Offshore Wind Technology and Status - Structural Integrity of Offshore Wind Turbines - page 23

• Foundations and substructures that allow deployment in deeper waters;

• Installation methods to automate deployment;

• Large turbines (10 MW or greater);

• Downwind rotors;

• Direct drive generators;

• Composite towers;

• “Smart” composite blades;

• Offshore high-voltage direct current transmission subsea back-

bones; and

• Alternative turbine designs: upwind and downwind multiple rotor

concepts.

A variety of deepwater floating platforms has been proposed, but only
one full-scale prototype has been installed in deep water and connected
to the grid. This single-turbine demonstration prototype, called Hywind,
was installed in Norwegian waters in September 2009. Such floating
designs are at too early a stage to gauge properly their potential to com-
pete cost-effectively in the energy market, although the 2.3-MW Hywind
prototype was expensive compared with commercial offshore wind sys-
tems installed on fixed substructures (Statoil 2010a).

U.S. Offshore Wind Energy Potential

The resource potential for offshore wind power in the United States has
been calculated by the National Renewable Energy Laboratory by state on
the basis of water depth, distance from shore, and wind speed. From a
gross calculation of windy water area, the capacity of installed wind power
was estimated on the basis of an assumption that a 5-MW wind turbine
could be placed on every 1 km 2 of windy water (Schwartz et al. 2010). The
calculations show that for annual average wind speeds above 8.0 m/s, the
total gross resource of the United States is 2,957 GW, or approximately
three times the generating capacity of the current U.S. electric grid:
457 GW for water shallower than 30 m, 549 GW for water between 30 and
60 m deep, and 1,951 GW for water deeper than 60 m. This resource esti-
mate includes large areas where wind development probably would not
be allowed because of conflicts with other ocean users, environmental
restrictions, and public concerns. The studies have not yet been done to
assess the net resource from a marine spatial planning perspective when
such areas are excluded (CEQ 2009a; CEQ 2009b; CEQ 2009c).