A
review of offshore foundations for wind turbines was funded
by the UK government. The
MIT Offshore Wind Collaborative published several technical
reports on foundations and site layout for download. From
these and other sources, the Company has concluded that fixed, not floating, structures
are the most durable and cost-effective foundations for offshore
wind and wave energy generation. Also, if possible the use
of specialized offshore construction ships must be avoided.
These ships are used to place wind turbines on monopole
foundations. They do not exist in the USA and would have
to be built here at cost of $300M or more. The only
foundations that meet these two requirements - fixed and no
special ships - are
mobile jack-up platforms from the offshore
oil production industry adapted for renewable energy use.
This
technology is now in use in thousands of
offshore structures and vessels. It is a low-risk, effective
design.
The platforms are designed to withstand Force 5 hurricanes.
The platform can be installed in up to 250
feet of water depth. In comparison, monopole foundations are limited
to about 60 feet of depth. A
Texas company
is developing a mobile jack-up platform specifically for wind
power generation - review their website for much more
information and excellent pictures.
Unlike
the monopole foundations used for offshore turbines in the UK
and Europe, this technology does not require the use of a
specially-constructed crane ship to lift the turbine onto the
monopole offshore. Instead, the platform is assembled on
land with the legs raised up. The turbine is placed on the
platform. Then the platform and turbine are moved
onto a semi-submersible barge. The barge is partially flooded so
it creates a massive ballast below water that prevents the
turbine from tipping it over. The images below are used
with
permission.
The barge and
platform/turbine are
floated out to the site. The legs of the platform are lowered
down to the seabed. The platform then jacks itself up on
the legs until it stands high above the waves. The power from the wind turbine and wave
energy converters is transmitted from the platform to shore by a cable buried
about 3 feet below the seabed and under the beach.
The platform supports a wind
turbine plus wave energy converters of the
Oscillating Water Column type that are integrated into the legs
of the platform. These make power from the air pushed up
and down in the hollow and perforated legs by the passing waves.
The airflow turns an air turbine at the top of the leg. This is
just one way to generate wave power with the platform. Access to the platform is by standard offshore
platform service vessels and transfer systems. The
platforms can hold helicopter pads and even living and work
structures.
Addition of wave power to the
platform significantly improves its power performance.
Wave energy is predictable with 95% confidence up to 48 hours in
advance, and up to 50% confidence 5 days in advance. It is
much more steady than wind. This helps "firm up" the power
generated by the platforms. If the wind drops suddenly the
waves will continue for a while.
Each platform has potential
to make up to 10 MW of clean power. For large-scale power
generation, the platforms would be spaced about one mile apart
in an array, generating 10 MW/sq mile at rated power, and about
4 MW at average power or 40% capacity. 100 platforms
covering 10x10 miles could make 1000 MW of power, enough for a
city of about a 250,000 homes.
Construction of the
platforms in local shipyards and the operations at sea will
create hundreds of "green collar" jobs and stimulate the
waterfront economy in addition to the many other jobs and
benefits from a large project. A 1000 MW offshore wind
project is estimated today to cost about $4 billion to construct.
If the turbines and platforms can be manufactured close to the
site then the local economy benefits even more.
The wind turbine partner
has not yet been selected by the Company. However we have
been in discussions with
Clipper Windpower since early 2008 regarding their
Britannia offshore wind turbine. Here is a good
presentation about large offshore wind turbines. This is the largest
wind turbine under construction today and has potential to
achieve 10 MW rated output. We have already determined
that the Britannia turbine is complementary to the Titan
platform. There are other potential turbine suppliers such
as REPower and Siemens. The
DownVind project is examining the potential for large
deepwater wind farms and supports the largest offshore wind
turbine installed to date, the 5 MW "Beatrice" project wind
turbine.
Other ocean renewable
energy developers are focused on the energy generation
technology such as wind turbines or wave energy converters.
We are evaluating potential partnering arrangements to provide
the optimal solutions for using those technologies with the
mobile jackup platform.
