Building Offshore Wind Turbines in Port Saves Money
University of Delaware researchers have developed a new method for constructing offshore wind farms and proven that it is cheaper, faster and could make possible offshore wind deployment at a scale and pace able to keep up with the region’s scheduled retirements of nuclear and coal-fired power plants.
The researchers, led by Willett Kempton, professor in the College of Earth, Ocean and Environment, calculated that their process will cost up to $1.6 billion less per project than conventional approaches and take half the construction time.
The key insight that allowed Kempton’s team to make considerable optimizations in cost and deployment speed was that the entire structure, from seafloor mounting to the top of the turbine, can be assembled in one piece in port, moved as a unit, and in one step placed into the sea floor.
The reference design used 10-megawatt turbines with support structures, together standing twice as tall as the Statue of Liberty and weighing 2,500 tons. 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 in the ocean, we have an assembly line on shore,” 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 by suctioning large buckets to the seafloor rather than using steel piles. This also means that the foundation doesn’t penetrate as deeply into the seafloor, which reduces costs for everything from the attachment process to the surveying required in advance. And without pile driving noise, installation has no acoustic impact on marine mammals.
The UD team members included Kempton and CEOE colleagues John Madsen, a continental shelf geologist, and Jeremy Firestone, a wind power policy expert, as well as mechanical engineer David Burris.
The team designed a hypothetical one-gigawatt wind farm in the Delaware Wind Energy Area off Rehoboth Beach, using the port near Delaware City (now an abandoned chemical site and an operating refinery). One gigawatt is the size of the largest nuclear power generators; the power from each offshore development this size would power 300,000 houses.
“Delaware City is one of only a handful of ports on the East Coast that actually could support this kind of work in the future, at scale, although it would need some upgrades first,” said Kempton.
Madsen’s assessment of seafloors 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 installed blades would reduce lifetime. Transport with attached blades is also unstable. Instead, the researchers developed a mounting for transport and a method to attaching the blades in place at sea.
The project was funded by the U.S. Department of Energy.