What are Floating Wind Turbines? A Practical Guide to Advantages and Types

Floating Wind Turbine

Floating wind turbines are offshore wind turbines that are put on a floating frame to generate power in sea depths where fixed-foundation turbines are not viable. Floating wind farms have the potential to greatly enhance the amount of sea area available for offshore wind farms, particularly in nations like Japan that have limited shallow waters. Wind farms located further offshore can also help to reduce visual pollution, improve fishing and shipping channels, and reach stronger and more constant winds.

 

History of Floating Wind Turbine

Professor William E. Heronemus of the University of Massachusetts Amherst first proposed the concept of large-scale offshore floating wind turbines in 1972. The problem was not revisited by the mainstream scientific community until the mid-1990s after the commercial wind industry had established itself.

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In December 2007, Blue H Technologies of the Netherlands successfully deployed the world’s first floating wind turbine 21.3 kilometers (13.2 miles) off the coast of Apulia, Italy. The prototype was deployed in waters as deep as 113 meters (371 feet) to collect data on wind and sea conditions before being deactivated at the end of 2008. A tension-leg platform and a two-bladed turbine were used in the turbine. The exclusive rights to the two-bladed floating turbine technology developed by Blue H Technologies were bought by Seawind Ocean Technology B.V., which was founded by Martin Jakubowski and Silvestro Caruso, the creators of Blue H Technologies.

Principle Power, funded by EDP, Repsol, ASM, and Portugal Ventures, deployed the second grid-connected full-scale prototype in Portugal in September 2011. WF1 received a Vestas 2 MW turbine and produced over 17 GWh of electricity over the next five years. In 2016, the unit was dismantled and repurposed.

The 20 kW VolturnUS 1:8, a 20 m tall floating turbine prototype that is 1:8th the scale of a 6-MW, 140 m rotor diameter design, was deployed in June 2013 by the University of Maine. The VolturnUS 1:8 offshore wind turbine was the first grid-connected offshore wind turbine to be installed in the Americas. The VolturnUS concept incorporates a concrete semi-submersible floating hull and a composite materials tower to lower capital and operating expenses while allowing for local production. The DeepCwind Consortium, directed by the University of Maine, developed the technology through collaborative research and development.

Statoil backed out of a $120 million project to float four 3-MW turbines in 140 m of water at Boothbay Harbor, Maine, in 2013, citing a change in laws, and instead concentrated on their five 6-MW turbines in Scotland, where the average wind speed is 10 m/s, and the sea depth is 100 m.

Hywind Scotland, the world’s first practical floating offshore windfarm, was launched in 2017. It has a capacity of 30 MW and is located 18 miles (29 kilometers) off the coast of Peterhead. A 1 MWh lithium-ion battery system, is also included in the project (called Batwind).

After a 5-year trial phase near shore, Japan’s first floating turbine was launched on Fukue Island in 2016. Hitachi designed and built the 2-MW turbine.

The US Department of Energy selected Maine’s New England Aqua Ventus I floating offshore wind demonstration project, designed by the DeepCwind Consortium, to participate in the Offshore Wind Advanced Technology Demonstration program in June 2016.

Floating Wind Turbine
Chains anchor floating wind turbines to the sea floor up to a half-mile deep (Reference: nrel.gov)
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Floating Design Concepts

Eolink

A single point mooring mechanism is used by the Eolink floating wind turbine. This French business situated in Plouzané has patented a semi-submersible floating hull with a four-mast pyramidal configuration. The turbine is supported by two upwind and two downwind masts. It provides additional blade clearance and evenly distributes stress. The turbine spins around its single mooring point to face the wind, unlike most floating wind turbines. The mechanical and electrical interface between the turbine and the seabed is ensured by the pivot point. In April 2018, the Eolink grid linked its first 1/10th scale demonstrator of a 12 MW wind turbine.

Floating Wind Turbine
Single Point Mooring Eolink Floating Wind Turbine (Reference: wikipedia.org)

DeepWind

In October 2010, Ris DTU National Laboratory for Sustainable Energy and 11 foreign partners launched DeepWind, a four-year project to develop and test cost-effective floating Vertical Axis Wind Turbines with a capacity of up to 20 MW. The EU’s Seventh Framework Programme is funding the program with €3 million. TUDelft, Aalborg University, SINTEF, Equinor, and the United States National Renewable Energy Laboratory are among the partners.

Flowocean

Flowocean is a Swedish technology business based in Västers, Sweden, that has developed its own proprietary technology for floating offshore wind generation. FLOW is a floating offshore wind turbine system with two wind turbine generators on one floating platform that is semi-submersible. The wind turbines are continuously facing the wind because the construction weather vanes passively. Flow technology is a hybrid of Tension Leg Platform (TLP) and Semi-Submersible, giving the Flow unit the best of both worlds while being durable and light.

GICON

The GICON-TLP is a floating structure system based on GICON GmbH’s tension leg platform (TLP). The system may be deployed in water depths ranging from 45 to 350 meters. Four buoyancy bodies, horizontal pipes for the structural base, vertical pipes that pass over the water line, and angled piles for connection with the transition piece are the six key components. To connect all components, cast nodes are needed. The TLP can be fitted with a 6–10 megawatt offshore wind turbine.

Ideol

Ideol designed a steel floating substructure based on Ideol technology for a 3.2 MW NEDO project in Japan, which was fully coated in a dry dock before wind turbine installation.

Engineers at Ideol have created and patented a ring-shaped floating foundation with a central opening mechanism (Damping Pool) for optimizing foundation + wind turbine stability. As a result, the sloshing water in this central aperture dampens floater oscillations caused by the swell. To keep the system in place, foundation-fastened mooring lines are simply affixed to the seafloor. This floating base is suitable for all types of wind turbines and has smaller dimensions. This floating foundation, which can be made of concrete or steel, enables local building near project locations.

Ideol is the project leader for the FLOATGEN project, a floating wind turbine demonstration project based on Ideol’s technology that is being built by Bouygues Travaux Publics and is currently operational off the coast of Le Croisic on the Ecole Centrale de Nantes’ offshore experimental site (SEM-REV). This project, which is France’s first offshore wind turbine with a capacity of 2 MW, was finished in April 2018, and the unit was deployed in August 2018. It had a 95 percent availability and a 66 percent capacity factor for the month of February 2020.

Floating Wind Turbine
Ideol’s 2MW floating wind turbine constructed off France (Reference: wikipedia.org)

Nautica Windpower

For deepwater sites, Nautica Windpower has developed an approach that could reduce system weight, complexity, and costs. In September 2007, scale model testing in open water was conducted in Lake Erie, and structural dynamics modeling was completed in 2010 for bigger designs. The Advanced Floating Turbine (AFT) by Nautica Windpower has a single mooring line and a deflection-tolerant downwind two-bladed rotor layout that aligns itself with the wind without the usage of an active yaw system. Downwind turbines with two blades that can handle blade flexibility have the potential to extend blade lifetime, reduce structural system loads, and reduce offshore maintenance requirements, resulting in lower lifecycle costs.

SeaTwirl

SeaTwirl is working on a vertical axis floating wind turbine (VAWT). The idea aimed to store energy in a flywheel, allowing energy to be generated even when the wind has ceased blowing. The floater is a SPAR solution that rotates in tandem with the turbine. In the hub region, the design reduces the requirement for moving parts and bearings. SeaTwirl is situated in Gothenburg, Sweden, and is listed on the First North European growth market. In August 2011, SeaTwirl launched its first floating grid-connected wind turbine off the coast of Sweden. It was put through its paces before being deactivated. SeaTwirl debuted a 30 kW prototype in the Swedish archipelago of Lysekil in 2015, which is connected to the grid. In 2020, the company hoped to scale up the concept with a 1MW turbine. The concept can be scaled up to sizes much above 10MW.

VolturnUS

The VolturnUS concept incorporates a concrete semi-submersible floating hull and a composite materials tower to lower capital and operating expenses while allowing for local production.

VolturnUS is the first grid-connected floating wind turbine in North America. The University of Maine Advanced Structures and Composites Center and its collaborators lowered it into the Penobscot River in Maine on May 31, 2013. During its deployment, it was subjected to a number of storms that met the requirements of the American Bureau of Shipping’s (ABS) Guide for Building and Classing Floating Offshore Wind Turbines, 2013.

Wind turbines can be supported by the VolturnUS floating concrete hull technology in water depths of 45 meters or greater. It has been proven to dramatically lower expenses as compared to existing floating systems, according to 12 independent cost estimates from around the United States and the world. A third-party engineering assessment of the design has also been completed.

The New England Aqua Ventus I project, managed by the University of Maine, was awarded top tier designation by the US Department of Energy’s Advanced Technology Demonstration Program for Offshore Wind in June 2016. As a result, the Aqua Ventus project is now automatically eligible for an extra $39.9 million in DOE construction funding, provided the project meets its goals.

WindFloat

Principle Power invented and patented WindFloat, a floating base for offshore wind turbines. Windplus, a joint venture comprising EDP, Repsol, Principle Power, A. Silva Matos, Inovcapital, and FAI, built a full-scale prototype in 2011. The entire system, including the turbine, was installed and commissioned onshore. The complete structure was subsequently wet-towed 400 kilometers (250 miles) (from southern to northern Portugal) to its final installation location, which was previously the Aguçadoura Wave Farm, 5 kilometers (3.1 miles) offshore of Aguçadoura, Portugal.

The WindFloat was outfitted with a Vestas v80 2.0-megawatt turbine, which was installed on October 22, 2011. The turbine had produced 3 GWh after a year. This project will cost around €20 million (about US$26 million). This single wind turbine is capable of supplying enough energy to power 1300 houses. It was operational until 2016, and it was unaffected by storms.

Principle Power had planned a 30-MW WindFloat project near Coos Bay, Oregon, in 2013 that would have used 6-MW Siemens turbines in 366 meters of water and would have been operational in 2017, but the project was shelved.

By damping wave– and turbine–induced motion using a tri-column triangle platform with the wind turbine positioned on one of the three columns, the subsea metal structure is said to improve dynamic stability while still preserving shallow draft. The triangle platform is then “moored” using a traditional catenary mooring system, consisting of four lines, two of which are linked to the turbine’s support column, resulting in an “asymmetric mooring.”

A secondary hull-trim mechanism moves ballast water between each of the three columns as the wind changes direction and adjusts the strains on the turbine and foundation. This allows the platform to stay on a level keel while providing the most energy. Other floating designs, on the other hand, have used control systems to de-power the turbine in order to adjust for changes in turbine thrust-induced overturning moment. This method could allow wind turbines to be installed in previously inaccessible offshore sites, such as those with water depths greater than 40 meters and more powerful wind resources than shallow-water offshore wind farms generally experience.

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Economics of Floating Wind Turbine

Introduction

The technological feasibility of deepwater floating wind turbines is unquestionable, as the marine and offshore oil sectors have successfully shown the long-term durability of floating structures over many decades. The economics that permitted thousands of offshore oil rigs to be deployed have yet to be proven for floating wind turbine platforms. A floating structure will replace pile-driven monopoles or traditional concrete bases that are frequently utilized as foundations for shallow water and land-based turbines for deepwater wind turbines.

The floating structure must have adequate buoyancy to support the turbine’s weight while also limiting pitch, roll, and heave motions to safe levels. The wind turbine’s capital expenses will not be much higher than those of present marine-proofed turbines in shallow water. As a result, the cost of the floating structure and power distribution system will decide the economics of deepwater wind turbines, which will be mitigated by greater offshore winds and proximity to significant load centers (e.g. shorter transmission runs).

However, in 2009, the economic viability of shallow-water offshore wind generating was well understood. Representative costs have been well recognized since the late 1990s, thanks to empirical data gathered from fixed-bottom installations off the coasts of numerous countries. According to the World Energy Council, shallow-water turbines cost US$2.4-3 million per megawatt to construct, whereas deep-water, floating-turbine offshore wind’s practical feasibility and per-unit economics have yet to be determined.

Cost Data from Operational Windfarms

Only in 2009 single full-capacity turbines begin to be deployed in deep-water areas. Hywind Scotland, the world’s first commercial floating offshore windfarm, was launched in 2017. It cost £264 million to build, or £8.8 million per MW, which is around three times the cost of fixed offshore windfarms and 10 times the cost of gas-fired power plants. Its running expenses were also greater than fixed offshore windfarms, at around £150,000/MW. The Kincardine Floating Offshore Windfarm, a second UK project, is estimated to cost £500 million, or £10 million per MW, or seventeen times more than gas-fired power plants.

Cost Reduction Strategies

Floating turbines are growing both technically and economically viable in the UK and worldwide energy markets, according to new feasibility studies released in October 2010. “The greater initial expenses of creating floating wind turbines would be mitigated by the fact that they would be able to access areas of the deep ocean off the UK’s coast where winds are stronger and more reliable,” says the report. According to a recent UK Offshore Valuation study, harnessing just a third of the UK’s wind, wave, and tidal resources could create energy equivalent to 1 billion barrels of oil per year, which is the same as North Sea oil and gas production. The collaboration required to build transmission lines is a big hurdle when employing this strategy.

Carbon Trust published a paper in 2015 that suggested 11 cost-cutting measures. Researchers at the University of Stuttgart estimated the cost at €230/MWh in 2015.

Offshore wind in California is a good match for night time and winter consumption when grid demand is high and solar output is low. Humboldt Bay could be one of the few ports large enough to prepare offshore wind equipment.

According to research done by the Offshore Renewable Energy (ORE) Catapult’s Floating Offshore Wind Centre of Excellence, the UK floating offshore wind might achieve “subsidy-free” levels by the early 2030s (FOW CoE).

Oil Well Injection

When oil fields get dry, the operator injects water to keep pressure high enough that secondary recovery can take place. This necessitates the use of electricity, however installing gas turbines would result in the extraction process being halted, resulting in a loss of revenue. DNV GL, a classification company, determined that in some instances, a floating wind turbine can provide electricity for injection while the oil platform continues to operate, avoiding an expensive halt.

DNV GL, ExxonMobil, and others approved calculations in 2016 that showed a 6MW Hywind could save $3/barrel of oil by driving two 2MW pumps injecting water into an offshore oil well instead of traditional engines. Even on quiet June days, at least 44,000 barrels of treated water can be injected per day. In 2017, laboratory testing for the project began.

Off the coast of Portugal, a floating turbine is being towed out to sea for the WindFloat Atlantic project, which is now under development (Reference: e360.yale.edu)

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Tech Solutions

As a result, making floating and cost-effective wind farms will almost certainly necessitate the development of new technology. For example, controlling offshore engineering activities with robots and other autonomous technology – from studying the seabed to running, inspecting, and maintaining a floating wind turbine – might reduce worker risk and provide more effective control of these complex systems.

People inspecting offshore wind farms on a regular basis would be impracticable for the massive facilities currently under construction and certainly for those planned in the future. Instead, smart sensors embedded in all elements of a floating wind farm can monitor the structure’s performance in real time.

Machine learning, which uses data to educate computers to make their own decisions, might be used to advise us which anchor is the most efficient during design or whether a mooring line is at risk of failure during operation.

Machine learning can already adjust the positions of turbine blades to maximize the amount of energy they create or minimize damage in severe winds or storms using weather data. New methods that combine physics and machine learning can create accurate predictions with less data, which is particularly beneficial offshore, where data collection is challenging.

You can also watch this nice video to have an overview of floating wind offshore wind turbines.

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