Figure 1: Floating wind turbines being transported to the first floating turbine wind farm site (Hywind project) situated off the north-east coast of Scotland (Image courtesy: Terje Aase/Shutterstock.com)
Surface climatologies of wind speeds show that wind speeds over the oceans are often higher than over land. However, it remained largely unexplored to what extent one may utilize this promising potential of the faster winds from a purely geophysical view point. Will placing many turbines, which are sources of drag as far as the atmosphere is concerned, simply slow down the winds to levels onshore?
From studies of wind farms on land we know that the energy extraction in multi-row wind farms is predominantly constrained by the rate at which kinetic energy is mixed down to hub heights from the faster winds aloft. On land this rate of kinetic energy transport is identified to be roughly 1.5 watts per meter squared.
We find that even if conceptual wind farms were spread over vast areas over the North Atlantic, the kinetic energy extraction rate over the entire wind farm remains high. In the annual mean the energy extraction rate is diagnosed at 6 watts per meter squared and higher. Furthermore, our results indicate that the circulation over the open ocean is able to sustain kinetic energy extraction rates sufficient to meet civilization's power needs of 18 terawatt over an area of 3 million kilometers squared.
Figure 2: a) Conceptual wind farm areas simulated in the North Atlantic and onshore. b) Kinetic energy extraction (KEE) rate for each wind farm shown in a). c) Integrated total generated power for all wind farm areas shown in a). Results show that for all sized domains KEE rates are at least three times as high in the North Atlantic as compared to onshore.
The study was conducted using a state of the art climate model. For domains shown in Fig2a wind turbine densities were specified and the extracted power as well as the drag force impacting the atmospheric flow were computed interactively.