at the hub of it all - Organic Power

Pumped storage
At the hub of it all
Asmall company based in West Cork in
the Republic of Ireland, Organic Power
has been developing the design and
permitting of pumped storage, wind and other
renewable projects in Ireland since 2007. It plans to
deliver clean, competitive, dispatchable electricity
by undertaking large scale projects which include
intermittent generation sources, energy storage and
dedicated HVDC grid infrastructure, gaining access
to appropriate markets which may be in a different
location to the energy resource.
This vision is embodied in the Mayo Atlantic
Renewable Energy eXport (MAREX) plan for 2017
where:
■ 1900MW of wind potential in Northwest Mayo in
Ireland represents the intermittent power supply.
■ The 6GWh, 1200MW Glinsk Energy Storage
Hub (incorporating a sweater pumped storage
project) provides the back up for intermittency.
■ A dedicated 500kV, 1300MW underground/
undersea cable link to the UK efficiently delivers
the clean electricity product to the UK market -
without compromising the Irish grid with levels
of energy it is not designed for.
■ 250kV HVDC power import cables connecting
wind farms will supply the project directly with
intermittent renewable electricity.
A new seawater pumped storage plant is set to play a central
role in an ambitious energy export scheme known as MAREX.
Irish company Organic Power gives more details about the
development taking place on Glinsk Mountain in County Mayo.
The system will deliver in the region of 6TWh of
renewable electricity per year to the UK by 2017,
equivalent to 1.6% of total UK electricity consumption
and 8% of the UK’s renewable electricity target
for 2016/17. Further development is planned to
increase renewable energy supply to MAREX for
2027, including wave and floating offshore wind. The
MAREX output figure is expected to rise to 9TWh/
yr, representing 2% of total 2027 UK electricity needs
and 5.3% of the UK 2027 renewable target [1].
The current status of the MAREX plan is that
scale and technology are defined on the basis of
available resources, environmental limits and market
access. Discussions with relevant stakeholders
are at various stages, and strong local support has
been given to the project. Locals clearly see the
potential development that can be unlocked by this
development. Further design and assessment work
is ongoing.
Final permit applications will be lodged with the
relevant authorities before the end of 2012. Subject
to permitting, project finance has been secured in
principle and the three year construction period
will commence in early 2014. The project will be
energised in early 2017.
Seawater pumped storage plant
The seawater pumped storage plant is conceived as
providing energy storage for wind and ocean power,
transforming these unpredictable energy sources into
reliable power available on demand. It will expedite
the long awaited potential to develop renewable
wind generated electricity in Mayo at a large scale.
It will also be ready to accept energy from wave and
Figure 1: Site plan
May 2012 www.waterpowermagazine.com 27

Pumped storage
Figure 2: Reservoir
embankment section
floating wind turbines (on a large scale) when this
technology comes of age, targeted for 2027. It will
also link the best wind resource in Europe to the UK
market, delivering clean power when it is needed.
The €480M project (excluding grid) is
commercially competitive at a build cost of €400/
kW excluding transmission systems. Construction
will generate 200 jobs for three years and justify the
immediate rollout of a dedicated grid connection to
the UK by 2017 as part of the MAREX plan.
Using seawater allows for larger and more
economical schemes without the need to use
valuable and limited freshwater resources. It will
also dictate that all wet elements are suitable for the
marine environment through the use of marine grade
steel, concrete, plastics etc. Experience from the
operation of the Yanbaru seawater pumped storage
scheme by JPower in Okinawa, Japan since 1999 has
shown that seawater is perfectly adequate for use in
such systems [2].
Glinsk Mountain in County Mayo has been
selected for this project because of its almost unique
qualities as a high, flat topped, mountain. Located
beside the sea, and not in an environmentally
designated site, it is composed of very hard,
impermeable and immensely stable schist rock.
The project site faces the Atlantic Ocean and the
upper reservoir is located on the plateau of Glinsk
Mountain where the reservoir base will be 288m asl
and 700m from the coastal intake. The Glinsk project
(see figure 1) will use the sea as the lower reservoir.
The design concept carried out by erm21c is being
advised on by JPower.
A total of 8.9Mm 3 of seawater can be pumped to
an average elevation of 292m asl to fill the reservoir
from empty, providing 6.1GWh of storage per cycle.
When released, the water from the reservoir will
generate electrical power at 1200MW from the four
variable speed 300MW reversible turbines for five
hours. The scheme will accept energy off peak for
8-19 hours per day depending on the available
wind energy. Electrical efficiency for the pumped
storage plant has been modelled from the design
at 75%.
Electric power sourced from wind (and later
ocean and floating wind power) will provide the
input power during off peak hours of electricity
demand. The facility will accept wind power from
the planned 1900MW of wind turbines (initially
in 2017) during off peak night time hours or
when generation exceeds demand, and use it to
pump seawater to the reservoir on top of Glinsk
Mountain [3]. The stored energy will be exported
via HVDC link to the UK for use during peak
times. The pumped storage scheme can deliver
power at maximum output for five hours per day,
approximately corresponding to peak demand in
the UK. It is further planned to accept seawater
pumped to the reservoir from 800MW of ocean
energy pumps, and power from 500MW of potential
floating wind turbines for 2027.
All above board
More than 550,000m 3 of peat must be removed from
the summit of the mountain to allow for reservoir
construction. This will be removed by transforming
the peat into a wet sludge and pumping it downhill
through pipes to a holding reservoir, where the peat
is dewatered and the water returned uphill for further
sludge activation. The system is a closed circuit with
water cleaning systems incorporated, and has been
designed on advice from KOOP Water Management
of Holland.
The reservoir embankment will be an earthquake
resistant reinforced earth system gravity retaining
structure (see figure 2) constructed with rock from
within the site, based on designs from Terre-Armée/
Reinforced Earth Company [4]. The geomembrane
system consists of a geocomposite. This is formed
from an impermeable PVC geomembrane laminated
during manufacturing to a geotextile providing
puncture resistance and increased dimensional
stability. The geocomposite will be applied to the full
face of the vertical walls either in front of (exposed
configuration) or behind (covered configuration)
the precast panel wall. PVC has excellent material
properties and weather resistance characteristics
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Pumped storage
SeaPower platform
AWE waveroller
and is commonly used to line pumped storage
reservoirs. An asphaltic liner will be used to seal the
reservoir floor. The combined sealing system will
securely prevent water leaking from the reservoir
into the surrounding environment.
A leakage monitoring and detection system will
be used to detect seawater leakage should damage
to the sheet occur. Underneath the sealing systems
of the reservoir a drainage system will be installed
in order to intercept possible leakage water. A
fibre-optic leakage detection and localisation
system (based on the heat-pulse method developed
by GTC Kappelmeyer GmbH [5]) will be fitted to
pinpoint possible leaks at critical points. This online
automatic system will enable immediate action
to empty the reservoir in case of leak detection.
It will prevent sea water from leaking into the
neighbouring environment. As the PVC sheet and
asphaltic are the top layers of the lining structure,
they can be repaired.
Going underground
To preserve the landscape in the area, the penstock
and powerhouse will be excavated underground. The
6.9m diameter penstock and 10m diameter tailrace
will be assembled within the excavated tunnel by
mounting FRC concrete panels (multi-segment in the
diameter), which are grouted into place to maintain
back pressure from the mountain (see figure 4). The
powerhouse will be located 50m below sea level, and
will consist of a cavern containing the pump turbines.
This cavern will be accessed by a vertical 150m deep
access shaft from the surface of the ground above.
The cavern will be connected to the sea by a 120m
long intake structure located below sea level in the
east facing cliff of the sea chasm.
The water intake is from a sea chasm at the north
eastern part of the site which provides wave shelter
on three sides, with a porous breakwater constructed
to shelter the fourth side. The breakwater is
composed of a tetrapod/X-bloc mound wave
attenuation structure located at the mouth of the
sea chasm. The main functions of the tetrapod/Xbloc
barrier will be: to minimise wave action and
reduce water level fluctuation during pumping; and
to dissipate the energy of the exiting water post
generation and protect marine habitat.
The water in the chasm will enter and exit the
tailrace through a below-sea-level sluiced water
intake structure, which will be constructed as a
caisson off site and floated into place for submersion
and fixing, prior to breakwater construction. Once
in place the caisson will be pumped out to allow the
final tailrace breakout to be completed in dry working
conditions.
Materials for the pump-turbine runner and the
guide vanes will be made from austenitic stainless
steel which has anti-cavitation, anti-wear and anticorrosive
characteristics. For high efficiency power
generation and pumping, a combination of variable
and fixed speed pump-turbines will be used.
Figure 3: Profile
through waterways
May 2012
www.waterpowermagazine.com
29

Pumped storage
Figure 4: Tailrace section
with wave pump water
delivery pipes
Existing mountain profile
Wave pump pressurised delivery
The inclusion of pressurised piped seawater delivery
from wave pumps provides a market and platform for
the development of wave energy conversion devices.
Six 500mm diameter valved delivery pipes will be
connected to the pressurised penstock upstream of
the powerhouse. Wave energy conversion developers
are working on large scale units (see illustrations
p29) which can pump high pressure water in large
volumes and are designed specifically for this type of
application, where electrical generation components
from wave energy convertors and associated
maintenance are eliminated. Sea-Power of Ireland
and AWE of Finland are collaborating in a detailed
assessment of supplying the Glinsk Energy Hub with
pumped seawater.
In the design of the Energy Storage Hub, pipe
work has been incorporated to allow the equivalent
of 200MW average electric power to be provided as
pumped water from ocean energy devices. This array
is proposed directly offshore from the Glinsk Energy
Hub, where sufficient depth and wave energy are
available within 1km. At a capacity factor of 20-25%
this would equate to an array of approximately
200x4MW wave pumps. Electricity input to MAREX
from such an installation would equate to a range of
160-200MW, producing approximately 1-1.3TWh/yr,
after pumping losses.
Environmental conservation
An Environmental Impact Statement has been
prepared by erm21c to assess the impact of the
project on the local environment. It details mitigation
measures to minimise impacts identified, including:
■ Landscaping the new profile of the mountain to
minimise visual impacts of views at the proposed
world heritage site Ceide Fields (pictured left).
■ Reducing discharge velocity in the chasm to
mitigate the impact of sea water discharge on
marine life.
■ Re-planting reservoir embankments with local
flora from the site.
■ Treating soiled water generated at the
construction site in sedimentation ponds before
discharging into natural streams.
■ Sowing fodder for endangered bird species Twite
Carduelis flavirostris in sacrificial plots [6]. ■
References:
[1] POYRY (December 2011), ‘Potential Impacts of Revised Renewables Obligation Technology
Bands’.
[2] TANAKA KUNINORI Electr. Power Dev. Co., Ltd. (2004). ‘Pumped-Storage Power Plant
Using Sea Water’. Journal of the Institute of Electrical Engineers of Japan.
[3] Mayo County Council. (2011), ‘Renewable Energy Strategy for County Mayo’
[4] Terre Armée Internationale (2012) ‘Sustainable Technology’. Available at: http://tinyurl.
com/7s9wutb.
[5] Aufleger M., J. Dornstädter, A. Fabritius, Th. Strobl (1998). Fibre Optic Temperature
Measurements for Leakage Detection – Applications in the Reconstruction of Dams.
Proceedings: Repair and Upgrade of Dams. ICOLD-Symposium‚ Rehabilitation of Dams‘ 4th
November 1998, New Delhi, India.
[6] Derek McLoughlin, MIEEM (2011) ‘Assessment of the Potential and Predicted Impacts on
Twite Carduelis flavirostris of the Proposed Sea Water Pumped Hydroelectric Storage
Scheme (SWPHSS) at Glinsk Mountain, Co. Mayo’.
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INTERNATIONAL WATER POWER & DAM CONSTRUCTION May 2012