Since ancient times windmills have been seen as a visually romantic source of energy. The grace and beauty of those slow-motion rotors have mesmerised people through the ages. The attraction of using natural resources to reduce carbon emissions and somehow retain the romance of the ancient ways drives the growth of the use of offshore wind farms to provide much needed greener energy. The UK is now way ahead of the rest of the world in the installation of wind turbines and along with the rest of Europe is harnessing the power of nature into providing power to their national grids. The USA under the Biden administration is also beginning to take wind farm technology investment seriously.

IRS Group foresaw the growth in offshore wind technology and has been providing specialist expert consultants at all levels for twenty years. Coupling that expertise with over thirty years’ worth of supplying staff to the Oil & Gas industry they have gained a reputation for excellence in this part of the power generation world. Building offshore wind foundations has involved IRS in supplying over 500 trades such as Superintendents, Supervisors, Welders, Platers, and Erectors to UK projects such as Beatrice, Moray Firth and Moray East. As the sector has grown so has the requirement for the necessary skills and experience.

As wind farm technology knowledge has scaled up and been harnessing the powers and advantages of higher wind speeds offshore, bigger turbine capacity, and larger wind farm areas, so has the requirements for anchoring them to the seabed.

To ensure stability in the challenging conditions a variety of foundations are currently in use. They all have their pros and cons.

Specifics and Comparisons of the Foundation Types

Gravity-Based Foundations

Using gravel, sand, or stones for ballast, and manufactured from precast concrete, Gravity Based Foundations are for use at depths up to 30 metres.

Pros:

• Use of Concrete and steel is cheaper.
• Engineering already proven in the Oil and Gas industry.
• Cranes not always required.
• Can be assembled onshore and towed to site, lowering risk and costs.

Cons:

• Dredging or seabed preparations required.
• The larger footprint can increase environmental concerns.
• During towing invasive species could be introduced to the foundations.

Monopile Foundations

Generally used in shallower waters at less than 35metres and fabricated from steel.

Pros:

• Good in sand and gravel soils.
• A simple design easily installed.
• Easily adapts to conditions.
• Cost-effective for installations up to 35 m.

Cons:

• Fabrication, installation and transport costs and risks increase for larger monopiles when deeper installations and hydrodynamic loads are possible.
• Installation noise can disrupt, maim, or kill marine life sensitive to pressure waves.
• Wind, wave, and seismic loading can affect and cause early fatigue damage to the structure if it is not allowed for during installation.

Tripod Foundations

These three-legged steel bases are designed for use at depths of up to 50metres and sit just below the waterline where they connect to the central turbine shaft.

Pros:

• No preparation required to the seabed.
• Good to go in softer soils, stiff clays and medium to dense sand.
• Economically advantageous at + 45m
• Better stability for the wind turbine.

Cons:

• Maintenance and construction costs can be high.
• Scouring to base may be necessary.

Jacket Foundations

These are formed from a steel framework similar to offshore oil structures where 4 tubular steel legs and struts are all connected diagonally.

Pros:

• Installation can use piles or suction caissons in stiff clays, medium to dense sands and even softer soils using longer piles that increase friction resistance.
• Can create an artificial reef as a new habitat for local species.
• A good cost-effective solution because of the ease of fabrication.
• Can be towed into position.

Cons:

• Can establish and spread invasive species.
• Need to keep structural integrity with longer maintenance downtimes.
• Can change local water patterns which may adversely affect marine ecosystems.
• Pile driving noise may affect marine life.

Floating Foundations

Floating technology has been in wider use throughout Europe, specifically Scotland and Portugal. The USA has been slower to take up this form, but some regulatory hurdles have been overcome in places such as Maine where the University has been conducting pilot projects to take advantage of strong offshore winds while limiting the environmental impact to their fishing and tourist industries. However, some projects are now in development on both the East and West Coasts.

Pros:

• Allows further reach even to over 200m.
• Can use 58% more offshore wind resources in deeper waters.
• Can be fabricated onshore and towed to site.
• Can be towed back to port for maintenance.
• Less impact to migrating bird life.

Cons:

• Requires longer cabling to secure the platform with continuous inspection and maintenance.
• Cabling and anchors may affect marine life.
• Towing can increase introduction of invasive species.