POWER December 2013 - 54

OFFSHORE WIND
with more interest given to turbines optimized
for higher capacity factors in average
wind speeds. In the current paradigm,
HAWTs have the highest efficiencies in the
higher wind speed ranges, and this results
in high megawatt ratings for the turbines
but low capacity factors, meaning that the
turbine will generate its rated capacity only
a small fraction of the time. This causes
" spiky power, " that is, much of a turbine's
power is made over a relatively short period
of time (Figure 2). For this reason, wind
turbine electricity must be associated with
storage in order to be considered as a baseload
power source.
In comparison, VAWTs in an impulse configuration
have a relatively high efficiency in
lower wind speeds because they have higher
blade areas as a percentage of swept area. This
could be thought of as the " barn door method "
of collecting energy from the wind: Although
not as efficient at higher wind speeds, impulse
type VAWTs will make power most of the time
the wind is blowing-making them more suitable
to power companies and mitigating the
need for time shifting or storing wind energy.
However, utility-scale energy storage would
still be beneficial to any electrical grid if it can
be done cost effectively.
Ocean Energy Storage
Much has been invested in trying to develop
energy storage technologies as a way to more
evenly distribute renewable power across
time. So far, only compressed-air storage and
pumped-hydro storage have the capacity to
practically " time shift " utility-scale energy,
but both require specific geological features
that are generally not found close to major
load enters. If the electrical generation occurs
over deep ocean water, though, energy storage
becomes much more convenient.
In another significant advantage for floating
dust & spillage.
You CAN control
Modular Skirtboard
Trac-mounted
components
wind turbine technology, the pressure of the
deep ocean waters under the turbines can be
used for utility-scale energy storage. A number
of different engineering approaches to this have
been explored using air or water. Coloradobased
Bright Energy Storage, for instance, has
a plan to pump air into huge bags in deep water,
while Dr. Alexander Slocum, a mechanical engineering
professor at the Massachusetts Institute
of Technology, suggests using excess wind
power to pump water from hollow concrete
spheres (made from fly ash) that are ballasted
by their own weight to the seafloor. Doubling
as an anchor for floating wind turbines, a 25meter-diameter
sphere could store up to 10
MWh of power, depending on depth.
Pairing deepwater wind generation with
Proper belt support
Effective edgesealing
system
Start with a good foundation: EVO®
SUCCESS STORY
Omaha Public
Power District
Omaha, NE
Overall, the biggest dust control improvement
has been the rebuilding of the coal transfer
points to contain dust.
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" We used to have lots of dust and spillage.
But now that all the transfer points have
been rebuilt, it's a night and day difference. "
said Kirk Estee, P.E. Material Handling
Supervisor, OPPD.
call 800.544.2947
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POWER | December 2013
Transfer Point System
energy storage could make wind energy the
most flexible of all energy sources. A 1-MW
wind turbine that is able to produce 10 MWh
over 24 hours could sell all 10 MWh during
the hottest hour of the next day at peak
prices. Wind farm operators could even begin
bidding in the frequency regulation market,
where the price per kilowatt-hour is five to
10 times the price that can be negotiated in
power purchase agreements. This would both
improve returns for investors and provide an
environmental bonus because turbines that
now provide frequency regulation, being
smaller and more flexible, have fewer pollution
controls. It is good for everyone when
clean flexible power is worth more.
Addressing Transmission
Concerns
But to accomplish frequency regulation from
the deep ocean, transmission capabilities are
obviously required. Several developments
have been made here, too. Trans-Elect Development
Co. has proposed the Atlantic Wind
Connection (AWC), a 6,000-MW transmission
backbone running from Virginia to
northern New Jersey, some 30 to 50 miles
out in the Atlantic Ocean. That $5 billion
plan has attracted more than $500 million
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POWER December 2013

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