Offshore wind turbines could benefit from tripod foundation. Here's how

The design is set for a comeback.
Ameya Paleja
Offshore tripod
Offshore tripod

TII Group/Facebook 

When speaking of wind farms, the image of turbines installed on a single foundation come to our mind. This, however, is true only for onshore wind turbines. As we enter a new era of wind power generation where offshore wind farms become more frequent, experts believe we are going to see a return of the tripod foundation.

While single or monopile foundations are also currently being used in offshore wind turbines, as we foray deeper into our seas, looking to tap into larger amounts of wind power, other ways of hoisting wind turbines are being explored.

Many construction companies have already moved toward floating platforms using either semi-submersible or spar buoys for their wind turbines. However, for these depths, even tripod foundations can be quite useful. Let's see how they are advantageous.

What are tripod foundations?

Offshore wind turbines could benefit from tripod foundation. Here's how
Tripod design foundation of a wind turbine

As the name suggests, tripod foundations have three-legged tripod bases that connect to a cylindrical central column below the waterline. This design is different from the three-pile foundation, which uses three separate pile legs that connect to a central support tower above the waterline. Above the waves, a turbine installed using a tripod foundation appears like a monopile.

The design for the wind turbine foundation is drawn from the lightweight and cost-effective three-legged steel jacket design used in offshore fields by the oil industry. The design allows forces from the tower to be distributed into three steel piles, each driven up to 65 feet (20 m) into the sea bed. The foundation is anchored into the seabed using a relatively small steel pile, about three feet (0.9 m) in diameter.

Pros and cons of tripod foundations

The greatest advantage of tripod foundations is that they can be deployed at greater water depths with only a minimum site preparation required prior to installation. The design is also well suited for areas where stiff clays or medium-to-dense sands are present. However, it can be used in softer soils, too, making it highly versatile in application compared to other methods of foundations available today.

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The design of the foundation provides extra stability to the wind turbine, which is an important factor to consider now since turbines are being built in greater depths of the sea. In water with depths of approximately 150 feet (45 m) or more, tripod foundations are considered an ideal choice as well as an economical one.

The design usually enjoys protection in areas that see frequent erosion. If required, scour protection can be added around the tripod base if the erosion rates are very high or the bottom currents are significantly strong.

Previously, the cost of construction and maintenance of tripod foundations was considered a disadvantage. However, as the size of turbines is increasing, the diameters of the monopiles are also increasing, making them increasingly difficult to construct. The tripod design, however, offers ease of construction as well as greater stability to the design and is poised for a comeback in the offshore wind power industry.