Renewables giant Iberdrola has inaugurated its 1.2GW Tâmega hydroelectric complex in northern Portugal that combines three hydropower plants with pumped hydro with a capacity to store 40GWh of electricity – sufficient to provide 11 million people with power for 24 hours.

Construction of the facility took almost eight years and cost some €1.5bn ($1.54bn).

The complex is made up of three power plants – Alto Tâmega, Daivões and Gouvães – and thanks to its pumping capacity can store energy to be used when it is most needed, for example on days of little solar irradiation or no wind.

Pumped hydro storage in theory is one of the best and most solid ways to back up intermittent renewable energy production, but building new plants often meets fierce resistance from local residents – particularly in Europe – due to the need for relatively large interventions in nature.

A 700MW pumped hydro storage project in the Bavarian Alps (Jochberg) was discontinued in 2014 due to local opposition based on environmental and tourism concerns, while China earlier this year switched on a 3.6GW plant in Fenging, billed as the world’s largest pumped hydro storage facility.

Iberdrola also reaffirmed its commitment to investing €3bn in coming years for wind and solar plants under development.

The utility’s chairman Ignacio Galán, who inaugurated the plant on Monday together with Portuguese prime minister António Costa, said the hydropower complex demonstrates that energy independence and decarbonisation – two of Europe’s major energy policy goals – are perfectly compatible.