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How to combine the injection of biomethane and production of own-use renewable electricity

By ENGIE - 16 December 2019 - 18:21

The Terres de Montaigu biomethane plant has a capacity of 22 GWh/year and is the result of close collaboration with the region, stakeholders in the farming sector and ENGIE. Installed in September 2019 in Saint Hilaire-de-Loulay, in the Montaigu commune in France's Loire-Atlantique département, this biomethane plant will convert around 30,000 tonnes of substrate from farms and agri-food factories across the region every year. Powered by its own 313 kWp solar photovoltaic self-production system, the plant will produce about 20% of its own electricity requirements.

Key numbers

Client challenges


  • Contribute to local economic development: recycling of organic matter and spreading over 2500 ha of land belonging to 24 farms partnering the project.
  • Develop renewable energies at local level: greening of the natural gas distribution network by injecting 2 million m³ of biomethane per year, equivalent to the annual consumption of 1800 gas-heated homes.
  • Reduce greenhouse gas emissions: 5000 tonnes of CO2 avoided per year – equivalent to the annual emissions of approximately 2500 new cars
  • Produce renewable electricity to meet the site's requirements


ENGIE’s solution


To meet the requirements of the zero-carbon transition and the circular economy in France's various regions, ENGIE is building local renewable gas production units in partnership with regional stakeholders. This new production unit should be able to recycle around 30,000 tonnes of substrate every year from farms belonging to the 24 farmers partnering the project, as well as agri-food plants and the local authority. The digestate produced is recovered and spread over farmland instead of chemical fertilisers.


A project which should also prevent approximately 5000 tonnes of CO2 emissions every year compared with the current situation. By methanizing these substrates, the plant will enable some 2 million m³ of biomethane to be injected every year.


The biomethane injection plant has been combined with a solar power plant installed on the buildings, which will meet approximately 20% of its electricity requirements.


The project will get investment subsidies from the ADEME (France's energy and environment management agency), as well as the Agence de l’Eau des Pays de la Loire (the water management agency for the Loire region).


ENGIE has a portfolio of nearly 80 projects in development, thus supporting its aim of producing 5 TWh/year of biomethane by 2030.


Expertise and offers


  • Biomethane injection unit with 24 GWh of installed capacity
  • Initiation, development, construction management, financing and operation-maintenance by ENGIE's team.
  • Use of reserves of organic matter so as to maximise production of biomethane and obtain the best digestate.
  • Redistribution of digestate for spreading over farmland and reduction in the use of fossil-origin fertilisers.
  • Combination of the production unit with a solar power plant installed on the buildings for own-use power production
  • Circular economy


“This new facility in Terres de Montaigu involving farmers from the region is a fine example of technological innovation being used to safeguard the environment and help deliver the energy transition".

Antoine Chéreau, Chairman of Terres de Montaigu, Mayor of Montaigu - Vendée