The access gallery to the future underground hydroelectric plant of the Redenat STEP / Image: Energy Revolution.
Work on the pumped storage energy transfer station (STEP) at Redenat (Corrèze) was abruptly halted in 1982. The only witnesses to the project: two completely submerged tunnels that stop right in the middle of the mountain. For nearly 40 years, EDF has been waiting for policies more favorable to large-scale electricity storage systems in order to revive it.
The systems of storage are a considerable asset for electrical networks. They make it possible to stabilize the frequency, to avoid blackoutsto accumulate the variable production of wind and solar power and to make nuclear power plants even more profitable.
There are several techniques for efficiently storing electricity: batteryI’pressurized air in the underground cavity and the STEP (pumped storage energy transfer station), which falls under hydroelectricity. The latter is the most used across the planet, because it allowsaccumulating very large amounts of energy over long periods of time.
France has 6 WWTPs for an installed capacity of only 5GW, i.e. 3.6% of the 139 GW of the national electricity generation fleet. Among the new WWTP projects, that of Redenat (Corrèze) is the most successful. Everything is ready: the pitch is perfectly marked out, the lower tank already existsthe technical characteristics have been defined and the land is reserved and uninhabited.
Characteristics of the Redenat WWTP project
|Storage capacity (RE estimate)||~20GWh|
|Annual production||1,400 GWh|
|Pumping flow||109 m3/s|
|Turbine flow||130 m3/s|
|Upper lake volume (total)||36 million m3|
|Upper lake volume (useful)||32.6 million m3|
|Lake Superior area||300 ha|
|Lower lake volume||187 million m3|
|Lake Superior tidal range||21m (winter) 3m (summer)|
|Lower lake tidal range||5 m (winter) 1 m (summer)|
A construction site stopped abruptly
The site began in the early 1980s with the drilling of two galleries of 700 m, from which the hydroelectric plant, a veritable underground cathedral, and the pipes connecting the two lakes were to be dug. But EDF, operator of the project, suddenly interrupted it in 1982.
The context was not favourable: low electricity costs at the time, cost of planing on the budget and questioning of hydroelectric concessions on the “cascade” of dams along the Dordogne.
In 40 years, no one has been able or really wanted to relaunch the Redenat STEP. Not even François Hollandeex-president of the departmental council of Corrèze who became head of state, who nevertheless had expressed interest for the project.
WWTP, a system that is not profitable enough?
Asked about this, EDF did not comment specifically on the Redenat project. The national energy company simply explained to us that “the current regulatory framework and economic model in mainland France struggle to bring out new STEP projectsin particular in the absence of specific compensation for flexibility. » Clearly, investing in this means of high-capacity electricity storage would not be profitable enough, for lack of sufficient remuneration.
“Nevertheless, we are making progress in ensuring that a framework conducive to development of this storage and flexibility tool emerges, as evidenced by the “Climate Resilience” law of August 22, 2021 which introduces the possibility of calls for tenders in support of the development of storage. » indicates the operator.
EDF resumed maintenance of the galleries in 2008 by drying them out, according to the local newspaper The mountain. However, during our visit, these two tunnels were completely submerged up to the vault and therefore impassable. In fact, they plunge to a lower level in the Lac du Chastang, which constitutes the lower reservoir of the future WWTP.
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