From the WSJ Energy Roundup (last week):
Offshore wind power in the U.S. got a big boost yesterday when a government report concluded the Cape Wind project off Nantucket Sound wouldn’t have any major environmental impact. If only it were so easy to get the wind farm up and running economically.
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Offshore wind power isn’t as mature or cost-competitive as the onshore variety. That’s because the capital costs—the bulk of wind power’s expense—are even higher. Turbines have to be bigger, more robust, and salt- and water-proofed. Maintenance costs are higher offshore. Transmission of electricity back to shore requires laying new undersea infrastructure. The result: a bill for offshore wind that’s about 25% higher than for the onshore variety.
It seems more polite to locate the wind offshore, away from people who might be offended, but lots of times it is simply impossible to release, er, harness, the wind effectively except in a crowd.