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The views expressed in this Report are those of the authors of the papers and contributors to the discussion individually and not necessarily those of their institutions or companies or of The Watt Committee on Energy Ltd. Published by: The Watt Committee on Energy Ltd 18 Adam Street London WC2N 6AH Telephone: 01–930 7637 This edition published in the Taylor & Francis e-Library, 2005. “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.” © The Watt Committee on Energy Ltd 1985 ISSN 0141-9676

ISBN 0-203-21033-6 Master e-book ISBN

ISBN 0-203-26815-6 (Adobe eReader Format)

THE WATT COMMITTEE ON ENERGY REPORT NUMBER 15

SMALL-SCALE HYDROPOWER Papers presented at the Sixteenth Consultative Council meeting of the Watt Committee on Energy, London, 5 June 1984

The Watt Committee on Energy Ltd A Company limited by guarantee: Reg. in England No. 1350046 Charity Commissioners Registration No. 279087 MARCH 1985

Contents

Members of the Watt Committee

v

Members of Watt Committee Working Group on Small-Scale Hydro-Power

vii

Foreword

ix

Introduction

xi

Section 1

Potential for small-scale hydro-power in the United Kingdom E.M.Wilson

1

Section 2

Hydro-electric plant and equipment J.TaylorC.P.Strongman

8

Section 3

Civil engineering aspects N.A.Armstrong

37

Section 4

Institutional barriers E.C.ReedD.J.HintonA.T.Chenhall

48

Section 5

Economics of small public and private schemes A.T.ChenhallR.W.Horner

57

Section 6

Conclusions and recommendations J.V.CorneyH.W.Baker

78

Appendix 1

Sixteenth Consultative Council meeting of the Watt Committee on Energy

81

Appendix 2

Government grants and funding available P.J.Fenwick

83

Appendix 3

Use of water for milling or power generation: circumstances in which a licence is required

86

Appendix 4

National Association of Water Power Users: Paper for the Watt Committee

93

Appendix 5

Abbreviations

99

THE WATT COMMITTEE ON ENERGY The Watt Committee on Energy

102

Policy

102

Members of Executive, March 1985

103 103

Recent Watt Committee Reports

Member Institutions of the Watt Committee on Energy March 1985

* British Association for the Advancement of Science British Ceramic Society * British Nuclear Energy Society British Wind Energy Association * Chartered Institute of Building * Chartered Institution of Building Services * Chartered Institute of Transport * Combustion Institute (British Section) * Geological Society of London * Hotel Catering and Institutional Management Association * Institute of Biology Institute of British Foundrymen Institute of Ceramics * Institute of Chartered Foresters * Institute of Cost and Management Accountants * Institute of Energy * Institute of Home Economics * Institute of Hospital Engineering Institute of Internal Auditors (United Kingdom Chapter) Institute of Management Services * Institute of Marine Engineers Institute of Mathematics and its Applications * Institute of Metals * Institute of Petroleum * Institute of Physics * Institute of Purchasing and Supply * Institute of Refrigeration Institute of Wastes Management * Institution of Agricultural Engineers * Institution of Chemical Engineers * Institution of Civil Engineers * Institution of Electrical and Electronics Incorporated Engineers

vi

* Institution of Electrical Engineers * Institution of Electronic and Radio Engineers Institution of Engineering Designers * Institution of Gas Engineers Institution of Geologists * Institution of Mechanical Engineers * Institution of Mining and Metallurgy Institution of Mining Engineers * Institution of Nuclear Engineers * Institution of Plant Engineers * Institution of Production Engineers * Institution of Public Health Engineers Institution of Structural Engineers * Institution of Water Engineers and Scientists * International Solar Energy Society—U.K. Section Operational Research Society * Plastics and Rubber Institute * Royal Aeronautical Society * Royal Geographical Society * Royal Institute of British Architects * Royal Institution * Royal Institution of Chartered Surveyors * Royal Institution of Naval Architects * Royal Meteorological Society * Royal Society of Arts * Royal Society of Chemistry * Royal Town Planning Institute * Society of Business Economists Society of Chemical Industry * Society of Dyers and Colourists Textile Institute

* Denotes present and past members of The Watt Committee Executive

Members of Small-Scale Hydro-Power Working Group

J.V.Corney N.A.Armstrong

Institution of Civil Engineers, Chairman Institution of Electrical Engineers and Institution of Mechanical Engineers H.W.Baker Institution of Civil Engineers A.T.Chenhall Institution of Electrical Engineers D.J.Hinton Institution of Civil Engineers R.W.Horner Institution of Public Health Engineers M.J.Kenn Institution of Mechanical Engineers E.C.Reed Institution of Water Engineers and Scientists J.Taylor Institution of Electrical Engineers Prof E.M.Wilson Institution of Civil Engineers

Acknowledgements

Commander G.C.Chapman, Mr J.A.Crabtree and Mr O.M.Goring attended several meetings of the working group as representatives of the National Association of Water Power Users. The Watt Committee working group on Small-Scale Hydro-Power is indebted to many individuals and organisations in the United Kingdom from whom information and comments were obtained in the course of this project, including the Central Electricity Generating Board, North of Scotland Hydro-Electric Board, South of Scotland Electricity Board, regional Water Authorities and (in Scotland) regional councils and River Purification Boards. The Watt Committee on Energy acknowledges with thanks financial assistance by the Department of Energy, which helped to defray the costs of the proceedings of the working group, and the advice given by Dr P.J.Fenwick of that Department. Note The data included in this Report were correct, to the best of the authors’ knowledge and belief, in January 1985.

Foreword

At any moment in time the Watt Committee has four or five working parties, each tackling a specific project. Those under discussion at the meeting of the Watt Committee Executive of 24th January 1985 were technician education, waste disposal in the energy industry, the second phase of our study of acid rain and passive solar building design. Two other projects awaited firm proposals, and a further two were temporarily suspended because they would be more realistic at a later date. The present Report on Small-Scale Hydro-Power contrasts strongly with its two immediate predecessors, which dealt with nuclear energy and acid rain respectively.* It shares with them, however, the desire to clarify what at the moment could hold up development. Our only previous report devoted entirely to renewable energy sources was No. 5 Energy from the Biomass. Reports No. 1 and, to a less extent, No. 2 include sections on renewable sources; Report No. 4 Energy Development and Land in the United Kingdom contains two coloured maps showing alternative source distribution in the United Kingdom and suggests locations for wind, solar, wave, tidal and geothermal installations. Discussions with a number of individuals about small hydro-electric generating capacity suggested that it was something of a Cinderella in that it was unlikely to save much fossil fuel, and the cost per kilowatt could vary greatly with the site and with the amount of outside help that would be required. Furthermore, there was no simple statement of the legal obligations. Like windmills (now elevated to ‘aero-generators’), small hydro-power has suffered a long period of neglect illustrated by idle water-mills and mill-ponds used to supply fish rather than energy. A great deal of money has been spent on aero-generator design and a full-scale unit is under construction in the Orkney Islands. If it comes up to expectations we shall see more schemes being built and used to save energy. The same should be true of hydro-power. To add to this Foreword would mean drawing on the Report itself. I end, therefore, with my personal thanks and those of the Executive to the numerous

x

people who have given information, time and voluntary effort to add to our understanding of the problems and the wider potential of small-scale hydropower. February 1985 J.H.Chesters Chairman, The Watt Committee on Energy

* Particulars of previous Reports of the Watt Committee on Energy are given on pages 61– 62.

Introduction

Despite the abundance of sites in the United Kingdom where small-scale hydropower could be exploited, only a very small proportion of such potential is at present developed. The Watt Committee on Energy was concerned at this lack of exploitation of a valuable resource and therefore decided to establish a working group to examine the potential for development of further small-scale hydro-power as a useful addition to the energy resources of the United Kingdom. Its object was to identify obstacles which may have inhibited development in the past and to make suggestions for further study/action, with the eventual objective of helping to overcome the main obstacles and stimulate new schemes. The working group was free to make its own definition of what was implied by ‘small-scale’, and decided, in broad terms, that this should be any resource below the size which the electricity boards had themselves considered worth developing. In electrical terms we considered this to be from 5 to 5000kW. We also decided, in order to limit the field of our study, that we would not include wave or tidal power, as these could properly form the subject of separate studies. The papers forming this Report have been prepared by various members of the working group and explore the potential for small-scale hydro-power development in the whole of the United Kingdom. Topics covered include the technical problems and legal, institutional, environmental and economic aspects which may have inhibited development in the past. The working group has been greatly helped and encouraged by the information and assistance provided by members of the National Association of Water Power Users who have direct experience of constructing and operating small private schemes. The number and variety of such schemes provide concrete evidence of the practicability of such development. The members of this Association are enthusiasts and have for the most part constructed and operated their schemes themselves. Whilst clearly beneficial to their owners as they stand, they would not all necessarily satisfy current economic criteria. Our studies have been purposely limited to developments in the United Kingdom, but many aspects will be equally applicable to developing countries, particularly where a public electricity supply is not available in the vicinity and

xii

the choice lies between hydro-electricity or, as an alternative, diesel generation with high-cost fuel. The papers in general deal with water power for the generation of electricity, as it is in this form that it is easiest to assess its value as a power source; however, where an alternative use for the power exists it may be simpler to harness the power for such use, as was done in the past, rather than to use it for electricity generation. The technology involved in the development of water power is not new, but there are few people who have experience of both the engineering and the legal aspects, which are complex and varied. It is the hope of the working group that, by bringing together these subjects in one report, the problems facing potential developers of hydro-power will become better understood and many more successful schemes will result. J.V.Corney Chairman, Watt Committee Working Group on Small-Scale Hydro-Power


Section 1 Potential for small-scale hydro-power in the United Kingdom E.M.Wilson Department of Civil Engineering University of Salford Salford Potential for Small-Scale Hydro-Power in the United Kingdom

1.1 Introduction The United Kingdom is not a country rich in hydro-electric resources. Only in Scotland and Wales are there mountains and rainfall on a scale large enough to offer opportunities for hydro-electric development of tens of megawatts. However, over the whole country there are hundreds of sites where modest amounts of hydro-electric energy could be generated, at powers measured in tens of kilowatts. The problem of assessing potential requires, first, some arbitrary definition of what ‘small-scale’ means, since many of the surveys made in the past have considered schemes only if their power capacity exceeded fixed values, frequently in megawatts. So far as this paper is concerned, ‘small-scale’ means from 5 to 5000kW. An arbitrary sub-division can be made to mini- and microhydro, with capacities above and below 500kW respectively. During the last five years several studies have been made of small-scale hydropower in various parts of the U.K. These have supplemented many previous investigations: for example, there have been at least six sets of estimates of Scottish hydro potential in one form or another, though most of them did not include small-scale projects by the definition above. The range of such estimates reflects uncertainty about the premise on which they should be based. Francis, of the Department of Energy,1 has suggested that there are three broad categories in which estimates may be placed, namely: (a) Gross river potential is approximately the summation of annual runoff times potential head.

2 SMALL-SCALE HYDRO-POWER

(b) Exploitable technical potential is Category (a) less that energy which it is technically impossible to exploit; it includes, for example, losses due to efficiencies of plant less than 100%, and heads too low for available plant. Category (b) tends to move towards Category (a) with time. (c) Economic exploitable potential is Category (b) less the energy which it is uneconomic to develop. Economic circumstances differ from case to case, so there is no firm boundary separating Categories (b) and (c). Much depends on the cost of energy being displaced: for example, displacement of public supply at 4p/ kWh enhances the value of a scheme compared with sale to the Electricity Board at 2p/kWh. It is worthwhile to recall an extract2 from the Report of the Mackenzie Committee (1962) in assessing hydro-electric potential in Scotland: ‘To have any real meaning, the estimates of potential water power must be related to economic considerations…’ Most published studies deal with Category (b), and, since regional investigations cannot by their nature deal with site-specific details and economic analyses, guidelines based on minima for flow and head have to be adopted. In trying to assess the small-scale potential of a region the researcher has to use all the evidence he can find. For this paper, the existing hydro-electric capacity has been determined, together with published and unpublished assessments of further moderate potential; from these, an estimate has been made of small-scale potential. In the case of Wales and England there is better evidence, in the form of recent small-scale potential surveys,3,4 and these have helped in the extrapolations required. However, it must be said that in all that follows there is room for considerable error and the judgements made are inevitably subjective. 1.2 Hydrology Estimates of the occurrence and volume of flow passing a proposed hydroelectric site must be made if the development is to be properly sized and assessed. River flows are determined by the hydrology of the catchment and the consequent runoff and groundwater contributions. The river flow from a catchment is dependent upon area, location, orientation, rainfall, climate, topography and geology. In considering small hydro sites it is impracticable to consider all these variables in detail, and it is usual to resort to one of a number of estimating techniques. However, in some locations there may be an established Water Authority gauging station nearby where daily flow records over several years are available. Provided the gauging point (usually a weir or a calibrated river section) is not very far distant, a simple areal correction may be all that is required to adjust the measured flows to those at the required site. An HMSO publication5 details the location of established gauges—most are located on larger well-developed rivers. The local Water Authority may have

POTENTIAL FOR SMALL-SCALE HYDRO-POWER 3

additional gauges which could prove useful, and in every case an approach to the Water Authority is worthwhile to obtain flow data and to establish if there are any requirements for compensation flow. For run-of-river hydro-electric projects, the daily flow duration curve (FDC) provides the required data. The FDC shows the percentage of time that certain values of discharges are equalled or exceeded. Duration curves for long periods of runoff (in excess of 5 years) are utilized in deciding what proportion of flow should be used for generation, since the area under the curve represents volume and hence directly affects energy output. Figure 1.1 shows FDCs for the River Itchen at Allbrook, near Winchester, and the River Ogwen, near Bethesda, North Wales. The shape of the curve is also of importance: a generally flat curve represents a river with few flood flows, probably extensively supplied from groundwater; a steep curve indicates a ‘flashy’ river with frequent flood flows and comparatively low flows during dry weather. Such characteristics indicate the system of flow adjustment that is required to utilise the flows available. In cases such as the River Itchen where flows are relatively steady, a daily adjustment of flow may be all that is necessary. However, for ‘flashy’ rivers such as the Ogwen, continual flow adjustment may be necessary to utilise all that is available. In general, where there are no constraints on the scale of development, the 30% exceedance flow from the FDC may be adopted as a first estimate of the designed capacity for the scheme. Following the evaluation of costs, energy outputs and value of energy production for several capacities, both above and below that corresponding to the 30% exceedance flow, the design parameters may be modified to optimise the size of installation. For run-of-river sites, the FDC is fundamental to the calculation of energy output. Where long-term flow records at a particular site are not available, it is necessary to estimate the FDC from other readily available data, using an empirical method. Such methods of flow estimation depend on physical and climatic conditions affecting the catchment. Rainfall data are often utilised, as they are generally widely available and cover longer periods than river discharges. One such method is through the use of unitised FDCs.6 FDCs from established gauging points are unitised by dividing through the relevant catchment area and annual rainfall so that they represent flow from 1km2 of catchment with an annual rainfall of 1 metre. Such unitised curves can be used to represent the general flow conditions of a particular region. When applied to a specific catchment within that region, the unitised curve is factored by the appropriate catchment area and weighted annual rainfall. This method has the advantage that FDCs are produced from which energy can be directly calculated. The accuracy of the FDC produced is dependent on the similarity of the particular catchment to the gauged catchment, since even within the same region significant hydrological differences can exist.


Figure 1.1 Flow duration curves: river with few flood flows (left); ‘flashy’ river (right).

1.3 Scotland The first published estimate of hydro-power potential was that of the Water Resources Committee in 1921.7 The potential was estimated at 1700GWh per annum. This is the lowest of the Scottish estimates, probably because of the rudimentary nature of Scottish electrification in 1921 and, perhaps, the strong lobbying of non-resident Scottish landowners. In 1942, the Cooper Committee suggested a potential of 4000GWh per annum, and shortly afterwards the Hydro-Electric Development (Scotland) Act 1943 was passed setting up the North of Scotland Hydro-Electric Board (NSHEB). When NSHEB published its development scheme in 1944, it foresaw 102 projects producing 6270GWh per annum. This figure was revised again by Williamson,9 who suggested that the annual output could exceed 8000GWh. In 1962, the Mackenzie Committee reported a technically viable potential of 7250GWh per annum, and in 1981, with a resurgence of interest in hydro development—after a 20 year lull—NSHEB re-estimated the Scottish potential and concluded in a paper to the Economic and Social Research Council that the technical potential was 8500GWh per annum (2700MW installed) and that the


economic exploitable potential was 5100GWh (1630MW installed). Since this last study considered the lower power limit to be 50kW, it is clear that there is a large number of quite small sites in Scotland that have not yet been assessed. This is hardly surprising, since small schemes do not justify the transmission lines and access roads which are necessary in many parts of the country. From such evidence as exists already, it is probable that small-scale schemes in Category (b) with a total potential output of at least 180MW are technically exploitable, though the proportion of these which would also merit a Category (c) classification, as being economically viable, could only be an informed guess —perhaps a third, or 60 MW, producing, say, 260GWh per year. Table 1.1 Total potential hydro-electric power in the United Kingdom

Scotlan d Wales Englan d Norther n Ireland Total

Existing hydroelectric installations

Further major developments proposed but not built

Technically exploitable*

Economically exploitable*

Estimated small-scale (5kW–5MW) sites

MW

GWh/y MW

GWh/y MW

GWh/y MW

GWh/y

1270

4000

350

1100

180

790

60

260

120 9†

246 20

2308 –

390 –

70 32

300 160

25 14

110 75‡

Negl.

1

40

110

35

150

18

75

1399 4267 620 1600 317 1400 117 520 Notes * Power capacity estimated at 30% exceedance, which on most British rivers gives a 50% plant factor or thereabouts, †includes Kielder scheme (under construction). ‡These values reflect the high utilisation factors of water supply schemes, which are typically >60%.

1.4 Wales In Wales, as in England, public electricity supply is the responsibility of the Central Electricity Generating Board. The present installed capacity of CEGB hydro-power stations in Wales is 114MW, producing annually about 215GWh. In addition, there are Water Authority schemes totalling about 5.7MW, producing 41GWh per annum. The load factors represented by these figures, 0. 22 and 0.82 respectively, demonstrate only that the CEGB values peaking


capacity highly, whereas Water Authorities are using near-constant discharges to produce and sell energy to their Electricity Boards. The hydrometric areas covering Wales have recently been examined for their small-scale potential for the Department of Energy by Salford University.3 Some 565 sites were identified: they would have a combined capacity of about 70 MW and an annual energy output of 300GWh. The arbitrary lower power limit in this study was set at 25kW and the estimate of scheme capacities ranged from that figure to 3200kW, It is estimated that up to 50% of these sites might come within Category (c). 1.5 England The first published data about the hydro-electric resources of England were again those of the 1921 Water Resources Committee, which suggested an energy production of 180 GWh per annum. The Committee made it clear that this was by no means the total potential, which they were unable to estimate. A recent study4 of the English water industry commissioned by the Department of Energy, and again limited to powers of 25kW or above, has revealed 66 sites with power potential of 8.4 MW and potential energy of 48 GWh per annum. The economically exploitable proportion of these is indeterminate, but it may be about two-thirds. There are, in addition, certainly some hundreds of sites unconnected with the water industry that could be developed, and many others would generate powers of less than 25kW, the total of which has not been estimated since data are widely dispersed and have not been systematically examined. To provide a first indication, it would be reasonable to quadruple the water industry potential and to assume that one-third of these extra sites would be economic. These assumptions lead to Category (b) and (c) figures of 32MW, 160GWh and 14MW, 75GWh respectively. 1.6 Northern Ireland There has been no recent study of small hydro potential in Northern Ireland. More than 200 existing weirs are technically exploitable, but there are few examples where electricity is being generated. There are several excellent sites on the Six Mile Water and Blackwater Rivers which would almost certainly be economic also. The western part of Ulster was not fully developed for water power during the industrial revolution; nor were the upland sites on the Antrim plateau. It is estimated that there may be up to 100 new sites for small-scale installations. Based on topography, rainfall and comparison with similar areas more intensively studied, it would be reasonable to assume a technical potential of


about 150GWh per annum. This is equivalent to about 3% of current Northern Ireland electrical generation. A Category (c) figure might be about half of this. Two larger schemes on the Lower Bann and the River Mourne have been well researched and would certainly now be economic. They would have a total installed capacity of 40MW and would generate 110GWh per annum. 1.7 Summary The information given in this paper is summarised in Table 1.1. The estimates in this paper are based on the sources cited, on the references and on private communications from A.T. Chenhall and F.G.Johnson of the North of Scotland Hydro-Electric Board and Dr S.R.Cochrane of Queen’s University, Belfast, which dealt, respectively, with Scotland and Northern Ireland. It is now reasonable to assume that there are upward of 500 sites in the U.K. where small-scale hydro-power could be developed with a better-than-even chance of economic viability. References 1.

2. 3. 4.

5. 6. 7. 8.

9.

Francis, E.E. Small-scale hydro-electric development in England and Wales. In Conference on Future Energy Concepts, Institution of Electrical Engineers, London, Jan 1981. Electricity in Scotland: Report of the Committee on Generation and Distribution in Scotland. HMSO, Cmnd 1859, London, November 1962 (the ‘Mackenzie Report’). Department of Energy. Report on small-scale hydro-electric potential of Wales. University of Salford, Department of Civil Engineering, Oct 1980. Department of Energy. Report on the potential for small-scale hydro-electric generation in the Water Industry in England. University of Salford, Department of Civil Engineering, April 1984. Department of Environment. Surface Water: United Kingdom, 1976–80. HMSO, London, 1981. Wilson, E.M. Engineering Hydrology, 3rd Edition, p. 117. Macmillan, 1983. Report of the Water Resources Committee. HMSO, London, 1921. Hydro-electric works in North Wales. Further developments. Report to North Wales Power Company, September 1944. Freeman, Fox & Partners and James Williamson, 25 Victoria Street, London SW1. Internal Report No. 54. Williamson, J. Water power development in Great Britain. I.C.E. Joint Summer Meeting, Dublin, 1949.


Section 2 Hydro-electric plant and equipment J.Taylor and C.P.Strongman Merz and McLellan Newcastle upon Tyne Hydro-electric plant and equipment

2.1 Introduction The Watt Committee working group on small-scale hydro-power was set up to examine the potential for development of further low-head hydro-electric power as a useful and economical addition to the energy resources of the United Kingdom and to make suggestions for further study and action. When the working group discussed its terms of reference, consideration was given to extending its examination to overseas potential. A decision was made, however, to limit the study to development in the U.K., but with the thought that it would be welcome if, in doing so, the working group could encourage developments by U.K. plant and equipment manufacturers for which there might be sales opportunities overseas. Subsequently, the scope of the examination was changed from ‘low-head’ to ‘small-scale’ hydro-power, thus covering the entire head range of installations of small capacity. This Section of this Report is confined to the mechanical and electrical plant and equipment, although it excludes penstocks and gates (normally considered as part of the civil works) and the civil engineering aspects, statutory and legal matters, potential in the U.K., environmental considerations and so on, which are dealt with in other Sections. 2.2 Definitions There are many definitions of small-scale hydro-power, and it is not possible to be precise about them because the concept is somewhat subjective. The electrical engineer thinks of a definition in terms of the output of the generating set,

HYDRO-ELECTRIC PLANT AND EQUIPMENT 9

Figure 2.1 Vertical Francis turbine.

whereas the hydraulic engineer places more emphasis on head and flow, which define the selection and size of the plant and whose product gives output. The civil engineer, although inextricably bound by the head and flow, is also concerned with the physical dimensions of the plant and equipment insofar as they affect the design of the civil works. For the present purpose, it is proposed to consider a definition in terms of electrical output. Output of the generating set in the range 0–10MW, and even higher, has been quoted in several papers and publications; consequently there is a tendency to avoid defining what small-scale hydro really means—perhaps the International Electrotechnical Commission (IEC) should give some attention to this. The present working group decided to confine itself to an upper limit of 5 MW, largely because of the anticipated potential for future small-scale hydro-power in the U.K. Within this range other definitions are referred to, as indicated in Table 2.1, but there can be no hard and fast rule. Table 2.1 Definitions of hydro-electric schemes Small hydro Mini-hydro Micro-hydro

2–5MW 500kW-2MW 500kW


A further category was suggested by one source, namely pico-hydro, covering sets of 15 kW; but in fact there is no real logic in using ‘pico’—or indeed ‘micro’—unless these terms are related mathematically to the size of the plant. Although generating set sizes in the 15 kW range are not likely to be of interest to utilities for possible connection to the Grid,* such hydro-electric development should be encouraged. Many potential and existing private developers, such as members of the National Association of Water Power Users (NAWPU), find this to be a very useful range for domestic, farm and small local ‘cottage industry’ applications in rural areas of the U.K. This paper is confined to small-scale hydro-power installations designed for the generation of electricity. It is acknowledged, of course, that direct mechanical energy can be provided more cheaply than electrical energy. The concept of harnessing water for mechanical energy goes back for centuries, during which the water-wheel was used to produce small amounts of power for grinding corn and later was developed for direct-drive industrial uses: there remains a large number of old water-mills in the U.K. which could be developed. Indeed, many of them have been developed already, as publicised by NAWPU, and are used for stone-grinding, processing grain for animal feedstuffs, cornmilling, paper manufacture, flour-milling, snuff-grinding, the manufacture of cloth and textile products, wood working, forestry work, farm machinery etc. 2.3 General The technology of hydro-electric power is well established in the U.K., and includes plant that is in service, the design and manufacture of plant and consulting engineering services. The scope of the technology extends from small to large generating sets and includes their associated valves and ancillary plant. Manufacturers of plant such as water turbines, pump-turbines, waterwheel generators and generator-motors have supplied their equipment for power stations in the U.K. and abroad. Whereas many of the schemes were landmarks in hydropower development on account of size or design innovation, others were for ‘runof-the-mill’ schemes. There are numerous examples of plant that is now regarded as being in the category of small-scale hydro. Consulting engineering services for hydro-electric power have also been provided in the U.K. for many years. Again, a full range of types and sizes of scheme has been covered; notable major schemes have been engineered as well as small ones, the extent of the service and the design and engineering resources being adapted as required. Many of the small schemes in fact constitute the

* The legal and financial conditions for connection of private electricity generating capacity to the national public electricity supply network (the ‘National Grid’) are summarized in Sections 4 and 5 of this Report.


Figure 2.2 Horizontal Francis turbine.

initial power developments in the country or region. The associated plant and equipment can originate from companies abroad as well as from British firms; consequently, experience in the application of suitable plant is both shared and extensive. Examples of small-scale hydro-power installations in the range presently considered are numerous in Scotland, operated mainly by the North of Scotland Hydro-Electric Board (NSHEB) but also privately (for example, the aluminium works at Lochaber and Kinlochleven). There are also a few small schemes in England and Wales, but few in Northern Ireland. Most of the possible types and arrangements of generating plant are already well represented in the U.K. installations. Although some plants have been in service since the turn of the century, the 1920s saw an increase in activity; then, with the formation of the NSHEB in 1943, many small schemes were planned and installed until about the early 1960s. Currently the NSHEB is proceeding with a number of small run-ofriver developments. With regard to design and manufacture, most large generating-plant manufacturers in the U.K. also cater for the small-scale hydro-power market, and


Figure 2.3 Kaplan turbine.

there are smaller companies that specialise exclusively in this field. In view of the limited U.K. potential for the development of hydro-power, much of this plant has been manufactured for installation abroad. The selection of generating sets and plant for small-scale hydro-power applications is firmly based. Likewise, the selection of water turbines to suit the hydraulic conditions and of generators compatible with the loads or systems to which they are connected is made generally in accordance with established procedures. Nevertheless, there is scope for simplification and standardisation. This also applies to the ancillary plant. 2.4 Water Turbines All the available conventional types of water turbine are suitable for small hydropower applications. The most common turbines for low- to medium-head applications are the Francis and the Kaplan or propeller type. Apart from the vertical-shaft arrangement, the latter may be arranged as a bulb turbine, in which the turbine and generator are accommodated in an enclosure within the water passageway itself, as a tubular turbine, where the generator is located outside the water passageway, or as a straight-flow turbine (Straflo), in which the generator rotor is mounted on the periphery of the turbine runner. In addition, the crossflow turbine, which is a partial admission (impulse/reaction) type, can be used for low- to medium-head applications. For high-head applications, Pelton and Turgo impulse turbines, which can be supplied for very small outputs, are employed.


In the selection of the type of turbine there are overlaps between the different designs that can be adopted for a given head; therefore other factors, such as speed, submergence and efficiency, have to be compared. Other possibilities are centrifugal pumps in reverse rotation and marine bowthrusters (ships’ propellers). Further possibilities, such as river-current turbines and commercial lift hydro-engines, are at the experimental stage, and have been disregarded in the present study. 2.4.1 Francis turbine The Francis turbine (Figures 2.1 and 2.2) is of the reaction type, in which the runner receives water under pressure in an inward radial direction and discharges substantially in an axial direction. The main components of the Francis turbine are the fixed-vane runner, spiral casing, adjustable guide vanes and draft tube. The Francis turbine is suitable for a head range of about 10–300 m and ratings of 100kW. The shaft arrangement can be vertical or horizontal. 2.4.2 Kaplan/propeller turbine The Kaplan turbine (Figure 2.3) is an axial-flow reaction turbine and is basically a propeller type with adjustable blades. The water enters the spiral casing and after passing the runner blades flows through a draft tube to the tailrace. This type of turbine has a high efficiency over a wide range of heads and output and has a high specific speed. Governing is achieved by means of adjustable guide vanes and runner blades. The propeller turbine is similar to the Kaplan but does not have adjustable blades. 2.4.2.1 Bulb turbine With the bulb-turbine arrangement (Figure 2.4) the generating set is contained in a capsule accommodated in the water passageway. It is a very compact and selfcontained unit. There can, however, be problems with cooling the generator and access to the generator itself, although for small units the generator can be removed in its entirety for maintenance. For reasons of economy the generator must be of small diameter and therefore low inertia, thus limiting the application of bulb sets to connection with electrical systems of adequate size to maintain electrical stability. The bulb turbine is suitable for a head range of about 5–20 m and ratings of 300kW.


Figure 2.4 Bulb turbine.

2.4.2.2 Tubular turbines With the tubular turbine (Figure 2.5), the generator is located outside the water passageway with a long shaft drive and a simple seal arrangement; the generator is therefore easily accessible for maintenance. A gearbox can be accommodated between the generator and turbine if required to enable a high-speed—and thus cheaper— generator to be employed. It is suitable for heads up to about 15m and ratings of 50kW and upwards. 2.4.2.3 Straight-flow turbine The Straflo turbine (Figure 2.6) is a development of an earlier design in which the generator is located on the periphery of the runner; there is therefore adequate space for a large generator with large rotational inertia. The arrangement is compact, and there is no drive shaft. Consequently, the size of the water passageways, and hence the extent of the civil works, can be considerably reduced. This type of turbine is suitable for a head range of about 2–30 m and ratings of 500kW. 2.4.3 Cross-flow turbine The cross-flow turbine (Figure 2.7) is a radial/impulse type of low-speed turbine. Its dimensions at low head and high flow are greater than those of comparable conventional turbines. It has simple blade geometry and lower construction costs than the conventional turbine. For low heads, the blades can be manufactured


Figure 2.5 Tubular turbine.

from cheap materials because the bending forces are low. Efficiency is modest but the curve is flat over a wide flow range. Gear boxes can be employed to increase speed to suit economical generator designs; however, they reduce the efficiency. This type of turbine is suitable for a head range of about 2–200m and ratings up to about 1MW. Accordingly, it is quite suitable for the lower end of the microhydro range, because of its versatility and relatively low cost. 2.4.4 Pelton turbine The Pelton turbine (Figure 2.8) has an impulse wheel on which are mounted cupshaped buckets that have a radial partition or splitter in the centre to divide the impinging water-jet which issues from a nozzle on the end of the penstock. The wheel is encased to prevent splashing. The governing mechanism is an adjustable spear or needle and a jet deflector. This type of turbine is suitable for high heads — within the range 20–1000m—and ratings from 10kW upwards. For low outputs one or two jets would be employed and a horizontal shaft arrangement would be appropriate.


Figure 2.6 Straight-flow turbine.

2.4.5 Turgo turbine The Turgo turbine is an impulse turbine actuated by a water jet in which the water enters on one side of the runner and discharges at the other. It is suitable for heads of up to about 300m. The Hydec unit, manufactured by Gilbert Gilkes and Gordon Ltd. (see Table 2.4) is a turbine and generator package incorporating a Turgo water turbine. 2.4.6 Pumps running in reverse Conventional water turbines, as described here, with the exception of the ‘domestic’ types, are expensive compared with centrifugal pumps run as turbines. Consequently pumps running in reverse as turbines are commonly employed on micro-hydro installations in developing countries. This has prompted pump manufacturers to investigate the turbine characteristics of their pumps. Since a centrifugal pump lacks guide vanes, other means have to be used for starting, stopping and loading the set, for instance by adjustment of inlet-valve opening. Developments in this regard are taking place, and for sets using induction generators connected to the grid pumps run in reverse appear to be satisfactory. The lower runaway speed compared with a Francis turbine should give cost advantages.


Figure 2.7 Cross-flow turbine.

2.4.7 `Domestic turbines' Some manufacturers are turning their attention to the ‘domestic’ user sector, i.e. consumers in the range 10/15 kW. Although this is at the bottom of the range considered by the working group, the market, both in the U.K. and overseas, is likely to be substantial, but generally only for private purposes or for small rural communities. Indeed, a large majority of installations listed by the NAWPU falls into this category; none is connected to the Grid, undoubtedly because the costs of connection and of complying with the technical and other regulations could not be recovered. Other Sections of this Report refer to these institutional barriers. Of the 120 or so installations listed by the NAWPU, only three are gridconnected and these are sets in the range 80kW–100kW. Nevertheless, whatever their size and for whatever purpose they are built, they all contribute to the tapping of a renewable energy resource. Whereas the domestic range of turbines, some of which are made from engineering plastics, will no doubt be marketed at relatively low prices, they cannot be compared with the more conventional turbines in the upper range of set sizes considered here. The standards to which these turbines are manufactured and installed, although adequate for their purpose, may be somewhat different from those for an installation that might be designed to supply a local isolated community of several consumers for which a charge might be made and for which some cognizance would have to be taken of the various regulations. The


Figure 2.8 Pelton turbine.

domestic-type turbine referred to, when available, may well be competitive, both technically and economically, with standard pumps used as turbines. 2.4.8 Waterwheels Waterwheels—as stated earlier, in the past the traditional method of harnessing water primarily for mechanical energy —appear to be no longer manufactured except by a small firm in Cornwall. Many existing wheels have, however, been refurbished, some as museum pieces; but others have been put into service for generation and direct-drive purposes. 2.5 Generators Two types of generators are employed in hydro-electric installations: synchronous and asynchronous (or induction) type. In addition, for micro installations, standard induction motors may be employed.


2.5.1 Synchronous generators Synchronous generators are normally employed for generating sets connected either to an isolated system or a grid system. If they are connected to a grid, synchronising equipment is required. 2.5.2 Induction generators An important factor in the employment of asynchronous or induction generators, which are basically induction motors driven above synchronous speed, is the system to which the generator will be connected and the capability of that system to supply the necessary magnetizing power. The fact that the induction generator derives its excitation from the system and cannot therefore run completely isolated (capacitor bank excitation excepted) is a disadvantage where a suitable system is not available. It also suffers from the disadvantage that the natural inertia of the generator is considerably less than that of the equivalent, specially designed, synchronous generator. This can, however, be compensated for by adding a flywheel. These disadvantages are to some extent offset by the following important advantages. A separate excitation system is not necessary: this relieves the unit of sliprings, brushes, field circuit breaker, discharge resistor and automatic voltage regulator. Expensive synchronizing equipment is also not needed; the generator circuitbreaker is simply closed at or near synchronous speed and the machine pulls itself into step. As a consequence, the machine is generally without stability problems. Because of these factors the generator may require less maintenance than the equivalent synchronous generator; it is also cheaper. Its efficiency is somewhat lower than that of a synchronous generator, but this is relatively unimportant when considering hitherto uneconomic installations. There are speed and output limitations but they would probably not apply within the output range of small hydro. Although, generally, experience on induction generators of large size is limited, a number have been installed by the NSHEB in the range 50kW–5MW. 2.5.3 Standard induction motors The use of standard squirrel-cage induction motors, instead of the wound-rotor type, as generators is a possibility and, provided that care is taken to avoid overspeeding, this is a cheap solution for small-scale hydro-power. Overspeeding can be avoided by the use of overspeed release clutches.


Figure 2.9 Excitation systems: (a) static compound excitation; (b) brushless compound excitation. Figure 2.10 Basic governing system.

2.6 Excitation Systems and Automatic Voltage Regulators Existing types of excitation systems can be supplied to synchronous generators used for the generating-set range that is considered here. Such systems include shunt excitation using a controlled rectifier, compound excitation and brushless exciters. The choice depends upon the performance required.


For unattended machines thet supply a local load the selfregulating generatoris an obvious choise. In principle, it derives its excitation from the armature voltage and current of the generator via a compounding circuit. An important benifit of this arrangement is that excitation is sustained when the generator is subjected to ashort circuit. It is usual for a compound sysyem to include an automatic voltage regulator in order to achieve closer voltage control and assist rapid voltage correction following sudden load chnages. In the case of mini- and microinstallations, the excitation and regulation equipment can with advantage form a generator-mounted package. A brushless generator may also be preferred so that maintenance requirements are minimised (Figure 2.9). Larger machines, especially those connected to the grid, need an excitation control system matched to the requirements of the generator and supply system. 2.7 Governing The principles that apply to the governing of large hydro-electric generating sets are relevant to small sets. The objective is to maintain constant speed or frequency by controlling the turbine flow to match changes of load; it is assumed here that the plant is needed to supply an isolated system or local load, or to play a major part in the frequency control of a small system. Associated factors are the time taken to achieve the desired flow and the flywheel effect of the set. Governing requirements therefore have an influence on plant costs. In addition to their basic function, governors also facilitate starting, stopping, synchronising, parallel operation of generating sets and load sharing between them, and provide security against prolonged overspeeding. Should the small generating sets feed into a large system, governing may not be considered necessary, particularly in the case of induction generating sets. Then the governor actuator could be dispensed with, leaving the remaining mechanism to serve as an output or load controller. However, means for starting, running-up and shut-down of the set must still be provided. The main elements of governing systems (Figure 2.10), which apply equally to large and small hydro sets, and alternative possibilities are itemised below. 2.7.1. Governor system 2.7.1.1 Actuator The actuator is a stable device or mechanism located on the governor head which senses a speed change and converts it into the displacement of a collar or other component serving as a signal to an amplification system. The actuator can be


Figure 2.11 Oil supply for governing system.

driven directly from the set by gears or belt—which is common on very small sets—or by an electric motor supplied from a permanent magnet generator on the set. A variation on this is the electronic governor head, in which the speed signal, obtained from a toothed-wheel pick-up, is processed by electronic means. The output from the actuator is then applied to a hydraulic servomotor via a pilot valve. 2.7.1.2 Servomotor Since the forces available from an actuator are small (in relation to those required to alter turbine spears, deflectors, guide vanes, runner blades etc.) it is necessary to amplify by employing servomotors. These are controlled by a pilot valve with oil as the pressure medium. The servomotors can be single-acting, opposed by a spring, as often employed for Pelton turbines, or double-acting, as applied on Francis and Kaplan turbines. On micro sets and where the operating forces are reasonably low, independent hand-wheel control may be sufficient.


2.7.1.3 Pressure oil For spring-opposed servomotors, a storage receiver for the oil supply is not always necessary. For double-acting servomotors, providing large forces over a short operating time, pressure-oil receivers are needed (Figure 2.11). In both instances, a pumping set provides the pressure-oil supply. 2.7.2 Alternative possibilities 2.7.2.1 Output controller The application of a microcomputer to the output control of a hydro-electric generating set is an economical alternative to the conventional mechanical or electronic governor; this has been done by the NSHEB at Sloy power station. In addition to providing continuous control of the frequency and power output of the generating set, the controller can cater for sequential control of the run-up and shut-down operations and the monitoring of the plant. The output controller acts on the conventional servomotor equipment of the governing system. It is perhaps too early to say whether or not the microcomputer governor will match the reliability of the conventional mechanical or electronic governors. On the other hand, improved speeds of response can be achieved without loss of stability. 2.7.2.2 Load controller A wholly electrical system for speed governing that has recently been introduced for micro installations may possibly be extended to the low-power end of the mini-installation range (Figure 2.12). It is applicable to installations that operate independently of a public supply network or other parallel connected generators. Speed is regulated by maintaining constant active load on the generator. The flow through the turbine is constant at constant head at the full load value, and the available hydraulic energy is converted to electrical energy at all times, leaving no imbalance to cause significant speed changes. Any positive difference between generator output and supply-system load demand is absorbed in a dumping or ballast resistor. The only back-up that may be necessary is an inlet valve to isolate the turbine in the event of failure of the speed/load regulator or of a bypass valve. The ballast resistor and its regulator can take various forms. For example, discrete resistor sections can be selected by electromagnetic or solid-state switching; alternatively, a phase-controlled triac, or anti-parallel thyristor pair


Figure 2.12 Constant load controller.

with a single ballast resistor, may be employed. The regulator unit compares speed, and load, against fixed references to provide switching signals. Power dissipated in the ballast resistor need not be wasted. For example, water can be heated for use in a space-heating system or for a hot water supply. Even if the surplus energy has to be wasted, there will be no cost penalty, since for such an installation it has to be accepted that there must be a constant flow, which when not needed for energy would run to waste. Where water economy has to be practised, some form of secondary governing or water-flow regulator may be necessary if the normal demand is considerably less than the rated output of the machine. If sudden load increases of any significance cannot occur, or are not allowed to, such regulation can be quite simple. 2.7.2.3 Hydraulic brake The hydraulic brake incorporates a fly-wheel brake, on to which the water is diverted in the event of load rejection. The tendency to overspeed is thereby opposed and the rate of flow can remain constant. The system is applicable to impulse turbines. 2.7.2.4 Eddy-current brake An older form of electrical governing is the eddy-current brake, in which the load is adjusted to suit the output of the set. The power absorbed by the braking


device plus the system load equals the power output of the turbine. The braking device consists basically of a series/shunt-wound magnetic frame, similar to a d.c. motor, in which the main shaft revolves. On the end of the shaft a ferrous drum is mounted which rotates in the magnetic field set up by the frame. The shunt winding is connected to the generator terminals, and the eddy currents that are set up in the drum as it rotates absorb power and cause a braking effect. As the load on the generator varies, so does the current in the series winding of the braking device, partially neutralizing the shunt field. Accordingly, the power of the turbine is shared by the system load and the braking device. 2.7.2.5 Variable-speed operation An alternative method of electrical governing for small-scale hydro, now made possible by the development of large power static-variable frequency converters, is to allow the turbine to ‘free run’. This is a method adopted for wind-driven generators and considered for some wave-energy systems. The generators operate at variable frequencies according to the load, and the output is converted to direct current controlled at a constant value by a current regulator, and back again to alternating current (Figure 2.13). In effect, the power is transmitted to the a.c. system via a back-to-back d.c. link. The disadvantages are the need to vary a number of units to suit the constant flow as the load varies, the low efficiency at part load and the need to design for fairly frequent runaway conditions. 2.8 Electrical System Design In order to limit total costs and thus assist in the justification of small hydro projects, economies have to be made, not only in the selection of turbine, generator, governing and excitation, but also in the electrical system itself. Although a unitised system, comprising a generating set connected directly to its own step-up transformer, is common for most large installations, it is sensible and rational with small hydro-electric installations, if there is more than one set, to connect them through circuit breakers to a common busbar at generator voltage with a single step-up transformer to the transmission system. Not only is this cheaper than the unitised scheme, but it provides good operational flexibility. It should be mentioned that reactive power sharing is more easily accomplished with the unitised arrangement, however. When bussing at generator voltage, care must be taken not to exceed the fault-carrying and breaking capacity of the switchgear and connections; the method of generator earthing and protection must also be carefully studied. Off-site supplies for station auxiliaries can, however, be provided relatively cheaply.


Figure 2.13 Variable-frequency generator method of load control.

2.9 Protection When small generating sets are connected to an Electricity Board’s network, obligatory electrical protection is necessary to safeguard the network (Figure 2.14). This obligatory protection is set out in Engineering Recommendation G47/1 issued by the Electricity Council. In addition some guidance is given in Engineering Recommendation G26.*


Figure 2.14 Typical protection diagram for asynchronous generator connected to Grid. Asterisk (*) indicates obligatory protection.


Figure 2.15 Typical protection diagram for synchronous generator connected to isolated system.


For a micro-hydro installation connected to an isolated system, simple overvoltage, undervoltage and restricted earth fault protection would probably be sufficient (Figure 2.15). The great dilemma facing the developers of such an installation is that they may well find that the cost of protecting the plant is almost as expensive as the equipment that it is protecting. 2.10 Control Programmable sequence controllers/microprocessors are almost universally available for starting, stopping and controlling the generating set. They use programming languages that are relatively simple to understand and are userorientated, so commissioning and subsequent programme changes can be effected by the operating personnel. The use of microprocessors also reduces engineering and commissioning time, since control logic can be modified during the course of engineering and at commissioning without the need for wiring changes. The use of microprocessors can extend from simple start/stop control initiated by a single pushbutton operation to full remote operation, in which the generating sets can be controlled and monitored fully automatically by signals received from a central control command (if the station is connected to a grid system) or by means of local water level or flow detection equipment (if it is an isolated station). At present, micro-processors are relatively expensive for micro- or mini-hydro installations. For such installations, simple manual starting and stopping with the minimum of monitoring may be the right solution. However, if a microprocessor is employed it can carry out sequential control of starting and shutdown as well as continuous control of the frequency and power output of the generating set. It may therefore be economic for the upper range of small hydro installations. 2.11 Design and Engineering Large hydro-electric projects require specialists in almost every discipline of engineering. They are usually headed by a project manager, who supervises and coordinates these disciplines, with a team of engineers, each of whom is responsible for a section of the work. Careful monitoring of the engineering and progress in the manufacturer’s works and during construction, with computerised critical path scheduling and cost control, is necessary.

* Recommendation G59, revising these recommendations, is expected to become available about March 1985.


By contrast, this treatment cannot be given to small installations, as their capital costs are not sufficiently high to warrant expensive engineering management. Consulting engineers, specialising in hydro-electric project design and engineering, have therefore adapted to this situation by Table 2.2 Small hydro-electric installations in Scotland Station

Gross head, m

Plant Station capacity, kW

Gross head, m

Plant capacity, kW

Sron Mor

52

1×5000

14

1×160

Cuaich Loch Ericht

27 55

1×2500 1×2200

10 26

1×160 1×550

Mullardoch Achanalt Lochay

28 20 182

1×2400 1×2400 1×2000

Glenmoristo n Beannachran Loyne Tunnel Stronuich Pitlochry Orrin

10 14 42

Lubreoch

17 30

1×54 1×4000

Meig Dan Tobermory

15 42

Dalchonzie Lednock Ceannacroc Lairg Cassley

28 92 91 10 114

1×4000 1×3000 1×4000 1×3500 1×1 500

Luichart Torr Achilty Clunie Dam Elvanie Duchally

18 14 18 35 26

Striven Loch Gair Lussa Storr Lochs

124 110 117 138

Quoich Misqeach Kerry Falls Gaur

38 37 57 30

Kilmelfort

112

Invergarry

64

1×285

Mucomir

7

10

1×30

Kerry Falls

57

Vaich

7

1×320

Nostie Bridge Loch Dubh (Ullapool) Morar

151

2×3000 2×3000 2×1200 2×950 and 1×800 1×2000 and 1×83 1×1750 and 1×200 2×500 and 1×250 2×625

1×210 1×50 1×200 and 1×56 1×76 1×200 and 1× 80 1×85 1×100 1×175 1×300 1×325 and 1× 125 1×350 1×350 1×500 1×160

Culligran

60

1×2000

167

2×600

Gorton

79

1×100

6

2×375

Errochty

92

1×525


Station

Gross head, m

Plant Station capacity, kW

Gross head, m

Plant capacity, kW

Chliostair (Harris) Gisla (Lewis) Shin Awe Barrage

126

2×500

Claddoch

197

1×100

48

1×540

*Bonnington

–

2×5000

6 1×100 *Stonebyres – 2×3000 7 1×433 The schemes listed here are those operated by the NSHEB and SSEB that give output of 5 MW and below. * South of Scotland Electricity Board.

employing a small number of experienced staff on these projects, so as to eliminate time spent on optimisation of alternative designs: the choice is left to the general engineering experience of the engineers assigned to the work. Simple specifications together with standard conditions of contract should also be employed. This reduces not only the manufacturer’s works and construction costs but also tendering costs. Clients also have a responsibility for keeping the engineering costs of an installation to a minimum. Some may get deeply involved and place heavy demands on the man-hours allocated to the engineer responsible for the design. In addition, much time and expenditure can be wasted in discussion of the technical requirements with the public utility to whose grid the installation may be connected. For example, the interpretation of obligatory protection requirements may have to be set against different system configurations. The Recommendations of the Electricity Council, referred to in section 2.9, are by no means clear and definitive for every situation, and developers have found that the adoption of these Recommendations is time-consuming. For auxiliaries systems, it is not always possible to simplify the specifications to the same extent as for the generating sets, since details of auxiliaries circuits have to be calculated and scheduled irrespective of the size of the generating set —except perhaps for micro-installations. There is, however, considerable scope for producing what have come to be regarded as ‘mini-specs’. 2.12 Conclusions To summarise, the turbine type is determined by the hydraulic conditions, operating requirements and economic considerations. Standardisation of water turbines in general is difficult because they are ‘sitespecific’, and it is rare that site conditions match those which are best for a standard turbine. However, for micro installations there is a case for giving serious consideration to standardisation, since the plant and equipment represent


Figure 2.16 Cost envelopes.

a large proportion of the total cost and these costs can be reduced by some measure of standardisation—even though some sacrifice in operational flexibility and efficiency may be the consequence. Such standardisation might extend to the


selection of materials and of runner sizes for specific head ranges, resulting in standard casings, shaft and bearing arrangements etc. With regard to generators, whenever possible only standard generators should be specified. The employment of standard induction motors run as generators should be considered for grid-connected mini- and micro-installations. Where small synchronous generators are employed, the self-regulating set or a brushless system may be the best solution for the excitation. For the mini- and micro-range of sets, manual start-up and stopping with appropriate auto-trip facilities should be adequate. A micro-processor may possibly be employed, however, to cater for sequential starting and stopping and continuous frequency and power output control if the cost is right. Protection of the installation should be as simple as possible and the minimum necessary to safeguard the plant. If the sets are grid-connected, cognizance must be taken of the Electricity Council’s Recommendations. From studies made, the future development of small-scale hydro in the U.K. is likely to be mainly in the mini- and micro-hydro range of set sizes and the summary and conclusions (Section 6 of this Report) have been biased towards this. Whilst Section 2 is confined to small-scale hydro in the U.K., it is recognized that in developing countries a considerable degree of improvisation in hydro-electric engineering is practised. It is unlikely, however, that such improvisation would be tolerated in the U.K. for grid-connected installations. Finally, what are the costs of the electrical and mechanical equipment associated with small-scale hydro?—an easy question to ask, but a difficult one to answer. Much depends on the country in which the equipment is manufactured and installed. If it is in a developing country, with relatively inexpensive labour, it will be cheaper than in a developed country. Indeed, U.K. manufacturers are known to arrange for some of their heavy engineering and sub-assembly work to be done in the Far East because of the high cost of labour in Europe. Figure 2.16 indicates the form of cost envelope, showing cost per kilowatt plotted against set output across the head range. The curve has been derived from actual installation costs and budgetary information provided by manufacturers and public utilities in the U.K. It does not pretend to be definitive, and many installers will say that the work could be done much more cheaply. These claims must, however, be measured against the institutional barriers that may or may not apply; the standards of engineering that are set also affect the cost. The cost curve illustrated in Figure 2.16 most certainly does not claim to represent the installer who buys a small ‘domestic’ turbine for private use: he is not bound to provide sophisticated control and protection requirements, and may not be hampered by too much bureaucracy. As to the costs of installations in the U.K. that are connected to the Grid, the envelope of costs shown in Figure 2.16 is realistic.


Table 2.3 Small hydro-electric installations in England and Wales Station

Plant capacity, kW

Cwm Dyli

1×2000 1×1000 1×2000 Dolgarrog 1×5000 1×5000 Mary Tavy 3×220 2×650 Morwellham 2×320 Chagford 1×31 The schemes listed here are those operated by the CEGB that give output of 5 MW and below. Table 2.4 Suppliers of water turbines in the United Kingdom Supplier

Address and telephone number

Types of turbines

Boving & Co. Ltd.

Villiers House, 41–47 Strand, London WC2N 5LB (01) 839 2401 Canal Iron Works, Kendal, Cumbria LA9 76Z Cathcart Works, Glasgow G44 4EX (041) 637 7141 Cambridge Road, Whetstone, Leicester LE8 3LH (0533) 863434 Ringwood, Hampshire BH24 1 PE (04254) 2405 Mill Lane, Island Road, Ballycarry, Co. Antrim, Northern Ireland (09603) 78610 Ajax Works, Whitehill, Stockport, Cheshire SK4 1NT (061) 4806507 Forest Road, Grantown-onSpey, Morayshire, Scotland PO Box 2, Luton LU1 3LW (0582) 31144

Francis; Pelton; Kaplan; Propeller; Tubular

Gilbert Gilkes & Gordon Ltd. Weir Pumps Ltd. GEC Energy Systems Ltd.

Armfield Engineering Ltd. Newmills Hydro Ltd.

F.Bamford & Co. Ltd.

MacKellar Engineering (Grantown-on-Spey) Ltd. Hayward Tyler Pump Company Evans Engineering & Power Company

Priory Lane, St Thomas, Launceston, Cornwall PL15 8DQ

Francis; Pelton; Turgo Impulse; Hydec Francis; Pelton; Tubular; Reversed pump; Kaplan Francis; Pelton; Kaplan; Propeller; Deriaz; Tubular Francis; Pelton; Crossflow; Kaplan Francis; Pelton; Propeller (Kaplan); Turgo Impulse

Propeller (Kaplan); Tubular; Francis; Pelton (micro) Micro-hydro propeller; Cross-flow; Pelton Reverse pump (submersible generator and other types); Pelton Reaction and impulse turbines up to 100 kW; water turbines (under 1200


Supplier

Flygt Pumps Ltd. Dorothea Restoration Engineers Ltd.

Portmore Engineering Ltd.

Swift Industrial Developments Ltd. Water Power Engineering

Westward Mouldings Ltd.

Address and telephone number (0566) 3982

Colwick, Nottingham NG4 2AN (0602) 614444 Southern Works, 68 Churchill Road, Brislington, Bristol BS4 3RW (0272) 715337 Portmore Road, Lower Ballinderry, Lisburn, Co. Antrim BT28 2JS, Northern Ireland (0847) 651528 PO Box 8, Romsey, Hampshire SO5 OGT (0794) 40714 Coaley Mill, Coaley, Dursley, Glos. GL11 5DS (0453) 89376 Greenhill Works, Deleware Road, Gunnislake, Cornwall

Types of turbines kW); U.K. Patent holders for electronic loadgoverning systems Submersible propeller Reconditioned Francis turbines

Cross-flow

Axial flow impulse with flow control Cross-flow; Reaction; Second-hand and overhauled turbines Water-wheels

Disclaimer. The particulars given in Table 2.4 are given in good faith, but the Watt Committee on Energy takes no responsibility for their accuracy or for any omissions or for the fitness of the equipment listed either generally or in any specific scheme. Developers should discuss their requirements with the suppliers and seek appropriate advice.

In Tables 2.2 and 2.3, small hydro-electric installations (5MW and below) operated by the NSHEB and CEGB respectively are listed. In addition to these, a large number of private hydro-electric installations in the U.K. operate at heads from about 0.5m to 220m and outputs between 1.5 kW and 200kW: among them, most of the recognised turbine types are employed. Only two or three of these are connected to the electricity boards’ systems. The remainder are used for private purposes only, and some have direct drive applications. NAWPU can supply reasonably complete lists of them. Details of suppliers of water turbines in the U.K. are given in Table 2.4. The authors are indebted to the Partners of Merz and McLellan and to their colleagues in the firm, as well as to the other members of the working group, for their valuable help in the preparation of this paper.


Bibliography 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

Water Turbines for H-E Power. Gilbert Gilkes and Gordon, Kendal, 1974. Small Hydro-Power Fluid Machinery. Winter meeting of American Society of Mechanical Engineers. Chicago, Illinois, USA, 1980. The Power Guide. Intermediate Technology Publication, 1979. Gaal, V. et al. Small hydro-electric power stations—a contribution to the solution of the energy problem. Brown-Boveri Review. July/August, 1983. Gordon, J.L. Small hydro puts new challenge to consultants. Energy International, August, 1980. Wilson, E.M. Small scale hydro-power developments in the U.K. World Energy Conference, New Delhi, 1983. Micro Hydro Developments. Hydro Power, December, 1980/January 1981. Energy Department gives qualified ‘Yes’ to small hydro. Electrical Review, April, 1979. Teichmann, H.T. International standardization of small hydro schemes. Water Power and Dam Construction, May, 1983, Generating profits on a small scale. The Engineer, 11/18 August, 1983. Giddens E.P. et al. Small hydro from a submersible pump. Water Power and Dam Construction, December, 1982. Generators for small hydro applications. Hydro Power, December, 1980/January, 1981. Pereira, L. Induction generators for small hydro plants. Water Power and Dam Construction, November, 1981. Water Power from Weissenburg-Ossberger-Turbinenfabrik GmbH. Garman, P. Development of a turbine for tapping river current energy. Appropriate Technology, September, 1981. Submersible generator. Electrical Review, 23 September, 1983. Friedlander. Reviving low-head and small hydro. Electrical World, August, 1980. Makansi. Equipment options multiply for small-scale hydro. Power, May, 1983. Small hydro needs its own experts. Water Power and Dam Construction, December, 1982. Marshall, A.F. et at. Microcomputer control of hydro turbines. Proc. I. Mech. E., April, 1983. Nair, R. Development potential for low-head hydro. Water Power and Dam Construction, December, 1982.


Section 3 Civil engineering aspects N.A.Armstrong North of Scotland Hydro-Electric Board, Edinburgh

Civil engineering aspects

In most cases, the end-product of a hydro-electric scheme is electricity produced by the generator and driven by the turbine prime mover. Although the generating plant is vitally important, it is nevertheless usual that the major part of the capital cost of a hydro-electric scheme is absorbed by its civil engineering aspects. This Section brings to the attention of the developer of a potential small hydro-electric scheme the salient questons of civil engineering to which he should be giving consideration when assessing the feasibility of the scheme. 3.1 Aqueducts There is a large variety of types of hydro-electric schemes. The upper end of a typical scheme (Figure 3.1) is dealt with first here, and other aspects are dealt with progressively, working downstream to the tailrace, the civil aspects of most of the types that are normally encountered being briefly described. The beginning of a conventional hydro-electric scheme is at a point where water collects, usually a loch or lake, a headpond or a river, providing a head of water. This is what the developer has noticed to make him interested in its potential for power development. This collection point is fed by run-off from rainfall or snow, falling over its upstream catchment area and draining naturally until it reaches this point. It is often possible, and if so generally worthwhile, to increase the amount of natural water that is available by tapping adjacent catchment areas that would not naturally drain into the selected point. This is usually done by constructing some form of aqueduct system. A first basic point for the developer, therefore, is that the aqueduct system will almost certainly require planning permission.


Figure 3.1 Main features of typical scheme.

Next, if it is relatively small and does not create a safety hazard for people or livestock, the aqueduct can be left open; otherwise, it requires to be either covered or fenced (Figure 3.2). A buried aqueduct eliminates these hazards, and overall is generally less expensive. An open aqueduct’s gradients should permit the water to flow at a reasonable speed to achieve a self-cleaning capability if grit, debris or stones can gain access; if the rate of flow is slow, the aqueduct is liable to become blocked and to overflow, particularly on curves or bends. The presence of large boulders which could readily block the aqueduct if they enter the system should be checked with care. Consideration should be given to making the aqueduct as impermeable as possible by lining it with suitable material, such as slate, flagstones, granite slabs, bitumen, concrete or steel plate etc. Problems may arise if the aqueduct is open and liable to spill; this might seriously affect its banking, which could then be breached and far progressively. Provision should therefore be made to allow the aqueduct to spill automatically at predetermined points so that excessive water is ejected safely. Alternatively, if possible, the amount of water allowed into the aqueduct system may be limited; for example, the aqueduct may be fed from a river through a pipe which limits the entry of water. A rough guide to the size of the aqueduct, if it feeds a storage reservoir, is that it should be capable of handling five times the average flow of water. It may be necessary to bridge the system where it is crossed by rights of way.

CIVIL ENGINEERING ASPECTS 39

Figure 3.2 Concrete-lined aqueduct, with bridge for sheep.

A last consideration with regard to the aqueduct is the possibility of tunnelling to tap an adjacent catchment area. Tunnelling is likely to be expensive. The minimum practical tunnel diameter is approximately 2m, and the current cost of construction is around £1000000 per kilometre. 3.2 Storage Reservoir The provision of the storage reservoir may necessitate the building of a dam. The most important aspect of this in the U.K. is whether it is liable to come within the terms of the Reservoirs Acts. At present, the Act in force is the 1930 Reservoirs (Safety Provisions) Act.1 A new Reservoirs Act was passed in 1975, but its first phase is only now being brought into operation. A reservoir comes within the scope of the new Act if its stored water exceeds 25000 m3 (883000 ft3 or 5500000 gallons) in volume. This is about the same as the quantity of stored water that came within the scope of the 1930 Act. It is not a large quantity: for example, if the average depth of the reservoir were 3 m, the dimensions of the area containing this volume would only be around 90 m×90 m. Every new dam that is subject to the Reservoirs Acts has to be designed, and its construction must be supervised, by a civil engineer from a panel appointed by, for England, the Secretary of State for the Environment, and the Secretaries


of State for Scotland and Wales, and on completion a certificate is issued. A list of the appointed engineers can be obtained from the Institution of Civil Engineers1 or the Department of the Environment.3 The dam must then be inspected not less than once every 10 years, again by an engineer selected from the panel of appointed engineers. A new feature of the 1 975 Reservoirs Act is that every dam that is subject to the Act is required to have, in addition to the 10-yearly inspecting engineer, a supervising engineer selected from a further panel of appointed engineers;1,3 he is appointed to keep a watchful eye on the dam and to ensure that any recommendations made at the inspections are carried out. He reports to an enforcing authority. In Scotland this is the local regional or islands council, and in England and Wales it is the Greater London Council or appropriate county council. From 1 April 1 986 it will be necessary for all undertakers of large raised reservoirs to appoint a supervising engineer and to be responsible for payment of his fees in respect of each dam that he supervises. It is probable, in the case of a supervising engineer’s duties, that the payment, including travel and other expenses, for a dam inspection at the present time can be expected to be in the region of £1000 to £1500. 3.3 Dam Small dams are usually constructed on the gravity or embankment principle (Figure 3.3) and are of earth or rockfill. The type of dam selected may depend on its locality: for example, there may be a ready source of suitable material nearby. Alternatively, the type of dam may be determined on environmental grounds if it must be of a type that blends with the surrounding terrain. The likely severity of floodwater could be another influence on the choice: for example, a concrete gravity dam might be considered superior to an embankment dam. An embankment dam requires a waterproof membrane. If the dam is relatively small, the membrane could be a simple wall with fill on either side; it would also require an upstream protection face, such as stone or rock, to counteract any eroding wave action. Some possible weaknesses of an embankment dam are as follows. (1) There is a danger that the dam may be overtopped with flood water, which could then affect its vulnerable downstream face. (2) If it is necessary to have an opening through the dam for flushing out gravel and stones etc., the opening could create a permanent potential source of leakage. By contrast, the small concrete gravity dam does not suffer these problems: it can probably be constructed using standard deliveries of ready-mixed concrete but care is needed to ensure that it is well founded on bedrock to prevent its being overturned.


Figure 3.3 Embankment dam prior to installation of 1-m high top wave-wall gabions.

A serious operational problem could be the build-up of gravel, sand etc. behind the dam, especially in river schemes. The scheme must therefore incorporate means to flush out this material. Usually this is done by running a culvert through the dam, with a flushing gate. The gate can be on either the upstream or the downstream face of the dam; if the gate is on the upstream face, it may be difficult to clear gravel from the gate’s tracks, and this might prevent it from operating correctly; if on the downstream face, the culvert is always under full pressure and water will certainly ultimately find any weakness. The following are practical suggestions if it is proposed that the dam shall scour through a culvert. (1) The culvert can be continued upstream of the dam to act as a scouring channel. (2) The optimum gradient is 1:20. (3) The width of the culvert should exceed its height by a ratio of about 5:3. It is important to ensure that when the gate is opened water does not prevent access for the purpose of reclosing the gate.


(4) When scour is operated, the rate of flow must not be too low; otherwise, gravel may collect under the gate and consequently it will be difficult to close it. (5) Conversely, if the rate of flow is too high, only local scouring will take place around the entrance to the culvert. (6) Some arrangement should be made to enable the dam to be deliberately drained. Dams must be designed to cope with floodwater—by discharging usually over a spillway, or occasionally by opening gates. Guidelines for the quantity of floodwater for which the design of the dam must provide are contained in a Floods and Reservoir Safety booklet,2 published in 1978 and obtainable from the Institution of Civil Engineers. Although its recommendations are not mandatory, the inspecting engineer would generally expect its requirements to be met. The guide requires that the dam be categorised as follows: (a) by location, that is, in terms of the risk to life and property downstream; (b) by type, that is, in terms of its ability to withstand overtopping. The booklet gives guidelines on the period of time in years which, once the dam has been categorised, must be considered for determining the maximum possible flood that may occur. The longer the period, the more severe the flood that can be expected. A small dam would possibly be based on a 150-year flood, or on an even shorter period if the affected community is small and the risk negligible; but a dam may be required to contain a 10000-year flood, or even more, if a community with a higher density would be at risk. The probable maximum flood (pmf) that can be realistically expected at the dam is dependent on the probable maximum precipitation (pmp), rain plus snow if applicable, for a given duration over the relevant catchment or drainage basin under the worst flood-producing conditions in the catchment area. Using these data, the booklet provides guidelines on the amount of flood water that the dam must safely discharge. If in any circumstances the dam would prevent water from going down the residual river section (between the dam and the place where the power station is located), it may be necessary to discharge ‘compensation water’—that is, to make good the shortage of water in that section of the river. This could be to meet fishery requirements or to maintain a summer amenity, for which the river bed must be kept wet and fresh. About 5% of the average flow is normally considered to be an adequate discharge for these requirements. 3.4 Pipeline If the water is conveyed to the power station through a pipeline, the cost can be relatively expensive. Nevertheless, a good choice of types of pipes is available. It


Figure 3.4 Fibre-glass penstock pressure pipe; diameter, 0.4 m.

may be necessary to bury the pipeline for reasons of amenity. A small hydroelectric scheme may have the pipeline above ground: that requires the construction of supports. Pipes suitable for small-scale hydro-electric schemes may be of steel (to BS 3601), ductile cast iron, glass fibre, reinforced plastic or asbestos cement (to BS 486). Steel pipes are the commonest. The pipes are usually internally protected by a spun bitumen or epoxy pitch coating. If below about 1m in diameter, they are difficult to recoat internally, as a painter cannot readily gain access. Corrosion effects can be reduced if the pipeline is always full of water, but steel pipes require periodic attention to contain corrosion. Standard sizes are available —up to 2m in diameter—but there is no limitation on size. The working pressure of the available pipes is virtually unlimited. The pipe joints may be flanged or welded, or Viking Johnson couplings may be used. Supports are required about every 12m for an above-ground pipeline. The painting of a steel pipeline requires some care. If a bitumen type of paint is used, the pipes may require to be recoated internally every 5–8 years. The paint should last longer if it is applied by means of a spun bitumen process— that is,


when applied to new piping. A bitumen coating usually suffers abrasion damage, particularly on the base. When repainting, it is often difficult to apply the paint to the invert owing to leakage and condensation, even when dehumidification equipment is used. External paint has a life of around 12–15 years; the more sunlight it is exposed to, the shorter its life. Normally, micaceous iron oxide paint is used. Ductile cast iron pipe is now becoming a very serious competitor: it is available in standard sizes up to 1.6 m in diameter. Its working pressure is suitable for a head of around 250m of water at

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