In simple terms fixed bottom wind turbines are turbines that are individually anchored to the sea bed: some are anchored using a structure called a monopile, others are fixed with what’s called a jacket foundation.

Monopiles are hollow steel cylindrical tubes approximately 8 meters in diameter with wall thicknesses of 8-10cm (imagine a really massive steel drinking straw). Using a hydraulic device, monopiles are hammered into the seabed to depths of between 30-40 meters (or more, for bigger turbines). A turbine is then attached to the monopile via a transition piece. Each monopile requires thousands of tons of rock armour to protect the base of the turbine from hydrodynamic erosion.

Jacket foundations are lattice structures consisting of three or four legs and are normally attached to the seabed by fixing each leg to a pre-driven monopile. Again, thousands of tons of rock are required to protect the base of each leg from hydrodynamic erosion. Current technology allows fixed bottom turbines (using either single monopiles or jacket foundations) to be installed in water up to 70 meters deep.