+ All Categories
Home > Documents > Ocean Energies

Ocean Energies

Date post: 08-Dec-2016
Category:
Upload: hoangkien
View: 228 times
Download: 1 times
Share this document with a friend

If you can't read please download the document

Transcript

Ocean_Energies/0444882480/files/00000___b7f12f6a919c240421c9375add1e6654.pdf

Ocean_Energies/0444882480/files/00001___98d425317440b4c49f1561b6e15e7ff5.pdfOCEAN ENERGIES ENVIRONMENTAL, ECONOMIC AND TECHNOLOGICAL ASPECTS OF ALTERNATIVE POWER SOURCES

Ocean_Energies/0444882480/files/00002___6abf4835b47e2acff3309c78a324eab6.pdfFURTHER TITLES IN THIS SERIES Volumes 7-7, 7 I , 15, 16, 18, 19, 21, 23, 29 and 32 are out of print.

8 E. LlSlTZlN SEA-LEVEL CHANGES

9 R.H. PARKER THE STUDY OF BENTHIC COMMUNITIES

MODELLING OF MARINE SYSTEMS

TROPICAL MARINE POLLUTION

10 J.C.J. NIHOUL (Editor)

12 E.J. FERGUSON WOOD and R.E. JOHANNES

13 E. STEEMANN NIELSEN

14 N.G.JERLOV MARINE PHOTOSYNTHESIS

MARINE-OPT~CS 17 R.A. GEYER (Editor)

SUBMERSIBLES AND THEIR USE IN OCEANOGRAPHY AND OCEAN ENGINEERING

20 P.H. LEBLOND and L.A. MYSAK WAVES IN THE OCEAN

22 P. DEHLINGER MARINE GRAVITY

24 F.T. BANNER, M.B. COLLINS and K.S. MASSIE (Editors) THE NORTH-WEST EUROPEAN SHELF SEAS: THE SEA BED AND THE SEA IN MOTION

25 J.C.J. NIHOUL (Editor) MARINE FORECASTING

26 H.G. RAMMING and 2. KOWALIK NUMERICAL MODELLING MARINE HYDRODYNAMICS

27 R.A. GEYER (Editor) MARINE ENVIRONMENTAL POLLUTION

28 J.C.J. NIHOUL (Editor) MARINE TURBULENCE

30 A. VOlPlO (Editor) THE BALTIC SEA

31 E.K. DUURSMA and R. DAWSON (Editors) MARINE ORGANIC CHEMISTRY

33 R.HEKINIAN PETROLOGY OF THE OCEAN FLOOR

34 J.C.J. NIHOUL (Editor) HYDRODYNAMICS OF SEMI-ENCLOSED SEAS

35 B. JOHNS (Editor) PHYSICAL OCEANOGRAPHY OF COASTAL AND SHELF SEAS

36 J.C.J. NIHOUL (Editor) HYDRODYNAMICS OF THE EQUATORIAL OCEAN

37 W. LANGERAAR SURVEYING AND CHARTING OF THE SEAS

38 J.C.J. NIHOUL (Editor) REMOTE SENSING OF SHELF-SEA HYDRODYNAMICS

39 TKHIYE (Editor) OCEAN HYDRODYNAMICS OF THE JAPAN AND EAST CHINA SEAS

40 J.C.J. NIHOUL (Editor)

41 H. KUNZENDORF (Editor) MARINE MINERAL EXPLORATION

42 J.C.J NIHOUL (Editor) MARINE INTERFACES ECOHYDRODYNAMICS

43 P. LASSERRE and J.M. MARTIN (Editors)

COUPLED OCEAN-ATMOSPHERE MODELS

BIOGEOCHEMICAL PROCESSES AT THE LAND- SEA BOUNDARY

44 I.P. MARTINI (Editor) CANADIAN INLAND SEAS

45 J.C.J. NIHOUL (Editor) THREE-DIMINSIONAL MODELS OF MARINE AND ESTUARIN DYNAMICS

46 J.C.J. NIHOUL (Editor) SMALL-SCALE TURBULENCE AND MIXING IN THE OCEAN

SEA BOUNDARY 44 I.P. MARTINI (Editor)

CANADIAN INLAND SEAS 45 JC.J. NIHOUL (Editor)

46 J.C.J. NIHOUL (Editor)

THREE-DIMINSIONAL MODELS OF MARINE AND ESTUARIN DYNAMICS

SMALL-SCALE TURBULENCE AND MIXING IN THE OCEAN

47 M.R. LANDRY and B.M. HICKEY (Editors) COASTAL OCENOGRAPHY OF WASHINGTON AND OREGON

40 S.R. MASSEL HYDRODYNAMICS OF COASTAL ZONES

49 V.C. LAKHAN and A.S. TRENHAILE (Editors) APPLICATIONS IN COASTAL MODELING

50 J.C.J. NIHOUL and B.M. JAMART (Editors) MESOSCALE SYNOPTIC COHERENT STRUCTURES IN GEOPHYSICAL TURBULENCE

51 G.P. GLASBY (Editor) ANTARCTIC SECTOR OF THE PACIFIC

52 P.W. GLYNN (Editor) GOBAL ECOLOGICAL CONSEQUENCES OF THE 1982-83 EL-NINO-SOUTHERN OSCILLATION

53 J. DERA (Editor)

54 K. TAKANO (Editor)

55 TAN WEIYAN

56 R.CHARLIER and J. JUSTUS

MARINE PHYSICS

OCEANOGRAPHY OF ASIAN MARGINAL SEAS

SHALLOW WATER HYDRODYNAMICS

OCEAN ENERGIES, ENVIRONMENTAL, ECONOMIC AND TECHNOLOGICAL ASPECTS OF ALTERNATIVE POWER SOURCES

DEEP CONVECTION AND DEEP WATER FORMATION IN THE OCEANS

57 P.C. CHU and J.C. GASCARD (Editors)

58 P.A. PlRAZZOLl

59. T. TERAMOTO DEEP OCEAN CIRCULATION, PHYSICAL AND CHEMICAL ASPECTS

WORLD ATLAS OF HOLOCENE SEA-LEVEL CHANGES

Ocean_Energies/0444882480/files/00003___3d9e85562a1277ccac6d002eea5861b4.pdfElsevier Oceanography Series, 56

OCEAN ENERGIES ENVIRONMENTAL, ECONOMIC AND TECHNOLOGICAL ASPECTS OF ALTERNATIVE POWER SOURCES

Roger H. Charlier University of Brussels (VUB), B- 7050 Brussels, Belgium

and

John R. Justus The Library of Congress, CRS/SPRD, LM4 13 Washington, DC 20504, U. S. A.

This book has received the support of the University Foundation of Belgium. Dit boek kreeg de steun van de Belgische Universitaire Stichting. Ce volume a beneficie de I'appui de la Fondation Universitaire de Belgique.

ELSEVIER Amsterdam - London - New York - Tokyo 1993

Ocean_Energies/0444882480/files/00004___2cf5dcb87ace04e9987a76b99bf0e1d7.pdfELSEVIER SCIENCE PUBLISHERS Sara Burgerhartstraat 25 P.O. Box 211,1000 AE Amsterdam, The Netherlands

L i b r a r y o f Congress Cataloglng-In-Publlcation D a t a

C - a r l i e r . R o g e r H e n r i . Ocean e n e r g i e s e n v i r o n m e r f a l . e c o n o m i c . a n d : e c h n o l o g l c a l

a s p e c t s o f a l t e r n a t i v e p o w e r s :urces / R o g e r H. C - a r l i e r a n d J o h n R. J u s t u s .

p . cm. - - IEIsevier O c e z l o g r a p h y s e r i e s , 36) I n c l u o e s D i b l i o g r a p h i c a l r e i e r e n c e s a n d i n d e x .

1 . C c e a i e n e r g y r e s o u r c e s . 1. J u s t u s . J o h n R . 11. T i t l e . ISBN 0-444-88248-0

_ - . . I . S e r ' e s . - J 1 6 3 . 2 . C 4 8 2 8 1993 1 3 3 . 7 9 C 9 i 6 2 - - a c 2 0 9 2 - 3 2 7 9 5

CIP

ISBN: 0 444 88248 0

0 1993 Elsevier Science Publishers B.V. All rights reserved.

No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publishers, Elsevier Science Publishers B.V., Copyright & Permissions Department, P.O. Box 521, 1000 A M Amsterdam, The Netherlands.

Special regulations for readers in the U.S.A.- This publication has been registered with the Copyright Clearance Center Inc. (CCC), Salem, Massachusetts. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the U.S.A.. All other copyright questions, including photocopying outside of the U.S.A., should be referred to the copyright owner, Elsevier Science Publishers B.V., unless otherwise specified.

No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the materials herein.

This book is printed on acid-free paper.

Printed in The Netherlands.

Ocean_Energies/0444882480/files/00005___436fc452712a590c184e3db4f399c10b.pdfThis book is dedicated to Dr: Patricia Simonet Charlie4 Professor Emerita, University of Illinois, Chicago,

and to my children Connie and Jac

Roger H. Charlier

Ocean_Energies/0444882480/files/00006___400abbd73b7fa9e26f880c9ed1d35358.pdfThis Page Intentionally Left Blank

Ocean_Energies/0444882480/files/00007___9f5324cc368fa9056f5cc0189e612b8a.pdfVI I

PREFACE

Do dreams come true? Apparently some do. A library floor could be filled with books, articles and reports pertaining to tapping ocean energy. Yet, only one sizeable project has ever been carried through to completion, though past proposals, appropriately updated, occasionally stir again. In some respects considering tidal power as part of the strategy to reduce reliance on petroleum for electricity generation is somewhat like reinventing the wheel. For hundreds of years small tide mills furnished the mechanical power necessary to operate saw- and floor mills, various shops and even breweries. These mills used tidal current and the rise and fall of tides. As they performed some of the tasks carried out elsewhere by wind mills, the French appropriately dubbed them moulins a marCe and the Lowlanders getijenmolens. They dotted coastlines and estuaries from Russia to Spain and were eventually brought to the New World.

De BClidor perceived in the eighteenth century the potential of such tide utiliza- tion in electricity generation. Since then tide harnessing literature has frequently appeared in learned journals, though occasionally an ebb sets in. Tide mills lingered on - with a relic still at work here and there - but like the wind mill, they had become obsolete and were rapidly displaced by newer forms of energy generation. The shortage of fossil fuels at the end of the Second World War brought a revival of interest in tidal energy : not mechanical but electrical power was to be generated, and a Severn River barrage was contemplated but never even got to the stage reached by the defunct Passamaquoddy project in the thirties. Dutch coastal wind mills tapped ocean energy and a short-lived attempt at harnessing ocean water temperatures was made in the Ivory Coast (West Africa); test facilities were built, over the last few years, in Hawaii and on some other Pacific Ocean islands. Salt ponds experiments have been conducted in Israel. An attempt at bioconversion on the California coast should also be mentioned.

Nuclear power soon was thought of as the panacea, while cheap and abundant petroleum displaced coal. Wind mills had to be rescued as landmarks and tide mills were completely forgotten.

Supporters of tidal power nevertheless convinced the Electricit6 de France to build, twenty years later (1956), a plant on the estuary of the River Rance. It not only proved successful, it prompted the development of the so-called bulb turbine now in use at hydropower plants as well. While ebb-and-flood generation in tidal schemes has been considered by some as not worth the additional cost, and even the installation of bulb turbines has been challenged, all existing and planned tidal power plants include them, though Straflo turbines are being considered.

Ocean_Energies/0444882480/files/00008___9f970cfae7da504f37400c7c6e6b268d.pdfVIlI Prtfa ce

If large size plants are not numerous, the principal reason is economics. The hurdle exists similarly for all schemes to tap the various ocean energies, not just the tides. They require considerable capital investment and the cost of a generated kilowatt is higher than that of one delivered by conventional or nuclear plants. However, new construction methods, improved technology, the rise in price of petroleum and gas, the respective lifespans of thermal, nuclear, tidal and other plants, are rapidly closing the economic gap. In fact several recent studies claim that tidal power is already cost competitive while Mini-OTEC made a profit in 1981. Furthermore small schemes, a sort of revival of the tide and wind mills perhaps, could make a significant contribution to the power needs of relatively isolated sites or regions.

Strangely, perhaps, while rather few plants have been built, tidal power technol- ogy improves steadily and rapidly, and while every effort was made to update the text up to the time of publication, the author foresaw further fast-paced progress in the areas of construction and turbine development.

In such a Book of Ocean Energies the chapter on tidal power summarizes the various aspects of tide harnessing and embodies the ideas expressed at 1985 symposia.

While perhaps, in the near future, the contribution of tidal energy to the overall needs in energy may be increased, several other ocean sources of energy could be tapped. For some, for instance waves, literally hundreds of patents for energy extraction have been taken out. For several, actual pilot plants have been built. I mentioned these other sources of energy some fifteen years ago and have been fascinated by the enthusiasm of researchers in these fields and their sustained optimism in the face of detractors and proponents of nuclear alternative.

Georges Claude remained for decades the champion of utilizing the difference of temperatures of surface and deeper waters to produce electricity. He spent his personal fortune trying to convince investors and governments of the soundness of the system but no real attempt to harness this energy was ever made until the ill-fated undertaking of the SociCtC de 1Energie des Mers near Abidjan. But the idea refused to die and with the energy crisis interest in what has become to be known as OTEC plants took an upswing. In the chapter covering this topic, my co-author retraces briefly the early proposals, and then covers comprehensively all schemes suggested thus far. As Mini-OTEC has turned a profit, it was appropriate to examine in some detail the economics of ocean thermal differences harnessing. Another interesting aspect of the problem triggered by the Mini-OTEC experiment, is the use of ocean temperature differences for small local schemes. While emphasis, within the limited support given by the US. Department of Energy to Ocean Energy, has certainly favored OTEC, there are not sufficient funds, nor is encouragement particularly sanguine. The Japanese, on the other hand, are actively pursuing efforts towards OTEC implementation, which, in fact, are ahead of other nations. One may wonder whether Claudes dream will ever come to fruition on a commercial scale, and, yet, the promise of OTEC is considerable. The chapter provides an exhaustive bibliography, the result of constant updating

Ocean_Energies/0444882480/files/00009___59b1039511b7d9fd278c62fb73f8bc8f.pdfPreface IX

efforts, on the part of both authors, during the several years it took to complete this book.

British government support whipped up great expectations for the future of ocean waves energy harnessing and I sincerely believed that the subsequent flurry of papers and books heralded an era of experimental plants. I was very distraught when the announcement came in the spring of 1982 that no further funds would be allocated. That some schemes were abandoned as too costly to implement can be understood, but some devices seem to hold practical, viz. economical promise. Will wave energy remain tapped only for clapping of bells, lighting of buoys and some lighthouses, and to discreetly illuminate a bal musette facility on a California pier? Norwegian researchers developed some attractive alternatives to the conventional projects that envision using the pounding of waves or their lifting capacity and a pilot plant was placed into service. And again, the Japanese launched a first, the Kaimei barge, which has provided reasonably priced electrical power to a coastal community.

Harnessing of ocean winds has been proposed both on land and on natural and artificial islands. Here the technology exists, subject to refinement. In Sweden, encouraging results have been booked; on Puerto Rico, the wind turbine implanted on Culebra Island has provided power less expensive than fossil fuel. True, again, some projects are grandiose, even prohibitively expensive, and some others overlook navigation problems. Yet, ocean winds, particularly on islands, and along some coastlines, could add to the power supply. The recent use of ocean winds as suppletive power for ship propulsion opens vistas which may, in turn, lead to onshore developments of marine wind uses.

Geothermal energy tapping has steadily expanded. While there are considerable geothermal resources offshore, all interest is focused on land, and understandably so because of the substantially larger investment that would be required to tap submarine wells. Nearshore wells could perhaps be drilled in the future; the technology is known from land operations, the experience of drilling at sea has since long been acquired from extracting petroleum and natural gas at sea. As an energy source for small communities, land operations remain far more likely than marine undertakings.

I was awed at the magnitude of the Coriolis Project and remain sceptical about the immediate probability of large scale ocean current energy harnessing. Only once, as far as I could ascertain, was an ocean current used to generate electricity, and that northwest Iceland scheme has been abandoned. Perhaps it is more likely to see run-of-the-river type centrals built that would take advantage of the tidal current. Such generating stations might usefully be considered for small communities or particular industrial plants in industrial and less developed countries alike. My co-author discusses the various schemes and the future of ocean current energy use in the light of the most recent developments and we have put together a comprehensive bibliography on the subject which will be published ulteriorly.

Bioconversion retained my interest as it involves both food and energy produc- tion aspects. Ocean farms, pilot installations, that is, have been installed; they met

Ocean_Energies/0444882480/files/00010___5e1980edc4dcc4a078e3056f49cc56f0.pdfX Preface

with untimely ends due to weather conditions and navigational accidents, but it was proven that, on a small scale, marine biomass can contribute to the overall energy picture.

Isaacs, Wicks, and others have studied the possibility of using salinity differ- ences to generate electricity. Osmotic power had been put to work in some seawater batteries, more than twenty years ago, but the cost of membranes has put a prohibitive price tag on a kilowatt that would be generated from a major plant. Thought has been given to schemes that would dispense with membranes. Differences in salinity have been put to work in some experimental solar ponds projects, particularly in Israel. The potential of salt water power is considerable, and it could add significantly to our pool of needed energy, but in this instance technology requires more than refinement and costs of the delivered kilowatt must be drastically cut.

I was tempted to cover in some detail fossil fuels extraction from the ocean, but since these are conventional non-renewable ocean energy sources discussed in hundreds of highly specialized publications, it appeared redundant to mention it here.

Ocean energy harnessing, whether the source is tides, temperatures difference, waves, winds, or any other, has been and remains controversial; in fact, it has been vocally endorsed, and as loudly opposed. With the cost of conventional and nuclear plants rapidly rising, with serious reservations about the safety of the latter and unanswered questions pertaining to wastes disposal, the ocean energy alternative becomes more attractive and more realistic. While ocean energy may not displace oil on its own, its contribution to the worlds power needs, may ultimately prove to be far from negligible, and a serious economic help to capital-poor, labor-intensive, distant sites in less developed countries.

ROGER H. CHARLIER

Ocean_Energies/0444882480/files/00011___a60005af4632c16bfecf80395d48d9d4.pdfXI

ACKNOWLEDGEMENTS

It has become commonplace to say in the acknowledgements that those who have helped bring this book to its completion are too numerous to mention and to proceed to list the names of all contributors. Yet, in this instance, it reflects the facts: literally dozens of individuals, organizations and commercial firms have provided generous help. There are, of course, some colleagues who gave more of their time than anyone else. My first thank you goes to my co-author John Justus who, notwithstanding very heavy obligations at The Library of Congress, wrote the comprehensive chapters on OTEC and current energy, and reviewed the chapter on waves; I am very proud to have had him on the team. Immense gratitude goes also to Gerald Wick, of the Zen Foundation in Los Angeles, whom I met at the Pacem in Maribus Convocation on Okinawa. An authority on waves and salinity energy harnessing he kindly agreed to act as a consultant for these two chapters and provided me with references and reprints that allowed me to constantly update the material; some parts of the chapter are based upon papers authored by Wick himself.

Next comes J. Constans, formerly of Eurocean and now with the Cousteau Foundation, who gave me permission to use some of the illustrations appearing in reports and publications he had written. To Claude Lebarbier of the ElectricitC de France goes my sincere gratitude for allowing me to incorporate segments of his report on ten years of experience at the La Rance tidal power plant.

The authors of the papers presented at the International Symposium on New Perspectives in Tidal Power (Darthmouth, Nova Scotia, 1982) joined me in making the volume most comprehensive on the latest in tidal power.

The ElectricitC de France, Sogreah, Lockheed, Kelco, and so many others have enabled me to illustrate adequately the volume, and so have the U.S. Department of Energy, the Tidal Power Corp. of Canada, and Aerovironment, Inc. Their photographs are identified in the text.

A special note of appreciation must go to HAECON N.V., Ghent, Belgium, and its CEO Christian De Meyer, PE., who generously allowed me to use its reproduction facilities and materially helped in getting the manuscript in final shape. HAECONs decade of interest and its confidence in the future of alternative energy sources from the ocean has proven an inspiration and a steady motivation.

John R. Justus wrote the chapter on ocean currents, took on the lions share of the OTEC contribution, substantially contributed to the various bibliographies and provided all-around advice.

Ocean_Energies/0444882480/files/00012___aa2e810f1b6320efffee876e96d0405e.pdfXI I Acknowledgements

And, of course, there are my family, particularly my wife Dr. Patricia Simonet, Professor at the University of Illinois, Chicago, who gave me support and critical reading service, Dr. J. Rudy Senten, Professor at the Higher Institute for Technical Engineers, who provided help with the index, and Mrs. Evelyn De Bock and Elsie De Smet, who did the final typing. To all a boundless thank you.

Ocean_Energies/0444882480/files/00013___38482706ed16de52830089cae6a92022.pdfCONTENTS

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Acknowledgements ...............................................................

CHAPTER 1 . STATE OF THE ART ................................................

Introduction ...................................................................... Tidal energy . . . . . . . . . . . . . . . . . . . .................................. Wave energy . . . . . . . . . . . . . . . . . . . .................................. Thermal energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Current energy ...................................................................

Salinity energy ....................................................................

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

..................................

...................................

Geothermal energy ....................................................

CHAPTER 2 . OFFSHORE WIND POWER STATIONS ..............................

Introduction ......................................................................

The resource ..................................................................... offshore sites ........................................

Historical background .............................. ..

.......................................... ...

..................................................... Turbine selection ................................................. . . . Types of turbines ..................................................................

Offshore winds power for less developed countries ............................ Availability of marine wind data .............................................

Windpower and economics ........................................................

environmental impact ......................................... Present U.S. WECS program ...................................................

Offshore WECS in the Federal Program ...................................... Problem areas in offshore WECS application ................................. Recent developments .......................................................

Other uses of wind energy ............................................... Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Harnessing offshore winds ........................................... ....

Efficiency of WECS .... .....................

............................... ...........................

VII

IX

1

1 1 3 5

12 13 16 17 18 19

21

21 24 26 29 30 30 33 36 40 47 48 49 49 51 51 52 54 55 55 58 60

Ocean_Energies/0444882480/files/00014___532412cc4e4229e710cfb11b6b327090.pdfXIV Content3

CHAPTER 3 . OCEAN CURRENT ENERGY CONVERSION ........................

The resource potential ...............................

Somc proposed schemes for extracting energy from the Florida current . . . . . . . . . . . . . . Other proposed schemes for harnessing the energy in ocean currents . . . . . . . . . . . . . . . . .

The Mediterranean-Dead Sea Canal project . . . . . . . . . . . . . . . . . .

Technological development ........................................................

The Qattara Basin project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tidal estuaries . . . . . . . . . . .

Environmental considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Costs and developments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.................................

CHAPTER 4 . SOLAR PONDS . . . . . . . . . . . ....

Introduction ...................................................................... Electricity production . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Resource . . . . . . . . . . . . . . . .................................. Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

... . . . . . . . . . . . . . . Costs and development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CHAPTER 5 . WAVES ...................... Energy from the ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The potential use of wave energy .................................................. Ocean waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Apparatus design. installation and starting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Encrgy conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Environmental impact. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Conversion systems . . . . . . Wind waves . . . . . . . .

The birth of waves ............................. Characteristics of wavcs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wave-power resource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

System evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . .

I-listorical development . . . . . . . . . . . . . . . ............................. Wind waves power harnessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Concentration schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Economic considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sea-wave lens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

lntervcntion in wave orbits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....................

Controlled point absorber ......................................

.................... ......................

Utilization of the pressure field . . . . . . . . . . . . . . . . . . . Utilization of mass transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Mauritius project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

63

63 65 69 76 77 80 81 85 88

95

95 95 97 97 99 99

102 102

105

105 106 107 107 108 108 109 110 110 111 1 1 1 112 113 119 122 123 127 129 129 132 136 143 146 147

Ocean_Energies/0444882480/files/00015___fdae642b31166e2af3b981433673015f.pdfContents xv

Dam-Atoll . . . . . . . . . . . . . . Accclerativc devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other recent devices ........................................................

Transmission to shore ............................................................. Economics of converters .......................................................... Technological problems .................... . . .

Prospects for wave power ......

.............................................................. t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

........................ Recent developments

Current developments in Japan .............................................. Current development Current developments in Portugal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tierrabomba Island project .................................................. Gorlov Scheme . . . . . . . . ..................................

Kvaerner Brug and Norwave ......................

The basic concept ..................................................... on ..................................

e .........................................

Brugnoli Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

..........................................

Johns Hopkins Universitys PWECS . . . ....................

Operation ....................... ....................... Pumps . . . . . . . . . . . . . . . ............................................. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

147 149 150 153 154 158 161 163 164 166 166 167 168 169 169 170 170 170 172 173 173 177 181 182 184

CHAPTER 6 . CURRENT ASSESSMENT OF OCEAN THERMAL ENERGY POTENTIAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

Ocean thermal energy conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Resource potential ..................................................... Regions of potential OTEC utilization Historical overview of the technology a nological concept . . . . . . . . . . . . . . . .

.................................

..................... ..........................................

Summary of OTEC research and development activities . . . . . . . . . . . . . . . . Worldwide .................................................................. Sea solar power .............................................................

Recent design concepts .................................. . . . . . . . . . . . . . . . . . . ...

Open-cycle plants ..................................................

Mist lift cycle ...................................................... ....................................

Closed-cycle plants . . . . . . . ............................ .....................

Systems components and related problems in the ocean environment - exchangers ................................................................. Turbines ..................................... . . . . . . . . . . . . . . . . . . lnstrumcntation and controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

187 187 189 190 191 195 199 199 203 203 207 207 21 1 212 214 225

225 234 234

Ocean_Energies/0444882480/files/00016___7adee07f4290348a5372fbe846c9dd00.pdfXVI Contents

Anchoring. mooring. and dynamic positioning ......................... Sea water system (SWS) and cold water pipe . . . . . . . . . . . . . . . . . . . Power transmission cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Power plant systems construction techniques . . . . . . . . . . . . . . . . . . Environmental research and considerations ........................................

Additional considerations related to costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Commercializati ........................ Other factors in Mariculture . . . . . . . . ....................

Hydrogen ........................

International legal/political considerations .... . . . . . . . . . OTEC industry benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CHAPTER 7 . IS TIDAL POWER COMING OF AGE? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Historical background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tidal power in America ........................................................... Tidal phenomenon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The resource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Site selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Possible systems ............................................................

Tidal current power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The tidal powcr plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Power equations . . . . . . . . .......................... . . . . . . . . . . .

Characteristics of operating plants .............................. Transmission and storage ....................................................

The Rance River plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design of the Rance River plant ............................................. Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Other problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Environmental considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Corrosion problems . . . . . . . . . . . . . . . . . .

The Soviet experimental station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Small tidal power plants in China .................................................. Tidal powcr in Suriname . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tidal power in the Bay of Fundy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Updating of thc Bay of Fundy project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Estimates of project cost .......................................................... Financial feasibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Costing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Production estimates and new turbine designs ................................

235 235 239 24 1 246 248 252 254 260 261 26 1 264 266 266 266 267 268 269 210

273

273 274 280 282 283 286 288 289 290 291 294 296 299 302 303 303 304 305 306 307 307 309 309 310 310 312 312

Ocean_Energies/0444882480/files/00017___c87d018c6c2f6cb6ecfe4e53e50d63b5.pdfContents XVII

Value of tidal energy ..............................................................

Environmental impact ....................................................... Comparison tidal/nuclear and tidal/coal ................................

The turbine ................................................................. The powerhouse ............................................................ The barrage ................................................................

Aims of the project: environmental impact ....................................

Advantages, disadvantages, and economics of tidal power ........................... The future ........................................................................

Advantages of the Straflo turbine ............................................

Projects around the world .........................................................

Tidal power twenty years later . ......................................... Small-scale tidal power plants ................................................

The Fay and Smachlo model ................................. Tidal energy conversion ............................................... Tidal currents, etc ............................................... Optimization studies ..................................................

Measuring tidal ranges ...................................................... Introduction of the telemetric system ...................................

Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Energystorage .............................................................. Environmental impact ....................................................... Economics ................................................................. Recent developmcnts .......................................

Japan ................................................................ Argentina .................................................

.............................................................. .........................................................

United States of America . . . . . . . .................................... Korea ................................................................

Conclusion ..................................................................

CHAPTER 8 . SALINITY ENERGY .......................................... Salinity ........................................... .................... Magnitude of the resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Energy extraction .................................................................

Electrodialysis ................................... . . . . . . . . . . . . . . . . . .

Concentration of the free energy ............................................. Osmotic pump ..............................................................

Technical problems ...............................................................

Corrosion and fouling ................................................

Direct mechanical osmotic effect utilization ..................................

Vapor pressure difference utilization ......................................... Expansion and contraction ..................................................

Electrodes .......................................................... Membranes .................................................................

Resistance - electrical and hydrodynamical .................................. Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

314 315 315 316 320 322 323 323 323 325 326 327 327 327 328 330 332 334 335 336 336 337 340 341 342 342 342 343 345 346 346

347

347 349 352 352 352 362 365 366 366 368 368 368 369 369 370

Ocean_Energies/0444882480/files/00018___ee675866227a72536881fda2afcfd9f8.pdfXVllI Contents

Environmental effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Energy from geothermal brines ....................................... Energy from salt domes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Energy from salt pans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Costing - electrodialysis plant ............................... A look into the future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Current funding and problems for research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CHAPTER 9 . GEOTHERMAL ENERGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Geothermal energy ................................................... Background ...................................................................... Resource ............................................

Tapping energy at sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Geochemical characteristics an ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Geographical sites .............................

Exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Exploration limitations .................................... . . .

Power from wet-steam (hot-water) deposits ......................................... The total-flow concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Power from geopressurized deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Power from hot tight rocks (hot dry rocks) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Power from magma systems ....................................................... Environmental impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . osits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The binary cycle ........................ ....................

Othcr U.S. sites ................................................

Costing .......................................................................... Conclusions ............................

CHAPTER 10 . MARINE BIOMASS ENERGY . . ....

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plant description ................................................ Seaweeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Macrocystis pyrifera ..............................

ctivity ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Substrates and supports ............................. ........................

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .............................................................

Test farms ........................................................................ Future prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Elcctricity from marine biomass .............................................

370 371 372 373 373 377 377

381

381 381 384 386 387 388 390 390 391 391 392 392 393 395 399 399 400 400 402 402 405 405

407

408 409 409 411 412 412 414 415 419 420 422 422 425

Ocean_Energies/0444882480/files/00019___fc20b0c63372f44f0395352fa315fb93.pdfContents XIX

Methane generation .............................................................. 427 Economics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430 Environmental impact. ...................................................... 430

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433

References and notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451

Bibliography ...................................................................... 473 lndex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525

Ocean_Energies/0444882480/files/00020___e1a1bd62d057449f4f4c770296d2ef1b.pdfThis Page Intentionally Left Blank

Ocean_Energies/0444882480/files/00021___fd8811eeef30bfef8d825bb8fae7e085.pdf1

Chapter 1

STATE OF THE ART

La mer, la mer toujours recommence! Le Cimetikre Marin, Paul ValCry

INTRODUCTION

Ever since increases in petroleum prices, a frantic search for alternative sources of energy has rekindled an interest in ocean-derived energy. Optimistic prog- noses about large untapped oil and gas reserves on continental shelf and slope, possibly even on the seabed, have been made. In addition a re-evaluation of non- conventional energy sources has been conducted in many countries, particularly Great Britain, the United States, Japan, France, West Germany, Australia, Korea, India and Argentina.

In many respects we are somewhat re-inventing the wheel, because some of the proposed alternatives were once tapped, but then fell into disuse as fossil fuels, particularly petroleum, took over. In the search for additional energy we have implemented nuclear power. On land we are taking a close look at solar energy, using ponds or thermal water systems, central receiver systems, or gigantic mirrors, proposing photovoltaic schemes or even satellites. We are thinking of changing over to a hydrogen economy, we have experimented with fuel cells and K-fuel; have squeezed oil out of shales and sands; have used domestic trash and waste wood; have tapped copaibas and euphorbias; have turned grain and cane into alcohol fuels. Even the quaint windmill is being resurrected alongside gigantic-bladed wind turbines capable of generating as much as 60 kW of power.

This chapter will review briefly the state of the art in ocean-derived and related energy sources.

TIDAL ENERGY

Tidal energy was harnessed hundreds of years ago when tide mills dotted coastlines in England, Wales, Brittany, the Lowlands, Spain, Russia, and even the Atlantic coasts of Canada and the United States. Both the vertical rise and fall of the tides, and the ebb and flood of the tidal currents can be put to work. To tap the

Ocean_Energies/0444882480/files/00022___79ec13284e90e1a75440fd0b109bfc51.pdf2 Chapter I

tide itself requires a dam across a tidal embayment, basin, or estuary; the water rise and/or fall will drive a generator. Although geographically limited by the magnitude of tidal ranges, progress in the development of low-head turbines and the possibility of using removable plastic barriers instead of dams, may reduce considerably the currently prescribed minimum ranges. Plants have been constructed and are operating in France, the former Soviet Union, and China; plans for implementation of schemes in Korea and Canada could move beyond the planning stages quite soon. An optimistic worldwide potential of 3 million MWe is usually quoted; high capital costs are usually cited as a deterrent, but the continued increases in oil prices and the steady increases in construction costs of conventional and nuclear plants are rapidly closing the cost gap.

An alternative to using the tide itself is the utilisation of the flow of the tidal current: diverting a part of that flow into a channel where it turns a wheel.

The number of sites suitable for tidal power plants is limited by several factors. The long dam needed to close off an embayment is expensive to build. A head of less than 5 m (16 ft) is insufficient, unless the new low-head turbines prove successful. A site too distant from its potential market may be undesirable, unless further progress is made on long-distance transmission cables or thought is given to production of a transportable fuel.

The Rance River and Kislaya plants use bulb turbines - an axial flow turbine of the Kaplan type that is placed in a horizontal hydraulic duct and completely

Fig. 1 . 1 . Seaward view of Rance tidal power station with city and harbor of St. Malo in background.

Ocean_Energies/0444882480/files/00023___735dac942b026acc41aee329dc211137.pdfSlate of the art 3

submerged. Such turbines have been installed in the Rock Island dam on the Columbia River as well. These bulb turbines can function both as a turbine and as a pump; however, recent studies are challenging the economic advantages of bulb turbines and newer plans call for the installation of Straflow turbines (Fig. 1.1).

Environmentally, tidal power plants have had little impact. At the Rance River installation, for instance, except for the relocation of some sand banks and the disappearance of some fish species, which were replaced by other fish species, no impact has been observed after more than 10 years of operation. Currently under construction or active consideration are an 18-MW station in Canada and a 12-MW facility in Maine.

WAVE ENERGY

Wave energy has been tapped for a long time; it has been used to activate buoys, to clap bells aboard ships, to light a pier in California, and to provide electrical power to a Japanese community. Such wave energy can be captured in many ways: there are turbines that are activated by waves, or by air columns, while relative-motion devices may also provide power. In 1979 the Lockheed Corporation unveiled its dam-atoll, a prototype of which is currently being built; in this system a vortex of spiraling water acts as a flywheel, as the water of the wave spills into the core of a submerged turbine. The structure, capable of producing 1-2 MW, has an 80-m (263 ft) diameter. In the air column system, the water as it rises and falls in a piston-like chamber, drives a generator. Various designs have been developed in many countries. In Norway, for instance, a program focuses on resonant heaving bodies as point absorbers, in Great Britain structures are beam oriented, and in Japan the waves energy is coupled into a tuned cavity of pressurized air. While as much as 50% of the waves energy can theoretically be retrieved, only between 5 kW/m to 4 MW/total can be generated (Fig. 1.2).

Floating plants function on the principle that wave motion can be converted into reciprocal motion with vertical floating plates creating a liquid pumping action. The potential is considerable, and the U.K. Central Electricity Generating Board estimated that all of Britains energy needs could be satisfied by putting wave energy to work. The power potential, per kilometer of beach, of an average wave is usually given as 40 MW. Implementation is thought to be possible by the turn of the century.

All wave-harnessing schemes are expensive to build; all are subject to poten- tial heavy damage and some to being wrecked in case of exceptionally severe storms. Dam-atoll and air column types have mooring problems and are expensive structures; floating plants are also expensive to install. Corrosion constitutes an additional problem, although lessons learned with the French tidal power plant may be put to very good use here. Earlier casts estimates had put a price of $2000-3000 per kW of wave-generated electricity [l], but more recent estimates have put the cost at $8000-18,000 per kW.

Ocean_Energies/0444882480/files/00024___b8b61ca8a36f339fd6b185cc4f5e1ad6.pdf4 Chapter 1

Fig. 1.2. Wave energy absorption machine on California beach.

The major systems currently being refined in addition to Lockheeds dam- atoll include Salters nodding duck, Cockerells raft, Masudas oscillating column, Hydraulics rectifier, and Isaacs tail tube buoy. Professor Salters nodding duck consists of a string of cone-shaped vanes all connected to a single chord or backbone. A rotary pump is driven by the wave-induced bobbing, and powers a generator. Sir Cockerells contouring raft is made up of three hinged pontoons, which follow the waves contours. The first pontoon moves freely with each wave and absorbs its initial impact. Consequently, the second pontoon moves less, and the third one is relatively stable. The up and down motion of the three pontoons causes hydraulic jacks, secured on each hinge, to drive fluid into a motor which turns a generator.

Commander Masudas scheme involves a hollow concrete cylinder with pipes in the top and an air bubble above the waterline. Air is sucked into the pipes or forced out of them as waves fall and rise, thereby driving a turbine. The Hydraulic Research Station designed a passive system placed on the seabed: water is led through a channel from a high-level to a low-level reservoir, thereby driving a turbine. Finally, the Isaacs tail tube buoy is a float with a tail tube about 100-170 m (328-558 ft) long. Successive waves raise the level inside the tube, thereby building up pressure that drives a turbine.

Ocean_Energies/0444882480/files/00025___9c6fac85e1d29d67c9da9bd796717e7c.pdfState of the art 5

THERMAL ENERGY

Although most ocean energy may be considered as solar energy, the most direct harnessing of ocean solar power is probably through a thalassothermal plant: it has been referred to for some time by the acronym OTEC, Ocean Thermal Energy Conversion (Fig. 1.3).

The basic principle is that in some areas of the world deep cold ocean water ascends to relatively shallow depths, while in these same areas the surface waters are quite warm from collected solar heat. OTEC uses this temperature difference to power a turbine and generate electricity. This system has the potential of satisfying

Fig. 1.3. Flexible joint (tube), Abidjan, 1955. Photography Energie des Mers.

Ocean_Energies/0444882480/files/00026___3ded5e6738c3bea3203851b349c5df8d.pdf6 Chapter I

Figs. 1.4. Convoy of floats, 5th December 1955, Abidjan. Photograph Energie des Mers.

Fig. 1.5. Convoy of floats, 5th December 1955, Abidjan. Photograph Energie des Mers.

a major share of the U.S. energy needs. The technology exists, and successful experiments were conducted as early as 1928. (Figs. 1.4, 1.5).

A plant was even built in the early 1950s in Abidjan, Ivory Coast, but was even- tually abandoned because it could not be operated as economically as conventional power plants and because of repeated failures of the cold water adduction conduit that reached to a 400 m (1312 ft) depth.

Technologies exist for both open-cycle and closed-cycle plants. The open-cycle scheme which is based on the ideas of Arskne dArsonval and which was imple-

Ocean_Energies/0444882480/files/00027___be1fdf9371e6a01d4586c338455e29aa.pdfState of the art

Fig. 1.6. Transportation of a flexible joint (tube), Abidjan. Photo Energie des Mers.

mented in Belgium, Cuba, and the Ivory Coast, uses low-pressure steam as the working fluid. It has mostly been superseded by the closed-cycle system, in which warm surface vaporizes an intermediate fuel, such as ammonia, propane or Freon; the vapors power a turbine and are subsequently condensed back to liquid by the deep cool waters. The working fluid is then recirculated (Figs. 1.6-1.8).

The basic design includes a floating platform or hull, evaporator, turbogenerator, and condenser, and a 400-1,000 m (1312-2381 ft) long large-diameter cold-water adduction pipe. The Japanese plant currently being used is a barge plant, but some designs include instead a spar-shaped platform. A mini-OTEC plant was launched in 1980 and has performed well. The Lockheed-built facility generates 50 kW

Ocean_Energies/0444882480/files/00028___b37efdb2c389b58b240bb82b06d35750.pdf8 Chapter I

Fig. 1.7. The vessel l l n i s i e adapted to accommodate the OTEC equipment. G . Claude in center of picture (white circle).

Ocean_Energies/0444882480/files/00029___34ed8a2417f448824298aa8925941bec.pdfState of the art 9

Fig. 1.8. Side view of OTEC equipment devised by G . Claude. (Sources, fig. 4-8: Archives of Socittt de IEnergie des Mers, and Centenary Memorial Volume of Georges Claude).

offshore of Hawaii. Large OTEC projects are aiming at the production of many more kilowatts: a prototype to be functional by 1986 would capture from 10 to 100 MWe; another scheduled to be placed into service in 1989 is a 500 MWe unit. Some sources foresee as many as 2 quads (or 1 million barrels of petroleum per day) by 2000. In Europe, two plants of up to 10 MW are under consideration (Fig. 1.9).

Geographically speaking the best sites are found in tropical areas, which, unfortu-

Ocean_Energies/0444882480/files/00030___49e213e78629959af5686a6e514f5487.pdf10 Chapter I

Fig. 1.9. Lockheed OTEC scheme. In mid-center: control room; tiny human figures provide iden of dimensions.

nately, are far from population concentrations, posing the problem transmitting the energy produced. However, OTEC plants could manufacture ammonia or extract hydrogen, both of which are transportable. In addition to these fringe bene- fits, thalassothermal plants can be coupled with desalination facilities, mariculture projects, biomass conversion schemes and chemical complexes.

The undertaking is not free of unsolved problems: in addition to corrosion, the matter of biofouling of heat exchangers has to be solved, the stresses exerted on the connecting of cold-water pipe to platform, building in situ or on land, the losses due to long-distance transmission. Although once heralded as a pollution-free electricity-generating system, OTEC has a non-negligible environmental impact; they include the leaching of trace metals from heat exchangers, condensers, and platform surfaces and from anti-corrosion and anti-biofouling paints; the effects of nutrient redistribution; marine organism impingement on the intake screens and

Ocean_Energies/0444882480/files/00031___47b36b509c93813aa3f53780121303de.pdfState of the art 1 1

fish entrainment into the OTEC system; accidental intermediate fluid spills; and the possible modification of temperature conditions in the surface waters.

From an economic viewpoint OTEC appears competitive with conventional electricity production. As with tidal power, fuel has a zero cost. Net power efficiency runs from 60% to 70%. With fuel costs for thermal and nuclear plants due to increase further, the generation of commercial utility electricity in an OTEC plant should be as expensive as, or even cheaper than those two methods; according to Harlan Cleveland, director of the H.H. Humphreys Institute of the University of Minnesota, mini-OTEC actually made a profit in August 1980 (pers. commun.).

The most publicized U.S. effort is the experimental OTEC plant off Hawaii. Placed on a barge, the mini-OTEC generated between 10 and 15 kW/h net. A pilot plant has been on the drawing boards for some time, slated to generate 40 MWe, a forerunner for a 400-MWe commercial plant, but the plant built in 1981 off Kailua-Kona (Hawaii) is temporarily out of commission owing to heat exchange pipe corrosion and bio-fouling. Some $50 million have been invested so far and designs have been ordered by the State of Hawaii for four 10-MW plants.

Additionally, an adduction pipe was disconnected; although its location is known, it is economically unretrievable. Yet, it was decided to keep working with pipes because submarine cables are substantially more expensive than cold water pipes; slanted pipes will be used.

Estimates about the total energy impact hold that OTEC plants could provide as little as 1/800th of the worlds energy needs, to as much as all the energy the United States currently consumes, from Hawaiian waters alone; the opinions vary widely. During the 1970s the U.S. government provided $120 million for OTEC development, but although the technology has been proven, according to Global Marine and TRW researchers, no U.S. government funding is being provided at this time.

In recent months great progress has been made on perfecting the cold water pipes, and what is presently needed is the testing, at sea, of the pipes. This is to be done at Kahe Point (on Oahu), near Honolulu, on a tower built by General Elecfric Corporation or on an artificial island. This latest effort, POCE (Proof of Concept Experiment), is to be carried out as follows: General Electric will place a steel tower in 100 m (330 ft) of water, 1.61 km (1 mi.) offshore, and a 138 kV ac submerged cable will connect the OTEC tower to a Hawaii Electricily Company 900-MWe plant; OTC (Ocean Thermal Corporation) will build an artificial island in concrete 180 m (300 ft) offshore in about 10 m (30 ft) of water, and link the OTEC facility with the HEC plant by means of an 138 kV ac overhead line.

OTEC development efforts have been very active in Japan. A 50-kW turbine was installed near Imari City (in Saga Prefecture) and a mini-OTEC has been functioning since November 10, 1979, in Shimane Prefecture, 80 km (50 mi.) off the coast (3553 N/13226 E). The Toshiba Corporation has constructed a thermal exchange plant on Naurus seashore: the cold water pipe, made of polyethylene, reaches depths of about 700 m (2297 ft); the maximum output is 120 kW and net power of 31.5 kW is realized [2].

Ocean_Energies/0444882480/files/00032___e9a77ed51eb2a2af1785323f12efa8ba.pdf12 Chapter I

WIND ENERGY

The wind provides considerable energy offshore, and sea- or land-based elec- tricity generating plants could tap it, using either windmills or wind turbines. With a windmill the wind drives the generator, and it can be quite effective in specific geographical locations. Sweden plans to get from 6% to 10% of its electricity from marine windmills by 1995; the United States has installed a wind turbine using offshore winds on the coast of Hawaii. These turbines have 17-m (56 ft) diameter generators; transmission units are placed at ground level. At best, with present technology, 35% of the aeolian energy is transformed into shaft power. Although at present such turbines generate no more than 60 kWp, building of 500 kWe units has been started. Wind turbines have a vertical axis, but are noisy due to blade vibration. Their contribution to regional grids and local power consumers can be appreciable (Fig. 1.10).

If the northeast trade winds were put to work on Hawaii they could generate as much as 400 MW. A wind scheme currently under construction and scheduled to be in service in 1984 will generate 80 MW but each kW/h produced will cost 7 c more than that produced by conventional means.

Fig. 1.10. Leidschendam (The Netherlands), windmills in the countryside (NNTO photo).

Ocean_Energies/0444882480/files/00033___5bbda847e89e6247100b4472f6d031fe.pdfState of the art 13

Regardless of the high construction costs of windmills, running up to $ 4 million/ MW, the United States plans to implement several plants, not all of them shore- based, by 2000. The University of Massachusetts William Heronemus proposed some years ago an offshore platform doubling as a self-propelled tank ship equipped to generate and liquefy electrolytically produced hydrogen. The ships wind turbines would tower 60 or 100 m (200 or 330 ft) above the platform and could pose a navigational hazard.

The German Messerschmidt-Bolkow-Blohm Company plans to build GRO- WIAN 11, a 5 MW windmill that will stand 120 m (394 ft) above the ground. A smaller model of this device designed by Rudolph Meggle, GROWIAN I (Grosse Windenergieanlage), will have an output of 370 kW, a 50 m (164 ft) tall steel tower, a 24 m (79 ft) blade, and a 7 m (23 ft) pod housing the gearbox and generator; the blade will rotate at 44 rpm. Erected in 1981 near Bremehaven, this downwind machine has a blade weighing 1.27 tons, far lighter than the 3-m-longer blade weighing 4.5 tons of the 2-MW Jutland windmill.

If the tests with GROWIAN I are successful, particularly with regard to energy conversion efficiency, then the three-times-larger GROWIAN I1 will be placed into service; GROWIAN I1 is twice the height of the U.S. Boeing Mod-2 machine located in southern Washington. This single-bladed device is cheaper, is as efficient, flaps freely with little bending; can be stiffened with a thicker and wider foil section, and is balanced simply by a counterweight. About 5% less power is generated in a single-bladed than in a multi-bladed system, but this power can be recuperated inexpensively by lengthening the blade slightly (Figs. 1.11, 1.12).

CURRENT ENERGY

Use of ocean current energy was once tried in Northern Iceland. The plant is no longer functional, but advocates of current from the current have not given up hope. Philip Richardson recently reminded us that most of the oceans energy is contained in eddies, which probably are the main mechanics for transporting kinetic and thermal energy in the ocean. And current has been produced using a low-velocity turbine.

The Gulf Stream, particularly near its origin, has been thought of as a source of energy to be tapped, for both its temperature differences and current energy. The Gulf Stream is the second largest ocean current, flowing from the Gulf of Mexico, through the straits of Florida, up the Atlantic Coast to the Newfoundland Banks, then spreading out toward Europe. It is some 90 km (50 mi.) wide and 900 m (2950 ft) deep; its flow reaches 220 km (136 mi.) a day. Temperatures vary in a vertical column 1000 m (3280 ft) deep between 16 and 22C, (6 and 72F), a gradient that could generate 180 GWh per year of electricity, but this estimate is purely theoretical because power would have to be transmitted over distances exceeding 1000 km (620 mi.). We are thus very far from obtaining 75 times the current U.S. consumption of energy from the Gulf Stream!

Ocean_Energies/0444882480/files/00034___c0f138adadfab4c74c3c18764d94987a.pdf14 Chapter I

Fig. 1 . 1 1 . Old stover and modern wind turbines side by side in contemporary landscape.

On the other hand, a cluster of turbines placed in the Florida Straits would furnish lo6 kW on a year-round basis, the equivalent of two large nuclear plants. Other marine currents could also provide substantial amounts of power, but energy

Ocean_Energies/0444882480/files/00035___e41701b4ad6ea0755efb874a153e91d7.pdfState of the art 15

Fig. 1.12. The Clayton wind turbine built for DOE under management of the National Aeronautics and Space Administrations (NASA) Lewis Research Center, Cleveland (Ohio).

harnessing may well constitute serious navigational hazards in areas of heavy sea traffic; nevertheless, various devices to harness current flow have been designed. Heronemus and his coworkers proposed a tethered free-stream, four-stage, six- bladed underwater windmill (or waterwheel): in a 2.2 m/s (7.2 ft/s) flow, which could extract 20 MW. Some 14 MW could be obtained using a free-stream Savonius- rotor power station, and 24 MW with a four-disk axial flow water turbine. Other proposals include parachutes attached to a continuous cable, and, the most recent scheme, the Coriolis turbine. (The Coriolis Project is discussed in more detail in a later chapter dealing with energy extraction from marine currents.)

Ocean_Energies/0444882480/files/00036___9f649959ef2d9a30e3163d3008df5050.pdf16 Chapter 1

Some schemes have also been proposed to harness the Cromwell current and even to dam the Straits of Gibraltar. The environmental impact of ocean-current utilization, may possibly include slowing of current. It is unlikely that prior to the turn of the century power from ocean currents will contribute even modestly to power production.

BIOMASS ENERGY

As hinted at previously, most of the solar energy reaching the earth is received by the oceans; ocean farming is one way of capturing some of that energy. Marine plants can be used as a source of fuel in the form of methane or liquid hydrocarbons. Biomass conversion can be based on near-shore cultivation or on marine plants grown in temperate climates. Keeping in mind that per hectare productivity in the sea considerably exceeds that on the land, marine biomass could be used as an energy source. Giant kelp (Macrocystis pyrifera) could be grown on offshore submerged floats. Such platforms, however, are costly and are impediments to navigation; if of considerable size, they are more vulnerable to weather conditions. Optimistic prognostications foresee substantial fuel production by the year 2000, but until the present only a very modest test facility has operated off Southern California. The basic principle is to grow kelp, using nutrients brought up from the deep, harvest them, and have them anaerobically digested to methane. Successful anaerobic conversion of kelp into methane in a seawater medium was achieved by United Aircraft Research Laboratories as far back as 1974.

The efficiency of biomass conversion has been increased; kelp can be coarsely chopped, then fed into a digester and will yield up to 0.312 m3/kg (5 ft3/lb). Harvests reach from 1.15 to 4500 dry ash-free tons per hectare per year with an average yield of 115 tons per hectare per year. The cost of production is approximately $17.50 per 100 m3 (3532 ft3), which is competitive with gasification. In 1981, the State University of New York, Stony Brook, started testing nine different species of seaweeds, all native to the Long Island Sound. Kelp conversion to liquid fuels, such as ethanol, is also under study.

Kelp reproduces its weight every four to six months. Howard Wilcox [3] and others calculated that for every 2.6 km2 (1 mi.2) a kelp farm could feed 2000 people and satisfy the natural gas needs of 300 people. It would require a 340-700 hectare (840-1730 acre) farm to produce 20 tons of methane gas. According to the Gas Research Institutes latest study it would cost from $ 3 to $ 6 to produce 10 Btu (309 kWh) [4]. One can hardly envision biomass conversion as more than a local source of energy, although it has additional economic significance as a source of ethanol, fertilizer and animal feed.

The Ocean Food and Energy Project originally aimed to establish by 1985 or 1990, either in the Atlantic or Pacific ocean, a farm system covering 40,000 hectares (98,800 acres), with nutrients artificially upwelled using wave-powered devices. As with all other ocean-powered systems, the major issue is economic feasibility.

Ocean_Energies/0444882480/files/00037___1470a412e5dde6a207a6c03a6e6dac93.pdfState of the art 17

The scope of the kelp farm program has been changed to ascertain what growth rates are actually possible in their culture. Of parallel interest is the EUROCEAN OTECIAquaculture project, which would use OTEC discharge water to fertilize a commercial aquafarm. The 0.5-1 MW capacity plant would be located on-shore in a tropical or subtropical area.

SALINITY ENERGY

British researchers have estimated that the energy potential resulting from the contact of fresh water and salt water can equal that of a waterfall, or of a hydroelectric dam 250 m (820 ft) high. The energy released by such large rivers as the Amazon and the Congo is tremendous as they debouch into the Atlantic Ocean. While all other forms of ocean energy have at one time or another been put to work, we have never tapped salinity energy or ocean geothermal energy. True, seawater batteries have been designed, and they are functional, though very bulky. The so-called dialytic battery uses one membrane allowing the passage of positive ions (such as sodium) and a second one allowing passage of negative ions (such as chloride) and thus sodium ions flow in one direction and chloride ions in the other. An electric current, that is, a flow of electric charges, results between electrodes, thus generating electricity as a result of the mixing of sea and river waters.

Salinity gradient energy converters are based on the osmotic process. When a solution of salt water is separated from a volume of freshwater by a semi- permeable membrane, pressure (osmotic pressure) is exerted on the membrane, which obstructs free passage of water, thus preventing both solutions from reaching equal salt concentrations. The technology to extract energy from such gradients is still in its early stages with technical, economic, and environmental problems unresolved. Membrane improvement and lower costing, as well as research in converter types (the device permitting passage of the liquid but not of the dissolved salts), is necessary.

Theoretically, 3.54 x lo9 kWp is available from several salinity gradients, while 1.5 x 1OO kWp is the estimated power demand for the year 2000. Sites where plants could be built are numerous: estuaries, hypersaline lakes or sinks, salt marshes, and evaporation ponds, which could even be coupled with solar energy systems.

While original interest in harnessing salinity power developed in the former Soviet Union, minor efforts are currently made in the United States and Sweden. Conversion to electrical power remains complex; heat of dilution in freshwater is small (OSC, 09F). Systems under investigation are principally inverse vapor com- pression (IVO), reverse electrical dialysis (RED), and pressure-retarded osmosis (PRO).

Ocean_Energies/0444882480/files/00038___36338ddcd5ea19c8484a8efababb4b56.pdf18 Chapter I

GEOTHERMAL ENERGY

Geothermal energy results from the heat of the earth, present as natural radioac- tivity in small amounts in all rocks. This heat increases with depth and is transferred to the surface by steam or water.

Geothermal proponents are optimistic and predict a production of 20,000 MW by 1995, perhaps even 400,000 MW by 2000, or 40% of the predicted total electric needs at that time. The technology exists; the use of geothermal energy is not new: Italy started tapping steam wells in 1907, Iceland in 1925, and New Zealand and Japan in 1955 and 1977, respectively. Fourteen units are currently generating electricity at The Geysers in Northern California, delivering 500 MW, an amount sufficient to service 150,000 people.

Geothermal energy exists as dry and wet steam, hot dry rock formations, magma, and geopressured water. This last type occurs widely under the Gulf of Mexico, on the Louisiana and Texas shelf; trapped by insulating clay beds, these deposits could provide heat energy, mechanical energy, and natural gas. Problems of geothermal energy utilisation are environmental (disposal of salt water, toxic liquid wastes, release of hydrogen sulfide and methane), technical (melting of drilling equipment and corrosion) and economic (reducing the cost of drilling).

Installed power at The Geysers, currently 918 MW, is due to be doubled by 1985, bringing it to 2000 MW in 1985, 4000 MW in 1990, 5500 MW in 1995, and 8000 MW in 2000. The next biggest effort is slated for Imperial Valley, California, but a 3-MW power plant came on line in 1981 in Hawaii, whose geothermal potential is estimated at 3000 MW. The worlds hottest hole was drilled in 1976 on the flank of Kilauea, on Hawaii itself, with a 358C (676F) temperature at the bottom. However, engineers are still coping with the transport of power to the other Hawaiian islands, separated by a 42 km (26 mi.) and 2134 m (7000 ft) deep channel (Alenuihaha Channel).

The Philippines are a close second to the United States in geothermal develop- ment, followed by Mexico. It is estimated that worldwide increase in geothermal power use runs about 15% per annum. The vapor-dominated process is considered a mature technology; steam-flash systems are in use in Mexico; two 10-MW plants using high salinity systems are under study; also under development are hot dry rock and geopressurized systems. Liquid-dominated systems constitute the largest resources. As for molten lava schemes, even though in Hawaii some pipes have been lowered into volcanoes, they remain very far from implementation.

At The Geysers the capital cost runs $600 to $800 per kW; the system is cost effective with the price of delivered electricity 5-10 e/kW. For median-temperature, low-salinity and high-temperature, high-salinity systems, the capital cost is between $1000 and $1500/kW and delivered electricity is 6-12 dkW. Other systems are most probably, at this time, not cost competitive.

While steam-driven turbines can produce electricity for 20-45 mills/kWh, hot dry rock systems can produce transportable hydrogen as low as $7.9/GJ ($ 8.33/106 Btu).

Ocean_Energies/0444882480/files/00039___97cfe3fcdeafadb55d2745636d403ec1.pdfState of the art 19

Geothermal energy has never been exploited at sea. A thorough study of the Gulf of Mexico geological basin - which covers a considerable land and sea area - revealed the existence of substantial energy resources. The energy could be tapped from underneath the ocean floor and provide impressive amounts of power; the technology is easily adaptable to marine surroundings. In contrast to all previously discussed ocean energy sources, geothermal energy is not renewable, once tapped and spent, the steam released from underground is not replaced, although current technology permits recycling of about 20% of the heat released by the plant. Although California coast geothermal reserves amount to over 200,000 MW for 30 years, only a part of this energy could ever be harnessed.

According to current views ocean-based geothermal plants would most likely be located near volcanoes, either insular or submarine, or near the boundary of tectonic plates. Recently a study was funded to assess the geothermal potential of the North Sea, and preliminary estimates reported in Ocean Industry held that the heat beneath each square kilometer of seafloor could be recovered at a rate equivalent to from 1 to 1.5 million barrels of oil for 20 years, requiring 10 boreholes up to 8 km ( 5 mi.) deep. Costing calculations of such projects lead to a production of heat at one-half the 1976 price of non domestic petroleum. In some locations a plant could be coupled with mariculture; usually mentioned as favorable sites, are locations near St. Lucia, West Indies; Kyushu, Japan; and the north coast of New Zealand. Using twin-hole and water-injection technology (a proposed method where two holes are drilled into a prospective area; water is then injected into one hole and steam is extracted from the other hole), hydrogen could be generated when the superheated water 1200C (2192F) reacts with iron in the magma, and methane could also be produced at lower temperatures.

In addition to a geothermal plants discharges creating higher surface water temperature, which could be reduced by using cooling towers, a subsidence might occur as large volumes of fluids are withdrawn from deep reservoirs where they were under pressure. The withdrawal would probably be offset in part, by migration to the reservoirs of water from adjacent muds. Noise, water, and air pollution are to be expected as well.

Utilization of ocean geothermal energy, however, will have to await further technological refinements, a thorough environmental impact assessment, and clari- fication of international legal issues dealing with energy tapping at sea.

SUMMARY

There is no doubt that exploiting the ocean for its alternative sources of energy holds considerable promise. It is extremely unlikely that we will ever recover the vast amounts of energy dissipated by the seas; but, there is every reason to pursue active research to improve existing technologies, to gather a realistic view of the environmental impact of ocean-power plants, to assess the suitability of sites, and to monitor the trends of existing markets and the development of new ones.

Ocean_Energies/0444882480/files/00040___914b47bffa97a9c87f732311f922a801.pdf20 Chapter I

Notwithstanding optimistic claims that in some areas a particular ocean energy type may provide all the necessary power, it is more realistic to view ocean power as a supplement and to think in terms of tapping several rather than a single type. It is equally pragmatic not to think in terms of capital-devouring grandiose schemes but to envision multiple, modest regional projects, which are economically sound.

By the turn of the century oil and gas will be scarcer and more expensive. The time is now to turn our attention to the ocean.

For Schmitt, there are three major challenges which the development of ocean energy uses faces [5]. They include low-pressure sources that require large con- version systems, fluctuation fluxes that require costly energy storage or back-up supplementary sources/systems, and the demands that are posed by the deployment and operation of ocean energy systems in a refractory environment.

Ocean_Energies/0444882480/files/00041___8f279e256e179c50ecd6dc2cc090fff4.pdf21

Chapter 2

OFFSHORE WIND POWER STATIONS

A wet sheet and a flowing sea, A wind that follows fast And fills the white and rustling sail, And bends the gallant mast

The songs of Scotland, Allan Cunningham

INTRODUCTION

When discussing tidal energy one could somewhat tongue-in-cheek speak of re- inventing the wheel. After all, tide mills had been in use centuries before the Rance River Tidal Power Station was finally built, and some still were. Not so long ago an American researcher suggested that instead of harnessing tides we use, far less expensively, tidal currents. When considering current thinking about capturing wind energy, we are somewhat re-inventing the windmill, albeit in a more sophisticated form (Fig. 2.1) [6]. A little less than a decade ago, proponents of harnessing winds were derided by the champions of nuclear power, and equated to latter day lovers of Dulcinea, a new breed of Don Quichottes [7].

Aeolian power is a term that originates from the name of the Greek god of the wind A c o k g and its Roman counterpart Aeolus. Various theories have been proposed to explain the origin of the winds which is likely to be related to a heat balance in the atmosphere around a rotating earth (eddy theory). As early as 1890, windmills were put to work to produce electricity and more than 50,000 mills were in use, in the United States alone, in the twenties and thirties. Their decline was precipitated by the Rural Electrification Program. Shortage of fuel during the Second World War acted as an incentive to reconsider wind utilization (Fig. 2.2).

Both in The Netherlands and in the U.S.A., according to rather recent reports, projects are under consideration to use ocean-wind energy so as to avoid land environment clutter. The term wind farms has been coined to designate groups of windmills located on a given site. Parallel research is pursued in Canada, Israel, Sweden and West Germany.

According to the San Francisco-based Transition Energy Projects Institute, off- shore windmills could generate all the electrical power needed by northern Cali- fornia. The University of Massachusetts team of Heronemus claims that a string of floating windmills anchored as far as 46 km (25 naut. mi.) offshore could provide electricity to shore via undersea cables. The entire island of Hawaii, in an effort to supply 50% of its electrical needs from indigenous renewable re-

Ocean_Energies/0444882480/files/00042___f464d4346940ca3ba9d0dcb00a131923.pdf22 Chapter 2

Fig. 2.1. Windmill still in use in Belgium (Flanders coast area) (photo: Belgian National Tourist Office).

sources, has been surveyed and monitored to find the best sites for a network of electricity-generating windmills based on NASA designs, which may include offshore facilities.

Ocean winds have of course provided energy to windmills for centuries. Today on-land wind turbines are in experimental use [8]. Wind energy is lost when obstacles stand in the air currents path. Absence of such obstacles-no buildings, no forests, no hills or mountains-makes coasts, islands and at-sea structures ideal sites for placing wind machines. Large experimental wind machines have been built in France, Britain, Germany, Denmark, the U.S.S.R. and the United States. Among these WECS (Wind Energy Converter Systems) the U.S.S.R. model had a 280,000 kWh/year output, but the largest, placed at Grandpas Knob (Vermont) generated 1.5 MWp in winds of 117 km/h (70 mph) and withstood windspeeds of nearly 200 km/h (115 mph) [9].

After a 6 year lapse, interest was rekindled in the United States early in the

Ocean_Energies/0444882480/files/00043___59af56bdc8e1cfac61d961ace1228c21.pdfOffshore wind power stations 23

Fig. 2.2. Modern wind-turbine concept.

1970s, and in 1975 a 100-kW system was placed in service near Sanduslq (Ohio). In 1976 a study was commissioned by the (U.S.) Energy Research and Development Administration to ascertain and assess the economic value of offshore multi units aiming at identification and classification of area offshore types, assessing utility requirements for offshore power systems, developing installation concepts including various floating and bottom-mounted designs, assessing current WECS for use in offshore environments, assessi


Recommended