Feasibility Study on Mini-hydroelectric Power. Plant for Rural Electrification. MSc. Thesis. By: Girum Teferi Tessema. (Department of Energy Technology.
ROYAL INSITITUTE OF TECHNOLOGY WORLDWIDE CAMPUS (Addis Ababa University, Ethiopia)
Project title: Feasibility Study on Mini-hydroelectric Power Plant for Rural Electrification
MSc. Thesis
By: Girum Teferi Tessema (Department of Energy Technology KTH student ID-No. 821210-A375)
Master of Science Thesis EGI-2013-165MSC EKV1001 Title
Feasibility Study on Mini-hydroelectric Power Plant for Rural Electrification
Girum Teferi Tessema Student ID-No. 821210-A375
Approved
Examiner
Supervisor
Date
Miroslav Petrov
Jens Fried
Commissioner
Contact person
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ACKNOWLEDGMENT
I would like to give Glory to God and the Virgin Mary without which the completion of this thesis would have been unthinkable. Next, I would like to express my deepest gratitude to my advisor, Jens EA. Fridh for his expert guidance, constructive comments, suggestion and encouragement without which this work could have not been completed. He has been a constant source of inspiration during my study period. I am also grateful to Dr. Ing. Abebayehu Assefa for his kind helps on different ideas and materials. Lastly, to my wife Tsigereda Teka for her patience and stood always by my side.
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TABLE OF CONTIENT ACKNOWLEDGMENT .................................................................................................................................................... ii LIST OF TABLES ........................................................................................................................................................... viii LIST OF FIGURES ..........................................................................................................................................................ix Figure 2.1 Average annual water surplus regions in Ethiopia [1]…………….……...........…. ...............................ix Figure 2.2 Scheme lay out with high head………………….………....…………….…………. ................................ix NOMENCLATURE ........................................................................................................................................................... x LIST OF ABBREVIATIONS AND ACRONYMS ........................................................................................................ xiii ABSTRACT ......................................................................................................................................................................... xiv CHAPTER ONE ............................................................................................................................................................... 1 INTRODUCTION.............................................................................................................................................................. 1 1.1 Problem Statement ............................................................................................................................................... 1 1.2 Objective ................................................................................................................................................................ 1 1.3 Method of attack .................................................................................................................................................... 1 1.4 Outline of the Report ............................................................................................................................................ 2 CHAPTER 2 .......................................................................................................................................................................... 3 LITERATURE REVIEW ........................................................................................................................................................... 3 2.1 Rural electrification In Ethiopia ........................................................................................................................... 3 2.1.1 Resource ........................................................................................................................................................ 3 2.1.2 Mini-Hydro Resources and Existing Experience in Ethiopia ................................................................... 4 2.2 Hydro Power Basics: ................................................................................................................................................. 6 2.2.1 Head and Flow ............................................................................................................................................... 7 2.2.2 Scheme layout and Available Head............................................................................................................ 8 iii
2.2.3 Hydrology Flow Rate ................................................................................................................................... 11 2.2.4 Power Output ............................................................................................................................................... 12 2.2.5 Efficiency ...................................................................................................................................................... 13 2.2.6 Energy Yield ................................................................................................................................................. 16 CHAPTER THREE ........................................................................................................................................................ 19 Hydro power Generation ............................................................................................................................................... 19 3.1 General Description about Hydro Power Generation .................................................................................... 19 3.1.1Types of Hydro Power ................................................................................................................................. 19 3.2 Basic Concepts of Mini-Hydro Power Generation .......................................................................................... 20 3.3 Scheme Components ......................................................................................................................................... 21 3.3.1 Dam and Weirs ............................................................................................................................................ 21 3.3.2 Intake structure ............................................................................................................................................ 22 3.3.3 Leats.............................................................................................................................................................. 29 3.3.4 Pipeline ......................................................................................................................................................... 32 CHAPTER FOUR ................................................................................................................................................................. 38 Electrical and Mechanical Equipment of Mini-Hydro Power Generation .................................................................... 38 4.1 Turbine ................................................................................................................................................................. 38 4.1.1 Impulse turbine ............................................................................................................................................ 38 4.1.2 Reaction Turbine ......................................................................................................................................... 41 4.2 Electrical Equipment, Generator ....................................................................................................................... 43 4.2.1Types of Generator used in Micro Hydro Power Generation ................................................................. 43 4.3 Devices Used for Speed Increment ................................................................................................................. 44 4.3.1 Belt drive ....................................................................................................................................................... 44 4.3.2 Chain Drive................................................................................................................................................... 45 iv
4.3.3 Gear Box....................................................................................................................................................... 45 4.4 Controlling and operation units ......................................................................................................................... 45 4.4.1Automatic flow and level controller- ........................................................................................................... 45 4.4.2 Parallel and Isolated Operation ................................................................................................................. 45 CHAPTER FIVE ............................................................................................................................................................. 47 ECONOMIC ASPECT OF SMALL HYDRO SCHEME......................................................................................... 47 5.1 Introduction .......................................................................................................................................................... 47 5.2 Scheme Components cost ................................................................................................................................ 47 5.2.1 Dewatering and diversion works ............................................................................................................... 47 5.2.2 Intake structures .......................................................................................................................................... 47 5.2.3 Automatic screen cleaning ......................................................................................................................... 47 5.2.4 Leats and tailraces ...................................................................................................................................... 47 5.2.5 Header tankers ............................................................................................................................................ 47 5.2.6 Pipelines – low and high pressure ............................................................................................................ 48 5.2.7 Turbo generators ......................................................................................................................................... 48 5.2.8 Power houses .............................................................................................................................................. 48 5.2.9 Electrical protection and switch gear ........................................................................................................ 48 5.2.10 Automatic flow/level controller ................................................................................................................. 48 5.2.11 Transformers.............................................................................................................................................. 48 5.2.12 Transmission.............................................................................................................................................. 48 5.2.13 Access road ............................................................................................................................................... 48 5.2.14 Installation and commissioning of turbo-generators ............................................................................ 48 5.2.15 Additional work bank protection and excavation .................................................................................. 49 5.2.16 Engineering Fee ....................................................................................................................................... 49 v
5.2.17 Contingencies ............................................................................................................................................ 49 5.2.18 Operation and maintenance fee.............................................................................................................. 49 5.2
Energy Value ................................................................................................................................................. 49
5.3.1 Export scheme ............................................................................................................................................. 49 5.3.2 Isolated Scheme .......................................................................................................................................... 49 5.3.3 Parallel operated schemes ........................................................................................................................ 50 5.3 Economics .............................................................................................................................................................. 50 5.4.1 Internal Rate of Return ................................................................................................................................... 50 5.4.1 Energy Cost ................................................................................................................................................. 51 CHAPTER SIX ............................................................................................................................................................... 52 Environmental Effect of Mini Hydropower Plant ........................................................................................................ 52 6.1 Hydrological Effect .............................................................................................................................................. 52 6.2 Landscape............................................................................................................................................................ 52 6.3 Social Effects ....................................................................................................................................................... 52 CHAPTER SEVEN ........................................................................................................................................................ 53 7.1 MARKET STUDY AND PLANT CAPACITY.................................................................................................... 53 7.2 Power Demand.................................................................................................................................................... 55 7.3 Electricity Pricing and Distribution .................................................................................................................... 56 CHAPTER EIGHT .......................................................................................................................................................... 57 POWER GENERATION SYSTEM DESIGN AND ANALYSIS ................................................................................ 57 8.1 Power Generation system ................................................................................................................................. 57 8.2 Power Generation Capacity .............................................................................................................................. 58 8.3 MATERIALS INPUTS ......................................................................................................................................... 59 8.3.1 Consumables ............................................................................................................................................... 59 vi
8.3.2 Utilities........................................................................................................................................................... 59 8.4.1 Sizing of Cross Flow Turbine ..................................................................................................................... 60 8.4.2 Turbine Efficiency ........................................................................................................................................ 60 8.5 Sizing of penstock ............................................................................................................................................... 61 8.6 Power Available From the River ....................................................................................................................... 62 8.7 Capacity Factor ................................................................................................................................................... 63 CHAPTER NINE ............................................................................................................................................................ 64 Cost Evaluation of Mini hydropower Generation ....................................................................................................... 64 9.1 Cost of the penstock ........................................................................................................................................... 64 9.2 Turbine Cost ........................................................................................................................................................ 64 9.3 Land, Building and Civil Work ........................................................................................................................... 65 9.4 Over Head Transmission line ............................................................................................................................ 66 9.5 Installation Cost ................................................................................................................................................... 66 9.6 Financial Evolution and Analysis ...................................................................................................................... 67 9.7 Man Power and Trainings .................................................................................................................................. 69 9.7.1 Manpower Requirements ........................................................................................................................... 69 9.7.2 Training Requirement ................................................................................................................................. 69 9.8 Pay Back Period ...................................................................................................................................................... 70 CONCLUSION and RECOMMENDATION ................................................................................................................ 71 10.1 CONCLUSION .................................................................................................................................................. 71 10.2 RECOMMENDATION ...................................................................................................................................... 71 References ........................................................................................................................................................................ 72
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LIST OF TABLES Table 2.1 An overview of renewable energy resource in Ethiopia………………................4 Table 2.2 Summary of technical mini hydro potential in Ethiopia per region……..............6 Table 2.3 Maximum Turbine efficiency at various rated power…………….......…............15 Table 3.1 Values of Manning’s roughness coefficient n for straight uniform Channel…..30 Table 3.2 Hydraulic radius for most coefficient leat section..............................................31 Table 3.3 Dimensions for most efficient leat section ........................................................32 Table 3.4 characteristics of commonly available pipe types.............................................33 Table 3.5 Relative Roughness..........................................................................................36 Table 7.1 electric Access coverage in southern regional state………..……………....…...54 Table7.2 Projected demands for electricity ………………..…………….…………………...55 Table 8.1 Classification hydro turbines according to head, flow rate and power output ..59 Table 9.1 cost of different components of the power plant…………………………..……...65 Table 9.2 Installation Cost..........………………………………………………………………67 Table 9.3 Manpower requirement and labour cost……………………...…………………..69
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LIST OF FIGURES Figure 2.1 Average annual water surplus regions in Ethiopia [1]…………….……...........…5 Figure 2.2 Scheme lay out with high head………………….………....…………….………….8 Figure 2.3 High head with leat……………………………………………………………………9 Figure 2.4 Low head scheme…………………………..….………………………………….….9 Figure 2.5 power house Dam …………………………………..………………………………10 Figure 2.6 Flow Duration curve for values of BFI(Base Flow Index) ………..……………..13 Figure 2.7 Turbine Efficiency Curves from Manufacturer’s Data………………….…….…..14 Figure2.8 Calculation of Energy yield for Cross flow and Impulse Turbine………………..17 Figure2.9 Estimation of Net Turbine Head…………………………..……………………..…18 Figure 3.1 Layout of a typical micro hydro scheme ………………………………………....21 Figure 3.2 Simple Diversion Wall forms Intake……………………………………………….23 Figure 3.3 High Head Intake……………………………………..……………………………..24 Figure 3.4 Low Head scheme ...........................................................................................26 Figure 3.5 Head Loss through Trash Screen ....................................................................28 Figure 3.6 Trash Screen Head loss Coefficient k..............................................................28 Figure 3.7 Common leat Profile.........................................................................................31 Figure 3.8 Moody Diagram................................................................................................35 Figure 3.9 Approximate pipeline design chart...................................................................37 Figure 4.1Pelton turbine....................................................................................................39 Figure 4.2 Turgo turbine....................................................................................................40 Figure 4.3 Cross flow turbine ...........................................................................................40 Figure 4.4 Kaplan Turbine.................................................................................................41 Figure 4.5 Francis Turbine ..............................................................................................42 Figure 4.6 centrifugal pump used as a Turbine.................................................................42 Figure 5.1 Internal Rate of Return against Present Value Factor ……..…………………..51 ix
Figure 8.1 power house lay-out …………………………...........……………………….……57 Figure 8.2Relative efficiency of turbines for mini hydropower generation …………....…61 Figure 8.3 Typical System efficiency of micro-hydropower generation …………….……62
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NOMENCLATURE
P= Electric power output (KW) W=Specific weight of water (KN/m3) Qi =Design Flow rate (m3/s) H= Hydraulic Head (m) o=Generation/ overall efficiency Qm=annual mean flow (m3/s) SAAR=Standard annual average rainfall for the catchment (mm) Ea=actual evapo-transpiration (mm) A= catchment area (km2) T- Turbine efficiency D- Drive efficiency P- Pipeline efficiency h=head loss through screen (m) K=trash screen coefficient t/b= ratio of bar thickness to bar spacing g=gravitational constant (9.81 m/s2) ø = angle of bars to the horizontal L-Length of settling bas in (m) Q-flow rate (m3/s) Vo-particle settling velocity (m/minute) W-width of chamber v=velocity (m/s) R=Area (m2)/wetted perimeter, hydraulic radius S=slop of the leat n=Manning’s coefficent xi
V=velocity (m/s) F=frequency N=rotational speed (revs/sec) P= number of pairs of poles hf=head loss in m f=friction factor L=Pipeline length in m v=flow velocity in m/s D=pipe diameter in m
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LIST OF ABBREVIATIONS AND ACRONYMS FDC-Flow Duration Curve FDVB –fixed distributor variable blade GRP-Glass Reinforced Plastic ICS-Inter-Connected System EEPCO- Ethiopia Electric Power Corporation BFI-base flow index
xiii
ABSTRACT Nearly two billion peoples in developing countries do not have access to electricity service. Renewable energy resources are a best option for rural electrification. In general Rural Electrification has for a long time been the top of the development agenda in many developing countries. Nevertheless, the vast majority of the rural population in these countries does not have access to electricity. Electric light is still a luxury enjoyed only by a few in developing countries like Ethiopia. Currently, only fifteen percent of the population living in urban and semi urban
areas
are connected to the national grid. The remaining populations are living in scattered rural villages and have very remote chances to get electricity from the grid. The only realistic approach to electrify the rural areas seems therefore to be the off grid or self contained system. The contribution of renewable sources of energy like micro-hydro power, to rural electrification are minimal at present. Increasing fossil fuel prices have provoked many countries to review the prospects for small scale hydro electric power generation. More over third world countries implement minihydroelectric power plants for covering energy shortage whilst reducing fuel costs. The power from water has been a source of energy for many centuries. Early developments utilized water wheels to drive mill stones and water pumps and then factory machines. Hydropower generating capacity is now generally concentrated in large high head power stations supplying their output to the national electricity grid. Mini-hydropower is one of the cost-effjective and reliable energy technologies to be considered for providing clean electricity generation. This paper discusses the detail analysis and application of Mini-hydroelectric power plant for rural electrification by integrating with economic aspects i.e determine the unit energy cost, payback time of the power plant and introduce new technology to the selected site of Ethiopia, Bench Majji Zone Neshi Village. xiv
CHAPTER ONE INTRODUCTION 1.1 Problem Statement The development of any country depends on the amount of energy consumed. Energy consumption is proportional to the level of economic development. In Ethiopia, the energy consumption per capita is very low and it is almost exclusively generated from biomass and this has a direct impact for the deforestation. The lighting system, in rural areas, use kerosene and it produces emission of pollutants. Furthermore, it has a direct impact on the health of the people. Ethiopia has a marvelous amount of hydro power potential. Because of the high initial investment cost, it is able to develop only two percent of its potential so far. To avoid the electric energy draught, renewable energy technologies like mini hydro power generation, solar photovoltaic and wind turbine can be used to electrify the rural areas.
1.2 Objective To analyze the technical and economical aspects of Mini-hydropower plant technologies for rural electrification in the selected site of Ethiopia is the general objective of this paper. The Specific Objective is to propose a mini-hydro plant for rural electrification with 500 KW generating capacity and having the possible shortest payback time.
1.3 Method of attack
Assess micro-hydro power resources and get the preliminary data for micro-
hydro power generation.
Meteorological data collection for the site in consideration (i.e. area, location,
orientation, climate, topography and geology and the amount of rain fail at the nearest station of the selected site) 1
System design for the energy source at the selected site using analytical methods.
Conduct economic analysis of the energy consumption methods.
Economic evaluation of the system to determine the payback time and their
feasibilities.
Make conclusion on the place where micro-hydro power generation will
be installed in selected sites of rural area of Ethiopia in the future scenario.
1.4 Outline of the Report Chapter Two reviews literatures about potential of renewable energy in Ethiopia and techniques of renewable energy techniques of renewable technology especially Minihydropower. Chapter Three presents detail components of hydroelectric power plant. Chapter Four describes Electro-Mechanical equipments of the power plant including controlling units. Chapter Five deal about general economic aspect of small hydropower plant. Environmental effect of Mini hydropower plant is explained in Chapter Six. Chapter Seven is about market study and the capacity of the plant. Power generation system and design is deeply explained in this the eighth chapter. In chapter nine, cost evaluation including payback period of mini-hydropower generation is intensely explained. Chapter ten presents conclusion and recommendation.
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CHAPTER 2 LITERATURE REVIEW Small hydro is the development of hydroelectric power on a scale serving a small community or an industrial plant. The definition of a small hydro project varies but a generating capacity of up to 10 megawatts (MW) is generally accepted as the upper limit of what can be termed small hydro. Small hydro can be further subdivided into mini hydro, usually defined as between 100 KW and 1,000 kW, micro hydro which is less than 100 kW. Micro hydro is usually the application of hydroelectric power sized for small communities, single families or small enterprise. Small hydro plants may be connected to conventional electrical distribution networks as a source of low-cost renewable energy. Alternatively, small hydro projects may be built in isolated areas that would be uneconomic to serve from a network, or in areas where there is no national electrical distribution network. Since small hydro projects usually have minimal reservoirs and civil construction work, they are seen as having a relatively low environmental impact compared to large hydro. This decreased environmental impact depends strongly on the balance between stream flow and power production.
2.1 Rural electrification In Ethiopia 2.1.1 Resource In Ethiopia there is a
massive energy resource potential , that, if utilized, could
minimize the present energy crisis prevailing in the country and enhance for the process of rural electrification. The total exploitable renewable energy that can be derived annually from primary hydropower , solar radiation, wind, forest biomass, animal waste , crop residue and human waste is about 1,959x103 T cal per year.[1] The following table illustrates the available Renewable Energy Resource in Ethiopia;
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No
Energy Resource
Energy in 10 2 T cal per year Potential
% Share
Exploitation
% Share
1
Primary Solar Radiation
1,953,550
99.7
1,954
73.08
2
Wind
4,779
0.24
239
8.94
3
Biomass, forest
800
0.005
240
8.97
4
Hydropower
552.1
0.03
138.00
5.16
5
Animal waste
111.28
0.01
33.73
1.26
6
Crop Residue
81.36
0.0004
40.63
1.52
7
Human waste
28.18
0.00014
28.18
1.05
1,959,901.93
100.00
2673.54
100
Total
Source CESEN and calculation by EEA
Table 2.1 An overview of renewable energy resource in Ethiopia
2.1.2 Mini-Hydro Resources and Existing Experience in Ethiopia Ethiopia is sanctified with large hydro power resources.
The gross hydro potential is
estimated to be 650 TWh/yr [3]. Out of this gross potential, the economically feasible hydropower potential of Ethiopia has been estimated to be 15,000 MW to 30,000 MW. Of this economically feasible potential, only 10% or 1500MW to 3000MW would be suitable for small scale power generation including Pico and Mini hydropower. The recent baseline survey done
for energy access projects reveals that the total
theoretical potential for mini hydro development is 100 MW or about 1000 projects of a typical capacity of 100kW. When the regional distribution is looked up, some parts of Ethiopia have considerable hydro resources while others with semi-arid and arid climate have none. There is also high variability of annual rainfall throughout the country. This indicates the corresponding runoff in the rivers and creeks available for micro hydro development follows the same variability. 4
Pico and mini hydro systems for village application are of the run-of-river type and water availability is the most important aspect. The design flow of the plant must not exceed the minimum dry-season flow of the water resource. Stand-alone hydro schemes without alternative or back-up systems run the risk of insufficient capacity due to lower water. 2.1.2.1 Regional Distribution of Micro Hydro Power The Central and Southwestern highlands of the country have an annual water surplus which provides the basis for run-of-river hydro development on small scale.
Figure 2.1 Average annual water surplus regions in Ethiopia [1]
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The potential of mini hydropower in Ethiopia as per region is tabulated as below: No
Region
Approximate Mini Hydropower
1
Oromia
35 MW
2
Amhara
33 MW
3
Benishanguel-Gumz
12 MW
4
Gambella
2 MW
5
SNNP
18MW
Table 2.2 Summary of technical mini hydro potential in Ethiopia per region [9] 2.1.2.2 Ethiopia Electric Power Corporation Mini-Hydro Station The corporation is used to install and operate a number of small hydropower stations in the micro and mini scale. This was used to supply towns as self contained system up to 1990’s when demand exceeds their capacity especially during the dry season. The interconnected system (ICS) was brought to these towns and the importance of the mini hydro systems was drastically reduced.
2.2 Hydro Power Basics: Hydropower is energy from water sources such as the ocean, rivers and waterfalls. “Mini-hydro” means which can apply to sites ranging from a tiny scheme to electrify a single home, to a few hundred kilowatts for selling into the National Grid. Small-scale hydropower is one of the most cost-effective and reliable energy technologies to be considered for providing clean electricity generation. The key advantages of Mini-hydro are high efficiency (70 - 90%), by far the best of all energy technologies, high capacity factor, high level of predictability, varying with annual rainfall patterns. Slow rate of change; the output power varies only gradually from day to day.
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It is a long-lasting and robust technology; systems can readily be engineered to last for 50 years or more. It is also environmentally benign. Mini hydro is in most cases “run-ofriver”; in other words any dam or barrage is quite small, usually just a weir, and little or no water is stored. Therefore, run-of-river installations do not have the same kinds of adverse effect on the local environment as large-scale hydro. The selection of the
mini hydropower technology serves both local and global
objectives. Some of the advantages are [4] A. It is renewable, non-polluting, utilizes indigenous resource; B. Mini hydro schemes permit the energy to be generated near where it to be used, leading to reduced transmission costs; C. It can be easily integrated with irrigation and water supply projects in rural areas; D. Micro hydro schemes permit the generation of mechanical energy to drive agro-processing machinery or establish cottage industries in rural areas; E. It is a much more concentrated energy resource than either wind or solar power; F. The energy available is readily predictable; G. No fuel and only limited maintenance are required; Against these, the main short coming is a site-specific technology [4]. 2.2.1 Head and Flow The possible power at the outset and this will be dependent upon the available head, the catchment of the river, the constraint
of the civil work and the final use of the energy. The
potential power of a hydropower site is evaluated by the following principle: 7
P=Qi g H o
where,
P= Electric power output (W=N*m/s) g=gravitational acceleration (m/s2)
=density (kg/m2) Qi =Design Flow rate (m3/s) H= Hydraulic Head (m) o=Generation efficiency 2.2.2 Scheme layout and Available Head To find out the gross head available at a site it is necessary to layout an interim plan. It may be dependent upon scheme type, and involves the location of the intake structure the power house and the channel for supplying water between the two. This conduit can take the form of an open channel contour canal a low pressure pipeline, a high pressure pipeline or a combination of any two or three. There are various forms of scheme layout possible:[10,11] 2.2.2.1 A high head and/ or medium- scheme where water is conveyed directly to the power house by a high pressure pipeline as shown in the figure 2.2.
Figure 2.2 Scheme lay out with high head[10,11]
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2.2.2.2 A High head and/ or medium scheme where water is carried from the intake structure to the turbine forebay by a low pressure pipe line and hence to the power house via high pressure pipe line.
Figure 2.3 High head with leat (this is a part of power plant which is open, contour-canals for the conveyance of water) [10,11]
2.2.2.3 Low head scheme -incorporating a diversion weir and intake works feeding water through a low pressure pipe line to the power house. Water is returned to the river by a tailrace channel.
Figure 2.4 Low head scheme[10,11]
2.2.2.4 The dam scheme is where the head is created by the construction of a bombardment incorporating a power house.
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Figure 2.5 power house Dam [10,11]
A number of factors
upon like
landscape, access, availability and comparative cost of
materials, the skills of the labour force, the requirements of other riparian users and land drainage requirements to choice the scheme layout . In the case of a previously developed hydropower scheme, this has subsequently fallen in to disuse, the scheme layout may already be determined to a large extent. The scheme layout determines the head available for generation. The head is either the vertical difference in level between the water surface in the turbine forebay and the water surface in the tail race for the schemes using pipelines and reaction turbines or the turbine runner for scheme using pipe line and impulse turbine. The other is that the vertical difference in level between the water surface immediately upstream of the power house and the water surface in the tail race for low head leated schemes and the power house dams. Head measurement methods can be performed by a surveyor level or thedolite, an altimeter or a surveyor’s staff, plumb line, tape, builder’s level, and total station. [10,11] 10
2.2.3 Hydrology Flow Rate The occurrence estimate and the volume of the flow passing a proposed hydro-electric site must be made if the development is to be properly sized and the installed capacity determined. The selection of rated flow is of important since the sizing and hence cost of all equipment and structures are dependent upon this parameter. The hydrology of the catchment area and the consequent runoff and ground water conditions determine the river flows. The catchment area is the whole of the land and water surface contributing to the discharge at a particular location. The river flow of the catchment is dependent upon many factors like area, location, orientation, rainfall, climate, topography and geology.
The volume of water in the river
available for generation is quantified by the annual mean flow. The appropriate installed or rated turbine flow is dependant up on the optimum sizing of the power generating equipments and the civil work in relation to the end use for the energy. The study of the effect of rated flow for economic return between undertaken for a number of sites of differing hydrological and scheme types. This analysis shows that optimum economic benefit is likely to be obtained when rated flow is set at mean annual flow minus compensation flow and accordingly this flow provides a reasonable first estimate for use in preliminary appraisal and potential studies.
2.2.3.1 Mean Flow For estimating mean flow several methods are available as shown below: Mean flow can be estimated Qm = ( SAAR-Ea)*A*10 3 8760*3600
where Qm=annual mean flow(m3/s) SAAR=Standard annual average rainfall for the catchment (mm)
11
Ea=actual evapo-transpiration (mm) A= catchment area (m2) Standard annual average rainfall for the catchment (SAAR) can be obtained from map produced by Ethiopian Metrological Agency. The actual evapo-transpiration can be obtained from potential evaporation (Ep). Ep is obtained from a Metrological Agency Map. The quantity SAAR-Ea can be termed as net rainfall.[12] 2.2.4 Power Output The power output from a potential mini-hydroelectric scheme is calculated by use of the Flow Duration Curve (FDC), Fig. 2-6, together with consideration of the efficiency and part flow characteristics of turbine and the overall efficiency of generation. An accurate assessment of annual power output cannot be over-stressed, since it is the quantity of energy produced which provides the income for such hydropower plant. Over estimation of the net turbine head and the FDC will lead to over sizing of generating plant, in the case of this lead to specification of an incorrect rotational speed for turbine which will lead to operation at reduced efficiency.
12
Fig 2.6 Flow Duration Curve for Values of BFI (base flow index) [13] 2.2.5 Efficiency It is necessary to obtain a value for the overall efficiency of generation, usually for output at the electrical generator terminals to calculate the installed capacity. This is a product of
13
turbine, drive and electrical efficiencies and should also make allowance for head loss in the pipe line where one is integrated. The efficiency of the turbine curve is plotted where relative efficiency against the percentage of rated flow and the curve for the main turbine type is shown as below for mini hydro power plants:
Figure 2.7 Turbine Efficiency Curves from Manufacturer’s Data[14] From the above curve one can understand that relative flat curve for the cross flow and impulse when compared to the Francis and propeller machines. The relative efficiency curve can be used only when a value has been obtained for likely peak efficiency. This efficiency is dependent upon a number of factors: design, size, manufacturing 14
tolerances etc. But there is a general increase in efficiency with increase in related power output. Typical Maximum Efficiency (%) No
Rated Power (KW)
Cross flow
Impulse
Francis
Propeller FDVB
1
2000
-------
90
93
89
2
1000
83
88.5
91.5
87.5
3
500
83
87
90
86
4
150
83
85
87.5
84
5
75
83
83
85
82
6
35
75
75
77
74
Table 2.3 Maximum Turbine efficiency at various rated power [2]
The efficiency of the turbine should be combined with drive efficiency, usually taken as 98%, and peak generator efficiency from the above graph, Fig 2-7. The pipe line must be made for frictional losses so that gross head is reduced to net head. Pipeline head loss can be considered as efficiency by dividing net head by gross head. The overall efficiency of the power plant is computed as below:[14] o = T. D.G.P Where-o-Overall efficiency T- Turbine efficiency D- Drive efficiency (mechanical and generator) P- Pipeline efficiency
15
2.2.6 Energy Yield The energy yield from a potential small scale hydropower scheme is calculated by use of the FDC, together with consideration of the efficiency and part flow characteristics of the turbine and the overall efficiencies of the generation. To evaluate the energy yield the following steps are used:[11] i. Select a value for design flow rate, Qi and express it as a proportion of Annual mean flow rate, Qm. ii. Set the lower flow limit for generating depending on the turbine type (Qi/6 for cross flow and impulse, Qi/3 for Francis and propeller) iii. Divide the adjusted FDC between Qi and Qm in to bands, usually 5-10%of time depending on the accuracy required. iv. Calculate the average flow within each band. v. Multiply the average flow in each band by Qm to convert to m3/s. vi. Compute turbine power output for each flow value by multiplying by net head flow, 9.81, and obtain T from the above table2.3 and figure 2-6 for estimating net head a graph of the form shown in the figure 2-8 is of use. vii. Convert turbine output to electrical output by multiplying by drive efficiency (0.98) and generator efficiency from figure 2-6. viii. Multiply electrical output by proportion of time and 8760 hours per year to calculate energy in each band. ix. Sum energy values to obtain annual energy yield.
16
Fig. 2.8 Calculation of Energy yield for Cross flow and Impulse Turbine [11]
17
[
Figure 2.9Estimation of Net Turbine Head[11]
18
CHAPTER THREE Hydro power Generation 3.1 General Description about Hydro Power Generation Hydropower engineering refers to the technology involved in converting the pressure energy and kinetic energy of water into more easily used electrical energy. The prime mover in the case of hydropower is a water wheel or hydraulic turbine which transforms the energy of the water into mechanical energy. Mechanical energy will be converted to electrical energy by using electrical generator [2]. 3.1.1Types of Hydro Power Generally there are four basic types of hydro power generation 3.1.1.1 Impoundment An impoundment facility, typically in a large hydropower system, uses a dam to store river water in a reservoir. The water may be released either to meet changing electricity needs or to maintain a constant reservoir level. 3.1.1.2 Run-of-river Run of river has a dam with a short penstock (supply pipe) directs the water to the turbines, using the natural flow of the river with very little alteration to the terrain stream channel at the site and little impoundment of the water. 3.1.1.3 Diversion and Canal In this type the water is diverted from the natural channel into a canal or a long penstock, thus hanging the flow of the water in the stream for a considerable distance. 3.1.1.4 Pumped Storage The demand for electricity is low, pumped storage facility stores energy by pumping water from
a lower reservoir to an upper
reservoir. During periods
of high electrical
demand, the water is released back to the lower reservoir to generate electricity. 19
3.2 Basic Concepts of Mini-Hydro Power Generation Mini-hydro schemes are smaller still and usually do not supply electricity to the national grid at all and it is usually refers to hydraulic turbine systems having a capacity of 100 kW just enough to provide domestic lighting to a group of houses through a battery charging to 100kWh which can be used for small factories and to supply an independent local mini-grid which is not part of the national grid. This small unites have been used for
many years, but recent increases in the value of electrical
energy and incentive programs have made the construction and development of microhydro power plants much more attractive to developers. Likewise small villages and isolated communities in developing nations are finding it beneficial and economical to use micro-hydro power generation [2]. The principle of operation, types of units, and the mathematical equations used in selection of micro-hydro power systems are essentially the same as for conventional hydropower developments. However, there are unique problems and often the costs of the feasibility studies and the expenses of meeting all regulatory requirements make it difficult to justify micro-hydro power developments on an economic basis.
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Figure 3.1 Layout of a typical micro hydro scheme [2,4]
3.3 Scheme Components 3.3.1 Dam and Weirs Mini hydropower plant in most cases are run-of-river in other words any dam or barrage is quite small, usually just a weir, and little or no water is stored. The costs involved in the construction of large impounding dams are such that the majority of small hydropower schemes are of the run-of river type and as such does not have storage. Low weirs are used and their primary function is to divert the water in to the intake work, providing adequate water depth to ensure submergence of the pipe line or adequate depth in the leat so that it can carry its design flow. A variety of materials can be used to construct weir including masonry, concrete, steel, timber, and composite. The simplest type of weir, often found in developing countries, is simply formed by placing boulders across the flow to divert water. These structure often being swept away during large floods which are common in the
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tropics. But labor is cheap and the boulders are easily replaced, such a diversion weir is often adequate. Permanent types of weir are usually constructed to raise the water level slightly, in which case they collect the bed load and debris carried by the water. To assuage this problem it is common to incorporate a sliding gate on the intake side of the weir, this permits sufficiently high speeds near the intake to remove debris. For low-head, high-flow sites, it is unlikely that a scheme will be economic if a weir to develop all the head has to be constructed. This site will only be economic where the weir is an existing feature or where a low head a low weir can be built on top of a natural ledge. For such areas flooding due to increase water levels can also be a problem, and it may be necessary to construct flood relief gates over at least a portion of the weir length. In Mini-hydro-power, dams are rarely used, however where they are, careful consideration to their design must be taken.[15]
3.3.2 Intake structure Mainly there are two main function of intake; to control the quality and quantity of water entering the leat or the pipeline. Penstocks and spillway are the usual means of controlling the amount of water entering the intake, whilst trash screens, skimmers and settling basins are used to control water quality. The design depends on the scheme layout and as such is site specific in nature integrating some or all of the above features. It is important that the location of the intake structure is of importance since use of local features can simplify the intake design. As usual intake structure is oriented perpendicular to the main direction of river flow so avoiding the problem of debris and bed load entering the intake particularly during flooding.
3.3.2.1 High and Medium head intake In this category the use of a leat supplies water to the turbine forebay (settling area), and those which pass water to the pipeline. A. Channel Scheme
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The channel scheme is the simplest form where no penstock and screens but a diversion wall is used to deflect debris and restrict the flow during floods.
Figure 3.2 Simple Diversion Wall forms Intake During flooding the water levels is significantly raised; the effectiveness of the wall in reducing flows entering the channel is limited. For that reason, adequate spillway facilities must be incorporated along the length of the channel to ensure that these flows are dealt with.
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In addition to this there is no control of bed load sediment entering the channel, and hence where such bed loads are high more sophisticated type of intake must be used. On the downstream end of the leated scheme is the turbine forebay. This forebay usually integrated with the settling basin, fine screen and spillway arrangement. For dewatering purpose stop log grooves are incorporated in the pipe line. B. Pipeline scheme The pipe line scheme where water is passed directly from the intake to the pipeline, it is necessary to remove all debris and most of the deposit from the flow prior to flow entering the pipeline.
Figure 3.3 High Head Intake[16] The intake includes course screens upstream of the penstock to protect it from damage by large floating materials. The penstock gate controls the quantity of water entering the intake, and this is supported by the insertion of a side spillway to accommodate temporary flow fluctuation. Settling area is used to catch suspended material and fine screen to allow removal of vegetation and other small debris. 24
As shown in the figure 3.3 the screen is placed above the base of the intake chamber on a concrete ledge which further helps to trap sediments.[16] 3.3.2.2 Low Head Intakes The preliminary settling basin is the weir and as explicated above the side sluice allows removal of sediment from the intake area. The surface skimmer at the entrance to the channel prevents large floating materials entering the leat. A coarse screen prevents damage to the penstock and large debris to enter the leat. The quantity of water entering the leat can be controlled by the penstock. In this category a bypass penstock is also included for additional flow control and to allow distilling of the leat.
25
Figure 3.4 Low Head scheme
26
3.3.2.3 Trash Screens This is a basic part of a hydropower to intercept all flow being passed to the turbine and remove all debris which cannot be safely being passed through the turbine. A serious of parallel metal bars can make the screen to scrape up the debris. It is usually installed at an angle of 45 deg to 60 deg to horizontal. Such position aids raking, and allows a degree of self cleaning as the flow velocity through the screen tends to move debris towards the top. When the quantity of water allow, this action can be used to permit self cleaning by allowing water to flow over the top of the screen and then taking some debris to the collector as shown in the picture below.[17] The screen head loss can be computed as below:
H=k(t/b)4/3 (V2/2g )Sin ø
where H=head loss through screen(m) k=trash screen coefficient t/b= ratio of bar thickness to bar spacing g=gravitational constant (9.81 m/s2) ø = angle of bars to the horizontal V=Velocity (m/s)
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Figure 3.5 Head Loss through Trash Screen [17]
Figure 3.6 Trash Screen Head loss Coefficient k[17]
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The flows are so large that annual raking is difficult automatic raking can be incorporated. In general an electrical supply will be required and this adds a border complexity in isolate areas. Electrically operated automatic screen are mostly employed at low head sites and due to their cost they can only be used for large design.
3.3.2.4 Settling basin The following formula illustrates the design settling basin: L=60 Q / (Vo W)
where L-Length of settling bas in (m) Q-flow rate (m3/s) Vo-particle settling velocity (m/minute) W-width of chamber
Even though for mini hydropower 2 m/minute settling velocity is often used to remove particles with diameters greater than 0.3 mm, the particle velocity is dependent upon particle size and type.[18]
3.3.3 Leats This is a part of power plant which is open, contour-canals for the conveyance of water. It is constructed to carry water from the intake works to the forebay in high heads or from the intake work directly to the power house in the low head scheme. For low pressure pipeline leats are often preferred and directly conveying water to the power house by high pressure pipeline. Its gradient, shape and the fabric can vary the flow capacity of the leat. There are two types of leat lined and unlined. Unlined are frequently employed as the expense is minimal and easily constructed and maintained relatively inexpert labour force. Lined leats can be constructed from a variety of material like masonry, concrete, clay, geotextile and sheet pile lining.
3.3.3.1 Design of leats Manning’s equation can be used to design the leat and it can be written as below;[12] 29
v=R2/3 S1/2/n
where v=velocity (m/s) R=Area (m2)/wetted perimeter, hydraulic radius S=slop of the leat n=Manning’s roughness coefficient from table 3.1
Material Type
n
Smooth timber
0.011
Cement-asbestos pipes, welded steel
0.012
Concrete-lined (high quality formwork)
0.013
Brickwork well-laid and flush-jointed
0.014
Concrete and cast iron pipes
0.015
Rolled earth: brick in poor condition
0.018
Rough-dressed stone paved, without sharp bends
0.021
Natural stream channel, flowing smoothly in clean conditions
0.030
Standard natural stream or river in stable condition
0.035
River with shallows and meanders and noticeable aquatic growth
0.045
River or stream with stones and rocks, shallow and weedy
0.060
Slow flowing meandering river with pools, slight rapids, very weedy and overgrowth
0.100
Table 3.1 Values of Manning’s roughness coefficient n for straight uniform channels [12] The shape of the leat is determined by the manning’s equation , characterized by its hydraulic radius, it is useful to note that given the profile to be used for the leat, there is a specific value for R which provides the most efficient section. 30
Figure 3.7 Common leat Profile
Table 3.2 Hydraulic radius for most coefficient leat section[18] The following table describes dimensions for most efficient leat sections
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No
Profile
Dimensions
1
Semi-circular
diameter, d=4R
2
Rectangular
depth, d=2R width, w=4R
3
Triangular
depth, d=2.8R width, w=5.7R
4
Trapizoidal
depth, d=2R width, w=4R/sinø
Table 3.3 Dimensions for the leat section [18] The following basic equation governs the flow capacity of a leat; Q=AV
where
Q=Flow rate A= Area (m2) V=velocity (m/s)
3.3.4 Pipeline Pipelines are used to convey water from intake works to the power house and basically classified as gravity and high pressure pipelines. 3.3.4.1 Gravity pipelines Run under the influence of gravity, and it is usually laid below ground in trenches on a gravel bed enclose. It can be made from concrete, lower pressure PVC and fiber glass. 3.3.4.2 High pressure pipeline This type is used to convey water from the intake work, forebay to the powerhouse. In this category the pipes are ductile iron, fiber glass and steel. The pressure rating and the site condition can matter the type of pipe. The selections of pipes are generally tabulated as below:
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No
Pipe type
Size range (mm)
Pressure rating (m of water)
Comment
1
Ductile iron
80-1600
250-400
Cost effective and durable when laid above ground.
In trenches do not require a
gravel surrounding but must be wrapped to prevent corrosion. Cement mortar lining reduces internal corrosion. Disadvantage is weight. 2
Steel tube(seamless)
80-400
Main advantages are high pressure rating
160-4000
and strength. Disadvantages are weight and requires for coating to protection against corrosion. Pipes are joined by on site welding which can be expensive.
3
PVC
80-600
Main advantage is light weight, hence easy
60-150
to install. Small range of sizes only and PVC Deteriorate due to UV light. 4
Glass Reinforced Plastic (GRP)
900-2500
60-260
Light weight, easy to install and cost
200-1000
60-240
effective.
200-2500
Gravity
The main disadvantage when laying below the ground require prepared bed or granular surround.
5
Concrete
300-2100
Gravity
