Denmark's Second Off-shore Wind Farm

by the CADDET Danish National Team

Introduction

Denmark's second off-shore wind farm was put into operation during October 1995 at Tunø Knob, close to the second largest city of Aarhus on the east coast of Jutland in Denmark.
The ten Vestas V 39 off-shore wind turbines, each of 500 kW, have been in full operation since the wind farm was inaugurated. In November 1995, its production was 1.3 GWh almost 40% more than originally estimated.
The wind farm is situated about 6 km off the shore of Jutland in an area where the sea depth varies from 3-5 m. The Tunø Knob area is of considerable environmental interest, both as a resting area for birds and as a beautiful part of the coastline and landscape. Furthermore, a careful archaeological investigation of the site has been carried out as part of the off-shore wind farm planning process.
The on-shore noise from the wind turbines has been calculated, at the nearest island of Tunø, to be less than someone whispering [15 dB(A)]. On the mainland it is inaudible.

Specification

Experience gained from both on-shore and off-shore wind turbines in Denmark has influenced the design of the new windfarm. Each turbine is a horizontal axis pitch regulated machine, orientated up-wind with a tubular tower, and a 3-bladed rotor of 39 m diameter. The turbines are mounted on specially-developed, reinforced concrete caisson foundations. Considerable emphasis has been given to the design and construction of the foundations. The turbines are connected to the national grid via a 6 km submarine cable to the mainland of Jutland.
 Each turbine is controlled remotely. The production manager can monitor the performance and operation of the wind turbine from an operation centre in Hasle. The control system is continuously collecting all relevant data. The data are transmitted via a radio system from the individual data-collecting unit of each wind turbine to computers at Hasle. On-site maintenance is estimated to be needed only twice a year, when engineers will sail to the wind turbines and carry out the regular scheduled maintenance programme.

Economy and Production

After one month of operation, the careful planning and the experience of the Danish engineers and entrepreneurs seem to have paid off. No problems have arisen and the November 1995 production has been an unexpectedly high 1.3 GWh. The total production price/kWh is expected to be DKK0.49 (where DKK is the Danish krone) with an annual total production of 15.0 GWh. The entire costs of the off-shore farm are estimated to be about DKK78 million.

Development and Demonstration

Being the second off-shore wind farm in Denmark, it has been possible to build on the experience gained already from the first off-shore wind farm at Vindeby. In order to gain as much experience as possible in planning and operating off-shore wind farms, which are regarded as one of the major development areas of Danish wind turbine technology and production of electricity, a special programme has been designed to gather experience and data. This includes:

  • A record of wildlife and marine biological movements including birds and their migratory paths, as well as other animals.
     
  •  A correlation of electricity production related to wind speed, wind direction and other parameters affecting the production, maintenance and effectiveness of the wind farm.

Conclusion

The Danish experience of off-shore wind farms will provide a background for future work to utilise off-shore wind energy not only in Denmark, but also internationally.


For more information contact the CADDET Danish National Team in Tølløse.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to
Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.