TOP PLANT: Walney Offshore Windfarms, Irish Sea, UK

Courtesy: DONG Energy

Owners/operator: DONG Energy and Partners/DONG Energy
Officially commissioned in February 2012, the two Walney Offshore Windfarms—Walney 1 and Walney 2—together have 102 wind turbines with a total capacity of 367.2 MW. With their combined capacity, the windfarms qualify as one of the world’s largest offshore wind energy facilities and provide clean electricity to approximately 320,000 UK households.

Long a seafaring nation, the United Kingdom (UK) is now in the forefront of nations embracing offshore wind power. In fact, the scale of offshore wind power currently being planned by the UK renewable energy industry is larger than in any other country.

When commissioned in February 2012, the 367-MW Walney Offshore Windfarms (Walney 1 and Walney 2) became the world’s largest offshore wind energy installation. Then in September 2012, construction of the even larger 500-MW Greater Gabbard Offshore Wind Farm off the Suffolk Coast was completed. Upping the ante, the 630-MW London Array offshore wind project is currently under construction. Looking farther down the road, other UK offshore wind farms in the pipeline will be even larger; these include Dogger Bank at 9,000 MW, Norfolk Bank at 7,200 MW, and Irish Sea at 4,200 MW.

Constructed in two phases during 2010 and 2011, the Walney Offshore Windfarms are located approximately 15 kilometers (km) off Walney Island in the Irish Sea. DONG Energy (50.1%), Scottish and Southern Energy (25.1%), and OPW (24.8%), a company jointly owned by Dutch pension administrator PGGM and Ampère Equity Fund (managed by Triodos Investment Management), are behind Walney (UK) Offshore Windfarms Ltd. DONG Energy served as the lead partner in the Walney Offshore Windfarms’ construction phase and is also the operator.

Construction Overview

The Walney facility was constructed according to the multi-contract model, working in close cooperation with all the contractors and suppliers, Jens Hansen, project manager with DONG Energy, told POWER in September. The project also optimized the installation time through parallel installation (Figure 1).

1. Uplifting work. During construction of the Walney Offshore Windfarms, which was handled in two phases—Walney 1 and Walney 2—crane barges, jack-up vessels, and tugs worked out of ports in the East Irish Sea, primarily Barrow and Mostyn Harbors. Courtesy: DONG Energy

“We installed the largest wind turbine foundations ever made—almost 70 meters (m) long and weighing more than 800 tonnes. In addition, our project was one of the first wind farms to use the new Siemens 120-m rotor diameter turbine with blade improvements,” Hansen said. “The entire Walney facility has a combined total of 102 3.6-MW Siemens wind turbines.”

“The offshore logistics for Walney 2 was a big challenge, but due to good planning it was all done according to the plan,” said Hansen. He explained that by approaching the Walney project via a multi-contracting strategy, project managers were able to mitigate and handle risks and uncertainties quickly. Consequently, project management had a high awareness of the dangers and potential upsides in the project and thereby increased their ability to do parallel installation with controlled risk exposure.

  • DONG Energy coordinated all the activities in the multi-contracting project. A number of subcontractors performed the following duties:
  • Seajacks from the UK installed the wind turbines.
  • Geosea and Ballast Nedam handled the foundation installation.
  • VSMC and Prysmian installed the cables.
  • Scaldis installed the offshore substation.
  • Tideway handled the scour protection.

Facility Operations

The Walney Offshore Windfarms are located in the Irish Sea, which is characterized by high tides and waves, and windy weather. The difference between high tide and low tide is approximately 8 m. The wind speed is estimated to average approximately 9.3 m/s at 80 m. Even though the wind farms cover an area of roughly 73 km2, they are located far enough from the coast that their visual impact is minimal.

Each of the 102 turbines generates electricity at a voltage of 33 kV. Offshore substations collect electricity from the wind turbines and step up the voltage to 132 kV for the local grid. “The Walney 1 offshore substation is connected to the national grid by a 44-km-long buried export cable at the substation in Heysham, whereas the Walney 2 offshore substation is connected to the national grid at Cleveleys near Blackpool, via a 43-km-long buried export cable,” Hansen explained.

The Operation and Maintenance (O&M) Base in the new purpose-built premises at Barrow’s Ramsden Docks consists of an office for administration, welfare, and catering for personnel and a warehouse for storing equipment for maintenance of the offshore wind farms. Two new purpose-built service vessels and a new service pontoon are in place to enable the transport of service technicians to and from the wind farms. From the O&M Base, turbine operations can be monitored 24 hours a day and a local crew of approximately 60 people will ensure that the Walney Offshore Windfarms are in operation for the next 25 years, according to Hansen.

“The wind conditions are very good and the area also has very good grid connection possibilities; hence, we have other wind farms in the area and therefore gain a certain synergy,” Hansen said. “When we have more activities in the area, DONG Energy as a company gains a better opportunity to work with the local community (like we have done with the Walney Fun Run) and to be an attractive employer for the skilled labor in the area.”

Monitoring for Possible Environmental Impacts

The marine environment and bird life in and around the facility were carefully studied before the wind farms’ construction was authorized. During the two years of construction, additional work was done to ensure that construction activities remained within acceptable limits for noise and other disturbances, according to Mike Robson, senior environmental advisor on the Walney facility team. In fact, as Hansen explained, “During the Walney Offshore Windfarms’ construction, we were not allowed to install the monopole foundation during the period from February until April 7 due to the spawning season for the sole.”

Wind farm personnel are now conducting post-construction environmental surveys. “Now that the wind farms are completed, a series of surveys will be carried out during the next few years to keep an eye on any possible impact the wind farms may have,” Robson said. “Only minor impacts are expected on the seabed sediments and the marine fauna, including fish and shellfish, encountered in and around the wind farms.”

Starting in late April 2012, survey vessels began taking samples to study marine organisms in and on the seabed, and a specially chartered fishing vessel is taking trial catches of fish using a scientific beam trawl. Also in 2012, a series of bird surveys will be made from a boat to count birds in and around the wind farms.

The surveys’ results will be presented to scientific advisors at the Centre for Environment, Fisheries, and Aquaculture Science, an executive agency of the UK’s Department for Environment, Food, and Rural Affairs. “The surveys will help to improve our knowledge of the sea and its resources in the Walney Offshore Windfarms’ area,” Robson said.

Powering the Future

With their projected annual production of approximately 1,400 GWh, the Walney Offshore Windfarms are set up to benefit from the UK Renewables Obligation Certificate regime, which will create value for the facility owners, explained Hansen.

He noted that the wind farms also benefit the local economy: “They will create jobs and business opportunities. A lot of persons have had direct and, maybe more importantly, indirect benefits from the wind farms’ construction activities and will also benefit for many years to come from their operations.”

Currently, the UK offshore wind energy sector appears to have the wind at its back. In 2011, Renewable UK, a leading UK renewable energy association, conducted a study of deployment trends that analyzed the existing pipeline of future UK offshore wind projects. The study projects that by 2016 there will be about 8 GW of installed capacity and a total of approximately 18 GW by 2020.

In terms of its contribution to net UK electricity production, offshore wind energy supplied around 1.5% in 2011. This amount will grow to between 7% and 8% by 2016 and to approximately 17% by 2020, according to Renewable UK.

Angela Neville, JD is POWER’s senior editor.