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Foundation structures


There is still a tendency to use the largest possible offshore wind turbines with higher outputs for new projects. These projects are planned at ever greater coastal distances and thus often also in greater water depths. A suitable foundation type must be selected for each location. The objectives here are both to ensure the stability of the structure over its service life and to use cost-optimised foundations. Because: the costs of the foundations represent a large proportion of the total investment costs of offshore wind turbines. Further requirements for offshore foundations are "simple" and fast production processes, "simplified" manageability during the installation process and general suitability for low-noise installation work. For the reasons mentioned above, the monopile foundation concept has developed over the past few years into the most frequently used foundation variant compared to jacket, tripod or tripile foundations. In 2017, almost 80 percent of newly constructed turbines were founded on monopiles. At the end of 2017, in total around 75 percent of offshore wind turbines were on monopiles and around 7 percent on gravity foundations. The remaining 18 percent are distributed between: jacket (7 percent), tripod (3 percent), high-rise pile cap (6 percent), tripile (2 percent), rest (< 1 percent).


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Data source: [Fraunhofer IEE]



The individual types of construction are suitable for different site conditions. Gravity foundations, monopiles and high-rise pile caps are mainly to be found in coastal and shallow waters. Of the most frequently used foundation structures, only the high-rise pile caps used in Asia are to be found in in the shallowest water (average 7 m) and shortest distance to the coast (average 9 km). The tripod und tripile foundations are found in locations the furthest from the coast, with an average distance of 96 kilometres. Floating structures are still in the test phase, in an average water depth of 85 m. The following figure shows the distances to the coast and the water depths in which the various foundation types are used.






Water depth and distance from the shore of different foundation designs

Data source: [Fraunhofer IEE]