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The Combined Cycle Gas Turbines (CCGT)

The energy mix in electricity generation in France

There are three main sources of electricity generation in France :

1) Nuclear production, where energy is recovered from controlled fission reaction in fissile materials in reactors fitted with steam boilers that drive steam turbines connected to alternators ;

2) Thermal production, where the electricity is generated from energy produced by burning fossil fuels such as oil, coal and natural gas. To a lesser degree, thermal energy can be produced using biomass (wood, straw, agricultural waste) and also through decentralised production by cogeneration units in which steam from industrial processes and heat networks is used to generate electricity ;

3) Hydroelectric production from dams where the gravitational energy of water is converted to electricity in turbo-alternators. Hydro power is one of the main sources of renewable electricity, along with wind farms and photovoltaic cells (Solar PV), two fast developing sectors.

Installed electricity generation capacity in France


Bilan prévisionnel 2016

(Source : RTE)

Breakdown of quantities of electricity consumed in France by source of energy


Bilan prévisionnel 2016

(Source : RTE)

Combined-cycle gas turbine power plants: how do they work ?

The electricity production system consists of two cycles, hence the name combined-cycle.




















The first cycle takes place in the gas turbine (1).The turbine is made up of four stages: the first stage is a compressor that feeds compressed air into the second stage, which accommodates the combustion chamber where the natural gas is burned. The hot gases produced by combustion then turn fins in the third stage, the expansion chamber. The turbine is attached to a shaft which drives an alternator (3) that produces electricity. The transformer (4) converts the voltage so that the electricity can be fed into the electricity grid (5). The second cycle takes place when the hot gases leave the gas turbine (2). They are fed into a recovery boiler (6) then released into the atmosphere via the chimney. They are composed of roughly 86% air, 9% water vapour and 4% CO2. The steam produced in this boiler is used in a steam turbine (8), which is also linked to the alternator shaft (3). After releasing its energy, the steam is transferred to a condenser (9) and then sent to the recovery boiler in the form of water (10) for conversion back into steam.


Location of combined-cycle gas turbine power stations in France

(Source : GRTgaz (2016))

Combined-cycle gas turbine power plants – Figures

  • Installed electric power: approximately ~450 GW (varies between manufacturers)

  • Average annual production: 2,200 to 2,500 GWh (annual requirement of 450,000 households)

  • Efficiency: 58 to 61% (varies between manufacturers)