The island of El Hierro, a part of the Canary Islands chain off the coast of Spain, is implementing a hybrid hydroelectric and wind plant to meet its energy needs using renewable sources. This facility integrates a pumped-storage plant with 11.32 MW of generating capacity and 6 MW of pumping capacity with an 11.5 MW wind farm. Working together, the two technologies will help create reliable, efficient and stable power supply for the 10,960 persons residing on the island.

This project, being developed by Gorona del Viento El Hierro S.A., is under construction. The facility is expected to be completed by the end of 2012 and operating by March 2013.

Understanding the situation

El Hierro, the smallest and most southwestern of the Canary Islands, is 250 km off the African coast in the Atlantic Ocean. Peak power demand on the island is 7.56 MW, and electricity is supplied by an 11.36 MW diesel plant. Annual energy demand on the island is about 35 GWh, and the growth rate has been 8% a year. This is expected to stabilize in the next three to five years at an annual rate of 4%.

Results of this situation are:

  • Dependence on foreign energy sources, through buying 100% of the fossil fuel consumed;
  • Increasing greenhouse gas emissions as energy consumption grows above the amounts Spain agreed to in the Kyoto Protocol; and
  • High cost of electricity generation on El Hierro of €0.242/kWh (US$0.318/kWh).

El Hierro has a total available wind energy resource of 49.6 GWh, which could completely supplant diesel generation while reducing the undesirable consequences mentioned above. Wind energy costs on average €0.072/kWh ($0.095/kWh).

Moreover, the island was declared a Biosphere Reserve through the Man and the Biosphere Programme of UNESCO in January 2000. This seal was awarded to El Hierro for the special conservation of its environmental and cultural richness, as well as for its efforts toward the progress and development of its people. This means any action aimed at reducing the anthropic pressure on its habitats through the self-supply of electricity via renewable means is considered of outstanding importance.

Within this framework, three organizations — the Cabildo of El Hierro (island government), Endesa S.A. and the Canary Islands Technological Institute (ITC) — formed Gorona del Viento El Hierro in 2004 to develop a project called the El Hierro Hydro-Wind Plant. The company is a partnership of the council (60%), Endesa (30%) and ITC (10%). The goal of this work was to make the island fully sustainable with its own renewable energy sources.

This possibility was included in the El Hierro Sustainability Plan, approved in November 1997, and the El Hierro Management Island Plan, which was approved in June 2002. Both plans helped move the project forward.

In March 2007, the general director of the Institute for Diversification and Energy Saving (IDAE) and the council president, representing Gorona del Viento El Hierro, signed an agreement governing the mechanisms for the provision of public funds, as well as control and monitoring of the actions of this initiative. This guaranteed the majority of the financing necessary to perform the relevant works. IDAE is providing its experience to this project by performing monitoring, inspection and control tasks during design, supply, assembly, start-up and operational testing, ensuring the correct application of budget funds.

The initial project was developed by Endesa and ITC (D. Juan Manuel Buil Sanz and D. Ramón Rodríguez Tomás) before Gorona del Viento El Hierro was formed. This project has been the basis of the entire development.

The partnership selected IDOM S.A. in March 2008 to provide engineering and consulting services. IDOM's responsibilities for this project include:

  • Consulting engineering services for hydro-wind plant design;
  • Basic and detailed design of the hydroelectric plant;
  • Basic and detailed design of the electrical, protection and control systems; simulation and analysis of the power system behavior; and design of system operation;
  • Procurement, site supervision and commissioning support;
  • Analysis of production electricity scenarios according to hydro-wind plant configuration alternatives and operation strategy definition; and
  • Definition of a feed-in tariff, which includes developing economic and financial models and hypotheses, tariff calculation and sensitivity analysis.

Project concept

The basic concept is to inject as much wind energy into the grid as possible to reduce diesel consumption. Wind energy presents two aspects that make this objective a challenge: variability of the resource vis-a-vis demand and uncertainty of supply. El Hierro demand increases the difficulty of the problem due to its variability. Peak demand is about 7.5 MW, and the lowest demand is about 3 MW.

With no relation between wind power and demand, four scenarios may occur:

  • Wind power is above or below energy demand;
  • Wind power and energy demand are similar;
  • Sudden decrease or increase in wind power; and
  • Wind generator trip.

Because energy production and demand must match in a continuous way, an additional element is required to absorb excess wind energy generated over demand, store it and supply it back to the system when wind generation is below demand. This element must also ensure stability of the grid regarding sudden variations in generation or demand. Thus, this additional element must have sufficient storage capacity to use as much wind energy as possible and capacity to respond to sudden surges to keep the system stable.

A system capable of covering these two requirements with proven technologies is hydroelectric pumped storage.

A preliminary configuration was designed based on a strategy in which 10% to 20% of the available wind power was added directly to the grid, with the rest being dispatched to the pumped-storage station in such a way that the demand not covered by wind energy was supplied by the hydro turbines. Dynamic response of El Hierro's electric grid to the sudden imbalance between generation and demand, due to connection or disconnection of pumps and generating units failing, was modeled to check viability of the strategy.

This initial configuration was:

  • Fourteen 500 kW pumps powered by induction motors, and adjustment power factor by means of capacitors;
  • Two 1.5 MW pumps connected by a variable speed drive with power factor compensation;
  • Two 12 MVA transformers with 20/6 kV transformer ratio, magnetized through the auxiliary services;
  • Four 2.83 MW Pelton turbines coupled to alternators of 3.3 MVA with 3 seconds inertia; and
  • Four compensation capacitors of 350 kVAr connected to 6 kV bars.