Northern California has some of the strongest offshore winds in the U.S., with immense potential to produce clean energy. But it also has a problem. Its continental shelf drops off quickly, making building traditional wind turbines directly on the seafloor costly if not impossible.
Once water gets more than about 200 feet deep – roughly the height of an 18-story building – these “monopile” structures are pretty much out of the question.
A solution has emerged that’s being tested in several locations around the world: wind turbines that float.
In California, where drought has put pressure on the hydropower supply, the state is moving forward on a plan to develop the nation’s first floating offshore wind farms. On Dec. 7, 2022, the federal government auctioned off five lease areas about 20 miles off the California coast to companies with plans to develop floating wind farms. The bids were lower than recent leases off the Atlantic coast, where wind farms can be anchored to the seafloor, but still significant, together exceeding US$757 million.
So, how do floating wind farms work?
A floating wind turbine works just like other wind turbines – wind pushes on the blades, causing the rotor to turn, which drives a generator that creates electricity. But instead of having its tower embedded directly into the ground or the seafloor, a floating wind turbine sits on a platform with mooring lines, such as chains or ropes, that connect to anchors in the seabed below.
These mooring lines hold the turbine in place against the wind and keep it connected to the cable that sends its electricity back to shore.
Most of the stability is provided by the floating platform itself. The trick is to design the platform so the turbine doesn’t tip too far in strong winds or storms.
There are three main types of platforms:
A spar buoy platform is a long hollow cylinder that extends downward from the turbine tower. It floats vertically in deep water, weighted with ballast in the bottom of the cylinder to lower its center of gravity. It’s then anchored in place, but with slack lines that allow it to move with the water to avoid damage. Spar buoys have been used by the oil and gas industry for years for offshore operations.