Growth through Research, development & demonstration in Offshore Wind
Growth through Research, development & demonstration in Offshore Wind
Monopiles are the most common foundations for offshore wind turbines. As turbines grow larger, monopiles also increase in size and weight. Nowadays, monopiles can be up to 80 metres or longer and weigh 1,500 to 3,000 tonnes. With 15 MW turbines already commercially available, we expect future monopiles to become even bigger.
When a turbine reaches the end of its life, the owner must remove the entire structure. To prepare for this, the offshore wind sector is developing new, efficient methods for removing turbines and their foundations.
We are studying a method for pile foundation removal that uses hydraulic extraction. In this approach, the pile is sealed and its interior is pressurised with seawater. This pressure pushes the pile upwards, freeing it from the seabed.
Hydraulic extraction is expected to be almost silent, causing very little disturbance to marine mammals. It also requires no excavation, so the seabed layers remain intact. This makes the method gentle on benthic life — the organisms living on or in the seabed.
In earlier GROW projects, HyPE-ST and HyPE-ST1.2, we successfully tested hydraulic extraction at small and medium scales across different soil types. We found that the technique can remove an entire monopile with very little noise. However, before it can be used confidently at full scale, it needs to be demonstrated first.
This project aims to create a roadmap that identifies the knowledge and practical gaps that must be resolved before a large-scale field test. There are still uncertainties about technical, operational and cost issues. In addition, we want to explore options for a pilot project to demonstrate the technology offshore. In this project, we start with the information and knowledge gained in the two earlier projects. We will carry out the following activities.
The first work package focuses on defining the specifications and requirements. It includes scanning the market for suitable solutions, creating conceptual designs, and reporting the technical options.
The second work package covers designing the workflow and selecting the necessary equipment and vessels. It also includes calculating the cost of hydraulic extraction, comparing it with alternative methods, and developing the business case.
The third work package involves identifying potential pilot locations, approaching owners of wind farms due for decommissioning, preparing the technical qualification plan, and drafting a pre-proposal for the pilot project.
The project must result in an overview of all key aspects needed to move confidently into the next phase of hydraulic pile extraction: an offshore test of the technology.
Alba Rodríguez Piedrabuena
+31 6 4644 3416
Test hall, with installed medium scaled monopile at the Testzentrum Tragstrukturen in Hannover.
One example of an operational aspects is that offshore monopiles have holes in them. These are to let the cables come out of the wind turbine to be connected to the network. But with a hole in the pile, you cannot build up the pressure. A hole-closing tool was designed. This was placed inside the monopile with a high-power magnet to hold in place and ensuring the hole is closed so the water cannot go out.
Under Pressure
This project is supported by the Dutch Ministry of Climate Policy and Green Growth and TKI Offshore Energy