By Jerome a Paris
Recent statistics have been published showing that Europe has now installed of offshore wind capacity, with more than a quarter installed in the past year and lots more to come in the next few years.
I discussed these numbers in more detail , but wanted to give you here some insights on what these numbers mean on the ground.
I recently visited the port site in Zeebrugge, Belgium, where the foundations for the Belwind offshore wind farm (the financing of which ) were stored before their installation. This is a good opportunity to give you a glimpse of the kind of logistics involved, and what kind of problems can happen (and how they are solved), on offshore wind installations.
Follow me for a tour of a small bit of Europe's fastest growing heavy industry.
As a quick reminder, there are 3 main types of foundations for offshore turbines: monopiles, gravity-based, and jackets/tripods.
Here are gravity-based foundations and tripods (you can see more pictures )
Monopiles have typically been used for smaller turbines and lowers depths, as their size (diameter and thickness) needs to increase with the load to be carried and their cost can become an issue. The price of steel will heavily influence the choice between the technologies when several are possible. In this case, with 3 MW turbines in 20 meter depth, monopiles were the most logical choice.
Foundations include two main parts, the foundation itself (the part that's driven into the subsoil) and the transition piece (the part that's affixed on top of the foundation and carries the turbine tower).
The transition piece usually includes the boat landing, access platform and j-tubes (the steel tube that protects the electrical cable going to other turbines and/or the transformer station, it is curved near the ground to allow the cable to go from its underground trench to the turbine, thus its name).
It also plays a vital role in that it corrects any flaws in the verticality of the foundation: turbines require the towers to be within one half degree of perfect verticality in order not to have to bear inappropriate loads, and it is not so easy to hammer 50 meter long steel columns in the sea ground to such precision; the transition piece is designed to be adjusted to provide the perfect position required for the turbine over the water.
Another aspect which requires a lot of precision is the roundness of the foundation and the transition piece. The two of them must fit together (more on this in a second), and the transition piece needs to be in the exact size for the first part of the turbine tower to be bolted on top of it — tolerances are below a centimeter (the bolts are big ones, a couple centimeters thick, but they need to fit in over the whole diameter of the two parts) for equipment measured in tens of meters.