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Chapter 4

Offshore Wind

Wind energy is one of the fastest growing renewable energy sectors, with
levelized costs of wind energy now comparable to the cost of electricity
generated by thermal power stations such as coal and gas. However, due to
lower surface roughness, the wind resource is higher offshore, and has further
advantages such as lower visual impact. In this chapter, following a general
introduction, the components of a wind turbine are introduced. Wind energy
resource assessment, which is a crucial part of macro-siting of wind energy
projects, is discussed in detail, and applied to a case study of the first offshore
wind energy project in the United States—Block Island Wind Farm. Finally, a
brief introduction to marine spatial planning is provided—the method of siting
wind energy projects. The objective of this chapter is to introduce the basic
technical aspects of offshore wind energy, and the reader is referred to more
specific books for further information.

4.1 INTRODUCTION

Wind can be defined as the movement of air over the surface of the Earth.
Because air is a fluid, the movement of air and water (in the ocean) follow the
same principles. A pressure gradient in the air (or ocean) leads to a flow from
regions of high pressure to regions of low pressure. Variations in pressure that
lead to pressure gradients are due to uneven heating of the Earth’s land and sea
surfaces—particularly the differences in heating between the tropics and high
latitude regions. Wind is, therefore, an indirect form of solar energy. Because
of the Earth’s rotation, these large scale wind patterns will be affected by the
Coriolis force (Section 3.6). Near the surface of the Earth, land or ocean, friction
slows down the wind, and surface roughness (e.g. topography, forests, waves)
is the main cause of this friction force. Therefore, the spatial and temporal vari-
ations in wind are controlled by solar radiation, Coriolis (i.e. Earth’s rotation),
and the Earth’s surface (mountains, buildings, ocean, etc.). These variations can
be studied at various scales: global wind patterns, regional climates, variations
within a wind farm, and around the blades of individual turbines.
The use of wind energy (e.g. for sailing) has a history extending back
thousands of years. The oldest wind energy device is possibly the Persian
windmill (Fig. 4.1) at Nashtifan, Iran, that was built around the 9th century [1,2].
The Nashtifan village is located in the northeast of Iran, in Khorasan Razavi
Fundamentals of Ocean Renewable Energy. https://doi.org/10.1016/B978-0-12-810448-4.00004-5
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