines from one core

What this tab covers The engineering methods that can do this conversion, compared on efficiency, scale, economics, limitations and reliability.

The same gas turbine core is used three ways: with a steam bottoming cycle, alone for fast peaking, or with a fan for flight.

Comparison

Method	Efficiency	Scale	Economics	Limitations	Reliability
Combined-cycle gas plant (CCGT)¹²³⁴⁵⁶¹²¹⁴²⁸	about 64% rated, 57% best field; US units built 2010-2022 about 49% and all US gas plants about 44% (both calculated from heat rates, HHV)	about 630-1,230 MW per block in EIA reference plants; Egypt's Beni Suef, New Capital and Burullus plants total 14.4 GW (3 x 4.8 GW)	USD 48-109/MWh	Exposed to gas prices; turbine order queues of four to five years.	Weighted forced outage rate of North American combined-cycle units was 5.7% in 2025 (4.2% in 2024); hot-section parts need scheduled replacement; fleets run 30 years or more.
Open-cycle / peaker plant¹⁵¹⁴	about 31-33% (calculated from Lazard's 10,275-11,175 Btu/kWh, HHV); EIA reference units about 36-37% (calculated from 9,142-9,447 Btu/kWh); best simple-cycle ratings 42-44% (LHV)	about 210-420 MW per unit in EIA reference plants; aeroderivatives are much smaller	USD 149-251/MWh at 10-15% utilisation	Low efficiency; costly per MWh.	Aeroderivatives reach full power in minutes and tolerate frequent starts.
Jet engines (turbofans)⁸	about 40% overall	one engine per wing on most airliners	A narrowbody fleet needs thousands of new engines a year.	Weight and safety limit cycle choices; 20-30% of core air is spent cooling the hot section.	Hot sections must survive long lives at material temperatures of about 1,200-1,650 C (2,200-3,000 F); efficiency falls several percent between overhauls.

Combined cycle is the efficiency leader at about 64% and the lowest-cost firm power where gas is cheap, but it is capital-intensive and now faces multi-year turbine queues. Peakers trade efficiency (31-44%) for low capital cost and fast starts, so they suit few hours a year. Jet engines optimise thrust per kilogram rather than efficiency alone and reach about 40% overall. All three share the same superalloy hot section, the same makers' supply bottlenecks and the same wear-driven maintenance cycles.

How each method works

Combined-cycle gas plant (CCGT)

One or more gas turbines exhaust into heat recovery steam generators that feed a steam turbine. Arrangements range from single-shaft 1x1 units to multi-shaft 3-on-1 blocks.

Open-cycle / peaker plant

A gas turbine alone, either a heavy industrial frame or a lighter aeroderivative adapted from a jet engine, started when demand peaks.

Jet engines (turbofans)

The core drives a large fan; most thrust comes from air bypassing the core. Higher pressure ratios, hotter turbines and bigger, slower fans raise efficiency.

Sources

Gas Turbines: Past, Present and Future (Efficiency Focus), S.C. Gulen, UTSR Project Review Meeting US DOE National Energy Technology Laboratory, 2021
GE HA Turbine Snags Another World Record for CCGT Efficiency POWER Magazine, 2018
Electric Power Annual, Table 8.1: Average Operating Heat Rate for Selected Energy Sources, 2015 through 2025 US Energy Information Administration, 2026
Natural gas combined-cycle power plants increased utilization with improved technology US Energy Information Administration, Today in Energy, 2023
Lazard's Levelized Cost of Energy+ (LCOE+), June 2025 Lazard, 2025
GE Vernova gas turbine backlog climbs to 116 GW Utility Dive, 2026
Commercial Aircraft Propulsion and Energy Systems Research, Chapter 3: Aircraft Gas Turbine Engines National Academies of Sciences, Engineering, and Medicine, 2016
Generators for power generation (product overview and references) Siemens Energy, 2025
Assumptions to the Annual Energy Outlook 2026: Electricity Market Module (Table 3, cost and performance of new generating technologies) US Energy Information Administration, 2026
NERC: Conventional generation outages rose as reliability risks become more systemwide (2026 State of Reliability) Power Engineering, 2026