Big Opportunities Beckon for Floating Wind
According to the Energy Technologies Institute, offshore wind deployment could reach 20-55 GW by 2050. Most of these platforms will be fixed-bottom, utilizing relatively shallow and near-shore sites that can be developed at the lowest cost. As this “low-hanging fruit” is taken, wind farms will need to move into deeper water, which is where floating wind will come into its own. Fixed-bottom projects have a number of issues, including challenging seabed geology, cabling and massive foundation structures, among others. Floating offshore wind could avoid a number of these uncertainties, unlocking deep water sites close to shore which would support conventional high voltage AC transmission, port-based O&M support, and lower installation and major repair costs by removing the need for expensive specialized installation vessels.
The USA has a significant floating wind resource available
The US Pacific coast, the islands of Hawaii and some areas of the Eastern seaboard are looking like good areas to implement the next generation of US OW projects.
The current designs are prototypes. They inevitably come with high price tags and long periods from blueprint to test turbine to the commissioning of a commercial array and power to the grid.
However the past few years of renewable energy has shown how costs – including CAPEX, OPEX and LCOE can come down dramatically. There is no reason to suppose that floating wind would be any different.
DNV-GL has already issued a standard, DNV-OS-J103, for floating wind systems.
Safety philosophy and design principles
Site conditions, loads and response
Materials and corrosion protection
Design of anchor foundations
Transport and installation
In-service inspection, maintenance and monitoring
Cable design (structural)
Guidance for coupled analysis
Although there is only one fully-functioning commercial array in the world (Equinor’s Hywind off Scotland), many other prototypes are being tested. Several of these are in the USA and this article will look at them.
There are many different types of floating wind designs being planned or trialled around the world. Currently there are three main categories of foundations for floating wind, though that does not mean that some innovative new design might not be a game-changer.
Spar-buoy: A cylindrical ballast-stabilised structure which gains its stability from having the centre of gravity lower in the water than the center of buoyancy. Thus, while the lower parts of the structure are heavy, the upper parts are usually lighter, which raises the centre of buoyancy. The the spar-buoy is typically fairly easy to fabricate and provides good stability, but the large draft requirement can create logistical challenges during assembly, transportation, and installation, and can constrain deployment to waters less than 100m depth. The Hywind design is representative of this type.
Spar-submersible platform: Buoyancy stabilised platform which floats semi-submerged on the surface of the ocean whilst anchored to the seabed with mooring lines. Often requires a large and heavy structure to maintain stability, but a low draught allows for more flexible application and simpler installation. The WindFloat turbine uses this foundation.
Tension Leg Platform (TLP): A semi-submerged buoyant structure, anchored to the seabed with tensioned mooring lines, which provide stability. The shallow draught and tension stability allows for a smaller and lighter structure, but this design increases stresses on the tendon and anchor system. There are also challenges with the installation process and increased operational risks if a tendon fails. A promising design is GICON-SOF.
Current Major Floating Wind Proposals
Castle Wind Morro Bay Project
This ambitious scheme to build around 1000MW of floating wind off the California coast is moving forward. The largest state has significant offshore wind resources. Some estimates suggest that up to 15 GW of offshore wind capacity are potentially available around California’s shores.
The wind farm is planned to be located over 30 miles offshore, taking advantage of a consistent wind resource with an average speed of 8.5 meters/sec. 100 floating OW turbines with a capacity of at least 8MW are proposed in this plan. Current timeframe envisages construction 2025 to 2027.
BOEM has received a total of three unsolicited wind energy lease requests from two potential developers: two lease requests from AW Hawaii Wind, LLC (AWH), the AWH Oahu Northwest Project and the AWH Oahu South Project; and one from Progression Hawaii Offshore Wind, Inc. (Progression), the Progression South Coast of Oahu Project. Each project proposes an offshore floating wind energy facility with a capacity of approximately 400 megawatts (MW) of renewable energy. The energy generated by the projects would be transmitted to Oahu by undersea cables.
Given that onshore wind turbines have been subject to protests in Hawaii, and the average wind speeds in the areas are 9.93 m/s and 9.08 m/s, this seems like a proposal that would satisfy local inhabitants as well as advancing Hawaii’s goals for renewable energy.
Maine Aqua Ventus
Maine Aqua Ventus will deploy two 6MW turbines on VolturnUS, the floating concrete semi-submersible hull designed by the University of Maine, which was already successfully tested in 2013-14. The 12MW project is expected to be installed 12 miles off the coast of Maine in 2020.
An interconnection AC cable will join the turbines, and then connect to a 34.5 kilovolt (kV) subsea power cable extending from the test site to a proposed onshore transition point.
The Maine Public Utilities Commission (PUC) approved the power purchase contract for the turbines in November 2019.
This looks like it will be the first significant floating wind array to be built in US waters.
The View from the Shore
Floating wind has a lot to recommend it, including decent wind speeds and a good capacity factor for many sites. Various states, particularly those bordering the Pacific Ocean, are considering floating wind projects as the waters are too deep for fixed-bottom platforms. Inevitably there will be technical difficulties and the investors will have to contend with heavy costs of development. These will be ameliorated as a production pipeline emerges and designs are standardised. We can expect to see dramatic reductions in LCOE as evidenced by other renewable industries.
The US offshore wind market is probably the most rapidly-developing renewable energy sector in the world. Follow #USOW20 for the latest news and expert opinions.
5th US Offshore Wind 2020 Conference and Supply Chain Exhibition
Your Gateway into the U.S. Offshore Wind Industry - Boston June 18-19, 2020
Join us at USOW20, the premier conference for businesses that are looking to invest, find partners or secure contracts in upcoming U.S. offshore wind projects. With over 2000 attendees and major decision-makers present, this is the most compelling event for anyone wanting in-depth insight into the expanding U.S. offshore wind market. Click here to find out more.
By Julian Jackson – writer on technology, arts, blockchain and cryptocurrencies