Environmental Engineering Reference
In-Depth Information
Chapter 5
Wind Power
I
NTRODUCTION
Wind energy is an indirect form of solar energy in contrast to the direct solar
energy described in previous chapters. Solar irradiation causes temperature
differences on Earth and these are the origin of winds. The wind itself can be
used by technical systems. Wind can reach much higher
power densities
than
solar irradiance: 10 kW/m
2
during a violent storm and over 25 kW/m
2
during
a hurricane, compared with the maximum terrestrial solar irradiance of about
1kW/m
2
. However, a gentle breeze of 5 m/s (18 km/h, 11.2 mph) has a power
density of only 0.075 kW/m
2
.
The
history of wind power
goes back many centuries. Wind power was
used for irrigation systems 3000 years ago. Historical sources give evidence
for the use of wind power for grain milling in Afghanistan in the 7th century.
These windmills were very simple systems with poor efficiencies compared to
today's systems. In Europe, wind power became important from the 12th
century onwards. Windmills were improved over the following centuries. Tens
of thousands of windmills were used for land drainage in The Netherlands in
the 17th and 18th centuries; these mills were sophisticated and could track the
wind autonomously. In the 19th century numerous western windmills were
used in North America for water pumping systems. Steam powered machines
and internal combustion engines competed with wind power systems from the
beginning of the 20th century. Finally, electrification made wind power totally
redundant. The revival of wind power began with the oil crises of the 1970s.
In contrast to the mechanical wind power systems of past centuries, modern
wind converters almost exclusively generate electricity. Germany became the
most advanced country for wind technology development in the 1990s. State
of the art wind generators have reached a high technical standard and now
have powers exceeding 4 MW. The German wind power industry alone has
created more than 45,000 new jobs and has reached an annual turnover of
more than
3500 million.
The high growth rate of the wind power industry indicates that wind
power will reach a significant share of the electricity supply within the next
two decades, and not only in Germany and Denmark (the other significant
centre of development). Therefore, the main deciding factors are the legislative
conditions. For instance, the Renewable Energy Sources Acts in Germany and
Spain were the basic conditions for the wind power boom in these two
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