Introduction - Wind Energy Meteorology: Atmospheric Physics for Wind Power Generation - page 1

Chapter 1
Introduction

The available wind energy, E wind in atmospheric flow, i.e. the kinetic energy of the
air, 0.5 qu 2

advected with the wind, u is quantified by the following relation:

E wind ¼ 0 : 5qA r u 2 u ¼ 0 : 5qA r u 3

ð 1 : 1 Þ

where q is air density, A r is the rotor area of the turbine and u is the average wind
speed over the rotor area. Equation ( 1.1 ) gives the available wind energy over the
rotor disk in Watt when the air density is given in kg/m 3 , the rotor area in m 2 and
the wind speed in m/s. Theoretically, turbines can extract up to 16/27 of this
amount (Betz 1926 ). It is an engineering issue how close one can come to this
theoretical limit. This is not discussed in this topic. The other challenge is that
wind speed and air density are not a constant. This topic is mainly about how wind
speeds vary with space (especially in vertical direction) and time in the atmo-
spheric boundary layer. Air density is addressed in Sect. 2.7 . This part of the
discipline meteorology is called ''wind energy meteorology'' today. We will start
with some basic thoughts on wind energy and a description of the structure of this
topic in this introduction before we will start to determine the wind speed and air
density and its variations in Chap. 2 .

1.1 Scope of the Topic

Mankind's need for energy will persist or even increase for the foreseeable future.
A sustainable supply will only be possible from renewable energies in the long run.
The presently used fossil energies are limited in their resources, produce air pol-
lutants during combustion and endanger the Earth's climate. Renewable energies
comprise water power, wave and tidal energy, geothermal energy, biomass, solar
energy, and—last but not least—wind energy. This volume focuses on the atmo-
spheric conditions which permit the generation of electricity from wind energy by
wind turbines. It has been written from the viewpoint of a meteorologist who has
many years of experience with the demands in wind energy generation.