Innovative Offshore Wind Power Foundations: Gravity-Based & Floating Wind Turbines

At Bygging Uddemann we specialize in the serial production of concrete structures for offshore wind power foundations. Our expertise lies in the design and construction of Hull, Spar, Semisubmersibles, and Gravity-Based Foundations (GBF).

Open seas are the ideal place to establish wind turbines.

Around 80% of the world’s offshore wind resource potential is in waters deeper than 60 metres. But building wind turbines fixed to the seafloor in deep waters is a complex process. The best way to overcome the difficulty is to set up floating wind turbines.

We can help you utilize the potential of floating wind turbines due to the construction of the floating foundations being quite suitable for the slipform technique. We can offer both our heavy-duty slipform system (for small scale projects) and our gantry slipform system (for larger scale projects). Both systems can be combined with our IP-CCV Transfer System which will provide any contractor with a one packet solution for the construction of foundations.

Why we need floating wind power?

The next decisive phase towards the goal of reducing carbon emissions and advancing renewable energy solutions is happening right now – and in the middle of this revolution, we find floating wind power. While traditional wind turbines remain and will most likely always be necessary, floating wind turbines allow us to take wind power to the next level in terms of the effectiveness of wind power, and the number of wind turbines.

The floating wind turbine is especially important to reduce emissions in India, China, and South-East Asia. These are the places where we need to establish renewable energy solutions of scale as an alternative to coal. But constructing wind turbines is easier said than done. Areas with big open spaces where the wind is powerful are usually very far away from the big cities – or there simply might not be sufficient space or powerful enough winds.

How does a floating windmill work?

The floating windmill is often referred to as third-generation wind power. Where the first-generation are the one’s on land, and the second-generation is constructed in the ocean, fixed to the seafloor.

A floating wind turbine looks like a traditional wind turbine but is constructed on a floating fundament. To keep the wind turbine from toppling over, the floating fundament utilizes the iceberg principle, where the majority of the structure is under-water.

Build towards the future with Bygging-Uddemann

One of our targets for the future is to contribute to creating sustainable, resistant, and including infrastructures. We believe that the floating wind turbine is a pioneering solution and a really big leap towards that goal. Contact Bygging-Uddemann today for more information about how we can become your partner for the construction and establishment of floating wind power solutions.

GBF

What is a Gravity Based Foundation (GBF)?

As the name suggests, a gravity-based foundation is a structure based on gravity, for facilities in a marine environment. The science behind it is that it uses gravity to hold the plant and the lifting force to make it float. The structure’s own weight helps to withstand lateral forces.

Common applications are oil platforms and offshore wind power. The conditions for gravity-based foundations are that the sea depth is at least 20 meters and that the seabed is sufficiently stable to withstand the pressure in the vertical direction.

Gravity-based platforms are usually made of concrete. They are robust and withstand harsh weather conditions at sea, and have proven to be a suitable choice even in Arctic environments.

With that said, there are certain requirements to consider when choosing concrete: the concrete must be able to withstand forces of up to 100MPa, be resistant to chloride and sulphate ions and in some climates, cope with stresses from ice formation and melting.

Installation of a gravity-based foundation

A challenge during construction and installation is the size of the facility, and that it must be designed to withstand large forces of nature. Material quality is therefore of the utmost importance.

The concrete bottom of the structure is built in a dry dock. Most requirements need to be placed on the dry dock to ensure its suitability. Examples of requirements are sufficient depth, taking into account the size of the base, the design of the base, the bearing capacity of the dock, its drainage system and its bottom material if the gravity-based foundation is placed directly on the bottom. The dry dock must also be waterproof, but have an openable exit so that the foundation can be towed out. It must therefore withstand enormous forces from all over the sea.

It is then transported out to a protected deep port, where it is moored. Thereafter, the towers are created by slipform casting in a continuous process.

The weights are then removed and the whole structure is towed out to the installation site using tug boats. Once there, ballast is placed to secure the foundation to the seabed.

Offshore wind power with gravity-based structure

Structures based on gravity for offshore wind turbines have been shown to have several advantages compared to the alternatives. In cases where the seabed is not sufficiently stable, however, other methods are preferred, such as different types of piling.

Two factors that speak for gravity-based structures over the alternatives are the environmental impact and the economic aspect. Since no piles need to be installed, the impact on the seabed is reduced, as is the noise level during installation. Mounting steel piles causes higher noise levels that can disturb the sea fauna. Concrete that is often used for the base is also a relatively cheap material. It can be used in deep water without any problems. Steel piles require larger diameters with increased water depth, which further contributes to the cost.

When building wind turbines of this structure, however, there are some challenges to take into account. Above all, it is important to be able to produce a construction that resists cyclic forces, ie forces that vary over time, which naturally gives more wear than static forces. These forces come from natural variations in wind speed and wave energy.

Offshore wind turbines with gravity-based construction are currently located in Sweden, Finland, Norway, Belgium and Germany in Europe and interest is growing in several parts of the world.

Maintenance of offshore wind power

Most offshore wind power plants built with gravity-based foundations are made of concrete. This has the great advantage that they require very little maintenance compared to, for example, metal constructions. Steel structures also have a shorter service life and need to be replaced more often. Concrete is a material that has less impact on the environment – when concrete structures need to be replaced after 20-50 years, the old ones can easily be recycled.

In summary, gravity-based constructions have several advantages over traditional piling methods: less environmental impact on the seabed, less noise that disturbs underwater life during installation, materials that require very little maintenance and withstand the test of time, lower material costs, flexibility in size – everything from huge oil platforms to wind turbines can be built according to this method – as well as the possibility to install in varying temperature conditions and climates. Wind power companies with offshore wind power thus have much to gain from switching to gravity-based technology in cases where it is possible.

Recommended Reading!

An overview of our range of solutions for Offshore Floating and Gravity Base Concrete Structures.