Design and development of megawatt wind turbines - Wind Power Generation and Wind Turbine Design - page 221

Figure 18: Blade mass - 10-turbine analysis compared to industry study set.

sketch /C/ and for winds above rated wind speed. The maximum defl ection outline
shows another view of the importance for the minimum tower clearance discussed
earlier in this chapter.
Figure 18 shows the 10-turbine analysis group (i.e. calculated), a curve fi t for
the industry study set using GFRP, and the industry study set for carbon spar and
GFRP hybrids. Clearly if one just scaled today's average technology to 10 MW,
the individual blade mass would be in excess of 40 tonnes. Since the larger
machines in the industry study set tend to incorporate a carbon spar or utilize some
form of an advanced GFRP construction, the industry trend projects the 10 MW
blade to be less than 40 tonnes. A carbon

− GFRP hybrid blade should be able to

achieve 32 34 tonnes per blade. Based on the past industry progress going from

1 to 5 MW, and with new technology yet to be discovered, it may be possible for a
10 MW blade to be designed in the 25 tonne range.
The majority of today's blades are made from GFRP incorporating either a box
spare or shear web construction. Figure 19 shows the typical mass and cost break-
down for an average sample of blades incorporating shear web construction [26].
The glass fi bre and epoxy or vinyl resin comprises the vast majority of the mass.
Manufacturing these blades requires a large amount of man-hours such that labour
accounts for nearly 1/3 of the total cost for a blade.
Today's mainstream blade construction technology requires signifi cant invest-
ment in mould tooling to form, cure and assemble large WT blades. A steel sub-
frame and backing structure is used build-up the basic upper and lower mould
shell tools. Curing heaters (electrical or temperature controlled fl uid channels) are
arranged throughout the surfaces prior to establishing the fi nal mould surfaces.
These are typically completed using a prototype blade (i.e. plug) to provide a form
for the fi nal tool surface made from high temperature epoxy resin within the upper

−