Object

Wind turbine blade

The largest composite structures made, built to last twenty-five years, and there is still no good answer to what happens to them afterwards.

A modern wind turbine blade is a hollow composite beam up to a hundred metres long, made of glass or carbon fibre in an epoxy or polyester matrix, with a load-bearing spar inside a shaped shell and balsa or foam cores in the panels.

The engineering constraint is fatigue rather than strength. A blade turns perhaps two hundred million times in its life, and every rotation is a full load cycle from its own weight alone, plus gusts, wind shear and tower shadow. It is one of the most heavily fatigue-loaded structures built.

Size is the economics. Power scales with the square of blade length, so blades have grown continuously, and at current lengths they are close to the limit of what can be transported by road at all.

History

Early blades were steel and aluminium and failed in fatigue. Glass fibre composites took over from the 1980s because a composite's fatigue behaviour under this kind of loading is far better than metal's, and because the shape is easier to make.

Carbon fibre appears in the spar caps of the longest blades, where the stiffness is needed to stop the tip striking the tower, and is used sparingly because of cost.

Cultural significance

The blade is where the material argument about renewable energy actually sits, and it is not the one usually made. The turbine is overwhelmingly steel and concrete by mass; the blade is the part with no established end-of-life route.

A thermoset composite cannot be melted and reprocessed. Retired blades are cut up and landfilled, ground into filler, or co-processed in cement kilns where the glass becomes feedstock and the resin becomes fuel — the best current option and not recycling. Cleavable epoxy chemistries and thermoplastic resin systems are being developed for exactly this, and none is yet standard. The first large cohort of blades is now retiring, so the problem has arrived on the schedule it was always going to.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

is made of

Epoxy resin — material · the matrix, and the reason a retired blade cannot be melted down
Carbon fibre — material · in the spar caps of the longest blades, where stiffness stops the tip striking the tower

is made using

7000 series aluminium alloy — alloy · in the root fittings and hub hardware rather than the blade shell

is used in

Energy generation — industry · and it is the part of a turbine with no established end-of-life route, where the tower and foundation are steel and concrete

Sources

Material World
Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Wind turbine blade back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

Wind turbine blade → is made of (in the spar caps of the longest blades, where stiffness stops the tip striking the tower) → Carbon fibre → is composed of (carbonised from a polymer precursor until little but carbon remains) → Carbon → is produced by (as synthetic graphite, made by driving the reaction past silicon carbide until the silicon boils away and leaves the carbon behind) → Acheson process → takes as input (sand and coke, heated to 2,500 °C, which is how silicon carbide has been made since 1893) → Sand → is composed of (almost everywhere, because quartz is what is left when everything else in a rock has weathered away — though a volcanic beach is basalt grains and a tropical one is broken shell) → Quartz
Wind turbine blade → is made of (the matrix, and the reason a retired blade cannot be melted down) → Epoxy resin → is produced by (the resin is made first and the network second — cure is a polymerisation carried out by the user rather than the manufacturer) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite
Wind turbine blade → is made using (in the root fittings and hub hardware rather than the blade shell) → 7000 series aluminium alloy → is produced by (zinc and magnesium into aluminium, then solution treated and aged — the strength comes from the heat treatment, not from the melt) → Alloying and melting → takes as input (the base metal of both brass and bronze) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (roasted to drive off sulfur, then reduced to copper) → Chalcopyrite
Wind turbine blade → is made of (in the spar caps of the longest blades, where stiffness stops the tip striking the tower) → Carbon fibre → is produced by (polyacrylonitrile filament, first oxidised in air at 200 to 300 °C so it will not melt, then carbonised above 1,000 °C — and the final temperature sets the stiffness, because it sets how ordered the carbon is) → Pyrolysis → takes as input (to make coke, and the coal gas that came off it lit European cities for a century as the by-product) → Coal → is sourced from (every coal seam in the world was a peat bog. Bury it, compress it, heat it, and it passes through lignite and bituminous coal to anthracite, losing water and volatiles at each step) → Peat → is sourced from (waterlogging is the whole mechanism: a bog is anoxic below a few centimetres, so the organisms that would decompose the plant matter cannot work, and it accumulates instead) → Water
Wind turbine blade → is made of (the matrix, and the reason a retired blade cannot be melted down) → Epoxy resin → is produced by (the resin is made first and the network second — cure is a polymerisation carried out by the user rather than the manufacturer) → Polymerisation → takes as input (as tetrafluoroethylene, which is where a substantial share of industrial fluorine chemistry ends up) → Fluorine → is produced by (electrolysis of potassium bifluoride, which is molten and conducts — there is no chemical oxidant strong enough to displace fluorine from a compound, so electricity is the only route and always has been) → Molten salt electrolysis → takes as input (after concentration, as one of the two routes to lithium chloride) → Lepidolite
Wind turbine blade → is made of (the matrix, and the reason a retired blade cannot be melted down) → Epoxy resin → is produced by (the resin is made first and the network second — cure is a polymerisation carried out by the user rather than the manufacturer) → Polymerisation → takes as input (into polyethylene, and via ethylene dichloride into PVC — the two highest-tonnage plastics between them) → Ethylene → is produced by (the principal product, and the largest-tonnage organic chemical made anywhere) → Steam cracking → takes as input (the European and Asian cracker feed; North American crackers mostly run on ethane from natural gas instead, and make a different product slate as a result) → Naphtha

These are the most distinct paths back. Wind turbine blade can be traced through others besides.

Downstream — what it becomes

Wind turbine blade → is used in (and it is the part of a turbine with no established end-of-life route, where the tower and foundation are steel and concrete) → Energy generation