Generating electricity from the tide, waves and wind (Version Francaise)

The module under development consists of a frame to which a generator/motor and a reel operated by a cable attached to an anchor are attached.
It is adaptable to all types of floats, in particular those supporting floating wind turbines.
Capable of resisting swell-induced movements, it reduces the stresses exerted on the mast and moving structures.
Attached to the seabed, it acts as a vertical elastic and dynamic anchor, reducing the passive mass of the float and cutting the cost of mooring lines.
Compared with any other device, it has the dual advantage
as a stabilizer, it produces electricity, rather than consuming it to activate ballast tanks, for example,
as a wave energy transformer, it harness all the power from the enormous volume of the float supporting the wind turbine. 

Introduction  

The growth in demand for electricity, particularly decarbonised electricity, no longer needs to be demonstrated. In Belgium, it is set to double by 2050 (Blueprint of grid operator Elia, 2024).
Elia publie un Blueprint sur le système électrique belge comme étape vers une stratégie à long terme pour une politique énergétique durable et compétitive d’ici 2050
 

Wind turbines  

Despite being less efficient than nuclear power stations (75%), wind turbines offer a number of advantages, particularly in terms of safety, energy independence, environmental protection and waste treatment. This is why a record 117 GW (equivalent to 14,625 wind turbines with an output of 8 MW) were installed in 2023 around the world, bringing the total installed capacity to 1,021 GW, mainly in China (46%) and the United States (16%). Europe as a whole accounted for 23% of this global capacity, or 236 GW, divided between Germany (67 GW), Spain (30 GW), the UK (29 GW), France (22 GW), Italy (15 GW), Sweden (13 GW), the Netherlands (11 MW) and Denmark (8 MW). 194/236
Belgium has 1,780 wind turbines. Of these, 516 are offshore, producing 51% of total wind power output. They are divided into 9 zones, fixed to the seabed at a depth of between 20 and 40 meters. The planned Princess Elisabeth Zone will comprise 3 zones spread over 285 km², with a total capacity of 2,300 MW. 

Floating wind turbines  

At depths greater than 50 meters, floating wind turbine technology takes over. The turbine is located at the end of the mast, which is attached to a float, itself anchored to the seabed by cables.
Floating wind turbines have a number of advantages: – they can take advantage of stronger, more constant offshore winds, thereby reducing the cost of producing energy; – they limit the environmental impact, with reduced visibility from the coast due to their remoteness; – they can be dismantled completely at the end of their life, with no residue left on site; – they make it easier and cheaper to install wind turbines on the quayside, before towing them to site.  Éolien en mer : posé ou flottant – Journal de l’éolien – Tout sur l’éolien 

Whether on land or at sea, wind turbine production is intermittent, as shown by their load factor, i.e. the percentage between the amount of electricity actually produced and the amount that could have been produced if they had been running continuously at maximum speed. On land, this factor is 25%, and at sea it is 45% for wind turbines fixed to the seabed, while it exceeds 65% if they are floating and moored offshore to take advantage of stronger, more constant winds.
It goes without saying that to be held in position in the ocean, these wind turbines need to be fitted with several mooring lines that are attached to the seabed and can be several hundred meters long. 

Stabilizing function of the Archibras module  

On the one hand, all wind turbines are subject to the vibrations that affect moving parts subjected to the action of the wind. These are compensated for by the considerable rigidity of the structures and the mechanisms acting on the blades.
On the other hand, all volumes floating at sea are subject to oscillatory movements in relation to the horizontal. Since they are due to the combined action of waves (swell) and winds, these movements, known as pitching and rolling, have a highly variable direction. Their amplitude varies between 1 and 10 degrees of inclination. They occur at intervals of between 5 and 20 seconds.
So, for example, located on a 50 m square float, which tilts by 2 degrees under the effect of the swell, the nacelle located on a 90 m high mast is the seat of a rocking movement with an amplitude of 3 m each time one side of the float sinks and then rises, i.e. every five or 20 seconds. The result is a bending force acting on the mast. In addition to the more aggressive sea conditions, these stresses become increasingly significant as the mast lengthens and the rotor diameter increases. 

In order to reduce these constraints, which shorten the lifespan of the boat, builders are using ever larger floats, which are fitted with water-filled ballast tanks to maintain the verticality of the mast. According to this principle, the mass of the float becomes 10 to 20 times greater than that of the mast and the nacelle. For example, a 250-tonne mast supporting a complete nacelle also weighing 250 tons is attached to a float with a total mass of around 10,000 tons. In some cases, the water in the ballast tanks is moved in a similar way to the processes used to stabilize luxury ships. In other cases, the floats are attached to vertical mooring lines using the Tension Legs Platforms (TLP) process. 

By their ability to slow the upward movement of the float at the position they occupy, our modules exert an inverse force that acts like an additional mass that would be placed in the same position. This significantly reduces the weight, and therefore the cost, of the float. What’s more, if there are several of them, located in different places around the perimeter, they can be controlled to act intelligently in response to the unpredictable movements induced by the swell. Acting vertically, they function as additional mooring lines, reducing their length and therefore their cost. 

Hydroelectric function of the Archibras module 

Since the stabilizing role of the module results from the mechanical resistance exerted by the generator, the amount of electrical energy produced is proportional to the braking power deployed to oppose the movements induced by the swell. 

This electricity production benefits from the wind turbine system. It also benefits from the float and all the difficulties that have been overcome to get it out to sea, including administrative measures and authorizations. 

It differs from intermittent sources of green electricity such as wind and solar because, although variable according to sea conditions, its production is constant, as are the movements caused by the swell.