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Renewables: The state of offshore wind as a viable renewable resource in the U.S.

by Dan Bihn, Enerdynamics Instructor

Today wind turbines generate about 3% of electricity in the United States — all of it onshore. Europe gets about 6% of its electricity from wind. But nearly 4 GW of its 900 GW of installed wind capacity now comes from turbines mounted on the seabed miles offshore. This is an impressive statistic considering the first commercial-scale offshore turbine was installed in 2001 and the real push for offshore didn’t really kick off until 2007.

 

Offshore wind isn’t easy and it isn’t cheap. Electricity and water don't mix. Steel and saltwater don't mix. And few things mix well with hurricanes. Not surprisingly the International Energy Agency (IEA) estimates that offshore wind costs two to three times more than onshore wind.

 

Why offshore wind?

So why would anyone want to put a 300-foot-tall wind turbine 20 miles out to sea?

 

The main reason is that is where strong, consistent, unobstructed winds are closest to coastal population centers. This results in wind output that more resembles a baseload power plant than a variable resource.  And there are other advantages: no need to buy land (try that 20 miles from New York City); no one is around to complain about their views being ruined (a 400-foot structure is completely over the horizon 25 miles offshore); and the length of wind turbine blades isn’t constrained by trucking limits on the autobahn or the interstate.

 

The largest onshore wind turbines are around 3 MW with 160-foot blades. However, Siemens is now building 6 MW offshore units with 250-foot blades, and larger designs are being actively pursued. The promise is that larger units can be more cost-effective.

 

Today’s seabed-mounted turbines are practically limited to shallow water 100-feet deep or less, so depth is a big concern. The most common mounting design is called a monopile where a single piling is used. These turbines are mounted on the seabed where single steel pile is driving 30 to 70 feet into the seabed. Turbines are assembled on location using huge floating cranes. Maintenance and repairs are costly, requiring a helicopter or the return of a floating crane. Both construction and maintenance need fairly calm winds and water (yet who wants to build a wind farm in calm winds?), so access can be limited to just a few months during the year.

 

The expansive continental shelf in northern Europe and the shoals of the east coast of the States provide good locations for monopiles. This is not true of the Pacific coast of the U.S. and places like Japan where ocean depths can plummet just a few miles off the coast. So this technology doesn’t work everywhere.

 

Floating may be the future

To surmount this obstacle, tomorrow's offshore wind turbines may float. For areas where monopiles are not ideal, the industry may turn to floating technology.  Three floating commercial-scale wind turbines are operating in Europe today. The various floating designs allow turbines to be anchored in deeper water (100 to 300 feet), which opens up significantly more locations.

 

Floating systems are much more complicated and currently more expensive, but they have many potential advantages. Virtually all the construction work can be done year-round onshore, and, when major maintenance is required, units can be towed back to port.

 

Initial offshore wind development in the U.S.

While the U.S. doesn’t have any commercial offshore wind turbines as of 2012, the idea isn’t new here. Since 2001, a group of developers has been proposing an ambitious 468 MW wind farm off the coast of Cape Cod — a project called Cape Wind. The plan is to build 130 3.6-MW turbines four to 11 miles offshore. The tips of the 182-foot blades will reach 440 feet above the water, making them visible onshore.

 

Being visible is the problem — and the source of local and regional opposition from the late Ted Kennedy to former Massachusetts Governor Mitt Romney. While the project is still officially in play, it seems unlikely it will be constructed. Time will tell.

 

But the idea of offshore wind in the U.S. is far from dead. In 2010, the U.S. Department of the Interior (whose jurisdiction extends to the offshore exterior) launched the “Smart from the Start” initiative to promote the construction of 10 GW of offshore wind by 2020 and another 44 GW by 2030.

 

A total of 10 GW of offshore wind along the Atlantic seaboard probably means 10 to 30 wind farms. Each could potentially construct its own underwater transmission line. Surprisingly, underwater transmissions lines can be cheaper than traditional overhead lines — especially when those overhead lines need to go through heavily populated areas.

 

But it may be more economical to aggregate the power from these future farms and use a single system to bring that power back to shore. This is exactly what Google and financial heavyweight Marubeni are proposing. It’s called the Atlantic Wind Connection — a high-voltage DC superhighway with floating substations. The 230-mile offshore transmission system would span the U.S. mid-Atlantic seaboard from New Jersey to Virginia, bringing 7 GW of proposed offshore wind power to the Atlantic seaboard. On May 15, 2012, the Department of the Interior moved its permit to the next stage.

 

Will wind lose out to solar?

In 2011, solar photovoltaics (PV) accounted for 47% of new power generation in Europe with only 21% coming from wind.

 

Policy-driven investments (feed-in tariffs and other subsides) in PV had a lot to do with that transformation, but the dramatically lower cost is the big news — it is 50% cheaper than it was just two years ago. China’s entry, and now domination of supply and demand, have dramatically accelerated PV’s cost decline.

 

And the fundamentals are in PV’s favor. PV is simple — each cell is structurally simpler than any single one of the 2+ billion transistors in a new Intel processor. So expect PV to keep getting cheaper. That’s just not the case with a 300-foot tall steel wind turbine, never mind one that is 20 miles out to sea.

 

Time will tell, but if PV continues down the price curve it is on, wind power — even onshore wind power — might not be the economic power generation technology of choice. If that happens soon enough, the U.S. may never see its first offshore wind farm.

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