Offshore Wind Technology and Status - Structural Integrity of Offshore Wind Turbines - page 15

ity relative to the rest of the country, making electricity from offshore
wind more economically competitive with other sources of electricity
generation in these regions (Musial and Ram 2010, Section 2, 10-22).
Offshore Wind Technology
Figure 2-2 shows a schematic of a typical offshore wind turbine, and
Figure 2-3 shows photographs of the common offshore wind turbines.
Most offshore wind turbines are robust versions of proven land-based
turbine designs. They are placed on freestanding steel monopiles or con-
crete gravity-base substructures. Although their architecture mimics that
of conventional land-base turbines, offshore wind turbines incorporate
significant enhancements to account for ocean conditions. The modifica-
tions include strengthening of the tower to handle the added loading from
waves, pressurization of the nacelles, addition of environmental controls
to keep corrosive sea spray away from critical drivetrain and electrical com-
ponents, upgrades to electrical systems, and addition of personnel access
platforms to facilitate maintenance and provide emergency shelter. Most
exterior components of offshore turbines require corrosion protection sys-
tems and high-grade marine coatings. Most of the turbine's blades, nacelle
covers, and towers are painted light gray to minimize visual impacts.
Lightning protection is mandatory for both land-based and offshore
turbines. Turbine arrays may be equipped with aircraft warning lights,
bright markers on tower bases, and fog signals for reasons of navigational
safety. To reduce operational costs and yield better maintenance diag-
nostic information, offshore turbines are often equipped with condition
monitoring systems (CMSs). The CMS measures vibration at various
points throughout the drivetrain (including the main shaft bearings,
gearbox, and generator). The CMS also monitors operational parame-
ters such as above-nacelle wind speed and direction, generator electrical
output, generator winding temperature, main shaft rotational speed,
bearing temperatures, and fluid temperatures and pressures of gearbox
lubricating oil and hydraulic control systems. Offshore turbines are also
usually equipped with automatic bearing lubrication systems, onboard
service cranes, and oil temperature regulation systems, all of which exceed
the typical maintenance provisions for land-based turbines.
Offshore substructure and foundation systems differ considerably
from land-based foundations. Land-based foundations typically consist