Construction of the second of EnBW's offshore wind stations is about to begin, with installation of the initial foundations and scour protection for the 288MW Baltic 2 project scheduled for late this year. The German energy company hopes that first power will be achieved by the end of 2013.
EnBW's offshore wind strategy is based around using its two Baltic Sea projects to develop its skills and experience before it tackles two more challenging projects in the North Sea, explained EnBW's head of offshore wind operations and maintenance, Michael Boll.
Speaking with Windpower Offshore, Boll said: "We bought four offshore projects and we began with the easiest, Baltic 1. Each project will be tougher than the last."
The company raised an additional €822m to finance its offshore wind programme earlier this year. It has a target to achieve 20% renewable energy supply by 2020, compared with 11% in 2010.
Seabed conditions have been the biggest challenge for EnBW when planning the construction of Baltic 2. Underneath layers of sand, soil surveys identified chalk. "This meant we had to recalculate our foundation engineering," explained Boll, since chalk can be unstable if it comes into contact with water.
As a result, the project will feature both monopile and jacket foundations — 39 monopiles and 41 jackets — with jackets being installed in those areas where the soil conditions are more demanding.
With Baltic 2, EnBW is also moving into deeper waters and building further from shore. Water depths for Baltic 2 range from 24m to 40m, compared with Baltic 1's 16-18m.
One of the reasons for EnBW's decision to buy the Baltic 2 project was the possibility of using AC cables for grid connection, said Boll. The company is familiar with AC technology.
Instead of connecting directly to shore via its own export cable, Baltic 2 will connect to an existing offshore electricity substation that was built for Baltic 1. Two AC cables of 62km each will be installed to link Baltic 2 with the Baltic 1 substation. From there, power will be transmitted to shore via Baltic 1's existing AC export cable and a second such cable that has yet to be built.
Work began last week on the Baltic 1 substation to prepare for the additional cables, with 50Hertz, the transmission system operator for Germany's Baltic Sea region, due to install the cables starting some time between October 2012 and February 2013.
Taken together, EnBW's four offshore wind stations will have an installed capacity of 1.2GW, with almost three-quarters of this capacity earmarked for the North Sea. The He Dreiht and Hohe See projects will each have a capacity of about 400MW. They will be located 85km and 90km from shore respectively.
Soil surveys have not yet been completed for the two North Sea projects, which will both be built in water depths of about 39m.
Looking ahead to the challenges that the North Sea will bring, Boll emphasised the North Sea's rougher conditions. "In the Baltic, there is generally a correlation between wind speed and wave height. When the waves are high, the winds are generally too strong to allow for work on turbines," noted Boll. "But in the North Sea, there can be high waves — of 6m perhaps — but the wind speed can be low and entirely safe for working on turbines."
EnBW's policy is to negotiate contracts on a project-by-project basis, said Boll, rather than to make multi-project framework agreements with suppliers. This means that although Siemens supplied turbines for Baltic 1 and will also supply for Baltic 2 (80 SWT 3.6-120, 3.6MW machines), it is not automatically the manufacturer of choice for EnBW's North Sea projects.