2024-01-07 18:25:08
On the banks of the Sèvre Nantaise, near Nantes (Loire-Atlantique), the Angreviers mill stands on five floors. Arcades follow one another on the brick wall. A tall chimney rises from the slate roof. In this old spinning mill, the turbine – which dates from before the Great War – has been producing electricity again for six years. The roadway, a small projection that carries the water, extends over 40 meters and creates a 1.70 m waterfall which activates the two-meter diameter machine.
Old systems
Laurent Pascail took over the Angreviers mill in 2011 to turn it into a gîte. Four years later, he became interested in hydroelectricity – producing electricity from hydraulic energy. To rehabilitate the valves and the turbine, out of service for more than forty years, the business manager invested €100,000.
He then sells his electricity to the EDF network, but is sorry to only obtain a return of 6% compared to the cost of the work.. “I took over the existing system, which is not designed for the production of electricity,” he admits. The turbine has a vertical axis and does not benefit from the significant flow of the Nantes Sèvre.
“Double or even triple electricity production”
“Our ambition is to replace the turbine with a paddle wheel (equipped with blades, with a horizontal axis) », assures Régis Contreau, co-founder of Énergie de Nantes (EDN). Since January 2023, this associative energy supplier in the Nantes region launched in 2021 manages the maintenance of the mill and recovers electricity. Last year, these hydroelectricity neophytes produced 57 megawatt hours – the equivalent of the needs of 30 homes. They hope that the new, more suitable wheel will be able to “double or even triple electricity production”.
“For housing, the needs are more winterspecifies Régis Contreau. The energy produced by the mills is stable during this period. » The association would ultimately like to reinvest other mills. The Nantes Sèvre had up to 143 sites. “We would like to install the turbine on a nearby mill”, he imagines.
Haute-Vienne, pilot territory
One department focused particularly on these small power plants. At the end of 2021, Haute-Vienne created a unique position in France for project manager for the development of the micro-hydroelectricity sector, “works whose power is less than 4.5 megawatts (MW)”, describes Pierre Roussel, who has held the position since the beginning. They only require authorization from the prefect to be operated.
“The objective is to bring out and support projects – micropower plants – which will produce enough energy to be economically viable,” specifies the engineer. Since his arrival, he has received around sixty requests, but no mill renovation has been able to completely see the light of day..“It takes between three and five years minimum,” explains Pierre Roussel. The creation of this pilot mission in Haute-Vienne is part of the objective of increasing hydroelectric production in the Nouvelle-Aquitaine region by 26% between 2020 and 2030.
“Clean, carbon-free energy”
Ambitions that are reflected on a national scale. The multi-annual energy program for the period 2019-2028 sets the objective of increasing the hydroelectric fleet – second source of electricity production, first for renewables, in France – but also of “set up a support system for the renovation of power plants between 1 MW and 4.5 MW”. Micropower plants represent less than 10% of national hydroelectricity production.
“The mills continuously produce clean, carbon-free energy, from 1 October to June 30. In addition, these are small production units distributed across the territory. argues Pierre Meyneng, president of the Fédération française des associations de sauvegarde des moulins (FFAM). “These sites have always been there, there were more than 80,000 in the country at the beginning of the 19th century.. They just want to leave,” adds the one who owns two works.
A study by the FFAM, published in 2022, estimated – “without having a very precise figure” – that 36,000 hydraulic mills could be equipped with a turbine in France and would make it possible to compensate for the annual electricity consumption of 1.3 million people.
Debates around mill thresholds
The thresholds, or roadways, of the mills are, however, the subject of certain criticism. Jacques Pulou, “mister rivers” of France Nature Environnement (FNE), deplores “the disappearance of migratory fish: salmon, sea trout, shad. The thresholds prevent them from reaching the breeding areas ». According to FNE, only 3% of fish succeed after ten obstacles encountered.
Since 2006 and the water law, numerous structures have been equipped to be “passable”. Others were destroyed in order to restore the ecological continuity of the waterways. The deputies adopted, in the climate and resilience law of 2021, an amendment aimed at “to definitively exclude the possibility of financing the destruction of mill reservoirs”.
“The erasure of the thresholds had the cumulative effect of lowering the water line, encouraging erosion, preventing the recharge of the water tables, evacuating floods more quickly downstream and promoting the completely dry in summer”, argues Jacques Mudry, state doctor in hydrogeology at the University of Besançon in the scientific journal Burgundy-Franche-Comté Nature.
“With climate change, there will be more and more periods when animal species will have to moverecalls Jacques Pulou. And this movement is conditioned by the reestablishment of this ecological continuity. »
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