Gravity-based foundation system for the installation of offshore wind turbines and method for the installation of an offshore wind turbine foundation system

Method for the installation of an offshore wind turbine foundation system comprising, wherein the system comprises:

• three floating concrete bases built with self-floating concrete caissons, equipped with valves for filling them with water and emptying the water out enabling their ballasting and anchoring at their final location,
• a metal structure which connects the three floating concrete bases by means of a connecting element to the wind turbine tower, and
• a metal element which connects the floating concrete bases to the wind turbine, metal element on which a docking area is installed, a maintenance platform and access stairs;
• and wherein each of the three floating concrete bases comprises a lower slab which is in contact with the terrain once the system has been submerged, an upper slab, a perimeter wall and interior walls or partitions that define a first group of interconnected cells;
• and
• wherein the method comprises the following stages:
• a first transport stage wherein the foundation system is towed from a collecting and/or assembly dock to the final location by using tug boats where the three floating concrete bases are anchored,
• a second anchoring stage wherein the foundation system is anchored until making contact with the seabed modifying the overall buoyancy by the controlled ballasting of some groups of cells in the three floating concrete bases with the operation of valves located in said bases, and
• a third refloating stage in the event of dismantling or repositioning of the foundation system by evacuating the water ballast from the previously ballasted cell groups to achieve positive buoyancy of the foundation system.