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The complexities of recycling begin to bite

WORLDWIDE: The wind energy industry is right to portray itself as a "clean" and genuinely green energy sector. With this image comes the responsibility of making sure that the sector does not rest on its environmentally sound laurels. Looming on the horizon are questions about wind-farm decommissioning and the recycling of end-of-life turbines, especially complex components such as blades.

With the first generation of modern wind farms having been built in Germany, Denmark and California in the late 1980s, these three locations will be at the forefront of dealing with waste and recycling issues as old wind farms are dismantled or, in most cases, repowered. Repowering involves the dismantling of existing turbines and replacing them with fewer, significantly larger, machines.

In Germany, the wind industry has suggested that repowering could reach a rate of 1GW a year, given that just under half of the country's approximately 22,000 turbines are more than ten years old. Another driver behind increased repowering in Germany is its newly revised Renewable Energy Act (see news story), which offers an improved financial incentive for repowered wind farms. In 2011, 170 old turbines with a combined generating capacity of 123MW were taken down in the country and replaced with 95 larger turbines with a combined capacity of 238MW.

The trouble with blades

But what happens to redundant turbines? So far, the majority of dismantled wind turbines have been bought by intermediaries that hope to sell them for re-commissioning in other countries, usually in eastern Europe and north Africa.

According to one intermediary based in the Netherlands, which holds a stock of such old wind turbines for export, it is possible that some will be disposed of rather than sold. Another company, active in wind-operation support and maintenance in northern Europe, says some waste plastics from old wind turbines are simply being "thrown in the rubbish". These plastics are likely to include blades or parts of blades.

Some wind-turbine components are made of materials that are easily recovered and have a good scrap value - such as steel and cooper, but hard-to-recycle blades are beginning to cause concern.

The issue is quietly rising up the agenda in Denmark, where a working group has been set up bringing together several important players including LM Wind Power, Siemens and Vestas, to share knowledge about recycling options. Co-ordinated by the Danish Wind Energy Association, the working group is partly driven by the fact that a new national waste strategy for Denmark is in the works, with the wind industry expected to account for its specific waste streams.

"Blades have been an issue for a number of years and there have been a series of isolated research projects," explains working group co-ordinator Anya Pedersen, an adviser at the Danish Wind Energy Association. Small-scale pilot projects have been undertaken in various European countries, but there has been little sharing of knowledge and results.

Questioned by Windpower Monthly on the issue, turbine manufacturer Vestas says in a statement that the responsibility of disposing of end-of-life blades rests with the wind-farm owner or operator. With the producer responsibility principle now a driving force behind waste policy in Europe, it is notable that several manufacturers have chosen to sit on the Danish working group investigating blade-related waste issues.

Life after decommissioning

The world's only industrial enterprise to recycle end-of-life turbine blades is in Melbeck, northern Germany. In its 60,000-tonne annual capacity plant, Zagons Logistik reprocesses blades and other products made from fibre-reinforced plastic for use in cement production. The end product is used by cement producer Holcim (see box).

Jorg Lempke, managing director of Zagons Logistik, believes the volume of used wind-turbine blades requiring recycling will increase substantially in a few years' time. This is because the wind farms that will soon begin to be dismantled have blades that were not built to last as long as the initial, 1980s, generation. "I would say that about 80% of the old wind turbines that have been dismantled are being sold for reuse elsewhere, but that will change when newer wind farms are dismantled. Their blades are not as strong and will need to be recycled," says Lempke. In part, this is because blades have become lighter and thinner than the heavier and less aerodynamic first-generation blades.

In the US there has been little discussion about material-recycling issues arising from wind-farm repowering. This frustrates Brian Stuart, director of wind development at Vibrant Energy Solutions in Minnesota, who would like to see more thought given to the development of a wind-energy recycling and remanufacturing industry. "Every turbine that has been installed will eventually have to be taken down," he says, adding that blade repair and gearbox remanufacturing may emerge alongside recycling services. "There's a huge market on the horizon," says Stuart.

To date, attention in the US has focused on the costs of eventual site restoration and ensuring that financial liability for these costs is properly assigned prior to wind-farm commissioning. In some cases, US developers are required to take out bonds and other financial products to prove they can meet decommissioning costs.

In Scotland, too, the authorities have begun to worry about wind farm decommissioning, including issues such as the removal of turbine bases and service roads.

An early focus on site decommissioning, however, may be misguided, given that many existing wind-farm sites may not be decommissioned for a very long time. Instead, they may be repowered repeatedly as technology develops and/or existing equipment wears out.

The prospect of restoring sites to pre-wind farm states may not be relevant for many years - but recycling end-of-life equipment may prove a more pressing issue in the years to come.

SECOND LIFE - REPROCESSING BLADES FOR USE IN CEMENT PRODUCTION

The world's only industrial-scale reprocessing of end-of-life windturbine blades is currently undertaken by Zagons Logistik at its factory in northern Germany.

The company's service begins with the use of a mobile saw that can be used in the field to cut large blades into shorter sections of 10-12 metres - which can then be transported in a conventional truck rather than a wider vehicle requiring police escort.

At the reprocessing facility, a stationery cable saw is used to reduce blade sections further, to about one metre in length. These sections then enter a crusher that has been modified to handle fibre-reinforced plastics. This reduces material size to about 30-50 centimetres.

The next stage sees the material being fed into a cross-flow shredder, which rotates 800 times per minute, reducing the chunks of waste blades further. A hammer mill then takes their size down to a maximum of 5 centimetres, after which they are mixed with other, wet waste materials. The addition of wet substances ensures that glass fibres from the crushed turbine blades are captured and bind to the rest of the mixed waste.

End product

The result is a compound that cement producer Holcim can use both as a substitute fuel, replacing coal-ash, and as a raw material, displacing some of its need for virgin washed sand.

Zagons Logistik is keen to secure larger volumes of waste turbine blades since its plant is running only at about one third of its full capacity. The company currently reprocesses about 400-500 tonnes of waste turbine blades each month.

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