How a wind-turbine blade is built
A modern blade is 60–115 m of composite that must survive a hundred million bends over 20 years, in rain, ice and salt. How it's designed, what it's made of, and why it's so hard to recycle.
The biggest composite parts on earth
A modern wind-turbine blade is 60 to 115 metres long — longer than a football pitch — and there are three on every turbine, across thousands of turbines. By sheer mass, blades are among the largest single uses of composite material anywhere.
A blade has to be three things at once: light, so the tower and bearings can carry and spin it; stiff, so it does not flex far enough to strike the tower; and extraordinarily durable, surviving of order a hundred million fatigue cycles over a twenty- to twenty-five-year life, out in rain, ice, salt and ultraviolet the whole time.
Inside a blade
A blade is a long hollow aerodynamic shell with a load-bearing spar inside, built much like an aircraft wing. The spar caps — thick bands of fibre running the length of the blade, one near the top surface and one near the bottom — carry the bending load as the wind pushes the blade; they are the stiffest, most heavily loaded part.
Shear webs connect the two caps like the vertical web of an I-beam, carrying the shear between them. The aerodynamic skins give the airfoil its shape and are usually a sandwich — thin composite faces over a light foam or balsa core — which resists buckling of the large, thin panels at very little weight.
How it is made
Almost all large blades are made by resin infusion. Dry glass fibre is laid up into one enormous mould half — the whole suction side, say — sealed under a vacuum bag, and liquid epoxy or vinyl-ester resin is drawn through the dry fibre by vacuum and then cured. It is the only practical way to make a part this large in a single shot.
Two half-shells are moulded this way, the shear webs are bonded in, and the halves are glued together down the leading and trailing edges to make the finished hollow blade. The scale is hard to overstate: the moulds are among the largest single tools in any industry.
Carbon where it counts
Glass fibre is the workhorse of blades — cheap, tough and stiff enough for most of the structure. But as blades grow longer, their own weight and the stiffness needed to clear the tower become limiting, and the numbers start to favour carbon fibre, which is far stiffer for its weight.
So the longest blades use carbon in the spar caps, where stiffness matters most, while keeping glass everywhere else to control cost. It is exactly the trade aerospace makes between glass and carbon — only here it plays out on a hundred-metre part built to a utility budget rather than an aerospace one.
The recycling problem
A thermoset glass blade cannot be melted down and reused the way a thermoplastic bottle can — the resin is permanently cross-linked. Today most retired blades are cut into sections and either landfilled or ground up to be burned as fuel in cement kilns.
It is an honest and awkward fact: the very mass that harvests clean energy at the top of the tower is the mass that is hardest to retire cleanly at the end. The industry is working the problem from both ends — recyclable epoxy resins that can be chemically broken down, and thermoplastic blades that can be re-melted — but for now it is the real environmental cost hiding behind a very green machine.
1. Which part of a wind-turbine blade carries most of the bending load?
2. How are most large wind-turbine blades manufactured?
3. Why do the longest blades use carbon fibre in the spar caps?