---
title: "Combined-cycle gas turbine (CCGT)"
description: "A combined-cycle gas turbine (CCGT) plant combines a gas turbine with a steam turbine driven by an HRSG that recovers heat from the gas-turbine exhaust. The arrangement raises overall plant efficiency from ~38% LHV for a simple-cycle gas turbine to 55–62% LHV for modern CCGT, with the latest H-class machines pushing 64%+."
canonical_url: "https://sylio.co/glossary/combined-cycle-gas-turbine"
last_updated: "2026-06-28T02:29:33.367Z"
---

A **combined-cycle gas turbine (CCGT)** plant combines a gas turbine with a steam turbine driven by an [HRSG](/glossary/heat-recovery-steam-generator) that recovers heat from the gas-turbine exhaust. The arrangement raises overall plant efficiency from ~38% LHV for a simple-cycle gas turbine to 55–62% LHV for modern CCGT, with the latest H-class machines pushing 64%+.

## Why HRSG cleanliness matters

CCGT plants are economically dispatched ahead of coal in most markets, but margins per MWh are tight and competition from renewables intensifies the focus on heat rate. Every 0.5% efficiency loss from HRSG fouling translates directly to fuel cost. [Sonic horns](/glossary/sonic-horn) on the [HRSG](/glossary/heat-recovery-steam-generator) gas path are increasingly part of the standard maintenance toolkit on modern combined-cycle plants.

## Cycling adds complication

Modern CCGT plants increasingly two-shift — running daytime and shutting overnight when renewable supply meets demand. Frequent start-stop cycling worsens HRSG fouling because cold metal surfaces during shutdowns condense moisture that bonds dust into a harder deposit. Continuous sonic-horn cleaning helps offset cycling-driven fouling acceleration.

## Related terms

- [Heat Recovery Steam Generator (HRSG)](/glossary/heat-recovery-steam-generator)
- [Duct burner](/glossary/duct-burner)
- [Selective Catalytic Reduction (SCR)](/glossary/selective-catalytic-reduction)
- [Heat rate](/glossary/heat-rate)