Europe
on blades at tip speeds of 300-500 kilometers per hour (200-300 miles per hour).
The current trend is the development
of larger offshore turbines with a higher
energy output so that the coatings, particularly those on the blades, have to be
even more resilient.
“For coatings companies the wind
turbine market, particularly offshore, is
a big opportunity since a typical wind
farm uses more coatings than an average
conventional power station,” said Anders
Voldsgaard Clausen, group power generation segment manager, Hempel, Denmark.
“Wind turbine coatings are sophisticated, complex chemical products, which
require highly qualified staff to develop
and formulate,” he added.
At the end of 2012, Europe had offshore wind turbine capacity of approximately five gigawatts (GW) of electricity
or 92 percent of the world total with
much of it in the northwest Atlantic
and North and Baltic Seas. The UK accounted for close to 60 percent of the
European total, Denmark 18 percent,
Belgium eight percent and Germany
six percent, according to figures from
the World Wind Energy Association
(WWEA), Bonn, Germany.
Over the last few years the UK, as part
of a big expansion in wind energy, has accounted for two thirds to three quarters
of the growth in global offshore wind
capacity. One in three of wind turbines
installed in the UK are now offshore.
Nonetheless, the center for offshore
wind turbine production and development
has been Denmark where wind turbines
were first introduced in the 1980s. The
country is the wind turbine manufacturing
base of Vestas Wind Systems of Denmark
and Siemens AG of Germany, the two
global leaders in wind turbine production.
It also has a number of major centers for
testing new prototypes and their materials.
The leading coating companies serving
the sector are Hempel, Jotun of Norway
and Netherlands-based AkzoNobel,
which are already the world’s major suppliers of marine coatings.
There are also a number of niche
players working on specialist coatings,
particularly for the new generation of
rotor blades.
Some companies, like BASF and Bayer
MaterialScience (BMS) of Germany, have
a strategy of being a supplier of a wide
range of materials, including coatings, for
wind turbines.
Coatings for the machines’ steel-framed towers and foundations make up
the largest segment of the offshore turbine coatings market in volume terms. It
tends to be dominated by marine coatings producers who can take advantage
of their expertise for coatings for maritime conditions.
“The easiest method of gaining the
confidence of the relevant parties (in
the offshore wind industry) is by demonstrating a track record in the offshore
environment,” said Clare McDermott,
business development manager for wind
energy at AkzoNobel.
A priority for OEM turbine manufacturers and wind farm operators is
that the coatings should need minimum
maintenance during their average 20-
year life cycle.
“Correct coatings specification, preparation and application will help protect
offshore wind assets for a specified time
without the need for major maintenance,”
explained McDermott. “Long-term costs
can increase substantially if assets are not
protected correctly from day one due to
the offshore environment being so harsh.”
Coatings producers are having to respond to changes like the building of
large turbines, new foundation types and
positioning of wind farms in deeper waters with even harsher conditions.
“(Existing foundations) may not be
the foundations of choice as turbines
increase in size and move into deeper
waters, with jackets, and even floating
turbines becoming more prevalent,” said
McDermott. “These structures are, in
general, more complex to coat.”
Much of the cost of mainly polyure-
thane-based coatings for towers and
foundations is in their application dur-
ing the manufacturing process, which
involves three coats—the primer, mid-
dle barrier and top coat. These can
take six to ten hours per coat to dry,
according to Hempel.
“One way of cutting the costs of the three-
coats application is to merge the primer and
middle phases into one so, with the top coat,
there are only two,” said Clausen.
Another option is a change formulations to speed up curing rates by combining
polyurethane with polyaspartic systems.
“Polyaspartic systems are very reactive
and might be applied in their 100 percent
solid content, so they are especially suit-
able for applications where high film
thickness and fast curing are necessary,”
said Maria Almato Guiteras, a BMS coat-
ings specialist. “Besides their use in blade
coatings, polyaspartics are the technology
of choice for protective coatings applied
on the towers of the wind turbines.”
The biggest technological challenge in
wind turbine coatings, however, remains
the protection of the blades, which not
only need a high level of resistance to ero-
sion by rain, hail, snow and ice as well as
UV light. They must also have durability
while maintaining the aerodynamics of a
variety of blade shapes.
The polyurethane and related coatings
materials have to be compatible with materials within the structure of the blades,
usually comprising epoxy resins and glass
or carbon fibres.
Unlike with coatings for towers and
foundations in offshore turbines which
are governed by standards such as
Norway’s Det Norsk Veritas, there are no
agreed standards for coatings blades.
“The turbine manufacturers have
adopted their own systems to differen-
tiate themselves,” explained Clausen.
“You normally have to customise your
coatings to meet the different needs of
manufacturers.”
With blades becoming even bigger
with lengths of as long as 90-100 meters,
the necessity for standards is even more
pressing. “The longer the blades the high-
er the wing tip speeds and levels of stress
and erosion,” said Clausen. “There are no
perfect solutions to this problem yet.”
The reward for coatings companies
in developing successful high tech prod-
ucts for the European offshore wind tur-
bine market is gaining a head start in the
fledgling global offshore sector. Once the
technologies for offshore conditions have
been proven to work there is likely to be
within a few years a large world demand
for them. CW
