The access gallery of the future underground hydroelectric plant of Redenat STEP / Image: Energy Revolution.
Work on the pumped storage energy transfer station (STEP) in Redenat (Corrèze) was suddenly stopped in 1982. The only witness to the project: two completely submerged tunnels that stopped 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 to revive it.
Storage systems are a huge asset to power grids. They make it possible to stabilize the frequency, avoid blackouts, accumulate variable production from wind and solar power and make nuclear power plants more profitable.
There are several methods for efficient electricity storage: the battery, compressed air in the underground cavity and the STEP (pumped storage energy transfer station), which is under hydroelectricity. The latter is the most used throughout the planet, because it allowsaccumulating large amounts of energy over a long period of time.
Why did EDF continue this unfinished tunnel for 40 years?
France has 6 WWTPs for an installed capacity only 5GW, ie 3.6% of the 139 GW of national electricity caliber. Among the new WWTP projects, the one in Redenat (Corrèze) is the most successful. Everything is ready: the pitch is perfectly marked, the lower tank is already therethe technical characteristics are defined and the land is reserved and uninhabited.
Characteristics of the Redenat WWTP project
|Drop the height||270m|
|Storage capacity (RE estimate)||~20GWh|
|Annual production||1,400 GWh|
|Flow pumping||109 m3/s|
|Turbine flow||130 m3/s|
|Lake surface area (total)||36 million m3|
|Upper lake grass (useful)||32.6 million m3|
|Places called Lake Superior||300 ha|
|Low 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 suddenly stopped
The site began in the early 1980s with the drilling of two galleries of 700 m, where the hydroelectric plant, a real underground cathedral, and the pipes connecting the two lakes had to be dug. But EDF, the project’s operator, abruptly stopped it in 1982.
The context was not favorable: low electricity costs at that time, cost of budget planning and questioning of hydroelectric concessions in the “cascade” of dams along the Dordogne.
In 40 years, no one has done or really wants to relaunch Redenat STEP. Not even François Hollandeformer president of the council of the department of Corrèze who became head of state, who nevertheless expressed his interest in the project.
Renewable energy storage: WWTPs disappear
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 that to us “The current regulatory framework and economic model in mainland France struggle to generate new WWTP projects, especially without the specific compensation for flexibility. » It is clear that investing in this way of high capacity electricity storage is not profitable enough, due to the lack of sufficient compensation.
“However, we are making progress in ensuring a constructive framework improve this storage and flexibility tool emerged, as evidenced by the “Climate Stability” law of August 22, 2021 that introduced the possibility of calls for tenders to support the development of storage. » indicates the operator.
EDF continued to maintain the galleries in 2008 by drying them out, according to local newspaper La Montagne. However, when we visited, these two tunnels had completely sunk into the vault and were therefore impassable. In fact, they fall to the lower level of Lac du Chastang, which constitutes the lower reservoir of the future WWTP.
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