A study by researchers at the University of Delaware has concluded that the most cost-effective way to build offshore windfarms is to assemble turbines and foundations in port.
Working closely with industry partners, University of Delaware (UD) researchers have developed what they claim is a new method for constructing offshore windfarms and have proved that it is less expensive and faster than alternatives, and could make possible offshore wind deployment at a scale and pace that would keep up with the region’s scheduled retirement of nuclear and coal-fired power plants.
The researchers calculated that their innovative process will cost up to US$1.6Bn less per project than conventional approaches and take half the time.
“In planning for offshore wind power, the big question is how we generate electricity cost-competitively, and at a scale that is both a relevant replacement for ageing power plants and also applicable to climate change,” said the project’s principal investigator, UD professor in the College of Earth, Ocean, and Environment (CEOE) Willett Kempton. “We’re the first people who have shown the engineering details, step-by-step, how to achieve that.”
The key insight that allowed Professor Kempton’s team to make such considerable optimisations in cost and deployment speed was that the entire structure, from foundation to the turbine, can be assembled in one piece in port, moved as a unit, and in one step installed on the seabed.
The reference design used 10 MW turbines with support structures, together weighing 2,500 tonnes. Figuring out how to build and move them around in port was the final hurdle surmounted in the five-year study’s new construction method.
“Instead of today’s method, carrying out parts separately and individually assembling each at sea, we have an assembly line on shore,” Professor Kempton said. “We spend more money in port, but we spend far less money at sea.”
In addition to cost savings, there are non-monetary benefits: shifting more of the assembly to land enables construction to proceed regardless of the weather and reduces time at sea from three days to 10 hours for each turbine installed. Integral to the method is to anchor the turbines using suction buckets rather than driving piles into the seabed.
The UD team members included Professor Kempton and CEOE colleagues John Madsen, a continental shelf geologist, Jeremy Firestone, a wind power policy expert, and mechanical engineer David Burris.
The team began with a dozen possible design solutions, which they whittled down to four construction scenarios worth evaluating for detailed engineering and cost. To assess the different approaches, the team designed a hypothetical 1 GW windfarm in the Delaware wind energy area off Rehoboth Beach, using a port near Delaware.
“Delaware City is one of only a handful of ports on the east coast of the US that actually could support this kind of work in the future, at scale, although it would need some upgrades first,” said Professor Kempton.
Madsen’s assessment of seafloor showed the new approach could be effective from Cape Hatteras, North Carolina to Massachusetts, and that it has the potential to work elsewhere after similar geological evaluation. Burris’ research on turbine bearing wear and failure led the team to conclude that transporting turbines with blades installed would reduce lifetime. Transport with attached blades is also unstable. Instead, the researchers developed a mounting for transport and a method to attach the blades in place at sea. Collaborating with active commercial partners provided much-needed industry expertise.
“We knew we had to do that to be realistic,” Professor Kempton said, adding that the co-operative effort with experienced partners gave their results added credibility to the wind energy industry. The project was funded by the US Department of Energy.