"The biggest potential for cost savings and risk mitigation in offshore wind is ensuring the fully integrated design of the structure from the wind turbine to the seabed," said Kim Andersen, offshore director at foundation supplier MT Højgaard. Manufacturers are usually brought in at the last minute, when it is too late to suggest cheaper or better ways of doing things or to avoid expensive mistakes, delegates heard.
Foundation manufacturers are usually only involved in the process — and given the design parameters, including structural load data — once the project has received consent, around 9 to 12 months before the final investment decision (FID), explained Benoit Tavernier, marketing manager of construction specialist STX Europe Offshore Energy.
Foundation suppliers are generally selected through a competitive tender, which does not allow for open and detailed discussions to optimise the design because of confidentiality issues. And the design is often still being developed at this stage, Tavernier added. Once the FID has been taken, the design certified and contracts signed, the pressure is on to build the project as quickly as possible.
In a case he said was fairly typical, Tavernier cited an example where a design specified that certain joints on a jacket had to be welded on both sides, which is not possible. Such a mistake could lead to a year's delay while the foundation was redesigned and recertified.
Likewise, while designers work to optimise the weight of the jacket, they are often unaware of the constraints of the steel market, Tavernier noted. This can lead, for example, to very complex steel specifications requiring many different thicknesses in small quantities, at a high cost.
"Designers can use less steel in the transition piece [of a monopile], but this can cause problems when fixing it to the foundation," Andersen added. Similarly, a lighter tower means a heavier foundation. Cooperation is needed to find the ideal combination. An integrated design approach could reduce the weight — and cost — of monopiles dramatically, Andersen argued.
An example of the gains that an integrated approach can achieve, is the jacket developed by STX and Areva for the latter's 5MW and 8MW turbines. The jacket is 30% lighter than one using the same structural calculations but not taking account of procurement and construction constraints, Tavernier stated.
Incorporating construction constraints would also allow for more standardisation in the manufacturing process, which would again help drive down costs. For example, the upper part of the jackets could be the same, while having all the same angles for welding would also help. Although every site, and therefore every foundation, is different, even small improvements could add up to significant savings at project level.
If all six offshore substations for projects awarded so far in France were made by one manufacturer, savings of up to 15% are possible, Tavernier argued, compared to a bespoke design for each substation based on specific customer specifications. This "standardisation effect" includes savings in engineering and gains from "the production learning curve", plus additional benefits in terms of quicker deliveries, he said.
The reason why this money "is being left on the table", as Tavernier put it, is that "procurement through competition is preventing the early involvement of manufacturing companies". MT Højgaard is looking at ways to open things up. The company is in talks with clients about how they could still tender but retain confidentiality, Andersen explained. Unless the industry finds some way to adopt an integrated design approach, "by choosing turbines early and foundations later, it is missing an opportunity to cut costs," he warned.