Grid Access
Author Onno Groß, a veteran journalist on maritime
topics, is based in Germany’s “Gateway to the World,”
the Port of Hamburg.
56 Living Energy · No. 9 | December 2013
Text: Onno Groß
Photos: Siemens, Werner Bartsch
Mammoth
Pillars
of the Sea
Tall as a redwood tree, the
newly installed HelWin1
transformer platform rises
up out of the North Sea. It
was erected recently with
utmost precision and marks
a significant stage in linking offshore wind power to
the grid.
Living Energy · No. 9 | December 2013
57
Grid Access
Kolumnentitel
Grid Access
A Crucial Link
A
58 Living Energy · No. 9 | December 2013
1. Offshore wind turbine
plants generate mediumvoltage AC power
mately 85 kilometers off the coast.
Siemens was commissioned to construct the platform by grid operator
TenneT in mid-2010. With the Italian
cable specialist Prysmian, the consortium is implementing a total of four
North Sea grid connection projects:
HelWin1 and HelWin2 off Heligoland,
BorWin2 off Borkum, and SylWin1 off
Sylt. The substructure and platform
were constructed at the Nordic Yards
2. Wind energy generated
by the wind farm turbines transformed to
higher AC power at the
substation platform
3. HVDC platform converts
the alternating current
from several substation
platforms to direct current for transmission
shipyard in Wismar and at Warnemünde on the Baltic Sea.
Pilings as Tall as Big Ben
The installation of the HelWin1 platform northwest of Heligoland began
in April 2013, and started with the
anchoring of the substructure, which
weighs 1,000 tonnes. Ten steel pilings,
which formed the structure’s jacket,
had to be rammed into the seabed.
Graphic: Siemens
s anyone who has ever stood in a
forest in front of a giant redwood tree knows, it is virtually
impossible to escape the lure of these
mighty giants. Firmly rooted in the
earth, the trunk may have a diameter
of several meters. In California, a road
has actually been hewn through one
of these arboreal mammoths.
The pilings of the newly erected transformer platform HelWin1 in the North
Sea rival the redwoods in height and
stability. The platform, which lies just
off the Heligoland archipelago, fills a
significant gap in the grid connection
of offshore wind farms.
“The steel structure and complex
construction made the HelWin1 project a real technical challenge. Now,
the platform has been raised safely,”
comments Marc Becker, lead project
manager for all offshore grid
connections at Siemens, with visible
relief. His elation at the success of
the weather-dependent venture is
audible. What has been achieved is
much more, after all, than the
pioneering installation of a colossus
in the North Sea, which had to
be completed within a narrow time
frame. Becker also relates other factors, such as the discovery of unexploded ammunition from World
War II and a complex approval
procedure. It is clear that the project
faced a number of initial hurdles that
had to be negotiated.
The HelWin1 converter platform
serves as a mainland link for the
energy generated by the offshore
wind farms “Nordsee Ost” (North Sea
East) and “Meerwind” (Sea Breeze).
The alternating current power
generated by the wind turbines is
transformed into low-loss direct current for transmission onto land,
known in technical jargon as highvoltage direct current (HVDC).
Siemens is one of the leading suppliers
of this technology, the market for
which is set to double its present volume of €3 billion globally over
the next five years. Particularly stable
and versatile HVDC platforms were
developed for the German North Sea
wind farms being erected approxi-
The acoustic emission was minimized
with the aid of an impact shell (cofferdam) designed to protect marine
mammals from the pile-driving noise.
At up to 3.2 meters in diameter and
boasting a wall thickness of 8 centimeters, the pilings are true steel giants,
whose length of up to 100 meters
makes them as tall as the famous
London landmark Big Ben.
The platform stands at 22 meters
4. Subsea cables, some
more than 100 kilometers in length, transport the low-loss direct
current onto land
above sea level, perched significantly
higher than the maximum recorded
wave height of 19.32 meters. The second
step of the construction phase involved the platform’s transportation
to its final position 20 kilometers off
the coast of Heligoland. HelWin1 was
converted into a floating vessel for
this purpose, before being towed out
into the North Sea by three tugboats.
The outer doors were welded shut,
5. A converter station on land
transforms the direct current back into alternating
current for feeding into the
high-voltage grid and for
further transmission
while inside, all the bulkheads were
closed in order to create something
resembling an ocean-going “ship.”
World War II Legacy
This special form of transport was selected in order to ensure that as much
of the fabrication as possible took
place on land, thus avoiding the exorbitant costs incurred by construction
at sea. Accordingly, the complete HVDC u
Living Energy · No. 9 | December 2013
59
Kolumnentitel
Grid Access
Siemens is currently testing three different methods in connection with the
platforms’ installation. The self-floating transport used for HelWin1 and
BorWin2 is one option, while, in the
case of the SylWin1 project, the platform lies on a towed pontoon and is
positioned in situ. Finally, the platform used in the HelWin2 project is
lowered onto the prefabricated jacket
structure via a large floating crane.
Besides pioneering spirit, offshore
installations require technical backups to safeguard against malfunctions
and sufficient margins of tolerance.
“These days, when we assess a project,
we evaluate it on the basis of the
transport and installation processes.
We have learned from experience and
now know which challenges are involved,” emphasizes Becker. Installing
an offshore platform depends on a
series of controllable factors, but the
weather cannot be influenced so easily. All components must be robust, as
the costs at sea are ten times as high
as on land, while the cost in terms of
time is five times as high. The learn-
ing processes involved in cooperation
with the sanctioning authorities are
another factor.
A New HVDC Platform
Each Year
In the wake of the successful anchoring of HelWin1, 100 engineers and employees are finalizing the installation.
The platform must be fully functional
in time for the commissioning in November 2014. “With the installation of
our platform at sea, we have successfully mastered the most critical part of
this project and are now on the final
stretch for commissioning in 2014,”
states Karlheinz Springer, CEO of the
Power Transmission Division within
the Energy Sector of Siemens AG. With
a transmission rate of 576 megawatts,
HelWin1 will eventually supply electricity to over 500,000 households on the
German mainland. “We are certainly
confident of our ability to execute new
offshore projects,” says Becker. “We’re
now familiar with the installation process, we have reliable suppliers, and
we know how to cope with heavy
swell – in short, the expertise is now
on hand.”
Europe remains the most important
market for offshore HVDC technology.
Germany has developed clear expansion targets for renewable energies:
Network operator TenneT will be issuing one invitation to tender for platforms with a capacity up to 900 megawatts each year up to and including
2020, in order to comply with the grid
expansion obligation.
Wind power installation is also making rapid progress in Great Britain. In
Germany, 33 plants amounting to a
capacity of over 2,250 megawatts have
been approved to date, while a further
8,000 megawatts are planned by 2020,
and a total of 25,000 megawatts are
envisaged by 2030. In England, installation of up to 51,000 megawatts is anticipated. Many more mammoth offshore pillars will thus be required in
future. p
Onno Groß, a science journalist from Hamburg,
writes regularly on maritime issues for
newspapers and magazines such as National
Geographic and Handelsblatt.
platform was constructed in the shipyard. An impressive seven stories high
and with a surface area of 75 by 50 meters, it is as big as half a soccer field.
Transporting the 11,000-tonne platform
from the Baltic Sea around the tip of
Denmark ultimately took seven
days, and a further four were planned
for the installation. Although the environmental conditions in the North Sea,
which is 23 meters deep at this point,
are a more predictable aspect of the
project, the ambitious schedule was
threatened by the discovery of
two World War II torpedoes some distance away from the platform.
“The seabed surrounding Heligoland is
full of unexploded ammunition, which
first had to be removed,” explains project manager Marc Becker. Although the
discovery was not made directly in
the construction area, the detonation
60 Living Energy · No. 9 | December 2013
would have affected the acoustic
measurement equipment that is needed
for piling operations, with the result
that the latter had to be retrieved from
the water and later replaced. This took
a week.
The Art of Picking
a Weather Window
The platform was eventually positioned precisely above the pilings with
a deviation of just a few millimeters.
In a second step, it was connected to
the pilings within the jacket, a phase
whose completion depended on the
weather. “The process of threading
the platform onto the legs can only
be performed when the wave swell is
less than 70 centimeters,” explains
Randolph Schmid, Siemens Project
Manager Offshore. The final phase
involved the platform being hoisted
onto the pilings via hydraulic power.
As it was raised up with excruciating
slowness, centimeter by centimeter,
the faces of all Siemens participants lit
up with delight and relief. The window
of opportunity had been chosen with
pinpoint accuracy: one day’s journey
to the location, two days’ positioning,
and two days for the threading. Raising the platform required a further
day. Says Schmid: “It’s primarily a
matter of checking the weather forecast and not losing one’s nerve.” The
August deadline for the installation of
HelWin1 had been agreed a year before, and Siemens was therefore able
to stick to the schedule. Although the
completion was preceded by a steep
learning curve, it did result in HelWin1
overtaking BorWin2 on the installation timetable.
Photos: Siemens
In order to transport the platform to its final location 20 kilometers beyond Heligoland, HelWin1 had to be converted into a floating
vessel towed by three tugboats.
As the main land conversion and transmission node for energy gathered by offshore farms “Nordsee Ost” and “Meerwind”, HelWin1
plays a crucial role in the integration of renewables into Germany’s grid.
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