Anchored in 80ft of water off the coast of Castine, Maine, the VolturnUS 1:8 – the first offshore wind turbine to be connected to the grid in North America – is a 65ft-tall floating turbine prototype that is one eighth the size of a full-scale 6 megawatt (MW), 423ft rotor diameter design.
Initial funding to develop the VolturnUS technology was received through the US Department of Energy (DOE) under a competitive grant opportunity submitted in 2008. At that time, the DeepCwind consortium led by the University of Maine was established, which includes approximately 30 partnering organisations, including Cianbro Corporation, the Maine Maritime Academy, the Pacific Northwest National Laboratory, Sandia National Labs and the National Renewable Energy Laboratory (NREL). Since its establishment, the consortium has attracted additional funding from a variety of sources, including the National Science Foundation ‘Partners for Innovation’ programme, Maine Technology Institute and the State of Maine.
The university-led consortium initially designed three 5MW floating turbines, then constructed and tested three different 1:50 scale models of these designs in a wave-wind basin – a spar, a semi-submersible and a tension leg platform (TLP).
According to Dr Habib Dagher, director of the advanced structures and composites centre at the University of Maine and director of the DeepCwind consortium, each model was subjected to 60 identical meteocean conditions based on wind and wave data the university had collected in the Gulf of Maine over a period of 12 years. The results of the tests, along with the specific conditions in the Gulf of Maine, including available supply chain, were used in an ‘optimisation process’ that led to the VolturnUS design.
The design eventually chosen for this project is based on a semi-submersible platform attached to a concrete hull and uses lightweight composite materials instead of steel. It also features an integrated buoy-based floating light detection and ranging (LiDAR) system to measure wind resources and other meteocean factors at heights of up to 600ft above the surface.
“A grid-connected 1:8 scale of a 6MW VolturnUS was constructed and deployed in 2013, to help de-risk the technology and verify the design assumptions,” Dr Dagher explained. According to Dr Dagher, the VolturnUS is a unique, patent-pending, floating wind turbine technology that utilises concrete and composite materials to construct the hull and tower, and an optimised hull design that can be fabricated dockside in 10m of water and towed out to sea.
“The unique corrosion-resistant hull-tower combination allows for re-use of these assets beyond the traditional 20–25 years life,” said Dr Dagher. “The durable concrete and composite technology used, and the dockside assembly method reduce the manufacturing and deployment logistics, and the resulting levelised cost of electricity. Farms can be constructed in water depths of 50 metres or more,” he added.
The VolturnUS project forms part of a broader DOE scheme, which is currently supporting seven offshore wind demonstration projects across the US, each charged with exploring a variety of technologies and strategies to lower the costs and technical challenges associated with offshore wind development.
In early 2013, the university, along with its industrial partners, won the first phase of a national competition from the US DOE to design and build two full-size 6MW units.
“This competition is called the advanced technology demonstration for offshore wind, in which the DOE plans to invest US$50.6 million, in each of three demonstration projects,” said Dr Dagher.
In moving towards full-scale deployment and large-scale grid connection, Dr Dagher explained, the current plan is to deploy two grid-connected 423ft diameter 6MW VolturnUS floating turbines, at depths of between 300ft and 500ft, 12 nautical miles offshore at the University of Maine offshore wind test site near the island of Monhegan – one each in 2016 and 2017. The ultimate aim is to establish a 12MW, US$96 million pilot-scale, grid-connected windfarm, known as Aqua Ventus, with berths for several large-scale turbines, in 2016.
When the technology is eventually scaled-up to full operational size, a chief goal of the consortium is to help reduce the cost of offshore wind so that it can start to compete with other forms of US electricity generation without subsidies. OWJ
© 2023 Riviera Maritime Media Ltd.