Comparative Cost Study of a 35m Wind Turbine Blade using Infusion and Prepreg Materials TechnologyIntroduction 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 Once the fabric stack is infused with resin the temperature is raised. Prepreg Processing Schematic WE Handbook. typically between 50 to 70 °C. to accelerate and complete the curing process.6. 1.1.Therefore the speed of an infusion is increased with increasing permeability of the fabric stack (D).Blade Cost Analysis: Prepreg vs Infusion Material Technology . and lay-up into the mould without any transfer or contamination from the resin. The resins used to manufacture prepregs have inherently high viscosities and are therefore solid at room temperature allowing easy handling. increased with increasing pressure gradient (ΔP).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. Once in the mould prepregs are then cured under vacuum at elevated temperatures. cutting. 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. typically between 80 and 120 °C for industrial applications. taking a financial approach to the model enables the clear identification of key parameters and their influence on the cost of a blade. 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. higher levels of automation. Return on Total Assets Each step is described in detail below with assumptions and presentation of the comparative results. The structural arrangement for both infusion and prepreg blades is a structural box spar section.e. Summary of Methodology The blade model was developed to provide a financial analysis of the two manufacturing technologies. the requirement for chilled storage and shipping. WE Handbook.6. 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.Blade Cost Analysis: Prepreg vs Infusion Material Technology . and carbon fibre utilization (infusion of carbon fibre is increasingly seen as unviable). 3. the increased processing temperatures required for prepregs can also increase tooling costs. as a consequence of the inclusion of higher performance resins. prepregs are more expensive per kg than the equivalent resin and reinforcement in an infusion process. i. Profit. However. 2. However. The blade has no pre-bend. and the additional processing step of “prepregging” . which will have a significant effect on the life-cycle cost of a blade. and fast deposition rates and automation capability. controlled fibre alignment in unidirectional products (a key benefit for mechanical performance).1 Blade Structural Design Blade Overview The blade model is based on a 35m blade manufactured using a shell and box spar structural arrangement. the model only provides analysis on blade manufacturing and does not consider service life and performance. the primary structural member. Unfortunately.Prepregs are often supplied in roll format and provide the benefits of highly controlled resin content. higher performance resins than with infusion. higher mechanical performance. Furthermore. Asset Turn. 3. consisting of two unidirectional spar caps and biaxial sandwich shear webs. However. prepregs provide some benefits with respect to process reliability and repeatability. this target deflection has been adjusted to ensure that all blade designs meet or exceed the required minimum ultimate strength criteria. towards the tower. The box spar supports two aerodynamic shell fairings joined at the leading and trailing edges of the blade.The root section is integrated into the box spar. The fatigue strength has not been considered for the stiffness based comparative study. has been chosen to be met by both design options. In this case. a target flapwise tip deflection. As a result of this adjustment the blade stiffness is significantly higher than would be required for an optimised blade design. WE Handbook.6.Blade Cost Analysis: Prepreg vs Infusion Material Technology . Blade Construction 3. Furthermore. 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.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. the characteristic value will be very close to the mean test result. this change is small compared to the effect of the variation coefficient. This is calculated by dividing the material characteristic value. However. v is the variation coefficient. bending moments and torques.000): WE Handbook. An aeroelastic model has been used to calculate the corresponding section shear forces. Note that no aeroelastic iteration has been performed to assess the effects of final stiffness and inertia distributions on the above aerodynamic loads. The partial safety factors generated by GL are as follows where N is the number of fatigue cycles (10. If the test results are very reproducible. Therefore. Buckling stability has been restricted to spot checks. The partial safety factor. giving a low standard deviation and variation coefficient. the greater the variation in the test results (large standard deviation and variation coefficient) the lower the characteristic value.35 is used. 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. Rk. is determined from a statistical equation that quantifies the reliability of the test data. by the partial safety factor.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. γMx. The characteristic value will also decrease as the number of tests decreases.5. 3. Ultimate design loads have been obtained by factoring these up by the required Germanischer Lloyd (GL) general load factor of 1. Rd. towards and away from the tower.Blade Cost Analysis: Prepreg vs Infusion Material Technology . Rk.6. with and against rotation directions.4 Design Allowables The value of the allowable stress/strain is known as the design strength of the material. is calculated separately for the general static strength/stiffness analysis and the fatigue analysis. as well as edgewise bending. The partial safety factor is obtained using Equation 3: (Equation 3) where for both static and fatigue analysis a general safety factor of γM0 = 1.000. and n is the number of tests. γMx: Rd = Rk /γMx (Equation 1) The characteristic value. 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. from Equation 1.Blade Cost Analysis: Prepreg vs Infusion Material Technology .8 GL Partial Safety Factor 2.02% -0. 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.18 Design Allowable 1. WE Handbook.Factor General Safety Factor Ageing – C1 Temperature – C2 Manufacture – C3 Post-cure – C4 General Strength 1.8 42. the maximum design allowable strength that can arise in a blade laminate during operation is calculated.0 Total Material Safety Factor GL Partial Safety Factors 2.35 1.0 37.44/8.0/1.18 Therefore. Material Prepreg UD 1600g Prepreg UD 1600g Infusion UTE 800g Infusion UTE 800g Prepreg UD 1600g Infusion UTE 800g Test Tensile Strength Compressive strength Tensile Strength Compressive strength Fatigue (10e7) Fatigue (10e7) Char. 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.1 (U/D or stitched) 1. and due to the high fibre alignment in collimated unidirectional prepreg.98% -0. Some typical values are illustrated in the table below.8 37.6.30% 0.74% 0. 3.21 2.0 37. Polynomial curve fitting functions are used to provide a convenient analytical representation of the blade geometry.1 1.35 1.35 N1/10/N1/14 (E-Glass or Carbon) 1. Slender beam theory assumptions are applicable to the BDP model (no shear deformation of cross sections). Strength (MPa) 952 687 821 511 952 821 Modulus 42.5 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.61% 0.21 7. The net result is the designer can utilize the higher design allowables for prepreg and reduce the material content in the blade.44 8.21 2. This is a consequence of the higher performance resin in prepregs preventing fibres from buckling.0 Fatigue 1.1 1.21 7.0 42.1 1. 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.21 2. Blade Section and Elements Each zone along the blade has a laminate input and laminate properties are computed based on classical laminate theory. The centre of gravity (CG) position and detailed mass distribution are also calculated. WE Handbook. Each blade section is divided into 12 elements.6 Results The design outputs for the blade are summarised in the following table. Bending stiffnesses EIxx. These elements are grouped into a number of laminate zones as shown in Figure 4. A similar calculation is carried out for the shear centre and torsional stiffness properties (GJ) of each section.6.The blade model is divided into a large number of sections with intermediate subsections (typical section spacing 0. spacing 1m).Blade Cost Analysis: Prepreg vs Infusion Material Technology . 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. EIyy and EIxy are then calculated by summing up contributions from each element around the section. It should be noted that no load iteration steps were made following the determination of the mass and stiffness distributions. 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) 3.2m) created by linear interpolation between input sections (typ. 38 m3 263 kg 70 kg 1.Blade Design Parameter Tip Deflection (m) Lead-Lag Deflection (m) Flapwise Frequency (Hz) Blade Mass (kg) Rotational Inertia (kgm2) Blade Design Output Infusion 2.Blade Cost Analysis: Prepreg vs Infusion Material Technology . WE Handbook.451 m2 140 m 2 3. and this needs factoring in to the BOM.6.142 6.87 x106 Prepreg 2.247 m2 3. These assumptions are summarised in the following table. For vacuum consumables a separate estimate has been provided for both infusion and prepreg blades.53 0. The assumptions used in the model to determine the gross material requirements are as follows: ¬ 5% additional consumption for Dry Fabrics and Prepreg.27 1.186 4. Material Component Biax 600gsm (XE600) Triax 900gsm (YE900) Uni-directional (EGL1600) Fleece surface veil Core (PVC/SAN 80kg) Structural adhesive Gelcoat Bill of Materials (composites) Infusion BOM 960 m2 485 m 2 Prepreg BOM 588 m2 522 m2 1.38 m3 263 kg 70 kg In addition to the BOM for composite materials some assumptions have been made as to the costs of other significant items in a blade. A consequence of kitting and nesting inefficiencies ¬ 10% additional consumption for Infusion Matrix.53 0. 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. A consequence of additional resin consumption in the core and the infusion delivery system ¬ 8% waste for Core Kitting.359 4.987 3. A consequence of kitting and nesting inefficiencies ¬ 20% additional consumption for Adhesive.79 x106 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.21 1. 849 30. a general estimate of time and resource is provided for both the infusion and prepreg blade models.000/€ 500 Bill of Materials (additional items) The composites BOM from the blade design output was then converted.800 1.000 € 1.312 Material Option Infusion Technology Prepreg Technology Bill of Materials Cost (composites) 5. The results are summarised in the table below.Item Root Studs Lightening Protection Painting Vacuum Consumables BOM Cost (€) 1.Blade Cost Analysis: Prepreg vs Infusion Material Technology . For simplicity the manufacture of the root section and the attachment of the root studs are included in the spar manufacturing process.6. Direct Costs The direct manufacturing costs are estimated from analysis of each processing step in the construction of the spar and shell components. As there are many different solutions to the root section of a blade.500 3. WE Handbook. The additional items were then added to both models to give the final BOM cost for the blades. to produce the total composite cost for each model. The summary of labour and time required for shell and spar component manufacture are summarised in the tables overleaf. using the additional consumption factors and current market volume pricing (April 2009). The labour required for each processing step is estimated together with the total elapsed tool time for each step. BOM Cost (€) 26. 5 0.5 Prepreg labour 4 6 2 4 1 4 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.5 5 1 2. This gives an additional direct labour cost of €360 based on 2 people kitting an entire blade in 6 hours.5 5 0.5 hrs 0.5 1.5 3.5 4 0.5 0.5 1 5 1 23 Infusion labour 4 12 1 12 12 4 12 1 6 6 1 6 5 0.5 1 5 1 18.5 0.5 5 0.5 1 Infusion labour 4 6 2 4 6 1 4 4 5 0.5 5 0.Process hrs Mould Preparation Gelcoat Application Gelcoat Part-cure Tissue Application Fabric/Prepreg Lay-up Vacuum Bag Application Infusion Cure Consumable Removal Adhesive Application Adhesive Cure Demould Total Mould Time 0.5 1 hrs 0.5 0.6.5 4 5 0. The total mould time for shell manufacture was also WE Handbook. It was assumed for the purposes of this model that the time and labour costs for pre-kitting prepreg and dry fabric are identical.5 Prepreg labour 4 12 1 12 4 1 6 6 1 6 Labour and Time for Shell Manufacture Process hrs Mould Preparation Fabric/Prepreg Lay-up Root Studs Vacuum Bag Application Infusion Cure Consumable Removal Demould 0.Blade Cost Analysis: Prepreg vs Infusion Material Technology 10 . The total direct labour costs for blade manufacture were then calculated using a standard labour rate of €30/hr.5 0. WE Handbook.calculated as this is required to determine the output capability of the blade plant for each composite technology route.245 6. The annual plant output is used to allocate indirect costs and depreciation costs of infrastructure and tooling CAPEX. to each blade.105 6. Annual blade production output was then used to allocate annual indirect costs to each blade. The total direct costs are summarised below. Infusion Blade Direct Labour (€) Total Direct Costs Prepreg Blade 4. electricity.1 Indirect Labour The annual indirect labour cost was calculated using the headcount assumptions in the table below: Position Plant Manager Maintenance Manager Warehouse Process Engineer Quality Engineer Electrical technician Maintenance technician Security Production Manager Planning and Logistics Finance Total Indirect Labour No 1 1 1 2 3 1 1 1 1 1 1 €770.6.Blade Cost Analysis: Prepreg vs Infusion Material Technology 11 . 6. and telephone taken from a European manufacturing plant with similar energy demands. rates. 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.2 Utility Costs The utility costs include gas. 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.000 6. Infusion Blade Total Plant CAPEX (€) Plant CAPEX WE Handbook. The total blade plant infrastructure CAPEX was depreciated over 20 years.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.350. and an increased level of automation.000 4. and tooling and associated manufacturing equipment.465.000 6.500 The total annual indirect costs are summarised below. CAPEX The CAPEX has been divided into manufacturing plant infrastructure. Floor Space Warehouse and Administration Spars Shells Finishing Total Manufacturing Plant Dimensions sqm 1.Infusion Blade Utility Costs (€/annum) Utility Costs Prepreg Blade 695.000 15.6.500 1.000 4. 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.150.900 7.000 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.000 12. Infusion Blade Indirect Cost (€/annum) Total Annual Indirect Costs Prepreg Blade 1.319. 7.000 . CAPEX requirements are summarised below. The estimates for the required floor space are summarised in the table below.Blade Cost Analysis: Prepreg vs Infusion Material Technology 12 Prepreg Blade 14.500 549. These costs are allocated to the blade as detailed in Section 8. 000 1. In this study for simplicity the female moulded box spar manufacturing route has been adopted for both the infusion and prepreg blade design.290 400.000 225.920 225.725.000 300. However. The two common approaches to design and manufacturing of blades are: Non structural shells with the structural box spar (used in this study).000 3. and 10 years for the kitting equipment to produce the annual depreciation rates in the table overleaf. The structural box spar design has some benefits in the manufacturing process and also allows integration of the root section.000 225. and.000 400.000 2.000 No Item cost (€) Total (€) Infusion Shell Mould Set Shell Plug Spar Mould Set Spar Plug Kitting Machine Total Tooling CAPEX 4 1 4 1 2 433.000 300.7.160 400. the consequence of having a female mould for the box spar increases the tooling costs compared to the shear web approach.000 4.200.2 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.000 1.000 199.270 1.000 799.000 150.000 150.600.458.000 300.000 1.Blade Cost Analysis: Prepreg vs Infusion Material Technology 13 .980 225. Item Prepreg Shell Mould Set Shell Plug Spar Mould Set Spar Plug Kitting Machine Total 4 1 4 1 2 650.725.080 The CAPEX was then depreciated over 5 years for tooling and plugs.000 400.733. WE Handbook.6. Structural shells with integrated spar cap and shear web connectors. 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.408. 5 340 85% 4 1.0 340 85% 4 1.600 80. The productivity was calculated from the shell mould cycle (the rate determining step for blade production). The higher productivity of the prepreg blade plant reduces the allocation of indirect cost and depreciation to the individual blade cost.000 240.000 915.6. and at an efficiency of shell mould utilisation of 85%.000 80.000 Infusion Shell Mould Set Shell Plug Spar Mould Set Spar Plug Kitting Machine Total Annual Depreciation Costs 346.206 Prepreg 18.000 45.Blade Cost Analysis: Prepreg vs Infusion Material Technology 14 .000 45. The productivity data is summarised below: Position Shell Mould Cycle Time (hrs) Operational Days/Annum Operational efficiency Number of Moulds Theoretical Blades/Annum Blade Productivity Infusion 23. 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.000 160.500 The annual indirect costs and depreciation were then allocated to each blade as illustrated in the table overleaf.Item Prepreg Shell Mould Set Shell Plug Spar Mould Set Spar Plug Kitting Machine Total Depreciation (€/annum) 520. WE Handbook.616 8.000 661.000 30.000 30. an operating schedule of 49 weeks a year at 24/7 . Blade Cost Analysis: Prepreg vs Infusion Material Technology 15 .105 1.101 The calculation of the individual blade cost does not give the complete financial picture on the differences between the two manufacturing routes. A summary of the costs in provided in the table below: Infusion Blade BOM Cost (€) Direct Labour Costs (€) Indirect Labour Costs (€) Depreciation (€) Total Blade Cost (€) Blade Cost Summary Prepreg Blade 30.000. 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.849 6. 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.094 504 548 2.052 35.245 977 1. The P&L analysis is summarised in the table overleaf.6.623 26. WE Handbook.065 1. A review of the manufacturing process.089 36. The main assumption in this analysis is that the sales price for both blades in the market is the same at €40. The structural engineering study has allowed the calculation of the BOM for both infusion and prepreg manufacturing technology.146 9. capital equipment and the manufacturing facility has then enabled calculation of the direct and indirect cost elements associated with blade manufacture.Infusion Blade Indirect Cost (€/blade) Plant Deprecation (€/blade) Tooling Deprecation (€/blade) Total Allocation Blade Cost Allocation Prepreg Blade 977 478 610 2.312 4.094 1. 500 blades per annum compared to 1.500 5. the blade market price would be €38.000 45.632. However.000.Infusion Blade Gross Sales (€) Material Costs (€) Direct Costs (€) Indirect Costs (€) Depreciation (€) EBIT (€) EBIT % Total CAPEX (€) Asset Turn ROTA (EBIT x AT) Blade Plant P&L Prepreg Blade 60. Model validation The indications are that the current market price for a 35m infused blade is approximately $US 50. The benefit of the weight saving of a prepreg blade is even more difficult to quantify as it affects the service life of other components of the turbine.174 12. as the majority of the contribution to blade cost is related to the materials the 35m infusion blade has a lower overall cost base than that of the prepreg blade. Repair costs have not been included but it is expected that the reliability of the prepreg process will reduce rework expenditure compared to the infusion process.000 3. This offsets the higher material cost for prepreg material and the associated additional depreciation from the more capital intensive requirements of using prepreg materials.380.116 5.150.500.2% 12.467.908.367.900 1.500 1.465.350.066. the allocation per blade of fixed indirect costs and the recovery of depreciation are reduced. However.30 for €/$.319.000 32. WE Handbook.97 49% Due to the higher productivity of the prepreg process of 1.Blade Cost Analysis: Prepreg vs Infusion Material Technology 16 .000.206 for infusion. There are some additional cost items that are not included in this model that are difficult to quantify. Using a 2009 year to date exchange rate of 1.000 4.362. this weight benefit can only be realised if the whole turbine system is optimised for light weight blades with a fully integrated design approach.4% 14.588 8.240.500 1.180 7.912 6.630 1.6.269.18 35% 48. This is 10% above the cost estimation for the infused blade in the model and therefore shows a good correlation. 5MW WTG’s and therefore providing a good baseline study. Summary A 35m blade design model was created to analyse the costs of blade manufacture using two material manufacturing technologies. ¬ The prepreg blade manufacturing is more suited to automated processes and allows increased productivity due to shorter manufacturing cycle times. resin infusion and prepreg. These productivity benefits partially offset the premium of prepreg material costs. The current analysis was based on a 35m blade design as this was representative of the mainstream blade size for 1. and the in-service performance and reliability of the blades.6. ¬ 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.Blade Cost Analysis: Prepreg vs Infusion Material Technology 17 . enable the design of a lighter blade with less material content than the infusion equivalent.10. and in particular the compression strength of the unidirectional glass. ¬ The higher mechanical properties of the prepreg materials. Therefore. The analysis has highlighted the main contributing factors of the manufactured cost of a 35m wind turbine blade. although a prepreg facility has a 24% productivity advantage. This will be realised by using higher performance materials like prepreg and ultimately the switch from glass unidirectional fibre to carbon fibre. The summary of the analysis is as follows: ¬ The model validation shows very good correlation with current market pricing of 35m blades. the selection criteria for materials technology will move away from material cost towards performance for the critical components of the blade structure. What the analysis has not quantified is the effect of manufacturing process on process reliability and repair frequency. ¬ The resultant financial analysis indicates that for a 35m blade design the infusion process is marginally more profitable than a prepreg blade. As blade lengths extend beyond 40m the design choices will become more critical as weight and strength become limiting factors. 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 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. WE Handbook.