Comparative Cost Study of a 35m Wind Turbine Blade using
Infusion and Prepreg Materials Technology
Introduction
Wind turbine blades are manufactured using advanced composite materials due to
their specific properties and their flexibility for component construction. In recent
years as blade sizes have increased, and as manufacturing output has accelerated,
the choice of materials and the production route has become increasingly critical. Two
material technologies have emerged during this rapid growth of the industry to meet
the increasing demands on output, performance and quality: Prepreg Technology; and
Infusion Technology.
These two technologies are well established and account for the majority of blades
currently in operation. However, the wind industry continues to develop higher MW
output turbines which require larger blades, and as a consequence the demands on
the materials and process continue to increase. As a response to the evolving market,
the debate on the most appropriate technology for blade manufacture is becoming
more intense.
The selection of a material technology is a complex issue as it has implications on
the whole supply chain. This study uses a simple comparative 35m blade model to
highlight the many parameters that need to be considered when making a strategic
choice between infusion and prepreg technology for blade manufacturing.
1.1
Composite Processing Technology
The majority of blade manufacturers using infusion technology use epoxy resin as
their chosen matrix, but polyester is also used in this process. Prepreg technology is
currently exclusively epoxy based. A simplistic overview of the fundamentals of the
two material technologies is presented in the following sections.
1.1.1
Infusion Technology
The general principal of infusion technology is to draw a resin into the reinforcing
fibres and fabrics using a vacuum. The vacuum reduces the pressure at one end of
the fabric stack allowing atmospheric pressure to force the resin through the stack.
The speed and distance that you can infuse a fabric stack will be dependent on the
following parameters:
The viscosity of the resin system
The permeability of the fabric stack
The pressure gradient acting on the infused resin
η
D
ΔP
The relationship between these can be simply defined using the following equation
with respect to the speed of the infusion process v.
v ∝
D x ∆P
η
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology Therefore the speed of an infusion is increased with increasing permeability of the
fabric stack (D), increased with increasing pressure gradient (ΔP), and decreased with
increasing viscosity (η).
Infusion Processing Schematic
The requirement for a low viscosity resin for the infusion process is met by using standard
liquid polyester or epoxy systems. Once the fabric stack is infused with resin the temperature
is raised, typically between 50 to 70 °C, to accelerate and complete the curing process.
1.1.2
Prepreg Technology
Prepreg is an abbreviation for “pre impregnation” where a fibre layer or fabric is
impregnated with a resin to form a homogenous precursor that is subsequently used
to manufacture composite components. The resins used to manufacture prepregs
have inherently high viscosities and are therefore solid at room temperature allowing
easy handling, cutting, and lay-up into the mould without any transfer or contamination
from the resin. Once in the mould prepregs are then cured under vacuum at elevated
temperatures, typically between 80 and 120 °C for industrial applications.
Prepreg Processing Schematic
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology Prepregs are often supplied in roll format and provide the benefits of highly controlled
resin content, higher performance resins than with infusion, controlled fibre alignment
in unidirectional products (a key benefit for mechanical performance), and fast
deposition rates and automation capability. However, as a consequence of the inclusion
of higher performance resins, the requirement for chilled storage and shipping, and
the additional processing step of “prepregging”, prepregs are more expensive per kg
than the equivalent resin and reinforcement in an infusion process. Furthermore, the
increased processing temperatures required for prepregs can also increase tooling
costs. However, prepregs provide some benefits with respect to process reliability and
repeatability, higher levels of automation, higher mechanical performance, and carbon
fibre utilization (infusion of carbon fibre is increasingly seen as unviable).
2.
Summary of Methodology
The blade model was developed to provide a financial analysis of the two manufacturing
technologies. Many assumptions have been used in the development of the model
and as a consequence the financial output is useful from a qualitative perspective only.
However, taking a financial approach to the model enables the clear identification of
key parameters and their influence on the cost of a blade. Unfortunately, the model
only provides analysis on blade manufacturing and does not consider service life and
performance, which will have a significant effect on the life-cycle cost of a blade.
The blade model was constructed using the following steps:
¬ Definition of a 35m blade geometry and structural design based on Class I loads
and fixed tip deflection
¬ Creation of a Bill of Materials (BOM) for both infusion and prepreg structural
design
¬ Determination of the direct labour required for blade manufacture form the detailed
manufacturing route for the spar and shell components
¬ Determination of the annual indirect labour and annual plant overheads based on 4
mould sets
¬ Determination of plant CAPEX and annual depreciation
¬ Determination of tooling CAPEX and annual depreciation
¬ Financial analysis of annual plant output: Blade cost, Profit, Asset Turn, Return on
Total Assets
Each step is described in detail below with assumptions and presentation of the
comparative results.
3.
Blade Structural Design
3.1
Blade Overview
The blade model is based on a 35m blade manufactured using a shell and box spar
structural arrangement. The blade has no pre-bend. The structural arrangement for both
infusion and prepreg blades is a structural box spar section, i.e. the primary structural
member, consisting of two unidirectional spar caps and biaxial sandwich shear webs.
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology The root section is integrated into the box spar.
The box spar supports two aerodynamic shell fairings joined at the leading and trailing
edges of the blade.
Blade Construction
3.2
Blade Construction Options
The blade structural arrangement described above is used as a common basis to
compare the following material options:
¬ E-Glass infused box spar and shells
¬ E-Glass pre-preg box spar and shells
3.3
Loads
The comparative study is based on equivalent stiffness which tends to be the typical
structural design driver for this size of blade. Flapwise blade stiffness is required in order
for the blade tip to clear the tower and for the ratio of first bending natural frequency to
rotor frequency to be sufficiently high to avoid resonance.
In this case, a target flapwise tip deflection, towards the tower, has been chosen to be
met by both design options. Furthermore, this target deflection has been adjusted to
ensure that all blade designs meet or exceed the required minimum ultimate strength
criteria. As a result of this adjustment the blade stiffness is significantly higher than
would be required for an optimised blade design. The fatigue strength has not been
considered for the stiffness based comparative study.
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology Minimum strength criteria relate to four ultimate load cases where aerodynamic loads
have been calculated to represent extreme gusts and wind shifts causing flapwise
bending, towards and away from the tower, as well as edgewise bending, with and
against rotation directions. Buckling stability has been restricted to spot checks.
An aeroelastic model has been used to calculate the corresponding section shear
forces, bending moments and torques. Ultimate design loads have been obtained by
factoring these up by the required Germanischer Lloyd (GL) general load factor of 1.5.
Note that no aeroelastic iteration has been performed to assess the effects of final
stiffness and inertia distributions on the above aerodynamic loads.
3.4
Design Allowables
The value of the allowable stress/strain is known as the design strength of the material,
Rd. This is calculated by dividing the material characteristic value, Rk, by the partial safety
factor, γMx:
Rd = Rk /γMx
(Equation 1)
The characteristic value, Rk, is determined from a statistical equation that quantifies the
reliability of the test data. Therefore, the greater the variation in the test results (large
standard deviation and variation coefficient) the lower the characteristic value. If the test
results are very reproducible, giving a low standard deviation and variation coefficient,
the characteristic value will be very close to the mean test result. The characteristic
value is calculated according to the process documented in Germanischer Lloyd (GL)
Rules and Regulations as follows:
(Equation 2)
where x is the mean of the test values, v is the variation coefficient, and n is the number
of tests. The characteristic value will also decrease as the number of tests decreases.
However, this change is small compared to the effect of the variation coefficient.
The partial safety factor, γMx, is calculated separately for the general static strength/stiffness
analysis and the fatigue analysis. The partial safety factor is obtained using Equation 3:
(Equation 3)
where for both static and fatigue analysis a general safety factor of γM0 = 1.35 is used.
The partial safety factors generated by GL are as follows where N is the number of
fatigue cycles (10,000,000):
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology Factor
General Strength
Fatigue
General Safety Factor
1.35
1.35
Ageing – C1
1.35
N1/10/N1/14 (E-Glass or Carbon)
Temperature – C2
1.1
1.1
Manufacture – C3
1.1
1.0/1.1 (U/D or stitched)
Post-cure – C4
1.0
1.0
Total Material Safety Factor
2.21
7.44/8.18
GL Partial Safety Factors
Therefore, from Equation 1, the maximum design allowable strength that can arise in
a blade laminate during operation is calculated. Due to the different material properties
within a composite structure the design is performed using strain values as these will
in general be consistent throughout the anisotropic composite structure. The allowable
strain values have been calculated using the characteristic strength values divided by
the average modulus and subsequently by the material partial safety factors. Some
typical values are illustrated in the table below.
Material
Test
Char. Strength
(MPa)
Modulus
GL Partial
Safety Factor
Design
Allowable
Prepreg UD 1600g
Tensile Strength
952
42.0
2.21
1.02%
Prepreg UD 1600g
Compressive strength
687
42.0
2.21
-0.74%
Infusion UTE 800g
Tensile Strength
821
37.8
2.21
0.98%
Infusion UTE 800g
Compressive strength
511
37.8
2.21
-0.61%
Prepreg UD 1600g
Fatigue (10e7)
952
42.0
7.44
0.30%
Infusion UTE 800g
Fatigue (10e7)
821
37.8
8.18
0.26%
Material Design Allowables
The values in the above table show that the prepreg design allowables are higher than those
for the infusion process and in particular for compression loading. This is a consequence of
the higher performance resin in prepregs preventing fibres from buckling, and due to the
high fibre alignment in collimated unidirectional prepreg. The infusion process uses slightly
lower performance resins due to the requirement of low viscosity and stitched unidirectional
fabrics which introduce a level of fibre waviness. The net result is the designer can utilize the
higher design allowables for prepreg and reduce the material content in the blade.
3.5
Blade Design Program (“BDP”)
The BDP is effectively a very detailed cantilevered beam model set up to perform
the analysis of a blade box structural spar and supported blade shell. Slender beam
theory assumptions are applicable to the BDP model (no shear deformation of cross
sections). Polynomial curve fitting functions are used to provide a convenient analytical
representation of the blade geometry.
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology The blade model is divided into a large number of sections with intermediate subsections (typical section spacing 0.2m) created by linear interpolation between input
sections (typ. spacing 1m). Each blade section is divided into 12 elements. These
elements are grouped into a number of laminate zones as shown in Figure 4.
Blade Section and Elements
Each zone along the blade has a laminate input and laminate properties are computed
based on classical laminate theory. Bending stiffnesses EIxx, EIyy and EIxy are then
calculated by summing up contributions from each element around the section. A
similar calculation is carried out for the shear centre and torsional stiffness properties
(GJ) of each section. The centre of gravity (CG) position and detailed mass distribution
are also calculated.
This information is used to calculate the required outputs for each load case in turn:
¬ Deflection curves
¬ Strain chordwise and spanwise distributions
¬ First bending natural frequency (Rayleigh’s quotient)
¬ Mass estimate
¬ Bill of materials (BOM)
3.6
Results
The design outputs for the blade are summarised in the following table. It should be
noted that no load iteration steps were made following the determination of the mass
and stiffness distributions. The reduction of the mass of the prepreg blade would reduce
the static and dynamic loads on the blade and therefore design iterations would enable
further optimisation of the laminate.
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology Blade Design Parameter
Infusion
Prepreg
Tip Deflection (m)
2.53
2.53
Lead-Lag Deflection (m)
0.21
0.27
Flapwise Frequency (Hz)
1.142
1.359
Blade Mass (kg)
6,186
4,987
4.87 x106
3.79 x106
Rotational Inertia (kgm )
2
Blade Design Output
4.
Bill of Materials (BOM)
The output from the blade design program provides the net material requirement but
does not take into consideration the level of waste or over consumption associated with
each manufacturing process, and this needs factoring in to the BOM. The assumptions
used in the model to determine the gross material requirements are as follows:
¬ 5% additional consumption for Dry Fabrics and Prepreg. A consequence of kitting
and nesting inefficiencies
¬10% additional consumption for Infusion Matrix. A consequence of additional resin
consumption in the core and the infusion delivery system
¬ 8% waste for Core Kitting. A consequence of kitting and nesting inefficiencies
¬20% additional consumption for Adhesive. A consequence of the difference
between theoretical and production bond line adhesive requirements
The BOM output from the blade design program is summarised in the table below.
Material Component
Infusion BOM
Prepreg BOM
Biax 600gsm (XE600)
960 m
588 m2
Triax 900gsm (YE900)
485 m
522 m2
Uni-directional (EGL1600)
1,451 m2
1,247 m2
Fleece surface veil
140 m
-
Core (PVC/SAN 80kg)
3.38 m3
3.38 m3
Structural adhesive
263 kg
263 kg
Gelcoat
70 kg
70 kg
2
2
2
Bill of Materials (composites)
In addition to the BOM for composite materials some assumptions have been made as
to the costs of other significant items in a blade. For vacuum consumables a separate
estimate has been provided for both infusion and prepreg blades. These assumptions
are summarised in the following table.
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology Item
BOM Cost (€)
Root Studs
1,800
Lightening Protection
1,500
Painting
3,000
Vacuum Consumables
€ 1,000/€ 500
Bill of Materials (additional items)
The composites BOM from the blade design output was then converted, using the
additional consumption factors and current market volume pricing (April 2009), to
produce the total composite cost for each model. The additional items were then added
to both models to give the final BOM cost for the blades. The results are summarised
in the table below.
Material Option
BOM Cost (€)
Infusion Technology
26,849
Prepreg Technology
30,312
Bill of Materials Cost (composites)
5.
Direct Costs
The direct manufacturing costs are estimated from analysis of each processing step
in the construction of the spar and shell components. For simplicity the manufacture
of the root section and the attachment of the root studs are included in the spar
manufacturing process. As there are many different solutions to the root section of
a blade, a general estimate of time and resource is provided for both the infusion and
prepreg blade models.
The labour required for each processing step is estimated together with the total
elapsed tool time for each step. The summary of labour and time required for shell
and spar component manufacture are summarised in the tables overleaf.
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology Process
Infusion
Prepreg
hrs
labour
hrs
labour
Mould Preparation
0.5
4
0.5
4
Gelcoat Application
0.5
12
0.5
12
Gelcoat Part-cure
0.5
1
0.5
1
Tissue Application
0.5
12
Fabric/Prepreg Lay-up
5
12
4
12
Vacuum Bag Application
1
4
0.5
4
Infusion
2.5
12
Cure
5
1
5
1
Consumable Removal
0.5
6
0.5
6
Adhesive Application
1
6
1
6
Adhesive Cure
5
1
5
1
Demould
1
6
1
6
Total Mould Time
23
18.5
Labour and Time for Shell Manufacture
Process
Infusion
Prepreg
hrs
labour
hrs
labour
Mould Preparation
0.5
4
0.5
4
Fabric/Prepreg Lay-up
4
6
3.5
6
Root Studs
5
2
5
2
Vacuum Bag Application
0.5
4
0.5
4
Infusion
1.5
6
Cure
5
1
5
1
Consumable Removal
0.5
4
0.5
4
Demould
1
4
1
4
Total Mould Time
18
16
Labour and Time for Spar Manufacture
In addition to the direct labour costs for component manufacture an estimate of the
labour for pre-kitting the fabric and prepreg prior to lay-up was also calculated. It was
assumed for the purposes of this model that the time and labour costs for pre-kitting
prepreg and dry fabric are identical. This gives an additional direct labour cost of €360
based on 2 people kitting an entire blade in 6 hours.
The total direct labour costs for blade manufacture were then calculated using a
standard labour rate of €30/hr. The total mould time for shell manufacture was also
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology 10
calculated as this is required to determine the output capability of the blade plant for
each composite technology route. The annual plant output is used to allocate indirect
costs and depreciation costs of infrastructure and tooling CAPEX, to each blade. The
total direct costs are summarised below.
Direct Labour (€)
Infusion Blade
Prepreg Blade
6,105
4,245
Total Direct Costs
6.
Indirect Costs
The indirect costs were determined by consideration of a manufacturing plant with
floor space for 4 blade production lines and the associated indirect labour of running a
plant. Annual blade production output was then used to allocate annual indirect costs
to each blade.
6.1
Indirect Labour
The annual indirect labour cost was calculated using the headcount assumptions in the
table below:
Position
No
Plant Manager
1
Maintenance Manager
1
Warehouse
1
Process Engineer
2
Quality Engineer
3
Electrical technician
1
Maintenance technician
1
Security
1
Production Manager
1
Planning and Logistics
1
Finance
1
Total
€770,000
Indirect Labour
6.2
Utility Costs
The utility costs include gas, electricity, rates, and telephone taken from a European
manufacturing plant with similar energy demands. It is assumed that because of the
higher curing temperatures of prepreg materials that the infusion process energy
consumption was 65% of the prepreg process consumption.
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology 11
Utility Costs (€/annum)
Infusion Blade
Prepreg Blade
549,500
695,500
Utility Costs
The total annual indirect costs are summarised below. These costs are allocated to the
blade as detailed in Section 8.
Indirect Cost (€/annum)
Infusion Blade
Prepreg Blade
1,319,900
1,465,500
Total Annual Indirect Costs
7.
CAPEX
The CAPEX has been divided into manufacturing plant infrastructure, and tooling and
associated manufacturing equipment.
7.1
Blade Plant Infrastructure
The CAPEX requirements for a manufacturing plant with 4 blade production line were
estimated using a nominal cost of 550 €/sqm for land and buildings. The estimates for
the required floor space are summarised in the table below.
Floor Space
sqm
Warehouse and Administration
1,000
Spars
4,000
Shells
6,000
Finishing
4,000
Total
15,000
Manufacturing Plant Dimensions
Mechanical and Electrical (M&E) CAPEX was estimated at 66% and 40% of the plant
land and buildings cost for prepreg and infusion technology respectively. The higher
M&E costs were assumed for prepreg technology due to the requirement for higher
control of environmental temperature for storage and use of prepreg materials, and
an increased level of automation. The total blade plant infrastructure CAPEX was
depreciated over 20 years. CAPEX requirements are summarised below.
Total Plant CAPEX (€)
Infusion Blade
Prepreg Blade
12,150,000
14,350,000
Plant CAPEX
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology 12
7.2
Tooling CAPEX
The tooling cost analysis is based on the standard master model approach where CNC
machined plugs are produced to enable the fabrication of female shell and spar moulds.
The two common approaches to design and manufacturing of blades are: Non structural
shells with the structural box spar (used in this study); and, Structural shells with
integrated spar cap and shear web connectors. The structural box spar design has some
benefits in the manufacturing process and also allows integration of the root section.
However, the consequence of having a female mould for the box spar increases the
tooling costs compared to the shear web approach. In this study for simplicity the
female moulded box spar manufacturing route has been adopted for both the infusion
and prepreg blade design.
The estimates in the following table for tooling CAPEX are based on the assumption that
there is a 50% premium for prepreg tooling due to the higher temperature performance
required.
Item
No
Item cost (€)
Total (€)
Shell Mould Set
4
650,000
2,600,000
Shell Plug
1
400,000
400,000
Spar Mould Set
4
300,000
1,200,000
Spar Plug
1
225.000
225,000
Kitting Machine
2
150,000
300,000
1,725,000
4,725,000
Prepreg
Total
Infusion
Shell Mould Set
4
433,290
1,733,160
Shell Plug
1
400,000
400,000
Spar Mould Set
4
199,980
799,920
Spar Plug
1
225,000
225,000
Kitting Machine
2
150,000
300,000
1,408,270
3,458,080
Total
Tooling CAPEX
The CAPEX was then depreciated over 5 years for tooling and plugs, and 10 years for the
kitting equipment to produce the annual depreciation rates in the table overleaf.
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology 13
Item
Depreciation (€/annum)
Prepreg
Shell Mould Set
520,000
Shell Plug
80,000
Spar Mould Set
240,000
Spar Plug
45.000
Kitting Machine
30,000
Total
915,000
Infusion
Shell Mould Set
346,600
Shell Plug
80,000
Spar Mould Set
160,000
Spar Plug
45.000
Kitting Machine
30,000
Total
661,616
Annual Depreciation Costs
8.
Allocation of Indirect and Depreciation Costs
The allocation of the annual indirect costs and the annual depreciation of the tooling
were based on the productivity of the blade factory. The productivity was calculated
from the shell mould cycle (the rate determining step for blade production), an operating
schedule of 49 weeks a year at 24/7, and at an efficiency of shell mould utilisation of
85%. The productivity data is summarised below:
Position
Infusion
Prepreg
Shell Mould Cycle Time (hrs)
23.0
18.5
Operational Days/Annum
340
340
Operational efficiency
85%
85%
Number of Moulds
4
4
Theoretical Blades/Annum
1,206
1,500
Blade Productivity
The annual indirect costs and depreciation were then allocated to each blade as
illustrated in the table overleaf. The higher productivity of the prepreg blade plant
reduces the allocation of indirect cost and depreciation to the individual blade cost.
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology 14
Infusion Blade
Prepreg Blade
Indirect Cost (€/blade)
1,094
977
Plant Deprecation (€/blade)
504
478
Tooling Deprecation (€/blade)
548
610
Total Allocation
2,146
2,065
Blade Cost Allocation
9.
Financial Results and Ratios
The calculation of the cost of manufacturing a blade has been obtained by the analysis
of a theoretical blade design and manufacturing model. The structural engineering
study has allowed the calculation of the BOM for both infusion and prepreg
manufacturing technology. A review of the manufacturing process, capital equipment
and the manufacturing facility has then enabled calculation of the direct and indirect
cost elements associated with blade manufacture. A summary of the costs in provided
in the table below:
Infusion Blade
Prepreg Blade
BOM Cost (€)
26,849
30,312
Direct Labour Costs (€)
6,105
4,245
Indirect Labour Costs (€)
1,094
977
Depreciation (€)
1,052
1,089
Total Blade Cost (€)
35,101
36,623
Blade Cost Summary
The calculation of the individual blade cost does not give the complete financial picture
on the differences between the two manufacturing routes. Due to the difference in
productivity of the two blade plants there will be an impact on the annual financial
performance and this is best demonstrated using a simple P&L financial analysis
and some common financial ratios. The main assumption in this analysis is that the
sales price for both blades in the market is the same at €40,000. The P&L analysis is
summarised in the table overleaf.
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology 15
Infusion Blade
Prepreg Blade
Gross Sales (€)
48,240,000
60,000,000
Material Costs (€)
32,380,180
45,467,912
Direct Costs (€)
7,362,630
6,367,500
Indirect Costs (€)
1,319,900
1,465,500
Depreciation (€)
1,269,116
1,632,500
EBIT (€)
5,908,174
5,066,588
EBIT %
12.2%
8.4%
Total CAPEX (€)
12,150,000
14,350,000
Asset Turn
3.97
4.18
ROTA (EBIT x AT)
49%
35%
Blade Plant P&L
Due to the higher productivity of the prepreg process of 1,500 blades per annum
compared to 1,206 for infusion, the allocation per blade of fixed indirect costs and the
recovery of depreciation are reduced. This offsets the higher material cost for prepreg
material and the associated additional depreciation from the more capital intensive
requirements of using prepreg materials. However, as the majority of the contribution
to blade cost is related to the materials the 35m infusion blade has a lower overall cost
base than that of the prepreg blade.
There are some additional cost items that are not included in this model that are difficult
to quantify. Repair costs have not been included but it is expected that the reliability of
the prepreg process will reduce rework expenditure compared to the infusion process.
The benefit of the weight saving of a prepreg blade is even more difficult to quantify as it
affects the service life of other components of the turbine. However, this weight benefit
can only be realised if the whole turbine system is optimised for light weight blades with
a fully integrated design approach.
Model validation
The indications are that the current market price for a 35m infused blade is approximately
$US 50,000. Using a 2009 year to date exchange rate of 1.30 for €/$, the blade market
price would be €38,500. This is 10% above the cost estimation for the infused blade in
the model and therefore shows a good correlation.
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology 16
10. Summary
A 35m blade design model was created to analyse the costs of blade manufacture using
two material manufacturing technologies, resin infusion and prepreg. The summary of
the analysis is as follows:
¬ The model validation shows very good correlation with current market pricing of
35m blades.
¬ The higher mechanical properties of the prepreg materials, and in particular the
compression strength of the unidirectional glass, enable the design of a lighter blade
with less material content than the infusion equivalent.
¬ The BOM costs for the prepreg blade are higher than those for the infused blade due
to the inherent additional costs associated with the prepreg manufacturing process
and the advanced resin systems used in prepregs.
¬ The Capital Expenditure for the prepreg process is higher than that of infusion due to
the higher temperature requirements of the tooling and the additional temperature
control requirements for the storage and use of prepreg materials.
¬ The prepreg blade manufacturing is more suited to automated processes and allows
increased productivity due to shorter manufacturing cycle times. These productivity
benefits partially offset the premium of prepreg material costs.
¬ The resultant financial analysis indicates that for a 35m blade design the infusion
process is marginally more profitable than a prepreg blade, although a prepreg
facility has a 24% productivity advantage.
The analysis has highlighted the main contributing factors of the manufactured cost
of a 35m wind turbine blade. What the analysis has not quantified is the effect of
manufacturing process on process reliability and repair frequency, and the in-service
performance and reliability of the blades. These lifetime service costs could become a
significant contributor to the overall cost and should be considered as a critical factor
when evaluating choices of manufacturing technology.
The current analysis was based on a 35m blade design as this was representative of
the mainstream blade size for 1.5MW WTG’s and therefore providing a good baseline
study. As blade lengths extend beyond 40m the design choices will become more
critical as weight and strength become limiting factors. Therefore, the selection criteria
for materials technology will move away from material cost towards performance for
the critical components of the blade structure. This will be realised by using higher
performance materials like prepreg and ultimately the switch from glass unidirectional
fibre to carbon fibre.
WE Handbook- 6- Blade Cost Analysis: Prepreg vs Infusion Material Technology 17