In western France (Brittany and Pays de la Loire), West Grid Synergy aims to design and experiment smart grid solutions to maximise biomethane injection into the transmission and distribution systems. This project inaugurated the first reverse flow of locally produced biomethane from distribution to transmission in France. The reverse flow unit is a facility that allows gas transfer from the distribution system to the transmission system thanks to a gas compression mechanism. It enables an increase in local storage capacity for biomethane injection into the distribution system. In 2019, in Pontivy and Pouzauges, GRTgaz has designed and settled the first two French reverse flow units. The objective is now to assess how they operate under real conditions to optimize infrastructure settings.