Gravity Base Foundation for Blyth

A robust and sustainable solution for wind turbine foundations at sea

The end of fossil fuels as a source of energy is getting closer. Stocks are running out all over the world, and the use of these fuels is a severe burden on the environment. This has made energy transition, the transition to sustainable sources like sun and wind, necessary. This is one of the reasons why ever more wind turbine parks are developed, especially at sea. However, the installation capacity in shallow waters is limited, specifically for large turbines with a high energy output (9-15MW). That is why many offshore wind turbine parks nowadays are installed further from the coast, in water of a greater depth (30 metres or more). Their installation calls for foundations that can absorb the strong wave and wind forces found there. However, at sea, the conventional approach of using piles is very expensive and labour intensive. And piling activities also disrupt the local ecology. BAM Offshore Wind therefore developed a solution to this problem that was both innovative and sustainable: a self-floating Gravity Based Foundation.

Self-floating
Our Gravity Based Foundation (GBF) is a concrete foundation for wind turbines that is produced on land, in a dry dock. From the dry dock where it has been produced, the self-floating GBF is floated to its destination and then immersed by ballasting it with water and sand. The GBF rests firmly on the hard sea bed and the wind turbine is then installed on this foundation.

Blyth Offshore Wind Farm demonstration project
The GBFs were first used for the Blyth Offshore Wind Farm, a demonstration project from the English/French EDF Energy Renewables energy company, off the coast in the north east of England. BAM Offshore Wind built the first five wind turbine foundations in a dry dock in Newcastle upon Tyne. These foundations are 30 metres in diameter and have a 60-metre long shaft. They have been immersed and the wind turbines have been put into use.

 

Ecological benefits
It is not only the absence of disruptions from the piling work (in the form of heavy sound waves) that offers important ecological benefits. The GBF can also attract marine life thanks to artificial reef formation on the foundations [link to the study by Wageningen Marine Research]. And what's more, the foundations can later easily be lifted from the sea bed again by removing the ballast sand at the end of the turbine's technical lifetime (approx. 26 years). This means that, other than with conventional solutions like monopiles and jackets, no remnants will be left behind in the sea bed.

Economic value
The GBF enables the offshore wind turbine park to generate local employment, thus also offering economic value. In the Blyth Offshore Wind Farm demonstration project, the GBFs were built on land by local employees and suppliers using a traditional building method. It is expected that the GBF will be used for much larger offshore wind farms in the future. If they have to be built in large numbers, BAM Offshore Wind will be using an industrialized production process to create a cost-efficient production method.

FLOW grant
Great strides have been taken with this innovation. This was partly made possible by the FLOW grant from the Dutch Ministry of Economic Affairs to promote a research programme that binds knowledge institutions with industry and strengthens the global competitive position of the Netherlands. Public and private parties worked together to make this innovation happen and both the environment and the economy stand to benefit from this. Furthermore, our national knowledge of offshore concrete construction has increased drastically, strengthening the Netherlands’ global reputation in this field.

The advantages of Gravity Based Foundation in brief:

  • The GBF is self-floating and is produced on land. This greatly reduces the need for expensive offshore installation activities and equipment.
  • It can be installed in hard seabed conditions and in medium-deep to deep water (30-60 metres).
  • The GBF is highly suitable for use as a foundation for the new generation of wind turbines (9-15 MW)
  • Piling is not necessary, and therefore disruption to marine life is minimised.
  • Positive, secondary effects on the local ecosystem due to the creation of a breeding ground for sea life; the caisson can act as an artificial reef.
  • The GBF is a good alternative to conventional foundation solutions at this depth.
  • The social impact of wind energy as part of energy requirements is becoming more important for governments with projects for which there are no grants; local employment and environmental advantages are added benefits of the GBF concept.
  • The GBFs are dismantled at the end of the turbine's service life.

Timelapse film of the construction of the GBFs.