IEEE Electrification - September 2022 - 23

agency for the promotion of energy saving and sustainable
energies [Instituto para la Diversificación y Ahorro
Energético (IDAE)], decided to publicly support the project.
Once the grant was announced (2007), the project development
begun. Civil works started in 2009. The IDAE awarded
a subsidy to the Cabildo of El Hierro due to the
innovative nature of the project as it could be useful for
other insular territories.
The construction of the wind-pumped hydropower
plant was marked by the insular condition of El Hierro:
remoteness from the continental territory, scarce communications
by air and sea, and the limitations of materials
on the island. Once the necessary land was acquired to
build the project that would make El Hierro an exemplary
territory in energy matters, the bureaucratic process was
one of the most difficult phases on the way to startup: an
environmental impact statement; an urban planning
license; and once the power plant was built, the authorization
of the startup and negotiating the economic compensation
for the electricity generated.
In June 2014, the wind-pumped hydropower station
was commissioned. During the first 12-18 months, the
power station ran in test mode, and it began fully commercial
operation in 2016.
Running the System and Lessons Learned
The hydro-wind power station of El Hierro is a perfect
example of a public-private partnership and a multilevel
governance approach for promoting RES in European
island regions. Gorona del Viento is a sustainable natural
living lab whose goal is to achieve full energy self-sufficiency
and lead the technological advancement of the
renewable energy sector in isolated territories.
El Hierro's Electrical System
The current electrical system of El Hierro, like the other
electrical systems of the Canary Islands, is a very small
and isolated one. Regarding peak power and yearly energy
consumption, the electrical system of El Hierro can be
classified as corresponding to a medium-sized island.
Along with the WPS subsection, there is only one conventional
power station in El Hierro (named Llanos Blancos),
with an installed capacity of 14.91 MW (several small
2-3-MW diesel generator sets).
The voltage levels of El Hierro's electrical grid are 20
and 0.4 kV. Given such levels, the island grid is considered
a distribution network (there is no transmission grid on
the island). The electrical energy demand in 2017 was
45 GWh, and it was 42 GWh in 2018 (demand reduction
partially thanks to energy-saving measures explained
later). In 2019, the demand suffered a slight increase due
to, among other causes, the increase in tourism. This
increase was dampened by the energy-saving measures
indicated, with an annual demand reaching 43 GWh. The
following sections describe the main elements of the current
electrical system of El Hierro.
The Wind-Pumped Hydropower Station
The hydro-wind power plant is responsible for the biggest
share of the island's renewable generation. Its gross capacity
is 22.8 MW, composed of hydro turbines (four Pelton
turbines with 2.83 MW each) and the wind farm (five wind
turbines with 2.3 MW each) (Figure 3).
The wind-pumped hydropower station has the following
main elements:
x an upper reservoir [Figure 4(a)]
x a lower reservoir [Figure 4(b)]
x a penstock [Figure 4(c)]
x a pumping plant [Figure 4(d)]
x a turbine operation plant [Figure 4(e)]
x a wind farm [Figure 4(f)]
x an electrical substation [Figure 4(g)].
The wind farm converts the primary energy into electricity
and injects it in the island grid. The hydraulic system
is used for energy storage, and its capabilities allow it
to collaborate in the primary, secondary, and tertiary frequency
regulation of the El Hierro power grid.
When wind energy production exceeds demand, this
surplus wind energy, which is not consumed by the
island's population, is used to pump water from a lower
reservoir at sea level to a higher reservoir located at an
altitude of 700 m. The potential energy stored in the upper
reservoir is used to produce electricity by means of the
turbines of the hydroelectric plant when wind power is
insufficient to cover the demand. The diesel engine-powered
power station that existed before the commissioning of the
wind-pumped hydropower station in 2014 still remains,
but only as a backup, and it comes into operation in exceptional
circumstances when there is not sufficient wind or
water stored to produce enough energy to meet demand.
The wind-hydro system design (Figure 5) is able to
cover approximately 70% of the yearly electricity demand
and 100% of the demand in the summer months (the period
with optimum wind conditions). Although there are
times when the demand of the island is covered exclusively
by renewable energies, it is not done exclusively
with inverted-based generation. This is because during
these periods, hydraulic turbines, which are synchronous
generators, are always online to account for the variability
in the wind resource, compensating and stabilizing the
grid. The storage capacity is able to cover the electricity
demand of the island for almost two days.
The hydraulic infrastructures, originally designed for
energy storage, also guarantee access to water for human
and agricultural consumption as it is connected to a seawater
desalination plant. The combination of wind and hydropower
successfully transforms an intermittent energy
source-wind-into a continuous, controlled supply and represents
an innovative contribution to the goal of maximizing
RES penetration in island or isolated electrical systems.
The control system of the wind-pumped hydropower
station is organized in different levels: scheduled operation;
primary and secondary regulation; and load
IEEE Electrification Magazine / SEPTEMBER 2022
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