Who will maintain floating offshore wind turbines?

The floating offshore wind market is in its infancy. The first signs of a new flourishing industry are on the horizon. However, who will maintain the floating offshore wind turbines?

O&M Market potential

Analysts at Conbit are forecasting the number of major component replacements on offshore wind turbines that can be expected globally until 2040. The results need a response from the market.

The maintenance market is limited in size. It shows that the turbines are unlikely to fail but when they do, how will major components be replaced?

Conbit's analysts have forecast that the first major components in floating wind turbines will need replacing in 2025. These initial replacements are expected to be in early phase technology and can be serviced by crane vessels. The market potential will grow from five major component replacements yearly from 2030 onwards to over 15 by 2035. These overhauls are predicted to be in very tall turbines and are further out to sea. Also, most of the projects will be in Europe and Asia. Floating wind turbines have global potential, which will result in a scattered market.

Characteristics

Due to the nature of floating offshore wind farms, the maintenance strategy is complex. The wind farms will be located in remote areas, further away from the shore. Logistical aspects and workability due to weather make extensive maintenance challenging. Furthermore, the turbines are becoming taller and their components heavier.

Exchange Strategies of Major Components

Two main strategies are considered viable: onshore overhaul and offshore overhaul. Onshore overhaul requires towing the turbine to shore. Offshore handling will require lifting in the offshore environment.

Onshore: Tow-to-port

The turbine will be disconnected from the wind park and towed to shore. Having arrived on the quayside, the major components will be replaced by a land-based crane. After maintenance, the turbine will be towed back to the wind park and re-connected.

Offshore overhaul

Two main approaches are considered feasible: lifting by crane vessel or lifting by temporary equipment. The traditional method for replacing heavy components in offshore turbines relies on the use of crane vessels. The crane vessel is positioned alongside and replaces the major component.

The use of temporary lifting equipment is now being developed by companies like Conbit and Mammoet. This lifting approach is based on lifting systems that are temporarily connected to the wind turbine. The lifting system will replace the major component before it is disconnected and transported back to shore.

The future of major overhauls

The currently available marine assets will not be able to serve the offshore wind market. The wind farm installation vessels are used to install bottom-fixed structures and are based on jack-up technologies. Because floating wind farms are located in deeper waters, it will not be possible to use the jack-up principle.

The market for replacing major components in floating offshore wind turbines is too small to allow for major investments in new crane vessels. No other application is identified for the new type of vessels required for this market.

If there is marine spread available that can replace major components, it will be occupied and unavailable for corrective maintenance. The global nature of the floating wind market will require lifting capacity in many parts of the world. One vessel cannot serve the whole market, because of long mobilisation times.



Tow-to-port is a realistic concept. However, this concept will require complex mooring and anchoring systems to make effective (dis)connection. The marine spread requirement should not be underestimated, and will impact the required weather window.

Another often overlooked challenge is the lack of land-based cranes suitable for performing the replacement on the quayside. The cranes were available during the construction phase but are unlikely to be near the floating wind farm due to other projects. These cranes are often servicing long-term projects because their mobilisation costs are high.

Conbit has chosen to use temporary lifting systems to replace major components in floating wind turbines. The equipment will be available for use in other industries, thus reducing the investment risk and actual rental costs.

Temporary systems can be transported to remote locations within a few days. The marine spread requirements are limited and suitable assets are readily available globally.

Temporary lifting systems

Two types of temporary lifting systems are currently being developed. One is based on modular equipment, while the other is a dedicated offshore turbine crane. Below you will find two concepts developed by Conbit and Mammoet respectively.

Modular systems by Conbit

Conbit is developing a lifting system based on the use of modular components that are assembled at the top of the wind turbine. Lifting is done by winches that remain at the base of the turbine.

Bram van Oirschot, Sales Manager at Conbit: “This is the right time to make provisions to enable the safe and economic replacement of components inside floating offshore wind turbines. Conbit is investing to serve the future offshore wind market."

Turbine crane by Mammoet

Mammoet is developing a dedicated turbine crane, which connects to the turbine tower and nacelle. All lifting is done from within the turbine crane.

Both concepts are in a late stage of development and nearing market-readiness. Both systems require less investment than new floating cranes. It is expected that the service based on temporary cranes will be more economic than the tow-to-port strategy. Both these systems can be transported to project locations around the world within several days.

The main challenge is to integrate the design of these systems with the turbine design. The loads resulting from these systems must be incorporated in the design of wind turbines. Conbit and Mammoet are both optimistic about the feasibility. Currently, the two parties are in discussion with turbine manufacturers to overcome this challenge. Load guidance during the lifting is also essential in both concepts. Both parties have created bespoke solutions and potential partners have been selected to address this aspect.  

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