Wind Energy - The Facts

A Guide to the Technology, Economics and Future of Wind Power

European Wind Energy Association

• Publisher: Routledge
• Year: 2012
• Print ISBN: 9781844077106
• eBook ISBN: 9781136548598
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Ecology
• Index: Biological Sciences

Wind power is often held up as the most accessible and cost-effective route to reducing our reliance on fossil fuels and improving our energy independence, yet knowledge of what it offers is often clouded by myths and misunderstandings, which can hamper its adoption.

This new book, the result of an ambitious project coordinated by the European Wind Energy Association, aims to present the facts about wind energy. It includes six sections discussing:

• technology
• grid integration
• economics of wind
• its industry and markets
• its environmental impacts
• the scenarios and targets for wind energy.

Contributions are drawn from nine leading research bodies across Europe, and the material is global in its scope. It is therefore an essential resource and reference for those whose work or study demands an in-depth examination of the subject, and for anyone who wants detailed, accurate and up-to-date information on this key energy source.

Acknowledgements

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:

Nicolas Fichaux	European Wind Energy Association
Henning Kruse	Siemens
Takis Chaviaropoulos	CRES
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
Jørgen Højstrup	Suzlon Energy A/S

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 can be measured, quantified 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 optimisation 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 considers 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 finished, 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 economics of a wind farm, and wind provides both the fuel to generate electricity and, potentially, loads that can destroy the turbines. This part describes how it can be quantified, harnessed and put to work in an economic 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 challenges, 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.

I.2 WIND RESOURCE ESTIMATION

Introduction

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 development 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?

• How does it compare to the EU and national electricity demands?

• What regions and areas offer good potential?

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 financing decisions. Once the wind speed on the site has been estimated, 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 investigation of the environmental and ownership constraints.

As its contribution to electricity consumption increases, in the context of liberalised energy markets, new questions are beginning to emerge, which are critically linked to the nature of the wind:

• How can wind energy be consolidated, traded and generally integrated into our conventional electricity systems?

• Will an ability to forecast wind farm output help this integration?

These questions, and more, are addressed in this chapter. The first 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, finally, recommendations are made about the important matters that need to be tackled in the near future to help wind energy play its full part.

Regional Wind Resources

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 insufficient to merit a wind farm development.

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.

COMPUTER MODELLING

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 fulfilled by local meteorological station measurements 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 specified height) across an area. This may take the form of a ‘wind atlas’, which represents the wind speed over flat homogeneous terrain, and requires adjustments to provide a site-specific wind speed prediction to be made with due consideration of the local topography. 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 geographical information system (GIS). Employing assumptions on the technology conversion efficiency to units of energy, it is possible to derive an energy estimate that corresponds to a defined area. This is typically expressed as Region X having a wind energy potential of Y units of energy per year.

CONSTRAINTS

Most wind energy resource studies start with a top-level theoretical resource, which is progressively reduced through consideration of so-called ‘constraints’. 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’ resour...

Table of contents

• Cover
• Title
• Copyright
• Table of Contents
• List of Acronyms and Abbreviations
• Acknowledgements
• Foreword
• EWEA Foreword
• Executive Summary
• Part I: Technology
• Part II: Grid Integration
• Part III: The Economics of Wind Power
• Part IV: Industry and Markets
• Part V: Environmental Issues
• Part VI: Scenarios and Targets
• Appendices
• Glossary
• References
• Index