Blow up and burn

 

The figures are impressive: there are more than 24,000 wind turbines in Germany. They cover about ten percent of Germany's electricity consumption. However, parallel to the ongoing expansion of wind energy, the operation of old turbines usually ends after 20 to 25 years for economic reasons. This is due, among other things, to the fact that subsidies under the Renewable Energy Sources Act (EEG) will then end. If the wind turbine operator has decided to cease operations, it must dismantle the turbine. As a rule, this is stipulated in the conditions of the building permits.

 

Between January and June 2014 alone, 102 wind turbines were decommissioned. They made way for more powerful successors. And the trend is rising. But what should be done with the old plants? Is there a risk of a glut of materials that are difficult to recycle? Just one example: From 2040 onwards, around 30,000 tonnes of rotor blades will have to be disposed of annually in Germany alone.

 

The dismantling of a wind turbine is just as complex as its construction. Huge cranes hoist rotor blades and the gondola, which weighs several tons, from the tower to the ground. After that, the steel tower will be dismantled piece by piece. The concrete foundation is crushed by pneumatic hammers.

 

A lot can be recycled. The scrap is melted down and returned to the steel production cycle. Generators and gearboxes often end up as spare parts warehouses and are cannibalized. Concrete rubble becomes road gravel.

 

Most of the work, however, is done by the disused rotor blades. This starts with the removal. In order to be able to drive away the parts, which are often dozens of meters long, with normal trucks, it is best to dismember them directly on site. It would be possible to saw them into pieces.

 

But researchers at the Fraunhofer Institute for Chemical Technology (ICT) in Pfinztal, Baden, are working on an alternative: They want to blast the wings into smaller pieces with precisely attached strings. "We have already carried out initial tests in our blasting bunker," says engineer Elisa Seiler. Further results are to be provided by a recently applied for research project.

 

True recycling of the rotor blades is hardly possible because they are made of composite materials, such as fiberglass mats that envelop an inner layer of wood. Separating the layers would be time-consuming. "Fiberglass-based rotor blades are shredded and burned in a special cement plant," says Fraunhofer researcher Seiler. For example, the high calorific value is used for energy-intensive cement production. The ash is added to the cement as an additive.

 

More and more often, however, robust carbon fibers are being used instead of glass fibers (carbon). These can also be burned, says Seiler, but the material is too valuable for that. "They cost ten times as much as glass fiber materials." Several processes are currently being developed to separate the valuable fibers from old wings and use them in new fiber-reinforced materials.

 

This work could lay the foundation for a lucrative recycling market. According to ICT, the amount of rotor blades produced will increase sharply in the coming years. According to calculations by the Fraunhofer researchers, they will reach their first maximum in 2027 with more than 30,000 tons, and 20 years later it should even be more than 40,000 tons per year - see diagram.

 

However, this business model is not completely secure. "In practice, little has been recycled so far," says Wolfram Axthelm, spokesman for the German Wind Energy Association BWE. The reason for this is that there has been a stable market for used wind turbines, even for old models with an output of less than one megawatt.

 

The majority of the dismantled German turbines, most of which are well maintained and with partly repaired rotor blades, are highly sought after in Poland, Russia and the former CIS countries. "With good care, turbines can be operated for much longer than 20 years," confirms Christian Schnibbe from wpd, the German market leader among wind farm project developers.

 

But what if an old wind turbine can only be scrapped? Who bears the costs? Theoretically, reserves and guarantees should be available for the dismantling. However, according to the Hessian state government, it was only since July 2004 that a sufficient dismantling security was required for an operating license. So it cannot be ruled out that the taxpayer will have to step in at some point, even if, according to the Federal Wind Energy Association, this has never been necessary before.

 

In the case of offshore wind turbines, the same questions and problems arise, except that here the dismantling is also much more expensive due to the significantly higher effort. The Federal Maritime and Hydrographic Agency (BSH) only issues permits for offshore wind farms if a sufficiently high level of dismantling protection is available. For a wind farm with 80 turbines, this amounts to an average of 50 million euros, explains Nico Nolte from BSH.

 

Possible income from the sale of old plants should not be taken into account. "In this way, we want to ensure that no costs fall back on the taxpayer," says Nolte. Offshore park operators could also apply for a 25-year extension of the operating time and thus postpone the expensive dismantling. This option is not available for onshore installations.

 

The dismantling of an offshore wind farm is time-consuming, because it is not only the wind turbines themselves that have to be dismantled, loaded and shipped ashore. The gigantic steel tripods under water would also have to be dismantled, along with the pillars rammed into the seabed. Currently, the dismantling concepts call for the seabed to be left in such a way that neither shipping, fishing nor the environment are affected. For example, the foundation pillars must be cut and removed at least one to two meters below the seabed.

 

Whether the remaining residues pose an environmental risk due to toxic metal components in the rusting steel is currently not something the BSH is able to assess. Overall, there is a lack of long-term experience in this still young offshore technology. Since the offshore wind farms are only just being built, the topic of dismantling will not become practically relevant for another 20 years at the earliest. Until then, the hope remains that the current risk assessments and cost calculations are not wrong.