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Rotor blades next to a wind turbine
Photo: Jochen Tack / IMAGO
Wind power is one of the pillars of the energy transition.
In Germany there are around 28,000 plants on land and at sea that generate electricity from wind.
And according to Economics Minister Robert Habeck, there should be many more.
He aims to double the current capacity within eight years.
In recent years, these wind turbines have become larger and larger.
Some of the rotor blades are more than 50 meters long and weigh more than 25 tons.
But their durability is limited - with repairs, a service life of around 20 years is possible.
Then the question arises: what to do with the leftovers?
Recycling poses major hurdles for professionals.
According to a study by the Federal Environment Agency (UBA), around 20,000 tons of rotor blade waste that is difficult to recycle can be expected every year in this decade alone, after which the amount will increase.
UBA experts fear that rotor blades will not be properly disposed of or exported abroad for sham recycling.
Nasty mix of materials
The parts must withstand high loads during use.
»The tip of the wing then moves at up to 400 kilometers per hour.
Smaller wind turbines even reach half the speed of sound and more,” says Dieter Stapf from the Karlsruhe Institute of Technology (KIT).
Rain, hail, small grains of sand or salt water at sea develop an immense force that causes problems for the material and limits its durability.
In the coming years, more and more plants will be demolished because the machines have reached the end of their useful lives.
The good news: 90 percent of a wind turbine can be recycled, such as steel and concrete.
The bad: A rotor blade consists of a mix of materials that can hardly be broken down into its individual components.
Two half-shells glued together made of fiber composites, light and stable glass and carbon fibers are mixed with epoxy and vinyl resins, among other things.
There are also metals such as iron, copper, aluminum and lead as well as plastic foams, balsa wood and paint with titanium dioxide particles.
For a long time, mostly glass fiber reinforced material (GRP) was used, as it is also used for boat hulls.
Carbon fiber reinforced composites (CFRP) are used in larger systems – similar to modern aircraft construction.
According to the UBA, around 200 different carbon fibers are on the market.
Even with waste incineration, residues remain
So far there is no established solution for the disposal of CFRP waste, says Stapf.
»Carbon fibers are so persistent that they cannot be completely degraded in nature or in landfills and even in modern waste incineration plants.«
In principle, the material can be recovered and reused using thermal processes.
But then it is no longer as resilient as new fibers.
GRP waste is used at least in cement production - the plastic contained as fuel, the mineral fibers as a component of the resulting cement.
In Germany, as well as in Switzerland, the Netherlands and some European countries, there are landfill bans for discarded rotor blades.
CFRP waste is taken to a kind of interim storage facility, for how long it is unclear.
It's different in the USA, there are landfills for discarded rotor blades.
Experts fear that material originating from Europe could end up in such states.
Particles resembling asbestos fibers
The careful handling of the leaves also has health reasons.
When the material is destroyed, the finest particles are produced, which are similar to asbestos fibers and must never be inhaled.
Caution is required even when transporting carbon fiber reinforced wings.
When the systems are dismantled, the leaves are sawn into pieces six to twelve meters long on site - water mist or housing are used to prevent the fiber fragments from getting into nature.
According to the UBA report, the insoluble and inert products can probably accumulate in the environment and also in living beings.
Research projects are being carried out to recycle the problematic composite materials, and it is possible that building materials can be produced from the ground material.
But it will take some time before these concepts work on a large scale.
There are also critical voices about the balsa wood used.
It is one of the lightest woods, is corky and comes from balsa trees in the rain forests of Central and South America.
According to the UBA, more than 90 percent of the balsa wood harvested worldwide is currently used in wind turbines, the rest is used for yacht and model construction.
As wind energy expands around the world, balsa deforestation is increasing.
The potential for further use as a secondary raw material is great for balsa wood, but has so far been completely unused.
So far, filler in the leaves, like the wood, has not been separated from the glass fiber reinforced plastic, as the UBA report says.
The entire material mix is simply crushed and recycled in the cement works.
Several wind turbine manufacturers have already announced sustainability concepts and want to develop zero-waste systems in the coming decades.
How exactly this is supposed to work is still unclear.
dpa/joe
