Chapter1, Ksiązki, WIND ENERGY - THE FACTS

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WIND ENERGY - THE FACTS
PART I
TECHNOLOGY
Acknowledgements
Takis Chaviaropoulos
CRES
Part I was compiled by Paul Gardner, Andrew Garrad,
Lars Falbe Hansen, Peter Jamieson, Colin Morgan,
Fatma Murray and Andrew Tindal of Garrad Hassan
and Partners, UK; José Ignacio Cruz and Luis Arribas
of CIEMAT, Spain; Nicholas Fichaux of the European
Wind Energy Association (EWEA).
We would like to thank all the peer reviewers for
their valuable advice and for the tremendous effort
that they put into the revision of Part I.
Part I was carefully reviewed by the following
experts:
Angeles Santamaria
Martin Iberdrola
Erik Lundtang Petersen Risø DTU National Laboratory
Jos Beurskens
ECN
Josep Prats
Ecotècnia
Eize de Vries
Planet
Flemming Rasmussen
Risø DTU National Laboratory
Simon Watson
Loughborough University
Félix Avia
CENER
Murat Durak
Turkish Wind Energy
Association
Nicolas Fichaux
European Wind Energy
Association
Jørgen Højstrup
Suzlon Energy A/S
Henning Kruse
Siemens
I.1
INTRODUCTION
Electricity can be generated in many ways. In each case,
a fuel is used to turn a turbine, which drives a generator,
which feeds the grid. The turbines are designed to suit
the particular fuel characteristics. The same applies to
wind-generated electricity: the wind is the fuel, which
drives the turbine, which generates electricity. But
unlike fossil fuels, it is free and clean.
The politics and economics of wind energy have
played an important role in the development of the
industry and contributed to its present success, but
the engineering is still pivotal. As the wind industry
has become better established, the central place of
engineering has become overshadowed by other
issues, but this is a tribute to the success of engineers
and their turbines. Part I of this volume addresses the
key engineering issues:
the wind – its characteristics and reliability; how it
destroy the turbines. This part describes how it can
be quantiﬁ ed, harnessed and put to work in an eco-
nomic and predictable manner. The long- and short-
term behaviour of the wind is described. The latter
can be successfully forecasted to allow wind energy
to participate in electricity markets.
The enormous offshore wind resource offers great
potential, but there are major engineering chal-
lenges, especially regarding reliability, installation and
access.
In short, Part I explores how this new, vibrant and
rapidly expanding industry exploits one of nature’s
most copious sources of energy – the wind.
•
can be measured, quantiﬁ ed and harnessed;
the turbines – their past achievements and future
•
challenges, covering a range of sizes larger than
most other technologies, from 50 W to 5 MW and
beyond;
the wind farms – the assembly of individual turbines
•
into wind power stations or wind farms; their opti-
misation and development; and
going offshore – the promise of a very large resource,
•
but with major new technical challenges.
Part I provides a historical overview of turbine
development, describes the present status and con-
siders future challenges. This is a remarkable story,
which started in the 19th century and accelerated
over the last two decades of the 20th, on a course
very similar to the early days of aeronautics. The
story is far from ﬁ nished, but it has certainly started
with a vengeance.
Wind must be treated with great respect. The wind
speed on a site has a very powerful effect on the eco-
nomics of a wind farm, and wind provides both the fuel
to generate electricity and, potentially, loads that can
I.2
WIND RESOURCE ESTIMATION
Introduction
new questions are beginning to emerge, which are
critically linked to the nature of the wind:
How can wind energy be consolidated, traded and
The wind is the fuel for the wind power station. Small
changes in wind speed produce greater changes
in the commercial value of a wind farm. For example,
a 1 per cent increase in the wind speed might
be expected to yield a 2 per cent increase in energy
production.
This chapter explains why knowledge of the wind is
important for each and every stage of the develop-
ment of a wind farm, from initial site selection to
operation.
Europe has an enormous wind resource, which can
be considered on various levels. At the top level, the
potential resource can be examined from a strategic
standpoint:
Where is it?
•
generally integrated into our conventional electri-
city systems?
Will an ability to forecast wind farm output help this
•
integration?
These questions, and more, are addressed in this
chapter. The ﬁ rst section looks at the strategic ‘raw’
resource issues, and the following sections provide a
detailed step-by-step evaluation of the assessment
process. A worked example of a real wind farm is
then provided and, ﬁ nally, recommendations are
made about the important matters that need to be
tackled in the near future to help wind energy play its
full part.
•
How does it compare to the EU and national elec-
•
Regional Wind Resources
tricity demands?
What regions and areas offer good potential?
•
Naturally, wind energy developers are very interested
in the energy that can be extracted from the wind, and
how this varies by location. Wind is ubiquitous, and in
order to make the choice of potential project sites an
affordable and manageable process, some indication
of the relative size of the ‘wind resource’ across an
area is very useful. The wind resource is usually
expressed as a wind speed or energy density, and
typically there will be a cut-off value below which the
energy that can be extracted is insufﬁ cient to merit a
wind farm development.
At the next level, it is necessary to understand the
actual wind resource on a site in great detail:
How is it measured?
•
How will it change with time?
•
How does it vary over the site?
•
How is it harnessed?
•
It is at this stage that commercial evaluation of a
wind farm is required, and robust estimates must be
provided to support investment and ﬁ nancing deci-
sions. Once the wind speed on the site has been esti-
mated, it is then vital to make an accurate and
reliable estimate of the resulting energy production
from a wind farm that might be built there. This
requires wind farm modelling and detailed investiga-
tion of the environmental and ownership constraints.
As its contribution to electricity consumption
increases, in the context of liberalised energy markets,
ON-SITE MEASUREMENT
The best, most accurate indication of the wind resource
at a site is through on-site measurement, using an
anemometer and wind vane (described in detail later in
this chapter). This is, however, a fairly costly and time-
consuming process.
WIND ENERGY - THE FACTS -
WIND RESOURCE ESTIMATION
33
COMPUTER MODELLING
reduced through consideration of so-called ‘con-
straints’. These are considerations which tend to
reduce the area that in reality will be available to the
wind energy developer. For instance, they can be
geographically delineated conservation areas, areas
where the wind speed is not economically viable or
areas of unsuitable terrain. Areas potentially available
for development are sequentially removed from the
area over which the energy resource is summed.
Different estimates of the potential energy resource
can be calculated according to assumptions about
the area that will be available for development.
The resource without constraints is often called the
‘theoretical’ resource; consideration of technical
constraints results in an estimation of a ‘technical’
resource; and consideration of planning, environ-
mental and social issues results in the estimation
of a so-called ‘practical’ resource. Such studies
were common in the 1980s and 1990s, when wind
energy penetration was relatively low, but have
been overtaken somewhat by events, as penetrations
of wind energy are now substantial in many European
countries.
On a broader scale, wind speeds can be modelled using
computer programs which describe the effects on the
wind of parameters such as elevation, topography and
ground surface cover. These models must be primed
with some values at a known location, and usually this
role is fulﬁ lled by local meteorological station measure-
ments or other weather-related recorded data, or data
extracted from numerical weather prediction models,
such as those used by national weather services.
Typically, these wind-mapping programs will derive a
graphical representation of mean wind speed (for a
speciﬁ ed height) across an area. This may take the
form of a ‘wind atlas’, which represents the wind speed
over ﬂ at homogeneous terrain, and requires adjust-
ments to provide a site-speciﬁ c wind speed prediction
to be made with due consideration of the local topogra-
phy. In some areas, ‘wind maps’ may be available;
these include the effects of the terrain and ground
cover. Wind atlases and wind maps have been produced
for a very wide range of scales, from the world level
down to the local government region, and represent the
best estimate of the wind resource across a large area.
They do not substitute for anemometry measurements
– rather they serve to focus investigations and indicate
where on-site measurements would be merited.
As a further stage in investigations, theoretical wind
turbines can be placed in a chosen spacing within a
geographical model containing wind speed values as a
gridded data set. This is usually computed in a geo-
graphical information system (GIS). Employing assump-
tions on the technology conversion efﬁ ciency to units
of energy, it is possible to derive an energy estimate
that corresponds to a deﬁ ned area. This is typically
expressed as Region X having a wind energy potential
of Y units of energy per year.
Wind Atlases
ONSHORE
Figure I.2.1 shows the onshore wind energy resource
as computed on a broad scale for the European Wind
Atlas. The map shows different wind speed regions.
The wind speeds at a 50 m height above ground level
within the regions identiﬁ ed may be estimated for
different topographic conditions using the table below
the ﬁ gure.
The wind speed above which commercial exploitation
can take place varies according to the speciﬁ c market
conditions. While countries such as Scotland clearly
have exceptional potential, with rising fuel prices and
consequently increasing power prices, every European
country has a substantial technically and economically
exploitable wind resource.
CONSTRAINTS
Most wind energy resource studies start with a top-
level theoretical resource, which is progressively
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