Jul 24 2014

A Case Study of the Anholt Offshore Wind Farm

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Background and Technology Overview:

In 2010 DONG Energy company received a permit to build an offshore wind farm in the waters that lie between Djursland and the island of Anholt in Denmark. The goal in constructing the wind farm was to replace the use of diesel-based electricity generation on the Anholt island as part of the movement led by the Danish Organization for Renewable Energy and the Danish Energy Agency to reach 25% electricity supply from renewable energy in Denmark by 2025 and 100% by 2050 (Andersen 2013). DONG Energy made use of 88 square kilometers, excluding turbine-radials, to construct the wind farm. The company purchased 111 SWT-3.6-120 wind turbines from Siemens with total project budget of 10 billion Danish kroner or about 1.65 billion US dollars. These 3.6-megawatt turbines have a total height of 141.6 meters with a hub height of 81.6 meters. The diameter of rotors is 120 meters. The turbines are stationed in the seafloor with driven monopiles and stabilized with gravity concrete bases and they sit in water 14 meters deep. Unlike traditional wind farm organizational patterns, the turbines of the Anholt Offshore Wind Farm are arranged in an unusual pattern that is governed by two principles. First, most turbines were placed around the edges of the farm area and second, most turbines were placed in undistributed airflow from the main direction which is West to Southwest (Wittrup 2011). This design increases productivity by 1.5%, which is the value of more than 100 million Danish kroner over the expected lifespan of the lifespan. The nameplate capacity of the wind farm is 400 megawatts which is just over 4% of the Danish national electricity production.

Initial environmental impact assessment:

The Anholt wind farm has had a low impact on the environment and ecology of the area. Research programs in Denmark have assessed the impact of previous wind farm construction projects and their operations and, accordingly, there is a great deal of data available for the Anholt project team. In assessing the impact of the wind farm, some categories of analysis included the impact on marine animals in the area and their habitats, noise calculations, air emissions, and potential risk to ship traffic. A significant amount of research was also done on the migratory and residential birds that are exposed to the wind farm area. Collision risks to water birds were assessed as minor due to the fact that the turbines only span 10-12% of the width of the Djursland-Anholt strait. Some migratory birds will potentially need to make a 3-5 kilometer adjustment around the wind farm, but otherwise the data does not suggest that collisions will occur frequently (Energi Styrelsen).

For marine animals, this data survey focused on Harbour porpoises, Habour seals, and Grey seals. There was said to be an “intermediate” amount of all three types within the project area. Impacts due to sub-sea noise emissions during the construction phase were assessed as moderate. There is potential for the seals and porpoises to relocate themselves temporarily during the construction phase but the noise affects will be short in duration and the animals should be able to return as soon as pile-driving activities are completed. Although they have a Sound Operational Power of 105-110 (dB), these turbines have no projected damage to the habitats or livelihood of marine life(Marine Animals, Energi Styrelsen). Ultimately, impacts on marine life during the construction phase are seen as minor, and, moving forward into the operational phase there is likely to be even less disruption to the local ecosystem (Energi Styrelsen).

The project team analyzed the risks to ship traffic throughout the wind farm area in great detail. There were two main ferry routes in the vicinity of the project area, which, with the cooperation of maritime authorities in Denmark, Sweden, and Norway could be remapped to be outside of the wind farm zone. Two traffic routes also intersected the project area and were thereafter terminated, and a single traffic route was created 3 nautical miles west of the wind farm. In fact, the new routing plans that were created as a result of the Anholt project were assessed to have increased maritime safety, regardless of the presence of the wind farms. The potential of an oil spill was computed using a risk matrix and was considered to be “acceptable.” The risk matrix analyzed data of impact studies where ships could potentially hit the wind turbines. Those studies took into account the most likely angles of impact and the part of the ships that would sustain the most damage should an impact occur (Risk to ship traffic, Energi Styrelsen). Air emissions were also an important component in considering the environmental impact. Emissions from the construction phase were predicted to be less than 1% of the annual national emissions in Denmark. The way in which the foundation of the monopoles was constructed allowed for 30-41% lower emissions than a construction type that used gravity based foundations. Air emissions for Anholt were projected to be lower than those in the construction and operational phases of the Nysted wind farm (Air Emissions, Energi Styrelsen).

Finally, a large portion of research was compiled on the predicted impacts on benthic habitats. Like most of the other impact assessments, benthic habitats were not viewed as being significantly altered as a result of the wind farm. A reduction of 5-6% in biomass of filter feeders and an increase in 10% in biomass of deposit-feeders were predicted within the overall area of the wind farm. Filter feeders are animals that feed by straining suspended matter and food particles from water such as tunicates and whale sharks. Deposit-feeders, however, feed on small specks of organic matter that have drifted down to the ocean floor, some examples being crabs, eels and shellfish. The changes in the biomasses of these organisms are a result of the obstruction of water flow from the turbines (Benthic Habitats, Energi Styrelsen). Although the methods used for predicting the impact on benthic habitats had a high degree of uncertainty, the project team nevertheless concluded that impact on habitats would be insignificant. Overall, by using data from other wind farm projects like Denmark’s Nysted operation, as well as undergoing their own analysis, the Anholt project team had everything in place to maintain a low environmental impact for both human considerations as well as the ecosystems in the area of installation.

Ships in the Anholt Offshore Wind Farm http://2.bp.blogspot.com/-ZCovoRdE9G8/Ui84LwaT6AI/AAAAAAAAC7w/IPxjupz6Zg8/s1600/offshore-Siemens-wind-energy1.jpg


Because DONG Energy chose to deviate from the traditional grid pattern and position the turbines in unusual patterns, construction costs were increased and another proposed Danish offshore wind farm lost its funding. This series of events led to a full devotion of DONG development and construction resources to the Anholt project which affected its construction techniques. The development team chose to utilize Port of Grenaa as a construction base and base for on-going operation (Blackwell 2012). The port is located 25 kilometers southwest of the wind farm.

In order to install the driven monopiles, the team used the Svannen heavy lift vessel and the first turbine was in stalled September 3, 2012 and was connected to the Danish energy grid September 21, 2012. In May of 2013 DONG Energy installed the fifty-ninth turbine making the wind farm in Anholt the largest in Denmark as it surpassed the Horns Rev 2 wind farm. Due to increased resources and attention, the construction team was able to perfect the operations of the Sea Installer vessel and it was able to erect a complete turbine tower. The Sea Installer was also able to install a turbine onto the tower in seven hours which significantly reduced the construction time for the farm. The mooring line and cable was installed with remotely controlled robots which reduced the need for many divers on this project. The transmission cables were constructed and are maintained by Energinet.dk (Hopson 2013). The generated electricity travels 25 kilometers to land through a three-conductor cable with a 26-centimeter diameter. From Port of Grenaa, the electricity is sent 56 kilometers further inland to a power hub for distribution (Kvarts 2010). All 111 turbines were finished on May 19, 2013 and reached full power in June of 2013.

Construction of a turbine for the Anholt Offshore Wind Farm http://earthtechling.com/wp-content/uploads/2013/02/anholt.jpg

Costs and financing:

DONG Energy, an integrated energy company based in Frederica, Denmark was the only company to bid on the Anholt Wind Farm project and received a license to build it in 2010. Thereafter, it was awarded the concession to build the wind farm by the Danish Energy Agency (Pau, 2012). The Anholt Offshore Wind Farm in Denmark has a cost of 1.65 billion USD but also includes a feed-in tariff of 17 US cents per kilowatt-hour for the first 20 tera-watt hours. Feed-in tariffs benefit production companies by subsidizing a part of their operation costs. This is a substantially higher tariff than similar projects have received. The Nysted Wind Farm close to the Rodsand sand bank in Denmark only had a power delivery contract of 12 US cents per kilo-watt hour (Pau, 2012). News-media as well as politicians have suggested that the tight schedule and sanctions regarding the project are the reasoning behind the increased price, and that Anholt needed to have a higher incentive to complete the project. The agreement with DONG Energy required that the first power should be produced before the end of 2012, and be fully commissioned by the end of 2013. DONG received a 240 million Euro loan from Nordic Investment Bank prior to investing in the Anholt project (Pau, 2012).

In March of 2011, DONG Energy sold 50% of the Anholt wind farm to a consortium that includes PensionDanmark (30%) and Pensionskassernes Administration (20%) for $1.14 billion. The agreement allowed the payments to be spread between 2011 and 2013. On April of 2014 both companies took over responsibility for operations and earnings in proportion to their investments. For the first 5 years of operation, the wind turbines will be under warranty from Siemens. After that period, DONG Energy will be solely responsible for the operations and maintenance of the turbines.  DONG signed a 15 year contract with PensionDanmark and PKA on planned maintenance and operation of the farm (Pau, 2012).


Metocean and Geological Characteristics:

The wind in the area of the Anholt Wind Farm has an overall wind speed of 6.3 meters per second, a water depth range of 14-20 meters, an extreme high water line of 1.7 meters, an extreme low water line of -0.9 meters, an extreme wave height of 4.1 meters, a max wave height of 5.7 meters, and an extreme current of 0.6-0.75 meters per second. The seabed is composed mainly of Holocene sand which provided difficulty in securing the turbines on the seafloor (Clemmensen 2014).


The Anholt Offshore Wind Farm is able to provide sustainable electricity to 223, 436 Danish homes that were previously powered by diesel-generated electricity. In providing non-fossil fuel-based electricity, the Anholt Offshore Wind Farm reduces Danish carbon emissions by 451,465 tons CO2 per year (DEA 2011).



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