Vindeby offshore wind farm
Total budget: € 11 mio. (1991 level)
Turbine price (incl. towers and installation): € 4.7 mio. (1991 level)
Wind Turbine: Bonus Energy 450 kW
Production: 5 MW (11 turbines)
Support structure type: Gravity based
Depth: 3-5 meters
Distance from shore: 1.5 – 3 km
Production start: October 1991
The world’s first offshore wind farm turns 20 this year. Building it required ingenious solutions in a large number of areas, and many of these solutions are still in use today.
By Karsten Prinds
We knew that if we failed, the idea of putting wind turbines offshore might have gone into oblivion.
Former Project Responsible Frank A. Olsen looks back at the decisive years in 1989 and 1990, when a regional power company set out to test the idea of moving wind turbines from land to the ocean. Because of a high population density and ambitious political targets for renewables, the Danish power company Elkraft anticipated that they could not combine those two things if they stayed onshore.
A small team of engineers was put together, and along with companies like Bonus, MT Højgaard and NKT, the first farm was designed. Bonus is now known as Siemens Wind Power, and part of Elkraft today is Dong Energy:
- It was exciting and satisfying. We had to create new solutions in a lot of areas, says Frank A. Olsen.
For example, onshore turbines had no security system against lightning. It is just not as large a problem onshore as it is offshore. Systems from the construction industry were adapted for the turbine and the engineers came up with the idea of introducing fiber optics for data transmission. That way, a lightning strike could not destroy all the turbine computers at the same time.
Corrosion was another obvious area where an onshore turbine would be challenged offshore.
- The whole idea of a sealed air environment was invented. Bonus installed dehumidifiers and let the air inside be slightly warmed up by the heat surplus from the generators. And to make it even more secure, we preferred components that could withstand corrosion, says Frank A. Olsen.
The world’s first wind farm, Vindeby, consists of 11 Bonus 450 kW turbines on gravity foundations. Notice the boat landings wooden poles – designed to crack in case of ice packs. Photo: Siemens
Designed to crack
Perhaps the most ingenuity was shown, when the engineers designed the boat landing. Instead of designing for durability, they dimensioned it to crack.
- The boat landing gave us a lot of speculations. We had to take ice packs into consideration as they occur every seventh year. But instead of designing the boat landings to last through ice packs, we dimensioned them to crack and slide off. It would be a lot cheaper to put the boat landings back on the support structure than to constructing them to withstand the pack ice, says Frank A. Olsen.
And in the 20 years, there has actually only been one case of pack ice, so the idea has turned out even more cost-effective.
In addition to its anniversary, Vindeby is also reaching its durability date. Elkraft expected the site to last 20 years. But Frank A. Olsen believes it will last twice as long - the turbines are very durable, and the concrete is built to last 100 years.
- The biggest threat for the current turbines is economics. Offshore sites are in short supply, and you could anticipate that someone would replace the old turbines and foundations with new ones to increase production, says Frank A. Olsen.