# Gas turbines and combined cycle: Engineering methods

Combined cycle, fast peakers and jet engines from one core

Source page: https://www.materialinsights.org/energy/e_gas_turbines/methods/

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)**^[1](https://netl.doe.gov/sites/default/files/netl-file/21UTSR_Gulen.pdf)^[2](https://www.powermag.com/ge-ha-turbine-snags-another-world-record-for-ccgt-efficiency)^[3](https://www.eia.gov/electricity/annual/html/epa_08_01.html)^[4](https://www.eia.gov/TODAYINENERGY/detail.php?id=60984)^[5](https://www.lazard.com/media/uounhon4/lazards-lcoeplus-june-2025.pdf)^[6](https://www.utilitydive.com/news/ge-vernova-gas-turbine-backlog-climbs-to-116-gw/826039/)^[12](https://www.siemens-energy.com/global/en/offerings/power-generation/generators.html)^[14](https://www.eia.gov/outlooks/aeo/assumptions/pdf/EMM_Assumptions.pdf)^[28](https://www.power-eng.com/business/policy-and-regulation/nerc-conventional-generation-outages-rose-as-reliability-risks-become-more-systemwide/) | 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 plant**^[1](https://netl.doe.gov/sites/default/files/netl-file/21UTSR_Gulen.pdf)^[5](https://www.lazard.com/media/uounhon4/lazards-lcoeplus-june-2025.pdf)^[14](https://www.eia.gov/outlooks/aeo/assumptions/pdf/EMM_Assumptions.pdf) | 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](https://www.nationalacademies.org/read/23490/chapter/6) | 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

1. [Gas Turbines: Past, Present and Future (Efficiency Focus), S.C. Gulen, UTSR Project Review Meeting](https://netl.doe.gov/sites/default/files/netl-file/21UTSR_Gulen.pdf) US DOE National Energy Technology Laboratory, 2021
2. [GE HA Turbine Snags Another World Record for CCGT Efficiency](https://www.powermag.com/ge-ha-turbine-snags-another-world-record-for-ccgt-efficiency) POWER Magazine, 2018
3. [Electric Power Annual, Table 8.1: Average Operating Heat Rate for Selected Energy Sources, 2015 through 2025](https://www.eia.gov/electricity/annual/html/epa_08_01.html) US Energy Information Administration, 2026
4. [Natural gas combined-cycle power plants increased utilization with improved technology](https://www.eia.gov/TODAYINENERGY/detail.php?id=60984) US Energy Information Administration, Today in Energy, 2023
5. [Lazard's Levelized Cost of Energy+ (LCOE+), June 2025](https://www.lazard.com/media/uounhon4/lazards-lcoeplus-june-2025.pdf) Lazard, 2025
6. [GE Vernova gas turbine backlog climbs to 116 GW](https://www.utilitydive.com/news/ge-vernova-gas-turbine-backlog-climbs-to-116-gw/826039/) Utility Dive, 2026
7. [Commercial Aircraft Propulsion and Energy Systems Research, Chapter 3: Aircraft Gas Turbine Engines](https://www.nationalacademies.org/read/23490/chapter/6) National Academies of Sciences, Engineering, and Medicine, 2016
8. [Generators for power generation (product overview and references)](https://www.siemens-energy.com/global/en/offerings/power-generation/generators.html) Siemens Energy, 2025
9. [Assumptions to the Annual Energy Outlook 2026: Electricity Market Module (Table 3, cost and performance of new generating technologies)](https://www.eia.gov/outlooks/aeo/assumptions/pdf/EMM_Assumptions.pdf) US Energy Information Administration, 2026
10. [NERC: Conventional generation outages rose as reliability risks become more systemwide (2026 State of Reliability)](https://www.power-eng.com/business/policy-and-regulation/nerc-conventional-generation-outages-rose-as-reliability-risks-become-more-systemwide/) Power Engineering, 2026

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_gas_turbines/index.md)
- [Overview](https://www.materialinsights.org/energy/e_gas_turbines/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_gas_turbines/correlation/index.md)
- [Science and limits](https://www.materialinsights.org/energy/e_gas_turbines/science/index.md)
- [Value chain](https://www.materialinsights.org/energy/e_gas_turbines/valuechain/index.md)
- [Unit economics](https://www.materialinsights.org/energy/e_gas_turbines/economics/index.md)
- [Equipment and suppliers](https://www.materialinsights.org/energy/e_gas_turbines/equipment/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_gas_turbines/links/index.md)