Combined expertise cuts wind turbine installation times

The offshore wind farms under development today are moving to more remote locations and increasing in capacity and size, bringing with them a host of new challenges. The biggest of these is created by a vast increase in the weight and height of turbines. This has driven the demand for a new-generation of monopile installation and maintenance vessels designed to cope with the industry’s future developments and needs.

Monopile installation vessels have traditionally been jack-up units and to some extent moored floaters. However, as foundation sizes have increased, jack-ups are predominantly used. They typically employ pile-grippers on static frames, with complex mooring arrangements to hold the pile steady until it can be securely and permanently fixed to the seabed.

“A pile standing on the seabed will self-penetrate to a certain level, but it is not stable,” explains Kristina Arutjunova, Director Sales and Marketing Innovations, Advanced Offshore Solutions, MacGregor. “Wave forces can be considerable, therefore the pile must be held still by a guiding frame on the vessel until it is driven down to a stable position. If the vessel is moored very securely, and the sea state is calm, a traditional pile-gripper, fixed to a static frame, can be used. However, these ideal conditions are often not seen offshore.”

Market-ready technology

Recognising this gap in the market and the need to offer operators a new monopile installation method that benefits from the latest automated solutions, MacGregor and Kongsberg Maritime embarked on a joint development project. Its aim was to deliver significant improvements in the operability, productivity and efficiency of future generations of monopile installation vessel fleets.

Both companies believed that substantial cost and time savings could be captured by applying motion-compensation technology, coupled with dynamic positioning (DP), to the monopile installation process. This resulted in the development of a new pile-gripper solution, which is now ready for the market.

“We have developed a core solution that tackles the efficiency of turbine and foundation installation vessels by replacing lengthy, temporary mooring processes with full DP in combination with an innovative guidance system and hydraulic frame mechanism,” says Gunnar Thorsen, Executive Vice President Business Development, Kongsberg Maritime.

Wider operational windows

“Our newly-developed pile installation method represents a considerable improvement over traditional methods,” Ms Arutjunova continues. “Piles can be installed in a wider range of sea states and operators are not longer constrained by waiting for ideal weather windows. Essentially, the motion-compensated pile-guidance frame ensures shorter installation times and increases operational weather windows, adding up to substantial cost savings. We are confident that the capabilities offered by this new system will meet the developing needs of the offshore wind energy capture market, especially as it addresses the fundamental issue of handling these larger turbines, but also the need to install a greater number of them more quickly and further offshore,” she concludes.

A new monopile installation method is now available

The jointly-developed new pile-gripper solution consists of the following components:

• Motion-compensated, hydraulically-operated pile-gripper: provides a precise, responsive and powerful hydraulic frame mechanism for holding monopoles in a vertical position in open seas
• A pile-gripper guidance control system: this works in tandem with the high-precision DP system and provides a coordination link between the pile-gripper and the DP system
• A pile-gripper servo control system: this translates vessel motion and monopile position data to movement in the actuating cylinders. It also monitors loads and the status of the pile for feedback into the guidance system.
• Abandon monopile capability: if there is a loss of position, the monopile is guided into the last possible position, and then the gripper is opened for abandoning the pile.