Anholt

Location and Site Characteristics

The Anholt Offshore Wind Farm is situated in the Kattegat Strait, Denmark, between the peninsula of Djursland and the island of Anholt. The wind farm covers an area of approximately 144 square kilometers, with a length of 20 kilometers and a width ranging from 4 to 12 kilometers. The shortest distance to the shore is about 15 kilometers, and the distance to the island of Anholt is around 20 kilometers. The water depths at the site range from 15 to 19 meters.

Capacity and Energy Production

The Anholt Offshore Wind Farm has a nameplate capacity of 400 megawatts (MW), making it one of the largest offshore wind farms in the world and the largest in Denmark until the inauguration of Horns Rev 3 in 2019. The wind farm is equipped with 111 Siemens SWT-120-3.6 MW wind turbines, each with a rotor diameter of 120 meters and a height of 141.6 meters. This capacity is sufficient to power approximately 400,000 Danish households, equivalent to around 4% of Denmark's total power consumption.

Ownership and Operation

The wind farm is jointly owned by Ørsted (50%), PensionDanmark (30%), and PKA (20%). Ørsted, formerly known as DONG Energy, is the majority shareholder and operates the facility. The partnership model allows the owners to share operating expenses and earnings, facilitating long-term investment in the project.

Construction and Installation

The construction of the Anholt Offshore Wind Farm began in January 2012 and was completed in September 2013. The project involved the installation of 111 monopiles, each driven 18 to 36 meters into the seabed, followed by the mounting of transition pieces. Specialized vessels, including the heavy lift vessel Svanen and the installation vessels Sea Installer and Sea Power, were used for the installation. The project required significant logistical efforts, involving 100 vessels, 3,000 people, and over two million working hours.

Technology and Infrastructure

Each wind turbine is connected to an offshore substation, which converts the power from 33 kV to 220 kV. The power is then transmitted to the Danish power grid via a 25-kilometer submarine cable and further 56 kilometers to the main power hub at Trige near Aarhus. The turbines are placed in an unusual pattern to maximize production, with most turbines along the edges and in undisturbed airflow from the main direction, which is west-southwest. This layout increases production by about 1.5%.

Maintenance and Monitoring

The wind farm is maintained and monitored by a team of around 50 people based in the port of Grenaa. The facility is equipped with a distributed control system (DCS) that collects data on wind speed, wind direction, and wave height, as well as the status and production of each turbine. Turbines are inspected annually, with one to three serviced during each planned visit. The service organization includes highly skilled wind turbine technicians, service vessel crew, and administrative functions.

Economic and Environmental Impact

The project was part of the Danish government's Energy Policy Agreement of 2008, aiming to increase the share of renewable energy. The wind farm cost approximately 10 billion Danish kroner (€1.35 billion, US$1.65 billion) to build. The owners receive a feed-in tariff of 1.051 DKK/kWh (about 17 US¢/kWh) for the first 20 TWh of production, which corresponds to about 12 years of operation. After this period, the power is sold on market conditions without subsidies. The wind farm reduces carbon emissions by 1.3 million tonnes of CO2 per year compared to a coal-fired power station.

Challenges and Incidents

The connection cable has experienced failures; in 2014, the land cable failed for a week, and in 2015, the sea cable failed, causing Anholt island to revert to diesel engines temporarily.

Conclusion

The Anholt Offshore Wind Farm is a significant contributor to Denmark's renewable energy targets, providing clean energy and reducing carbon emissions. Its construction and operation demonstrate the feasibility and benefits of large-scale offshore wind energy projects.