Offshore Wind Energy

One possibility being developed with wind energy is placing the wind turbines out in the ocean shore, where they are not invasive to property and the wind speeds are greater. The wind speeds around Hong Kong's shores are about 6 m/s at 60 m height. Turbine power is related to the cube of the wind speed, so to account for the greater power from higher occasional velocites we use an effective velocity of 7.5 m/s. The wind turbines are usually placed at 100 m height, and the increased height will cause the turbine to see an even higher velocity. To find this velocity we use the equation V=7.5*(100/60)^(1/7). This yields a velocity of 8.1 m/s seen by the turbine. The power produced by the turbine is Pi/400*(density)*(V)^3. Using the calculated velocity and standard density of air, we get a turbine producing 4.82 W/m2. If we then assume that they can be placed up to 10 km offshore over a third of the coastline, and using a coastline distance of 7330 km, we get a total turbine power of 41 kWh per day per person for Hong Kong.

Offshore wind turbines have two different structures, which are separated by whether they are shallow offshore or deep offshore. It is useful to separate these because the difficulty of maintaing deep offshore turbines. Approximately 1/3 of the area described above is shallow water, so for shallow offshore power we get 13.7 kWh per day per person, and 27.3 kWh per day per person for deep offshore power.