Some evidence has been produced that water is pumped (and additional load is generated), but that this water does not reach the upper reservoir. Instead it is sent down-hill again into the lower reservoir through the valve house unused (see Figure 10)(13). It has been suggested that GdV uses the easily controllable water pumps (6 x 500 kW plus 2 variable speed 1.5 MW electric pumps with power factor compensation) to maintain sufficient load in the grid and control grid stability (mainly through the 2 variable speed pumps with a combined rating of 3 MW).
 
While there is strong evidence pointing in this direction, such an operation mode (and such an incredible waste of renewable energy with the associated wear and tear in the pumps and pipelines etc.) does not seem to make sense under consideration of the advanced grid interface of the Enercon E70 turbines and the obviously successful operation of the FCU. Being equipped with a direct drive, multi-pole synchronous generator, the E70 allows a power factor variation in a wide range. With an installed wind power of 11.5 MW this range should be more than enough to stabilize the El Hierro grid with a peak demand of 7.6 MW even under conditions of high wind energy penetration. Figure 11 shows the range of reactive power variation which is standard to all Enercon turbines(14).
 
Considering the advanced grid interface of the Enercon turbines, the water “going-round-and- round” phenomenon most likely has another explanation, one only known to GdV.

The final design was an upper reservoir with 380,000 m3 and a lower reservoir with only 150,000 m3. The upper reservoir is constructed in an old, inactive volcanic crater, while the lower was excavated in a narrow valley close to the sea.  
When detailed geologic studies found weak rock under the planned reservoirs (and a similarly located water reservoir – Barlovento on La Palma – developed large leakages and failed in 2011) the size had to be reduced(3). The pumped hydro and wind project developed out of plans to have a large reservoir for irrigation in the inactive crater – this explains the size mismatch of the upper and lower reservoir. In order to use a full upper reservoir for electricity generation, 230.000 m3 of it would have to be dumped in the sea. But such an obvious waste of highly valued sweet water on a dry island – just to generate the islands electricity demand for 2 – 3 extra days – must be ruled out completely. Currently, no water is being used from the upper reservoir – so the extra size remains a complete waste …