In recent months, we have received repeated inquiries about erosion on wind turbines. Unfortunately, there are also increasing numbers of media reports in which the topic is presented in a highly distorted manner or even contains numerous false information.

This article therefore aims to provide an overview of the topic based on verifiable facts.

Different points of view

There are two main perspectives when considering the topic:

1. Owners and operators of wind turbines have always been interested in preventing erosion on rotor blades or in eliminating its effects through repairs. One reason is the reduced yield of turbines due to erosion. In addition, the repair costs are increasing if the area affected by erosion is not repaired quickly.
2. Another point of view has been discussed more and more in the media in recent months: Do particles that become detached from rotor blades cause a significant environmental pollution? Due to the current interest, this aspect shall be explained here.

Are rotor blades made of toxic chemicals?

Rotor blades consist of a few basic materials that are combined in a sandwich construction (i.e. layer by layer). Plastic foams or balsa wood are used as the sandwich core.

The shell of the rotor blade is made of glass fiber reinforced plastic. Carbon fibers are only used to a small extent in rotor blades because of their high price. Only the so-called spar caps on some rotor blades are made of carbon fibers. However, erosion only occurs at the "leading edge" of the blade, where raindrops and particles in the air hit the blade at high speed. No carbon fiber spar caps are installed in this area. It is therefore completely misleading when some reports say that tiny carbon fiber particles are released into the environment by wind turbines. This emission does not occur at all. Erosion only occurs at the leading edge of the blades and carbon fibers are never installed there.

The reinforcing fibers are embedded in a plastic matrix. This is either epoxy resin or unsaturated polyester resin. When processing these resins in their liquid state, strict health protection must be observed. However, when cured, they are completely non-toxic. This is why these materials are also popular in the hobby and creative sectors. [1][2]

The entire rotor blade is provided with a surface coating to protect it from environmental influences. This consists of a top coat, e.g. based on polyurethane or epoxy resin. So-called gel coats based on unsaturated polyester are also sometimes used. These coatings also have no harmful properties when cured. [1] [3]

How much material is removed by erosion?

Nobody has collected and weighed the abrasion of rotor blades yet. It is unclear how such an investigation can be carried out in practice.

However, the amount of material removed can be estimated based on the damage pattern. As mentioned, erosion only occurs on the leading edge of the rotor blade. It is the flank that cuts through the air at high speed. The affected surface can be narrowed down even more precisely. In fact, only about the outer third of the leading edge (near the blade tip) is affected by erosion [see Fig. 2]. The circumferential speed is the highest in this area. This is because the tip of the rotor blade travels a much greater distance per second than, for example, the flange. Therefore, particles near the blade tip hit the blade at the highest speed and erosion is greatest there.

cp.max has inspected and repaired rotor blades of thousands of wind turbines all over the world over the past 25 years. During this work, we have naturally also gained a lot of experience about the size and severity of erosion damages. This knowledge forms the basis for the following calculation.

Initial values:

- A blade length of 60 m is assumed. Current rotor blades can be significantly longer, but most existing turbines have a shorter blade length.

-The width of the erosion area is very limited at around 15 cm. Only a narrow strip on the leading edge of the blade is affected.

- The depth of erosion is assumed to be 5 mm. This corresponds to very strong erosion, which does not occur on all blades.

- The average density of the removed material is assumed to be 1,500 kg/m³.

 

Mass loss of a wind turbine in 20 years:

m = 20 m * 0.15 m * 0.005 m * 3 blades * 1500 kg/m³

     = 68 kg erosion per wind turbine in 20 years

     = 3.4 kg erosion per wind turbine in one year

It is noticeable that this value is much lower than many claims that can be found in current discussions. (Some of them talk about more than 100 kg per turbine per year.) [5] Anyone who has already seen numerous erosion damages on rotor blades will be able to comprehend this simple calculation presented here. And even if this estimate is a little too low, the magnitude will correspond to reality.

In contrast, sources that sometimes indicate erosion amounts that are more than 30 times higher fail to provide any evidence.

 

On a personal note:

Of course, cp.max, as a representative of the wind industry, could be accused of a lack of objectivity. However, ouraim is to provide fact-based information on wind energy issues. We do not deny that wind energy (like almost every human activity) has some negative impacts on the environment. Nevertheless, wind energy, along with other renewable energy sources, is one of the most environmentally friendly and cost-efficient ways of generating energy. In other words: We currently have no cleaner energy source.

 [1] https://www.umwelt-online.de/recht/arbeitss/uvv/bgi/655a.htm 
 [2] https://epoxid1.de/
 [3] https://www.bfr.bund.de/cm/343/XXVIII-Vernetzte-Polyurethane-als-Klebeschichten-fuer-Lebensmittelverpackungsmaterialien.pdf
 [4] https://windenergietage.de/2021/wp-content/uploads/sites/6/2021/11/29WT11_F17_1320_KWE_Erosion-am-Rotorblatt_Liersch.pdf
 [5] https://blackout-news.de/aktuelles/die-unsichtbare-umweltbelastung-durch-den-abrieb-an-windkraftanlagen/
 [6] Chemie in unserer Zeit (2021), Volume: 55, Issue: 6, Pages: 406-421
https://onlinelibrary.wiley.com/doi/abs/10.1002/ciuz.202100012

 

Additional information:

Fact check of the Bundesverband Windenergie: 
https://www.wind-energie.de/fileadmin/redaktion/dokumente/Aktuelles/Faktenchecks/20240801_BWE-Faktencheck_-_Erosion_an_Rotorblaettern.pdf