Offshore wind farms have been creating electricity off the coast of Denmark since 1991 and England, Germany and other countries on mainland Europe have followed suit, as have China, South Korea and Japan. It’s a different story in the US, where until recently there were no offshore wind farms in operation or even under construction. That changed recently with the start of construction of a small wind farm off the coast of Rhode Island.
The 30 megawatt, 5 turbine Block Island Wind Farm project in Rhode Island is scheduled to go online next year, producing enough electricity to power 17,000 homes. It joins a list of similar US projects currently in various stages of proposal, review, and approval, mostly off the East Coast, and one recently proposed for Morro Bay off the Central Coast of California.
The largest offshore wind farm in the world is off the coast of Cumbria in the UK and can produce a claimed 367.2 MW of electricity or enough to power 322,000 homes.
The reasons for the lag by the US vary, but can roughly be attributed to the high cost of construction, changing regulations, and personal lobbying. Perhaps the best known example of the latter is billionaire Bill Koch’s fight to stop the Cape Wind project near Cape Cod, which has now been stalled.
What makes offshore wind farms attractive is that there’s always an ocean breeze. Unlike onshore wind farms where wind can be inconsistent, especially in the summer months when weather can be fairly static depending on the region. That means offshore wind farms have the potential to create more energy per turbine than their onshore counterparts. According to the US Bureau of Ocean Energy Management (BOEM), a turbine at a site with an average wind speed of 16 mph would produce 50 percent more electricity than at a site with average wind speeds of 14 mph.
Off shore wind power has enormous potential. The National Renewable Energy Laboratory estimates a gross wind potential of 4,223 gigawatts (GW) off the coast of the United States alone – roughly four times the generating capacity of the entire US electric grid. One GW of wind power can supply between 225,000 to 300,000 average homes in one year.
While onshore wind farms have proved viable with Iowa, for example, getting 28 percent of its energy from onshore wind farms alone, they’ve not been without their detractors. Noise pollution, the death of predatory birds like hawks and eagles, and the negative impact on the land during construction are among the issues raised by their opponents. Most of these concerns go away when it comes to offshore wind farms. The further away from shore they’re constructed, the less noise pollution is created, the fewer birds affected, and the less the environment is impacted.
But there’s a catch … at least as far as the US is concerned. The Atlantic shelf off the east coast of the U.S. is shallower than that of the Pacific. So it’s easier to anchor windmills into the Atlantic shelf floor. The Pacific Ocean shelf, on the other hand, drops off fairly quickly away from shore, so wind turbines off the West Coast of the US have to float. This is why there’s more activity on the East Coast right now, and why the recent announcement of a possible wind farm off the coast of California was considered significant.
Whether an offshore turbine is anchored or floats, it technically works the same way as it does onshore. What’s different is that offshore turbines need to be constructed to more efficiently take advantage of the steadier winds and the harsher marine environment. That means the towers are taller, the rotor diameters are longer, and an assortment of modifications to the tower and base structure need to be made to handle the forces of waves and ice flows – all of which add to the cost of construction.
Many industry experts and government officials say that the potential for increased energy production inherent in offshore wind farms would offset those costs. This argument, which appears to have held up in other parts of the world, is about to be tested in the US.