DOCSLIB.ORG

The History and State of the Art of Variable-Speed Wind Turbine Technology

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The History and State of the Art of Variable-Speed Wind Turbine Technology February 2001 • NREL/TP-500-28607 The History and State of the Art of Variable-Speed Wind Turbine Technology P.W. Carlin A.S. Laxson E.B. Muljadi National Renewable Energy Laboratory 1617 Cole Boulevard Golden, Colorado 80401-3393 NREL is a U.S. Department of Energy Laboratory Operated by Midwest Research Institute • Battelle • Bechtel Contract No. DE-AC36-99-GO10337 February 2001 • NREL/TP-500-28607 The History and State of the Art of Variable-Speed Wind Turbine Technology P.W. Carlin A.S. Laxson E.B. Muljadi Prepared under Task No. WER13010 National Renewable Energy Laboratory 1617 Cole Boulevard Golden, Colorado 80401-3393 NREL is a U.S. Department of Energy Laboratory Operated by Midwest Research Institute ••• Battelle ••• Bechtel Contract No. DE-AC36-99-GO10337 NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Available electronically at http://www.doe.gov/bridge Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831-0062 phone: 865.576.8401 fax: 865.576.5728 email: [email protected] Available for sale to the public, in paper, from: U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 phone: 800.553.6847 fax: 703.605.6900 email: [email protected] online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste Table of Contents 1.0 Introduction............................................................................................................................................ 1 2.0 Fixed Speed Versus Variable Speed ..................................................................................................... 2 3.0 Methods of Implementing Variable Speed........................................................................................... 8 3.1 Introduction ...................................................................................................................................... 8 3.2 Variable Speed in Small Turbines–An Overview............................................................................. 9 3.3 Variable Speed in Large Turbines–An Overview............................................................................. 9 3.4 Generators....................................................................................................................................... 10 3.5 Reactive Power and VARs.............................................................................................................. 12 3.6 Power Electronics ........................................................................................................................... 15 3.7 Implementation of Variable Speed ................................................................................................. 17 4.0 Variable-Speed Machine Histories..................................................................................................... 19 4.1 NASA MOD-0 Plum Brook ........................................................................................................... 19 4.2 The Growian Variable-Speed Wind Turbine.................................................................................. 20 4.3 Bergey Excel................................................................................................................................... 22 4.4 MASA MOD-5B Wind Turbine System ........................................................................................ 23 4.5 DOE/Sandia National Laboratories/U.S. Department of Agriculture 34 Meter, Vertical-Axis Variable-Speed Test Bed......................................................................... 23 4.6 The Enercon E-40 Variable-Speed Wind Turbine.......................................................................... 24 4.7 The Gamma 60 Variable-Speed Wind Turbine .............................................................................. 25 4.8 Kenetech Windpower KVS-33 Variable Speed.............................................................................. 26 4.9 Nordic 400 Variable-Speed Wind Turbine .....................................................................................26 4.10 Advanced Wind Turbines AWT-26 Variable Speed with Doubly Fed Generator........................ 27 4.11 Northwind 100.............................................................................................................................. 28 4.12 The Vertical-Axis Variable-Speed EOLE at Cap Chat, Canada................................................... 29 4.13 The Danish Machine at Tvind....................................................................................................... 29 5.0 Conclusions: The Future of Variable Speed...................................................................................... 34 6.0 Power Conversion Design Details....................................................................................................... 35 6.1 Generators....................................................................................................................................... 35 6.2 Voltage-Frequency Converters ....................................................................................................... 50 6.3 Utility Interface............................................................................................................................... 55 7.0 A Look at Future Development .......................................................................................................... 56 8.0 Acknowledgements .............................................................................................................................. 59 Appendix A, Selected References .............................................................................................................. 60 iii 1.0 INTRODUCTION One of the earliest non-animal sources of power used by man was the wind turbine. Wind turbines have been in documented use for more than 1,000 years. The earliest wind turbine designs were extremely simple; turbines were allowed to rotate at a rate proportional to the velocity of the wind. They were used to pump water, grind grain, cut lumber, and perform a myriad of other tasks. For these purposes, varying speed seldom impacted the effectiveness of the windmill enough to justify the complications of closely controlling rotational speed. Allowing the machines to run at variable speed was in fact highly advantageous as it greatly increased the total energy that could be extracted from the wind. The earliest horizontal-axis windmill to use the principles of aerodynamic lift instead of drag may have been introduced in the twelfth century. These horizontal-axis sail turbines were allowed to run at varying speeds, limited only by braking or furling to control their speed during storms. These designs operated throughout Europe and in the Americas into the present century. In the 700 or so years since the first sail- wing turbine, designers discovered many of the key principles of aerodynamics without understanding the physics behind them. It was not until the nineteenth century that these principles began to be clearly understood. In the early nineteenth century the classic American water pumper was introduced. The need for this machine was driven by the phenomenal growth of agriculture in the American Midwest, beginning with the opening of the Northwestern prairie states in the early 1800s. More than a million of these machines dotted the Midwest and West starting in the early 1850s. Even now these multibladed farm windmills can be seen throughout the western United States and Canada, where the energy and storage requirements for providing drinking water for cattle are well matched to the wind water pumper’s power, the storage capacity of the associated stock tank, and the wind statistics of the Great Plains. These machines use the most rudimentary airfoils (often flat plates or slats of wood) and are allowed to rotate proportionally to wind velocity. For the purposes of direct mechanical water pumping, this variable-speed operation works effectively. Even though the American water-pumping design gives up something by its dependence on a flat-plate airfoil, its simplicity, ease of construction, and reliability still make it ideal for its intended purpose. The early twentieth century saw the start of the electric era. The rapid advances in motor, generator, lighting, and appliance designs by Edison, Steinmetz, Tesla and others offered the promise of an electric- powered utopia. The
Load more

Recommended publications
  • Amendment to Registration Statement Washington, DC 20530 Pursiiant to the Foreign Agents Registration Act of 1938, As Amended
    Received by KSD/FARA Registration Unit 02/28/2018 2:32:01AM ' J ° OMB N6. 1124-0003; Expires May 31,2020 UA Department of Justice Amendment to Registration Statement Washington, DC 20530 Pursiiant to the Foreign Agents Registration Act of 1938, as amended INSTRUCTIONS. Fite this amendment ibnn for any changes to a registration. Compliance is accomplished by Sting an electronic amendment to registration statement and uploading any supporting documents at https://www.fara.gov. Privacy Act Statement. Thefiling of this document is required for the Foreign Agents Registration Act of 1938, as amended, 22 U.S.C. § 61 i etseq., for the purposes of registration under the Act and public disclosure. Provision of the information requested is mandatory, and failureto provide the information is subject to the penally and enforcement provisions established in Section 8 of the Act Every registration statement, short form registration statement, supplemental statement, exhibit, amendment, copy of informational materials or other document or information filed with the Attorney General under this Act is a public record open to public examination, inspection and copying during the posted business hours of the Registration Unit in Washington, DC. Statements are also available online at the Registration Unit's, webpage: httpg//www.fara-gov. One copy of every such document, other than informational materials, is automatically provided to the Secretary of State pursuant to Section 6(b) of the Act, and copies of any ahd all documents are routinely made available to other agencies, departments and Congress pursuant to Section 6(c) of the Act the Attorney General also transmits a semi-annual report to Congress on the administration of the Act which lists the names of all agehts registered under the Act and the foreign principab they represent This report is available to the public in print and online ati httpst/fwww.
    [Show full text]
  • COMPREHENSIVE SEXUALITY EDUCATION in TEACHER TRAINING in EASTERN and SOUTHERN AFRICA United Nations Educational, Scientific and Cultural Organization MAY 2015
    COMPREHENSIVE SEXUALITY EDUCATION IN TEACHER TRAINING IN EASTERN AND SOUTHERN AFRICA United Nations Educational, Scientific and Cultural Organization MAY 2015 Comprehensive Sexuality Education in Teacher Training in Eastern and Southern Africa Table of Contents ACRONYMS ...........................................................................................................3 VOLUME 1 .............................................................................................................6 Preface .....................................................................................................................................................7 Figures and Tables ..................................................................................................................................8 Acknowledgements ................................................................................................................................9 Executive Summary ................................................................................................................................10 Chapter 1: Introduction and Background .............................................................................................15 Introduction ..................................................................................................................................................................................15 Background ...................................................................................................................................................................................15
    [Show full text]
  • The Danish Folk High School Adapts to a New World
    Denmark s informal, residential schools provide practical work experiences ———————————————————————————————————————————————————————————in humanistic, innovative settings. The Danish Folk High School Adapts to a New World merican observers of the Dan Grundtvig and Kold a new dignity ish folk high school movement SAMUEL S. CORL, III__ and pride of heritage. A have marveled at the human The early curriculum of the folk istic bent of these remarkable insti turmoil of the early years shaped high school reflected the nationalistic tutions, and their seemingly anti- these schools, and the ones to follow spirit of Grundtvig and Kold. Stu establishment romanticism. For more them, in natural harmony with both dents came for the winter to study than a century, these schools have the character of the rural Danes who Danish history, world history, geog been unique in their approach to began them, and the political and raphy, Danish language and litera preserving Danish culture, while religious radicalism of the inspirator ture, German, zoology, botany, furnishing a free and open oppor of the movement, Nikolaj Severin geometry, drafting, arithmetic, physi tunity for Danish youth to explore Frederik Gnmdtvig, pastor, poet, cal training, singing, and "intelligence national and world issues and prob and educator. training"—the analysis of moral, lems. Grundtvig railed at the "schools psychological, or statistical subjects. These are schools without credits, of death" which forced literate Danes At R0dding, much of that curriculum without examinations, without grades to abandon their language for the remains today. A typical folk high or certificates of attendance, and stuffy but prestigious Latin of the school, if there is one, offers world often, for Americans, characterized formal schools, and at the insistence and national issues, Swedish gym by a fluid, non-restricting curriculum.
    [Show full text]
  • U.S. Department of Justice Federal Bureau of Investigation Washington, D.C. 20535 August 24, 2020 MR. JOHN GREENEWALD JR. SUITE
    U.S. Department of Justice Federal Bureau of Investigation Washington, D.C. 20535 August 24, 2020 MR. JOHN GREENEWALD JR. SUITE 1203 27305 WEST LIVE OAK ROAD CASTAIC, CA 91384-4520 FOIPA Request No.: 1374338-000 Subject: List of FBI Pre-Processed Files/Database Dear Mr. Greenewald: This is in response to your Freedom of Information/Privacy Acts (FOIPA) request. The FBI has completed its search for records responsive to your request. Please see the paragraphs below for relevant information specific to your request as well as the enclosed FBI FOIPA Addendum for standard responses applicable to all requests. Material consisting of 192 pages has been reviewed pursuant to Title 5, U.S. Code § 552/552a, and this material is being released to you in its entirety with no excisions of information. Please refer to the enclosed FBI FOIPA Addendum for additional standard responses applicable to your request. “Part 1” of the Addendum includes standard responses that apply to all requests. “Part 2” includes additional standard responses that apply to all requests for records about yourself or any third party individuals. “Part 3” includes general information about FBI records that you may find useful. Also enclosed is our Explanation of Exemptions. For questions regarding our determinations, visit the www.fbi.gov/foia website under “Contact Us.” The FOIPA Request number listed above has been assigned to your request. Please use this number in all correspondence concerning your request. If you are not satisfied with the Federal Bureau of Investigation’s determination in response to this request, you may administratively appeal by writing to the Director, Office of Information Policy (OIP), United States Department of Justice, 441 G Street, NW, 6th Floor, Washington, D.C.
    [Show full text]
  • 100% Renewable
    100% Renewable — Edited by Peter Droege 234mm x 156mm trim size — PPC hardback — Spine width: 31mm — ISBN 978-1-84407-718-2 100% RENEWABLE 100% ‘This inspiring book is long overdue. It tackles The greatest challenge of our time is to build a an essential question for human survival in the world based on the sustainable use of renewable 21st century: will we be able to transform our power. Our massive dependence on fossil fuels lives, businesses, buildings, settlements and has upset the very climatic system that made the transport networks connecting them from human evolution possible. The global economy unsustainable, oil-based and greenhouse-gas- and its financial system are in jeopardy, running emitting into sustainable, fossil-fuel-free, zero- hot on overtly cheap yet increasingly costly and carbon metabolisms? This important volume and fast depleting oil. A 100% renewable world is its two dozen contributors show that this path is seen by many as an impossible dream in anything necessary, practical and affordable. Read this but the very long term. But not only do a growing book: its exciting, fresh insights will show you number of initiatives and plans dare to make the how to move from promise to practice.’ change but many have already achieved it. Marco KEinEr Director, Environment, Housing and Land This rich collection presents a series of pioneering Management Division, United nations efforts and their champions, and the paths to their Economic commission for Europe successes. Ranging from initiatives by individuals to visions for companies, communities and entire ‘100% renewable was always more than a Moon countries, it defeats tired economic and technical Shot or a Manhattan Project as we just could counter-arguments, showing how the schemes not imagine how it could ever happen.
    [Show full text]
  • Supreme Court of Denmark
    Strasbourg, 29 August 2006 CDL-JU(2006)034 Or. Engl./Fr. EUROPEAN COMMISSION FOR DEMOCRACY THROUGH LAW (VENICE COMMISSION) Supreme Court of Denmark Working document for the Circle of Presidents of the Conference of European Constitutional Courts (Vilnius, 7 September 2006) This document will not be distributed at the meeting. Please bring this copy. Ce document ne sera pas distribué en réunion. Prière de vous munir de cet exemplaire. CDL-JU(2006)034 - 2 - Table of contents A. Description........................................................................................................................2 I. Basic texts ...........................................................................................................................2 II. Composition and organisation ............................................................................................2 1. Structure of the Judiciary................................................................................................2 2. Composition of the Supreme Court................................................................................3 3. Procedure and organisation of the Supreme Court.........................................................3 III. Powers.............................................................................................................................4 IV. Nature and effects of judgments.....................................................................................4 B. The Constitutional Act of Denmark (extracts)..............................................................5
    [Show full text]
  • Strategic Planning for Small Business Institutes in Poland
    STRATEGIC PLANNING FOR SMALL BUSINESS INSTITUTES IN POLAND Sponsored by The U.S. Agency for International Development Developed by Solidarity Economic Foundation Gdafisk, Poland Polish American Enterprise Institute Poznani, Poland Center on Education and Training for Employment The Ohio State University Columbus, Ohio STRATEGIC PLANNING FOR SMALL BUSINESS INSTITUTES IN POLAND Randy Rollinson Walery Lach Zdzislaw Krajewski M. Catherine Ashmore Solidarnog6 Economic Foundation Gdaisk, Poland and Centec on Education and Training for Employment The Ohio State University 1900 Kenny Road Columbus, Ohio 43210-1090 1993 These materials were developed as a product of the Entrepreneurship Institute Project in Poland, funded under the U.S. AID grant EUR-0029-G-00-1040-00. o Copyright by the Center on Education and Training for Employment, The Ohio State University, 1993 and the Center for Enterprise Development. No part of this book can be replicated or used without prior written permission of the Center on Education and Training for Employment. ii FOREWORD The United States Agency for International Development (U.S.AID) sponsored this project as part of the U.S.Congress initiative entitled Secure Eastern European Democracy (SEED Ac:). This project is one of a number of university-based initiatives to provide education for university faculty in emerging countries about business management and economics in support of the newly established market economy. Since June of 1991, the International Enterprise Academy at The Ohio State University has worked cooperatively with the Solidarity Economic Foundation in Gdaiisk, Poland, to facilitate the creation of three Polish-American Enterprise Institutes in connection with the universities in Bialystok, Poznaii and Rzesz6w.
    [Show full text]
  • ED209124.Pdf
    DOCUMENT RESORE SO 013 627 .. ED 209 124 AUTHOR Brown, Lester R. TITLE Building a Sustainable Society. INSTITUTION Worldwatch Inst., Washington, D.C. iSPONS AGENCY United Nations Fund for Population Activities, New York, N.Y. REPORT NO ISBN-0-393-01482-7 PUB DATE 81 NOTE 440p. AVAILABLE FROM W.W. Norton 6 Company, Inc., 500 Fifth Avenue, New York, NY 10110 ($14.95 clothbound). ROBS PRICE MF01 Plus Postage. PC Not Available from F.DS. DESCRIPTORS *Conservation (Environment); Energy; Food; *Futures (of Society) ; Global Approach; Life Style; Natural Resources; Population Growth; Social Change; Social Problems; Soil Conservation; Urbanization; Values; *World Affairs; *World Problems TnENTIFIERS Oil ABSTRACT This publication discusses worldwide problems and issues of concern. There are two major parts. Bart Ideals with "Converging Demands." For those who regularly read theWorldwatch Papers, much of the material in this sectionwill be familiar. The matt:Jai is included here particularly for thesake of those readers abroad who do not have ready access to theInstitute's publications. Discussed are eiosion, biological systems under pressure,oil, food, and emerging economic and socialstresses. Part II, "The Path to Sustainability," comprises approaImately two-thirAs of tae publication. A number of issues are examinedincluding population growth, conservation of natural resources,renewable energy (e.g. wood, wind, and falling water), and changingvalues. The shape of a sustainable society--a sustainable transportationsystem, the resurgence of agriculture, newindustries and jobs, urbanization, greater local self reliance, andsimpler life styles--is examined. The means of transition to thissustainable society and the institutional challenges are discussed. Thepublication concludes with a subject finder.(Author/RM) *********************************************************************** Reproductions supplied by RIMS are the best that can bemade from the original document.
    [Show full text]
  • Anita Jansson
    Anita Jansson Africa Groups of Sweden (AGIS) Jansson wanted to go abroad and hence decided to take a course at the Travelling Folk High School in 1980 and went to Zimbabwe through them in 1981. At the course, she used the Africa Group’s study material and eventually started writing articles in their bulletin. She worked closely with the ANC and the Swapo offices in Stockholm and became close friends with the people there. She organised a number of rallies, boycotts, bazaars and information campaigns. The contacts with the other Nordic countries were strong, such as with Fællesrådet for det sørlige Afrika (FsA) in Norway and Sydafrika Kontakt in Denmark. Jansson was working on the ANC leaders meeting in Stockholm February 1990 and on Mandela’s visit in March the same year. Madi Gray: This is 22 August 2005, and we are interviewing Anita Jansson of the Africa Groups. Tell me Anita, how did you become involved in support to the struggle for Southern Africa? Anita Jansson: I started by doing a Travelling Folk High School course in 1980. I joined it when I wanted to do something else. I wanted to go abroad somewhere and I found this course, so I went to Zimbabwe in early 1981 for a few months. You know how these courses are, you have to study before you go and then you have to produce something afterwards, so during this course I had the first contact with the Africa Groups because in the study group we were using the Africa Groups book, Befrielsekampen i Afrika.
    [Show full text]
  • Volume 28 2001 Issue 90
    EDITORS The Review of African Political Economy (ROAPE) is published quarterly by Carfax Chris Allen, Jan Burgess and Morris Szeftel Publishing Company for the ROAPE international collective. Now 28 years old, ROAPE is a fully BOOK REVIEWS refereed journal covering all aspects of African political economy. ROAPE has always involved Ray Bush, Roy Love and Giles Mohan the readership in shaping the journal's coverage, welcoming contributions from grassroots organi- EDITORIAL WORKING GROUP sations, women's organisations, trade unions and political groups. The journal is unique in the Chris Allen, Carolyn Baylies, Sarah Bracking, comprehensiveness of its bibliographic referenc- Lynne Brydon, Janet Bujra, Jan Burgess, Ray Bush, ing, information monitoring, statistical documen- Carolyne Dennis, Graham Harrison, Jon Knox, tation and coverage of work-in-progress. Roy Love, Giles Mohan, Colin Murray, Mike Powell, Marcus Power, David Simon, Colin Editorial correspondence, including manuscripts Stoneman, Morris Szeftel, Tina Wallace, A. B. for submission, should be sent to Jan Burgess, Zack-Williams. ROAPE Publications Ltd., P.O. Box 678, Sheffield SI 1BF, UK. Tel: 44 +(0)114 267-6880; Fax 44 + (0)114 267-6881; e-mail: [email protected]. CONTRIBUTING EDITORS Africa: Rok Ajulu (Grahamstown), Yusuf Advertising: USA/Canada: The Advertising Bangura (Zaria), Billy Cobbett (Johannesburg), Manager, PCG, 875 Massachusetts Avenue, Suite Antonieta Coelho (Luanda), Bill Freund 81, Cambridge MA 02139, USA. EU/Rest of the (Durban), Jibril Ibrahim (Zaria), Amadina World: The Advertising Manager, Taylor & Lihamba (Dar es Salaam), Trevor Parfitt (Cairo), Francis, P.O. Box 25, Abingdon, Oxon., OX14 3UE, Lloyd Sachikonye (Harare). UK. Tel: +44 (0)1235 401 000; Fax: +44 (0)1235 401 550.
    [Show full text]
  • Placement of Orphans
    Jørn Holm-Hansen (ed.) PLACEMENT OF ORPHANS Russian and Nordic experiences Working Paper 2005:137 Title: Placement of Orphans Russian and Nordic experiences Editor: Jørn Holm-Hansen Working Paper: 2005:137 ISSN: 0809-6929 ISBN: 82-7071-597-2 Project number: O-2141 and O-2110 Project name:: Alternatives to orphanages in Russia Financial supporter Nordic Council of Ministers Head of project: Lars Kristofersen Abstract: The chapters in this Research Note are grouped in three sections. The first section (chapters 2–5) presents the international experiences. The second (chapters 6–7) presents the Russian background, whereas the third section (chapter 8–9) offers an updated presentation of Russian realities as to the placement of orphans. Summary: See introduction page 6. Date: December 2005 Pages: 88 Publisher: Norwegian Institute for Urban and Regional Research Sinsenvn. 47 B, Box 44, Blindern N-0313 OSLO Telephone (+47) 22 95 88 00 Telefax (+47) 22 22 37 02 E-mail: [email protected] http://www.nibr.no Org. nr. NO 970205284 MVA © NIBR 2006 1 Preface Developing alternatives to traditional orphanages is given priority in Russia as well as the Nordic countries, and experiences are shared among practitioners and researchers across state borders. This Research Note is a contribution to this. The Research Note is based primarily on papers and presentations from a Russian-Nordic network seminar arranged by the Norwegian Institute for Urban and Regional Research (NIBR) at the Norwegian University Centre in St. Petersburg in October 2003. The seminar was titled “Alternatives to traditional orphanages in Russia”, and was financed by the Nordic Council of Ministers’ Grant Scheme.
    [Show full text]
  • The Energy Transition to Energy Democracy
    The energy transition to energy democracy Power to the people Final results oriented report of the REScoop 20-20-20 Intelligent Energy Europe project Co-funded by the Intelligent Energy Europe Programme of the European Union Acknowledgements This publication is the Final results oriented report of the REScoop 20-20-20 Intelligent Energy Europe project. This project ran from the end of March 2012 until the end of March 2015. REScoop 20-20-20 is an initiative launched by most of the founding members of REScoop.eu, the Federation of groups and cooperatives of citizens for renewable energy in Europe, with the support of the Intelligent Energy Europe Program of the European Commission. Twelve organisations in seven countries joined forces to increase the number of successful citizen-led renewable energy projects across Europe. This publication is written by Dirk Vansintjan, board member of the Belgian REScoop Ecopower and acting president of REScoop.eu. The author wishes to thank Siward Zomer (ODE Nederland); Relinde Baeten, Daan Creupelandt, Tom Willems, Jan De Pauw, Jim Williame (Ecopower); Andreas Wieg (DGRV); and Laurie Guevara-Stone (Rocky Mountain Institute) for their contribution, for reading through the text and providing many valuable suggestions for improvement. Any errors remaining are my responsibility alone. I would like to thank Dan Frett for the English translation and editing (www.werkwoord. eu). Any mistakes are due to later additions by non native speakers. Thanks to Wim De Meulder (MeMO) for the layout concept. Photographs and illustrations are our own, or available via Wikimedia Commons, or used with authorisation. Anything written by ourselves can be freely used, quoted, copied and distributed when mentioning the author and REScoop.eu.
    [Show full text]