The hydraulic stock in the French grid represents the aggregated weekly fill level of lake-type water storage reservoirs and plants as measured at midnight on Mondays. It is expressed in MWh and sent to RTE by the generators, who are responsible for aggregating the data before publication. Hydraulic stock data is published every Wednesday at 12.30 pm, or on the following day if the Wednesday is a public holiday.
The head energy is that which can be generated in the (only) plant directly connected to the reservoir given its fill level. The data published relates only to the stock associated with head energy.
In France, the maximum stock of this type is 3,591 GWh.