I.1.1.2 Foundation installation equipment

Function

Foundation installation equipment is used to secure the foundation to the sea bed.

What it costs*

Equipment, third party crew to operate, bolting tools or grouting spread, generators, survey equipment and ROV are usually rented for the duration of the project, rental rates vary significantly depending on the characteristics of the wind farm. 

Who supplies them

Piling equipment: Cape Holland, Fistuca, IHC IQIP, Menck and PVE.

Noise mitigation: IHC IQIP and W3G Marine.

Key facts

Vessels have a range of onboard tooling, depending on type of foundation to be installed.

For monopiles, on-board hammer and anvil systems are used to drive the piles. On-board drilling systems are used where hammering is not possible due to ground conditions or environmental restrictions. In such conditions, monopiles are then grouted into position.

A hammer and anvil system may be rated up to 4,000 kJ and deliver 30-60 impacts per minute via a steel ram. Hammers can pile up to 9 m diameter piles. Larger piles may be tapered at the top to avoid any constraint.

A novel system in development is the use of a water column to drive the pile. The reported benefits are lower noise, fewer moving parts and less installation fatigue. Vibro piling has also been trialled and offers the potential of less noise and faster, lower impact piling.

Turbine locations are typically chosen to avoid areas where piling is likely to be problematic. For some sites, a vessel will be mobilised with drilling equipment to mitigate the risk to the project schedule in cases of pile refusal.

For pre-piled jackets, a reusable piling template is lowered to the sea bed and the pin piles hammered into the sea bed using the same process as for monopiles.

There is concern about the ecological impact of pile driving on marine mammals and the harbour porpoise in particular. Piling restrictions have been most common in Germany and the Netherlands.

There are three approaches to minimising the environmental impact of piling: avoidance, deterrence and mitigation.

For avoidance, the aim is to choose foundation technologies (for example, jackets or suction piles) and installations strategies (for example, timing or vibro piling) that have reduced impact.

For deterrence, the aim is to displace animals from areas of high noise levels by means of a ‘soft start’ or using a deterrence device. ‘Pingers’ emit aversive sounds into the marine environment for about 40 mins before piling. ‘Seal scarers’ are similar but emit higher density sounds for about 30 mins before piling.

The two main mitigation technologies are bubble curtains and noise mitigation screens. Other approaches are foam-wrapped piles, hydrosound dampers and resonator systems.

Mitigation systems are expensive both in terms of equipment and time and there has been a large amount of research to understand the enduing impacts of piling on marine mammal populations. Projects may monitor impacts during installation as part of this activity.