World’s largest floating wind farm proposed for California waters

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The world’s first full-scale floating wind turbine, Hywind, being assembled off Norway before being deployed to the North Sea(Credit: Lars Christopher CC BY-SA 2.0)

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California's central coast could become the site of the world's largest working offshore wind farm, a 765-megawatt producer surpassing the 630-megawatt London Array off the coast of Kent. If built, the Trident Winds energy project would include around 100 wind turbines set on floating platforms 33 miles (53 km) from shore and power more than 200,000 homes.

Each of the 100 turbines would produce more than 6 megawatts of electricity, powered by average wind speeds of 8.5 meters/sec (19 mph) for a nameplate capacity of 765 MW and a net capacity of 650 MW. The turbines would be anchored in 2,600 to 3,300 ft (800 to 1,000 m) of deep water using vertical load, drag embedded or torpedo anchors, depending on the seabed conditions. No pilings are required and the installation is reversible, meaning nothing would be left on the seabed if or when the project is decommissioned.

To reduce or eliminate wind shadow effects, the turbines would be placed 3,300 ft (1,000 m) apart, and connected electrically with inter-array cables. The produced energy would be sent to a floating substation which then delivers the combined payload to shore through a redundant system of export cables.

Most of the world's offshore wind farms are in waters less than 200 ft (61 m) deep, and sit on platforms attached to the seabed with concrete or steel pilings. Floating wind turbines use cables attached to their anchors, and to date are only found in test projects, such as Statoil's Hywind pilot park off the coast of Scotland.

But more than 60 percent of the best wind sources in the US, as determined by wind speed, duration and timing, are within 50 nautical miles (92.6 km) of the coasts, in waters typically too deep for traditional wind energy systems. And while it's cheaper and easier to install floating wind turbines – just tow and anchor – they're more expensive than fixed-platform turbines because their anchoring systems require more steel and need longer power cables to run electricity to shore. It's estimated that by 2020, floating wind turbines will cost around $9 million per megawatt compared to $4 million per megawatt for conventional, fixed-platform turbines. The hope is that as floating wind turbine technology matures, its costs will eventually come down.

Besides the issue of turbulent seas and harsh deep water conditions that could damage the turbines, the proposed location for the Trident Winds energy project is also prime migration ground for a number of whale species, so the platform cables could become an entanglement risk for the animals.

But the Trident group is so far undeterred, and is aiming for construction to begin in 2021 with a completion target of 2025. It also times well with the state's new law requiring half its energy to come from renewable sources by 2030.

A 30-megawatt wind farm is currently being constructed off Rhode Island to serve the needs of energy-challenged Block Island, but this would be the first major offshore wind farm in the US. It would be especially significant for California, which has some of the most stringent coastal development regulations in the world. Trident would work with the coastal city of Morro Bay, which closed its conventional 650-watt power plant in 2013.

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