A Rising
Tide
The UK has a technological lead in both the ­development and
the operation of tidal power. The Narec renewable test center
is now expanding its services for tidal applications. Siemens,
together with its Marine Current Turbines subsidiary, is using
this s­ ervice for testing of its new power train.
Text: Daniel Whitaker Illustration: Jochen Stuhrmann
56 Living Energy · No. 10 | May 2014
SeaGen U: array of submerged
devices (28- to 50-meter-deep
water). Underwater power train
means significantly lower capital expenditures per megawatt
installed and reduced cost per
kilowatt-hour produced.
Living Energy · No. 10 | May 2014 57
Ocean Power
O
n a cold day in January, the
North Sea waves, whipped up
by a gusty wind, pound hard
against the aging dock at Blyth, on
England’s northeastern coast. The
bleak weather seems to fit what has
befallen the town over the last half
century: The shipyards that built the
world’s first aircraft carrier, the HMS
Ark Royal, have closed; all three rail­
way stations are now gone; the Bates
coal mine is shuttered. And the town’s
great coal-fired power station, built
during the 1950s and 1960s, the first
in the country to have 275-megawatt
sets, finally saw its four chimneys
­demolished in 2003.
But appearances can deceive, and
Blyth now hosts a thriving new in­
dustry in which it is a world leader.
The activity takes place in a series of
giant new industrial buildings that
squat mysteriously on and around
the very dry dock where the HMS Ark
Royal was built. This is Narec – the
National Renewable Energy Centre.
Here, manufacturers and developers
from around the world have their re­
newable electricity generation units
tested before they can be placed out
in the elements that will drive them.
Ocean Power
The Reliability Premium
It’s hard to appreciate just how vital
this testing function is. Renewable
technologies are at early stages of
their development, and testing can
catch many problems and identify
lessons that will affect the technolo­
gy’s viability before units are finally
manufactured. In economic terms,
this matters because the initial capi­
tal expenditures and the cost of any
repairs and maintenance are the only
financial costs associated with renew­
able technology, which uses the natu­
ral elemental forces as free fuels.
Nowhere is testing more important
than with ocean power. Matthew
Reed, Engineering Director at Marine
Current Turbines Ltd. (MCT), ex­
plains: “The industry has learned it’s
very expensive to build and test a
prototype by putting it into the sea.
You need a certain level of maturity
before going into the water.” Reed is
at Narec to oversee nine months of
tests on a new 1-megawatt power
train, which will take the power gen­
erated by tidally driven rotors and
make it available for transfer into an
electricity grid.
Narec CEO Andrew Mill agrees. “Even
the smallest fault – say, a problem
with a fuse – could cost you a whole
season [until repair vessels are able
to reach the turbine] if it develops
at the wrong time. I’ve seen a mere
­sensor fault cost £400,000, as the
manufacturer pays to take the unit
out of the sea and put it back in
again, and that doesn’t include lost
generation.” Reed agrees: “Where
else is there such a premium on reli­
ability, due to repair costs? Perhaps
with space travel.” Mill looks out of
the window at the eleven offshore
wind turbines sitting in the North
Sea. “Narec is great value,” he con­
cludes. Offshore wind provides about
three quarters of the not-for-profit
entity’s business, while ocean power
accounts for the remainder.
An Accelerated Life
Reed’s company MCT has the world’s
most mature, proven tidal stream
­asset, a 1.2-megawatt generator at
Strangford Lough in Northern
­Ireland, which over five years has
generated more than 9 giga­watthours. Its lead in tidal stream tech­
nology is why Siemens purchased u
Siemens Power Train: Technical Details
Rotor diameter: 20
m (up to 24 m)
Tip speed: 12
m/s (up to 14.4 m/s)
Blade pitch capability: 270 degrees
Nominal rated rotor thrust: approx. 900 kN
Power to the grid: approx. 7 to 14 MWh/day*
Rotor speed: 11.5 RPM
Rated power: Each power train has a rated power of
1 or 1.02 MW** (combined power output of 2 MW per
turbine) at a current v­ elocity of 2.5 m/s (down to 2.25 m/s)
SeaGen S – the advantage of a
­surface-piercing device: Easy access
keeps operational expenditures
under control.
* site dependent (30% to 60% capacity factor reflected)
** after the main device transformer
58 Living Energy · No. 10 | May 2014
Living Energy · No. 10 | May 2014 59
Ocean Power
Ocean Power
a comparable situation to that of off­
shore wind around 15 years ago. In the
meantime, offshore wind has grown
tremendously.
He also explains why the UK is, quite
literally, ideally positioned as a tidal
stream power location. The island is
home to some great potential sites,
­especially on the Scottish and Welsh
coasts – including one at Skerries, off
the Isle of Anglesey in Wales, where
MCT hopes to establish an array that
could range from 10 to 30 megawatts.
The other is governmental support
via a “feed-in” tariff, at least until 2019,
that favors renewable generation.
Wörner’s colleague Marco Dornauer,
Head of the E HO Technology and In­
novation Department, describes how
tidal power turbine design is evolving
from MCT’s current SeaGen model,
where twin axial rotors are attached to
a crossbeam that can be raised up a
surface-piercing monopile, allowing
60 Living Energy · No. 10 | May 2014
On Trend
MCT and Siemens will be riding the
current main trends in tidal power.
The submerged and floating models
could be used in arrays exceeding 100
megawatts in power. At the same time,
increased scale combined with the rig­
orous pretesting offered by Narec will
lower tidal stream levelized costs of
energy from the ­current level of above
30 pence per kilowatt-hour. The great­
er depth capabilities will matter be­
cause, for instance, while Europe’s
­tidal potential is concentrated in UK
waters, two thirds of that is believed to
be at depths of more than 40 meters.
Narec seems similarly to be in tune
with current and likely future needs.
MCT’s power train followed a major
series of wind power tests for
­Samsung. Mill’s understanding of
what a world-class testing institution
requires comes not only from prior
experience in offshore oil and gas,
but also from previously heading the
­EMEC testing center in Scotland’s
­Orkney Islands. “Doing things in the
water just makes everything much
harder,” he reflects. “With oil and gas,
we built great drilling platforms to u
Possible Tidal Energy Sites
SeaGen F: a floating tidal
current device operating in
28- to 100-meter-deep
waters.
the remaining stake in the company
in 2012. The power train at Narec
shows what the two companies can
accomplish together. Successful MCT
technology has been ­enhanced by a
new, integrated power train concept
from gearbox to power electronics
and r­ elating to the grid connection –
all from Siemens businesses.
Inside one of Narec’s cavernous build­
ings, the power train is connected to
a giant gearbox for testing. ­Narec is
applying its Force Application System
siting in 35-meter-deep waters. For
projects on a multimegawatt scale,
the product road map foresees power
trains mounted on single monopiles
connected to an offshore platform for
power conditioning. To complement
the portfolio, floating structures will
reduce infrastructural and depth limi­
tations. All solutions use the same
qualified power train and therefore al­
low systematic learning and enable
economies of scale; hence the focus at
Narec on getting this component
right. With the power train, MCT/
Siemens offers a rare example of a sin­
gle company covering all elements
from generation to the grid.
(FAS), the only one of its kind fully
commissioned, to simulate the
thrust, and oscillating torque of the
most extreme possible sea condi­
tions. The FAS allows Narec to carry
out what it describes as a highly
­accelerated life test, which will deliv­
er the equivalent of 20 years of ­in-sea
life to the power train. There are also
a wave tank and two tidal ­devices,
one set to combine with the wave
tank to simulate the interaction of
wave and tidal forces.
Ever Larger
Back in Munich, Achim Wörner, Head
of the Siemens Hydro and Ocean
­Power Business (E HO), elaborates on
how quickly tidal stream technology
is now developing. “We now have ro­
tors 20 meters in diameter. They draw
on wind technology, but offer greater
power efficiency, since water is more
than 800 times as dense as air and
therefore can generate far more elec­
tricity per equivalent rotor size. The
tidal stream power market today is in
Tidal energy potential
Tidal power has huge commercial potential
•Global potential of up to 800 TWh (IEA estimate)
•By harvesting this global tidal energy, more than 150 million households could be
­supplied with green and sustainable power.
Living Energy · No. 10 | May 2014 61
Ocean Power
Ocean Power
Overview of Current Ocean Power T
­ echnologies
There are five ways in which the tidal forces of
the ocean can be converted into electricity.
•Today, the fastest-growing technology uses high-velocity tidal streams, usually found in constrained channels around
•Wave technology is at the testing stage, with part-scale
­prototypes of less than 1
megawatt.
terawatt-hours
Global potential estimate: 8,000
per year.
headlands. Can also be used with (nontidal) marine ­currents,
such as the Gulf Stream of the ­Atlantic.
•Thermal gradient utilizes temperature differences between
the sea’s surface and deeper water. At demonstration stage,
Main design approaches:
horizontal axis; vertical axis; ducted rotor; hydrofoil.
Precommercial full-scale prototypes of around
1 megawatt are already operating, with the first at the
UK’s Strangford Lough.
Global potential estimate: 800
terawatt-hours
per year.1
with small-scale devices of below 250
Global potential estimate: 10,000
kilowatts.
terawatt-hours
per year.
•Salinity gradient makes use of the difference in salt concentration at fresh-water/sea-water interfaces.
At concept stage: pilot devices offering less than
5 kilowatts.
•Tidal range (barrage) technology:
Global potential estimate:
Incoming tidal water is stored and then released to drive
1,600 terawatt-hours
per year.
wheels or turbines. Many operating plants already use this
mature technology. They date from the 1960s and can
­generate over 200
megawatts, using either ebb or
However, tidal stream technology – currently the most proven
tidal power, featuring long dams out to sea that would cre-
and technologically viable of the alternatives – a
­ ddresses this
ate water-level differentials.
relatively well, with a degree of consensus over the use of
terawatt-hours
per year.
A fully submerged solution can use lighter parts for
­simple installation and operations. Transformer and
­converter are anchored separately on the seabed.
62 Living Energy · No. 10 | May 2014
in achieving economic scale with standardized components.
flood generation. A related, as yet untried variant is dynamic
Global potential estimate: 300
1
Due to this plethora of technologies, suppliers face challenges
similar components to wind power (such as axial turbines),
where scale is already greater and technology more advanced.
Estimates from Siemens. By comparison, total world electricity production is less than 25,000 TWh/year.
create effectively an onshore envi­
ronment. But you can’t do that with
ocean power, and without testing, it’s
impossible to know how technology
designed on dry land will perform in
so different an environment.”
When I comment on the wintry
weather here at Blyth, he laughs and
tells me about the Orkney Islands,
which experience 20-meter-high
waves, winds of 160 kilometers per
hour, and tidal streams of up to
5 meters per second. That’s the sort
of territory that tidal stream power
claims as its own, says Mill: “Tidal
and wind involve getting into those
parts of the sea that everyone else
tries to avoid.”
Matthew Reed certainly has no in­
tention of avoiding the water or the
weather. “As soon as the 2,000 hours
of Narec testing are completed” –
equivalent to surviving 20 years of
life in rough seas for MCT’s power
train – “our turbine will be ready
to deploy.” p
Daniel Whitaker is a London-based freelance
journalist who has followed the energy and
­environmental sectors for many years. His work
has appeared in the Financial Times and The
Economist magazine.
Living Energy · No. 10 | May 2014 63