An offshore wind turbine in the Thames Estuary, England.
Some of the windiest places on Earth are in the sea. Offshore wind farms can take advantage of this in shallow coastal areas, where deployment and maintenance is feasible.
Offshore wind has several advantages. It doesn't get in the way of other land uses. Because the water is generally flat, offshore wind is less disturbed by turbulence from surface roughness. Offshore turbines can also be bigger because it is easier to transport big blades by sea than by land.
The biggest disadvantage is the cost of the infrastructure and maintenance. If anything goes wrong with a turbine, a barge must be hired to fix it. A lot of research effort is focused on reducing maintenance costs, for example by eliminating the complicated gearboxes that can break. Offshore wind turbines also have to be designed to withstand storms and strong winds, which are generally harsher in the sea.
According to a report Offshore Wind Energy by the Environment and Energy Study Institute in October 2010, the average power of an offshore wind turbine in Europe was around 3 megawatts in 2009. The capacity of future turbines is expected to increase to 5 megawatts, with some 10 megawatt turbines under development.
Another reason that offshore turbines are bigger is to justify the investment in the rest of the infrastructure required for offshore farms.
As of October 2010, 3.16 GW of offshore wind power capacity was operational, mainly in Northern Europe. Figures from Wikipedia: Offshore wind power.
Almost all deployed offshore turbines are fastened to the seafloor in some way.
Designs for floating turbines are currently being tested, see Wikipedia: Floating wind turbine.
Author: Tom Brown
Copyright: public domain
Date last modified: 11th Oct 2011
Peer-review status: Not yet peer-reviewed
http://www.flickr.com/photos/pjh/185488383/: by phault, Attribution 2.0 Generic (CC BY 2.0)
http://commons.wikimedia.org/wiki/File:Sund_mpazdziora.JPG: By Mariusz Pazdziora (Own work) [CC-BY-SA-3.0 (www.creativecommons.org/licenses/by-sa/3.0) or GFDL (www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons