JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 46

WIND ENERGY technologies

Fig. 1: CAPEX and OPEX cost difference based on
STRUCTeam's 80m reference blade, STL80-6MW

Fig. 2: Blade cost and sparcap weight differences based
on STRUCTeam's 80m reference blade, STL80-6MW

the overall resin cost reduction achieved
in the last 15 years is around 30%.
The adoption of epoxy was initially
driven by improved fatigue performance,
whereas the adoption of resin infusion for
blade manufacture was accelerated by the
availability of epoxy resin at the time. It is
also interesting to note that the creation
and the boom of the Chinese wind energy
sector were essential to this transformation of the industry.

to ramp up in production volumes. An
additional factor for the adoption of this
innovation was the ability for the blade
manufacturer to rely on industry leaders
all working in this direction, therefore
avoiding single sourcing.

Sparcap reinforcements:
high-modulus glass fibre
for primary load-carrying members
As the resin infusion process developed,
there was a transition from E-glass to
high-modulus glass in sparcaps. The
main value proposition for high-modulus
glass is the sparcap weight reduction,
around 20%, for a neutral cost compared
with E-glass sparcaps (Figure 2). Higher
modulus fibre was developed in the early
2000s and was first introduced into blades
in 2005. This was driven by the market
leaders Owens Corning and 3B (SaintGobain at the time), quickly followed by
CPIC. Nowadays, all new sparcaps tend
to be made of high-modulus glass and
currently represent 80-90% of the market.
The value proposition of high-modulus
glass has several sides. The improved static
and fatigue performance brought more robustness in a growing industry that, since
2005, has doubled the average rotor diameter. The supply of this higher performing
fibre could be based around the existing
assets (furnaces), therefore making it easy

46

PET foam as the core material
in the shell sandwich structure
In the 90s, various core materials were
used for blade manufacture including
honeycombs, balsa and PVC foam.
Honeycombs were rapidly discarded
because of their disadvantageous volumeto-cost ratio and replaced with balsa and
structural foams, such as PVC, PET and,
to a lesser extent, SAN. Balsa and PVC
have been the primary choice for blade
manufacture and have dominated the
market for a significant amount of time.
In 2005, 3A Composites launched the first
generation of PET foam for the wind market, which was successful due to its higher
temperature resistance compared to PVC.
As the industry developed manufacturing
methods with higher peak exotherm
temperatures, to increase curing speed
and improve cure cycle time, the nature of
the PVC foam has been a limiting factor in
many cases. PET, on the other hand, has
the necessary temperature resistance. It
also has the advantage of being fully recyclable, which is increasingly important as
sustainability is nowadays a key factor for
both material and blade manufacturers.
Specifically for the case of foam cores, it
is linked with significant savings since
10-15% of the foam produced ends up in

jec composites magazine / N°116 October 2017

dust through its transformation processes
(slicing, trimming, kitting) before it can
be fitted in a mould.
As opposed to PVC being manufactured
in a batch process, PET is manufactured
in a continuous process. This has been a
key factor in lowering the foam core cost,
reducing lead time and addressing a need
for a growing demand from the wind
energy industry. The automation of the
production process can also lead to new
supply formats where foam core production lines could be, in theory, installed
nearby or within the blade manufacturing
operations.
Where the value proposition of PET has
an interesting feature in comparison to the
two previous examples is that the mechanical properties are often being considered
"lower". This is true for strength properties
although, for example, 3A's second generation PET - Airex T10 - shows significant
improvements. More importantly, the
intrinsic properties of PET make it a relatively stiff material, therefore contributing
to the buckling resistance of wind turbine
shells. Looking at the practical example
of the STL80-6MW blade, we see that
with the second generation PET there is
a marginal blade weight increase with a
noticeable reduction in blade cost when
compared to the PVC/balsa reference
blade (Figure 3).
Sacrificing part of the mechanical properties for a major improvement in costs and
processability illustrates what has driven
manufacturers to PET at a substantial rate.
PET's mechanical performance relative
to cost ratio (i.e. MPa/€) has always been
better and this advantage is ever increasing. The adoption of PET is well under
way, with today a rapid adoption pattern
where ten years after its introduction,
this technology has captured 50% of the
market share previously held by other
foam core types. However, it is yet to
reach its full potential. More evolution
of this technology can be expected in the
next few years.
Conclusions from previous
technology developments
We have reviewed briefly the key suc-
Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #116 - October 2017
