Evolution of Modern Wind Turbines Part B: 1988 to 2008 - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 192

in the contiguous lower 48 states have a
coastal boundary, and these states use 78
percent of the nation's electricity. Of these
28 states, only six have a substantial land-
based wind energy resource. However, 26
of the 28 states have enough wind resources
to meet 20 percent to 100 percent of their
electricity needs if shallow water offshore
potential (waters less than 30 m in depth)
is added into their wind resource mix. If
deeper water wind resources are included,
the offshore wind power potential often
overwhelms other local options [Musial
and Butterield 2004, Musial 2007].
For many coastal states, offshore wind
resources are the only renewable energy
source capable of making a signiicant en-
ergy contribution. In many congested and
energy- constrained regions, offshore wind-generated energy may be necessary to supple-
ment dwindling fossil fuel supplies. NREL analysts estimate that the potential U.S. offshore
wind power resource (excluding Hawaii and Alaska) is greater than 2,500 GW, assuming (1)
all of the windy regions ( Class 5 or above) from the shoreline out to 50 nautical miles (nm)
are included, and (2) turbines can be installed in deep waters, up to 900 m deep on loating
platforms. This estimate assumes that one 5 MW wind turbine is placed on every square
kilometer of water with Class 5 winds. If Class 4 wind regions are included, the estimated
wind resource for the same assumptions grows to 3,570 GW of capacity.

Figure 3-48. Distribution of offshore wind
power generation capacity in Europe at
the end of 2007. [EWEA 2008]

Baseline Technology Description of Offshore Wind Power Systems

Wind Turbine Conigurations

Today's typical shallow-water offshore wind turbine is essentially an enhanced version
of the standard land-based turbine shown in Figure 3-40, with some system modiications to
account for ocean conditions. These modiications include the following:

- Structural enhancements to the tower to address the added loading from waves

- Pressurized nacelles and environmental controls to prevent corrosive sea air

from degrading critical drivetrain and electrical components

- Personnel access platforms to facilitate maintenance and provide emergency

shelter

- Corrosion protection systems at the sea interface and high-grade marine coat-

ings on most exterior components

- Warning lights, vivid markers on tower bases, and fog signals for marine navi-

gational safety.

To minimize expensive servicing, offshore turbines may be equipped with the following
systems that exceed the standard for land-based designs:

- Enhanced condition monitoring systems

- Automatic bearing lubrication systems

- On-board service cranes

- Oil temperature regulation systems