Demand and supply in the grid must be constantly balanced. Pumped-storage hydropower remains the only traditional and most cost-effective technology for large-scale balancing of power systems. Iberdrola has just opened Tâmega Gigabattery in Portugal. According to the European Energy Storage Association, the EU will need 200 gigawatts of energy storage by the end of the century and 600 gigawatts by 2050. Iberdrola's Tâmega Gigabattery is one of the largest pumped hydro storage projects in Europe for the past 25 years.

The facility, valued at 1.5 billion euros, has not yet been completed. It consists of two reservoirs connected to a tunnel, of which the engine room is located underground. Recently, another large pumped hydro storage facility came online in Switzerland.