AN INNOVATIVE CONCEPT
PHYSICS AT THE SERVICE OF ECONOMIC OPTIMIZATION
The Eolink floating wind turbine is the only wind turbine that has been specially designed for a floating application at sea. The concept integrates all the characteristics of its marine environment, taking advantage of the benefits and minimizing the constraints. The Eolink design makes it possible to install larger turbines at sea, a factor of competitiveness which helps to reduce the cost of energy (LCoE).
From the start, it was obvious that the nacelle orientation system was no longer needed. Even if this solution is used on land, to orient the rotor into the wind, the sea offers a new context in which heavy structures become easily mobile. This is what led Marc Guyot, founder of Eolink, to design a pyramid structure. Four masts describe the edges of this pyramid and meet at their tops, to support the turbine at two points. So installed, the turbine can be larger and capture more energy. The effectiveness of the concept has already been demonstrated by 2 prototypes and a 5 MW demonstrator is to be launched in the coming years.
In order to face the wind and transfer the energy produced to the grid, the floating wind turbine is anchored on a single point called SPM. The structure is connected to the upper part of the anchor point via two hawsers, while a dynamic cable carries electricity. In order to limit the influence of waves on power cables, the anchor buoy is located 20 meters below the surface.
Eolink has patented a pilotable orientation system for the float, in the event of misalignment between wind and current, rare on the high seas. It complements passive orientation and allows orientation to be controlled over a range of 120 degrees, thanks to a dynamic ballast system. This technology improves the production as well as the life of the wind turbine. It also makes it possible to divert the wake of the wind turbine on demand to optimize the overall yield of wind farms.
A pyramidal structure that is more resistant than a single mast
The first advantage is the low fatigue that the structure undergoes. Even if fatigue is not a common term, it is a very restrictive element for the mechanical dimensioning of a structure at sea. When an object at sea undergoes repeated little forces, such as those of waves, the structure is gradually damaged. This fatigue phenomenon is modeled during design. Eolink's structure does not present any highly constrained areas thanks to the distribution of forces between the 4 masts, unlike the mast foot of conventional architectures. Also, the service life and fatigue resistance are much better.
These two advantages allow the installation of 20 MW turbines.
What is resonance?
All structures can vibrate according to their own frequency. For example, the tuning fork vibrates at 440 Hz to play the A note. When designing rotating machines, care is taken to ensure that vibration sources do not excite the structure, in order to avoid resonance that could lead to ruin.
More energy produced
One knows that the key to competitiveness lies in the size of the turbines. Currently, the main design difficulty concerns the blades. For example, a 5 MW machine equipped with a 115 meter rotor produces 14 GWh per year, but 17 GWh with a 140 meter rotor. Their lengthening requires them to be weighed down, which leads to cyclic, critical inertial fatigue.
Thanks to a greater distance between the blades and the masts, the Eolink architecture allows to design more flexible blades, no longer risking colliding with the tower. The saving in mass thus achieved, makes it possible to lengthen the base of the blades. The gain in producible is 6% by keeping the generator of the reference solution, up to 11% if the torque is increased.
Eolink increases blades/tower distance
A lighter and less expensive structure
Another advantage of the pyramidal structure lies in its mechanical capacity to distribute the weight of the nacelle evenly among the 4 masts. As the stresses are better distributed, the steel thicknesses are reduced. In comparison, a single mast solution is 40% heavier. This difference represents a saving of 10% on the LCoE. Eolink thus achieves a mass of less than 200 t/MW, unique on the market. Finally, the float, made up of 4 columns, makes it possible to reduce the dimensions by 20% in length and width compared to a float with 3 columns. This also reduces the overall mass.
On the strength of these advantages, the gain in LCoE provided by the Eolink solution is estimated between 20 and 25%, compared to a reference technology.