POWER December 2013 - 55

OFFSHORE WIND
in investments from companies including
Google, Good Energies, and Marubeni.
Trans-Elect has received a " Determination of
No Competitive Interest " from the Bureau of
Ocean Energy Management and is proceeding
without an associated auction. Plans are
in effect to have the first phase-a $1.8 billion,
150-mile-long project from Delaware
Bay to Atlantic City-operational by 2016.
Notably, Trans-Elect, which was the nation's
first independent transmission company,
is betting on high-voltage direct current
(HVDC) cables, which it anticipates will
have cost and technical advantages over alternating
current (AC) transmission. Today,
almost all commercially available wind turbines
generate asynchronous AC current that
is converted to DC, and then the DC is inverted
back to three-phase AC at 60 Hz. However,
a number of capital costs, efficiency losses,
cooling systems, power quality problems,
and maintenance headaches must be borne
with this method. Wind turbines designed to
generate DC current may still need a transformer
to step up the voltage but would avoid
even having to sync with the rest of the grid,
making them simpler to implement by reducing
the balance of plant-which is especially
important at sea.
Though technically challenging, obtaining
permits for undersea cables may be easier than
for land-based lines. Also, transmission cables
could be brought ashore to existing grid connections
at retired power plants, many of which
are located on riverbanks or at coastlines near
major load centers. These could serve as perfect
locations for injection of high-current frequency
regulation and reactive power services
to keep the grid running efficiently.
Floating VAWTs Fit the Bill
Only one offshore turbine is operational in the
U.S., even though the country has the world's
second-highest onshore wind turbine capacity
(after China). The UK has more than one-half
of the 3 GW total worldwide installed offshore
wind generation, and it has ambitious plans
for even more offshore wind farms. However,
as Bloomberg New Energy Finance notes, because
the UK has a limited supply chain for
offshore wind turbines, about 80% of what the
country spends on wind technology still goes
to foreign contractors or turbine suppliers. Jim
Lanard, president of the U.S. Offshore Wind
Development Coalition, is quick to point out
that if the U.S. is to gain and keep legislative
support for the offshore wind industry, it will
have to generate domestic jobs.
Increased use of floating VAWTs could
do just that. First, the capital-intensive supply
chain needed to manufacture large roller
bearings, gears, forgings, and castings would
not be required. Steel fabrications and fiberDecember
2013 | POWER
glass components with relatively low capital
equipment needs are all that would be required,
so a supply chain based on these components
would scale up much more quickly.
Old shipbuilding sites and cargo transfer ports
could make for good candidates for wind turbine
manufacturing sites. The labor skill sets
could also be filled quickly and practically
deployed in many more coastal locations.
Floating VAWTs could also eliminate the
need for purpose-built ships that are required
to assemble seafloor-mounted HAWTs. This
is important because, having never installed a
foundation-based offshore wind turbine, the
U.S. lacks a fleet of the jack-up ships that are
necessary. And, unlike in Europe, the U.S.
cannot hire foreign-flagged ships to work in
U.S. territorial waters because it would violate
the Jones Act, a federal statute that regulates
maritime commerce in U.S. waters. The
U.S. already has a ready fleet of ships that
are capable of towing floating turbines out to
mooring fields, though.
By eliminating a seafloor foundation, the
cost structure of supply-chain issues and the
costs to assemble and service turbines at sea
can also be dramatically improved. As noted
previously, the further away from NIMBY
issues and state jurisdictions, the better the
wind resource becomes, but the ability to tow
a turbine back to the factory in a single day
mitigates risk, reducing both insurance and
banking costs for projects. Ocean transportation
and sighting combined with low turbine
speed could enable scalability to a huge size.
A Better Choice than HAWTs
However, most " floater " programs in development
in the U.S. today are designed to employ
HAWTs, which have a lot of developmental
inertia based on current onshore designs, their
supply chains, and government funding programs.
U.S. research consortium DeepCwind,
which is led by the University of Maine's
Habib Dagher, this year launched the first and
only offshore wind turbine off the coast of
Maine-a concrete-composite floating platform
HAWT prototype that is one-eighth the
size of a " VolturnUS " design envisioned for
commercial installation.
One problem is that it is difficult to make
conventional HAWTs float. They are cantilevered
structures, reaching high off their base
support with large masses and forces acting at
the top. It is a fundamentally unstable structure
in the context of floatation, but HAWTs
are the mainstay of the wind energy industry.
Almost all utility-scale wind turbines employ
three blades connected to a horizontal spindle,
which is mounted on top of a pole. There is no
debate that this design can be the most efficient
at capturing energy from wind, but a big
picture, smart grid, objective look should conwww.powermag.com
3.
Inspired design. One example of a
floating vertical axis wind turbine (VAWT) is
a design based on the rigid mainsail used on
America's Cup boats. The 60-ton VAWT design
adds three more sail plans and a masthead
ring for 1,800 square meters of projected
area. The bearings and generator are located
near sea level for easy on-site service and to
provide a stable low center of gravity. Courtesy:
American Offshore Energy
sider all of the issues and constraints involved,
not just the turbine's maximum efficiency.
Other structures are possible. Lightweight
structures can be achieved by using tension
and compression design principles rather
than the bending of a cantilevered structure.
Examples of such structures would include
bicycle wheels, suspension bridges, and sailboat
masts (Figure 3).
A 200-foot tall VAWT installed 30 miles
offshore would not be visible or audible from
land, dramatically reducing legal challenges
that can delay and increase costs of wind
projects. Having a high degree of solidity and
a low rotation speed avoids harm to birds and
provides excellent horizontal radar reflection
for maritime visibility with little vertical
reflections. Additionally, the VAWT has no
gearbox or oil reservoir, and all the components
on the turbine are waterproof and rustproof.
In the event of an occasional hurricane
or rogue storm, the turbines could be easily
reefed or sunk by remote control, allowing
them to ride out the storm safely beneath the
ocean surface. When the storm has passed
turbines may be again raised via remote control
and recommissioned with little effort.
Floating VAWTs enable a host of advantages
that dramatically improve the return on investment,
the reliability of the energy stream, and
the ability to usefully site the turbine. Because
VAWTs would have a completely different supply
chain than conventional HAWTs, their potential
to generate jobs may be increased. And,
if paired with HVDC power transmission and
deep ocean energy storage, floating VAWTs
could give the country's new offshore sector
fair winds in which to hoist its sails. ■
-Drew Devitt is founder of American Offshore
Energy and a former president of the
American Society of Precision Engineering.
55
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POWER December 2013

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