Sustainable decommissioning of offshore wind turbine foundations

 

The limited lifetime of offshore wind farms requires an efficient and safe decommissioning. The project Hydraulic Pile Extraction Scale Tests (HyPE-ST) studied the option of removal of offshore wind turbine foundations (monopiles) in a sustainable way. HyPE-ST project aimed at both the fundamental understanding and the demonstration of the feasibility of hydraulically extracting monopiles for decommissioning. The project was a one-year R&D Joint Industry Project executed within the GROW research program.

Offshore wind farms are being built in large numbers to meet the ever-increasing demand for renewable energy. However, wind farms have a limited lifetime. Wind farm owners, such as energy companies, therefore have the responsibility to decommission the wind turbines from the sea when needed. For instance, current offshore turbines were designed with a technical lifetime of 25 years.

Monopile foundations

This research project primarily focuses on monopile foundations. Monopiles are open-ended steel piles that can be up to 80 metres long and weigh up to 1,300 tonnes and are the most commonly used foundation type for offshore wind turbines. Currently, offshore (mono)piles are removed by cutting them off several metres below the seabed, which leaves behind tonnes of steel buried in the seabed. The HyPE-ST project aims at developing innovative and smart technology to remove the entire monopile in order to make it possible to recycle the steel.

Hydraulic extraction

In the Deltares’ Water-Soil Flume facility, scaled monopiles will be tested on the possible use of water-pressure to fully retrieve them from the seabed. The tests took place in different (engineered) soil conditions such as sands with varying densities, clay, and layered soils.

The HyPE-ST project is part of the GROW program and a joint industry initiative of Innogy, Deltares, DOT BV, IHC IQIP, Jan De Nul Group and ECN part of TNO. The project receives also financial support from the Topsector Energy of the the Dutch Ministry of Economic Affairs and Climate.