El Hierro, the westernmost of Spain’s Canary Islands, located in the Atlantic Ocean, is using a wind/hydro hybrid system to move towards a 100 per cent renewable energy supply.

El Hierro is a small volcanic island (278 km²), with a population of about 11,000. The island was declared a UNESCO Biosphere Reserve in 2000 due to its rare flora and fauna.

Prior to the implementation of a renewable energy system, the island relied upon imported diesel to produce 45 GWh/year via nine diesel units (13.36 MW total) located in the Llanos Blancos power station with a peak production of 7 MW.

The annual diesel consumption was 40,000 barrels, with emissions of 18,700 tonnes of carbon dioxide, 100 tonnes of sulphur dioxide and 400 tonnes of nitrogen oxides.

In an effort to remove El Hierro’s reliance on diesel, the role of the principal generator has been transferred to a wind power plant of five 2.3 MW turbines – total power 11.5 MW.

This is backed up by a pumped-storage hydropower system comprising an upper reservoir of 500,000 m³ at an elevation of 715 m situated in a volcanic caldera, and a lower man-made reservoir of 226,000 m³ at an elevation of 54.5 m.

In addition to providing electricity to the domestic and commercial sectors, the wind/hydro system also powers the island’s three desalination plants linked to the lower reservoir."

In generation mode the station’s four 2.83 MW Pelton turbines (total 11.32 MW) operate under a gross head of about 655 m at a flow rate of 2 m³/s. In pumping mode, the two 1,500 kW and fourteen 500 kW pump sets provide a pumping capacity of up to 10 MW.

In addition to providing electricity to the domestic and commercial sectors, the wind/hydro system also powers the island’s three desalination plants linked to the lower reservoir.

With this link, the El Hierro case not only provides a compelling example of how water storage supports energy security based on renewables, but also an example of the water–energy nexus in practice.

The diesel units remain in an operational condition to act as a backup. The plant was commissioned in 2014, and it has been claimed that hundreds of islands globally could use the same model.

This case study is featured in the 2015 Hydropower Status Report, which provides detailed analysis of recent global trends in hydropower development. You can download the full report here.