Off-shore wind power has a lot of advantages. Populations concentrate along shorelines, so the demand is close to the supply. Wind over water is more reliable than wind over land, and with no obstructions, so the supply is easier to generate. Unfortunately, land is easier to build on. Off-shore construction means very tall underwater towers, with a realistic limit of a few tens of meters. Some sites are too deep. The French, the Portuguese, and the Norwegians are all building floating platforms. There are depth limits, but they involve anchors and ballast, instead of massive poles.
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