Foundations can account for 30-50 per cent of the development cost of an offshore windfarm so their design, construction and installation is an incredibly important area the industry needs to focus on to continue to reduce the levelised cost of electricity from offshore wind.
Continuous improvement and a fair amount of innovation will be required in a number of areas, not least because the size of turbines continues to grow. OEMs are now offering 8-9 megawatt (MW) turbines and 12MW – even 15-20MW units in the longer term – are on the drawing board.
However, as experts at Atkins in the UK told the Offshore Wind Energy 2017 conference in London in June, foundations capable of supporting 10-20MW turbines are perfectly feasible.
Atkins has been reviewing foundation design, looking at potential future trends between now and 2025, including fixed and floating structures. It notes that foundation design is going to have to evolve quickly to meet the demands that new, larger, more powerful turbines will place on them.
Atkins believes that monopile foundations will continue to predominate in shallow water (0-40m), but the shift to larger turbines of 8MW+ will favour the use of jacket foundations. The use of gravity base foundations is also gaining momentum for offshore windfarms with challenging ground conditions and using floating structures is a great option for water depths exceeding 60m.
The results of Atkins’ research are reassuring as the company believes that reducing jacket weight by up to 10-15 per cent is possible. This was done by reviewing the requirements for installation, fabrication, and design parameters such as corrosion allowance and local jacket joint design.
Having carried out extensive market research on foundations, Atkins believes it has identified design drivers that can help reduce costs. It has also identified cost-saving opportunities for standardisation, a view shared by ST3 Offshore in Poland, which believes that although jackets are relative newcomers in the offshore wind space there is significant potential for design optimisation. It also believes that jackets can be an attractive alternative to the monopile cost-wise.
Working closely with Salzgitter and other major developers, ST3 Offshore has developed a standardised jacket foundation adaptable to most seabed types, water depths and turbines.