Comparative Study

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BULGARIA – SERBIA IPA CROSS-BORDER PROGRAMME 2007CB16IPO006 2011-2-229 Reclaiming Rivers for Implementation of Vital and Environment – Friendly Renewable Energy Source - RIVERS

COMPARATIVE STUDY OF SMALL HYDROPOWER STATIONS

The project is co-funded by EU through the Bulgaria–Serbia IPA Cross-border Programme.

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January 2014 This publication has been produced with the assistance of the European Union through the Bulgaria-Serbia Cross-Border Programme CCI No 2007CB16IPO006. The contents of this publication are the sole responsibility of and can in no way be taken to reflect the views of the European Union or the Managing Authority of the Programme.

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Preface

Comparative study of small hydropower stations was conceptually structured so as to:    

Assess engineering aspects of small hydropower plants; Provide basic information regarding the common turbine types (Francise, Kaplan, Banki and Pelton turbine) as well as innovative turbines; Provide elements and methods for economic appraisal and analysis of small hydropower plants and Cover environmental and social issues of small hydropower plants.

It was our intention to provide the up to date information about abovementioned thematic. We believe that this volume will be of benefit for engineers, potential investors in hydropower facilities, students and professionals of diverse disciplines. The contents of this publication are the sole responsibility of and can in no way be taken to reflect the views of the European Union or the Managing Authority of the Programme.

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Table of content 1. INTRODUCTION - ENERGY OF WATER IN NATURE .............................................................................. 5 2. ENGINEERING ASPECTS OF SMALL HYDROPOWER PLANTS ................................................................ 7 PART I ...................................................................................................................................................... 9 Analysis and comparison of different type of turbines (Pelton, Kaplan, Francis, Cross-flow, Bulb, Straflo etc.) with recommendations for application of every class accompanied with efficiency analysis. ............................................................................................................................................... 9 Classification of hydropower plants ................................................................................................ 9 Classification of turbines ............................................................................................................... 12 PART II ................................................................................................................................................... 24 Analysis of innovative types of turbines (Arcimedian screw turbine, VLH Turbine, Hoped pelton etc.) and their advantages as compared with conventional turbines ............................................ 24 Low head turbines ......................................................................................................................... 24 Archimedes Screw ......................................................................................................................... 26 VLH-Very Low Head Turbine.......................................................................................................... 30 The HydroEngineTM ...................................................................................................................... 33 PART III .................................................................................................................................................. 37 Economic appraisal and analysis of small hydropower plants (methods for determining the economic and financial feasibility of hydropower projects, presentation of basic tools for economic analysis, financial and cash flow analysis; methods for determining the costs and benefits). ........................................................................................................................................... 37 Energy Generation Economics ...................................................................................................... 37 Low Head Hydro Costs................................................................................................................... 38 Methods of economic evaluation.................................................................................................. 42 PART IV .................................................................................................................................................. 50 Environmental influences of small hydropower plants (for all small hydropower developments with special emphasize on Archimedian screw schemes). Social issues linked with small hydropower plants ........................................................................................................................... 50 Sources of environmental and social impacts ............................................................................... 50 Biological impacts - mitigation and compensation measures ....................................................... 53 Socio-economic impacts - mitigation and compensation measures............................................. 54 Literature ............................................................................................................................................... 57

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1. INTRODUCTION - ENERGY OF WATER IN NATURE Energy of water is the form of energy used the longest in the history of the world. It is a known fact that the solar heat causes evaporation of water mainly from the seas, lakes, rivers and streams. In addition, water contained in the ground also evaporates. The evaporation uses thermal energy. Using the energy means that it is not destroyed, but only changes shape, i. e. transforms from one form into another. In this case, solar energy that falls on the ground also heats up the water in the ground. Earth as a planet is ¾ water and ¼ land, i.e. ground. Therefore by heating water, solar energy transformed its form from light to heat. This energy is then transferred by the evaporated water to a higher level, i.e. position. If the rise of steam from the water surface is observed, it can be perceived that the rise of water in the form of water steam will last long enough for it to reach higher altitude and the right atmospheric pressure to condense and form clouds. Air currents carry the clouds above the elevated ground surface, i.e. over land higher than the sea surface. When the clouds, particularly above mountain ranges, cool enough to allow the small cloud drops to turn into large drops, it rains, while in case of lower temperatures and according to atmospheric circumstances snow or hail appear. Precipitation, therefore water, falls down to the surface. If this process of water evaporation and condensation is viewed as a physical occurrence, then it is clear that the evaporated water brought along energy in the form of heat, and when condensed in a cloud, that energy shifted into potential energy. During precipitation, one portion of potential energy is transformed into kinetic energy, which performs a mechanical operation of land erosion through hitting the surface with water. The remaining part of potential energy in precipitation remains captured in the water if it accumulates and if it is possible to use the fall of water from the place of surface and precipitation contact to the sea. On its route to the sea, the potential energy of water is successively transformed into kinetic energy that allows the water to overcome the obstacles of the river bed and erode the terrain. When the water reaches the sea, the entire process reaches the starting point again and completes the cycle. This process constantly repeats itself. From what was described so far, it is obvious that water affects nature both positively, maintaining the vegetation of the terrain and negatively, since it has an irregular flow to the sea that has a negative impact particularly on the surface of ground, removing hummus with floods and leaving the land barren and infertile.

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Water forms streams, brooks and rivers on its course. All these water flows form the drainage basin. This drainage basin is constrained by ridges. Ridges constraint the drainage basin from three sides, the fourth in most cases allowing the free water flow towards the sea. If the fourth side of the drainage basin is also ridged, then the impermeable ground allows the creation of a lake, while the permeable ground makes underground rivers. Solar energy that reaches earth can produce a power of P= 1,7x1014 kW. 19,6% is used for heating of the water, and land evaporates V= 5,2x1014 m3. 68% is precipitation in form of snow, rain etc., and 31% reaches rivers and streams, and eventually the sea. One percent reaches sea as an underground current (underground rivers). Realistically, the volume of water that flows into sea is V=5x1014 m3 and this is the main component of hydro energy. In theory, the estimated annual potential of water energy is A=1,4x1020 J. The possible potential power of the available energy potential is estimated to more than P=3x109kW. The energy that reaches earth is used (1) 35% for heating up the atmosphere, (2) 32,45% for heating up earth, (3) 2.5% for wind energy, (4) 9.9% for heating up the land, (5) 0.15% for vegetation, (6) 19.5% for heating the water surface and (7) 0.5% for producing water energy that can be used for obtaining other forms of energy. Theoretically, the estimated annual potential of water energy is A=1,4x1020 J. The maximum potential power of the available energy potential is estimated to more than P=3x109kW.

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2. ENGINEERING ASPECTS OF SMALL HYDROPOWER PLANTS The development of civilization is closely connected with the use of water energy enabling technical and technological development and the progress of civilization. Water wheels are considered to have been in existence for 22 centuries. It is thought that Ctesibius invented the water wheel with blades 135 years BC. In 2nd century AD in Illyria (western region of Balkan Peninsula) first constructions of water wheels with vertical axle for moving millstones for grinding grain appeared. This is the first time a natural force was used to benefit man, substituting the combined work of animals and people with water power. First hydraulic engines were water wheels. Up to the beginning of the 18th century, undershot wheels were used (scoop-wheels). At first they were mostly used for irrigation, later widening the field of application to crushing and pounding fiber for use in the manufacture of cloth and sawing timber in sawmills as well as for watermills, i.e. for moving millstones. Further development of water wheels led to the invention of overshot water wheels. The weight of water turns the wheel using the potential energy of water. This type of wheel also uses the potential energy of watercourse. Overshot and breastshot water wheels were introduced during the 14th century, using higher water fall H. The power obtained reached 7.5kW and was used for moving sledge-hammers in smithies and for extracting ore during mining process. Although they have become a historical rarity and represent a kind of nostalgia for the past, the aforementioned water wheels still exist in some underdeveloped regions of the world. There is a conviction in Serbia that the quality of flour from the water mill is better than the quality of flour from the electric mills. Water wheels have been widely used in the activities of peoples at that level of development. Transmission of power from the axle of the water wheel to the axle of the operating machine is conducted over shorter distance through a belt drive, later through transmission. Water wheels were main operating engines of industry and their historical use extends over several centuries. Since no improvement could significantly increase their power and efficiency, the need for a new water engine arose. Several solutions appeared, real turnpoints in the field of available water energy application. Reaction principle is introduced, i.e. Segner wheel is invented in 1750. This wheel represents a basis for the introduction of water turbines instead of water wheels. In Segner wheel, water acts on rotor with specially bent pipes with nuzzles. This working principle was later used by Lester Pelton with the construction of his own - water impulse turbine.

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The most significant work in the development of the theory of the operating process of water engines was conducted by D. Bernoulli (1700-1783) and L. Euler (1707-1783). D. Bernoulli discovered the fundamental law of hydrodynamics which gives a connection between the speed and the pressure in an incompressible fluid, which he published in 1738 in his work. Although published two and a half centuries ago, Bernoulli’s work is still being used in Fluid mechanics and the theory of turbomachines. Between 1751 and 1754 L. Euler developed the theory of water turbines, set the basic equation and described the process of using electric energy in water turbines. His ideas include introducing of a conductive device in combination with the runner in water engines. In 1817, Fourneyron designed his first reaction water turbine, which was much used at the time. Fourneyron’s first water turbine had the power of P=40kW. Between 1896 and 1899 the first large hydroelectric power plant was built in the Niagara Falls. Both water turbine and water wheel are rotative devices which transform the energy of water into mechanical energy. Inside water turbine, compression and kinetic energy are used. Introduction of water turbines with designs different than Fourneyron’s was a success. New turbines, named after the inventors appeared, like Jonval turbine and Gerard turbine. The construction of Jonval turbine is closely related to Euler’s research. Jonval turbine is a reaction shaft water turbine with a water conveying device. The runner has one or more guide vane rings. This turbine was used for unit works of Y=60-400 J/kg and flows of Q=from 22m3. Runner diameter reached D1= 5 m and more. Specific rotation frequency was within boundaries of nq=0.09-0.22 and the utilization level reached even η=0,85. These turbines were constructed for power to P=110kW. After 1905, Jonval turbine was no longer used and was soon successfully replaced by Francis water turbine, which is to this day almost unsurpassed in its field of application. Modern Francis turbines have developed into very different forms from the original, but they all retain the concept of radial inward flow.

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PART I Analysis and comparison of different type of turbines (Pelton, Kaplan, Francis, Cross-flow, Bulb, Straflo etc.) with recommendations for application of every class accompanied with efficiency analysis. The use of hydraulic turbines for the generation of power has a very strong historical tradition. The first truly effective inward flow reaction turbine was developed and tested by Francis and his collaborators around 1850 in Lowell, Massachusetts. Modern Francis turbines have developed into very different forms from the original, but they all retain the concept of radial inward flow. The modern impulse turbine was also developed in the USA and takes its name from Pelton, who invented the split bucket with a central edge around 1880. The modern Pelton turbine with a double elliptic bucket nozzle was first used around 1900. The axial flow turbine with adjustable runner blades was developed by the Austrian engineer Kaplan in the period from 1910 to 1924. Another type of impulse unit is the cross-flow turbine, also called the Banki or Michell turbine. The cross-flow principle was developed by Michell, an Austrian engineer, at the turn of the century. Professor Banki, a Hungarian engineer, developed the machine further.

Classification of hydropower plants In studying the subject of hydropower engineering, it is important to understand the different types of development. The following classification system is usual: Run-of-river developments (small dam scheme) The dam is used to concentrate the head, which raises the upstream water level. A dam with a short penstock (supply pipe) directs the water to the turbines or the powerhouse can be placed inside the dam. This scheme uses the natural flow of the river with very little alteration to the terrain stream channel at the site and little impoundment of the water. This is a common scheme for mini or micro hydropower plants where power is generated without inflow regulation. Run-of-river developments (diversion scheme) The water is diverted from the natural channel into a canal or a long penstock, thus changing the flow of the water in the stream for a considerable distance. Mixed scheme A dam can partly raise the net head and a long hydraulic conveyance circuit will raise the other part.

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Diversion and mixed scheme are often used in case of small hydropower plants. Storage regulation developments An extensive impoundment at the power plant or at reservoirs upstream of the power plant permits changing the flow of the river by storing water during high-flow periods to augment the water available during the low-flow periods, thus supplying the demand for energy in a more efficient manner. The word storage is used for long-time impounding of water to meet the seasonal fluctuation in water, availability and the fluctuations in energy demand.

Run of river diversion scheme - Photo Credit: Cleantech Magazine

Small dam scheme - Photo Credit: Water Encyclopedia

Mixed scheme - Photo Credit: Practical Action

Storage regulation developments- Photo Credit: California WaterBlog

Pumped-storage developments (reversible plants) Water is pumped from a lower reservoir to a higher reservoir using inexpensive dump power during periods of low energy demand. The water is then run down through the turbines to produce power to meet peak demands. Tidal power developments In some estuaries, tidal power can be economically harnessed to develop electric energy. These developments use the water flowing back and forth as a result of tidal action

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and the fact that there is a significant difference in elevation of the water surface in the estuary from one stage of tide to another. Storage, Pumped storage and Tidal developments are not used commonly for small hydropower plants.

Pumped storage developments- Photo Credit: Energy Storage Trends Blog

Tidal power developments - Photo Credit: Encyclopedia Britannica

If we consider the goal of hydropower plants developments then the following classification is usual: Single-purpose developments The water is used only for the purpose of producing electricity. Multipurpose developments Hydropower production is just one of many purposes for which the water resources are used. Other uses might include, for example, irrigation, flood control, navigation, municipal, and industrial water supply. Another way of classifying hydropower development is with respect to the manner in which the hydropower plant is used to meet the demand for electrical power. Base-load developments When the energy from a hydropower plant is used to meet all or part of the sustained and essentially constant portion of the electrical load or firm power requirements, it is called a base-load plant. Energy available essentially at all times is referred to as firm power. Peak-load developments Peak demands for electric power occur daily, weekly and seasonally. Plants in which the electrical production capacity is relatively high and the volume of water discharged 11

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through the units can be change readily are used to meet peak demands. In that case the storage of the water is necessary. Hydropower plants can be started and stopped more rapidly and economically than fossil fuel and nuclear plants, so the use of hydropower plants to meet peak loads is particularly advantageous. In some cases the hydropower plants were originally base-load plants but as large fossil fuel and nuclear power plants become operative hydropower plants are being used more and more for peaking power.

Classification of turbines The net head available to the turbine dictates the selection of type of turbine suitable for use at particular site. The rate of flow determines the capacity of the turbine. Hydraulic turbines have two general classifications, impulse and reaction. Reaction turbines are classified as Francis (mixed flow) or Propeller (axial flow). Propeller turbines are available with both fixed blades and variable pitch blades (Kaplan). Both Propeller and Francis turbines may be mounted either horizontally or vertically. Additionally, Propeller turbines may be slant mounted. Trade names have been applied to certain Propeller turbine designs such as Tube, Bulb and Straflo. The runner design principals, however, are the same. Impulse turbines convert the kinetic energy of a jet of water to mechanical energy. Impulse turbines are often used in small hydropower installations. The most widely used impulse turbines are: Pelton, Turgo and Crossflow turbines. Pelton turbines may be mounted either horizontally or vertically, but Turgo or Crossflow turbines must be mounted horizontally. Francis turbines A Francis turbine is one having a runner with fixed vanes to which the water enters the turbine in a radial direction, with respect to the shaft, and is discharged in an axial direction. Principal components consist of the runner, a water supply case to convey the water to the runner, wicket gates to control the quantity of water and distribute it equally to the runner and draft tube to convey the water to tailrace. A Francis turbine may be operated over a range of flows from approximately 30 to 105 percent of rated discharge. Below 30 percent of rated discharge, there can be an area of operation where vibration and/or power surges occur. The approximate head range for operation is from 60 to 125 percent of design head. In general, peak efficiencies of Francis turbines will be approximately 87 to 90 percent. The peak efficiency point of a Francis turbine is established at 90 percent of the rated capacity of the turbine. In turn, the efficiency at the rated capacity is approximately 2 percent below peak efficiency. The peak efficiency at 60 percent of rated head will drop to near 75 percent.

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Figure- Classification of turbines

Francis turbine - Photo Credit: Global Hydro Energy

Typical efficiency curve of Francis turbine

Francis runner- Wikipedia The conventional Francis turbine is provided with a guide vane assembly to permit placing the unit on line at synchronous speed, to regulate load and speed and to shutdown the unit. The guide vanes are usually actuated by hydraulic servomotor. In some cases small units may be actuated by electric motors, but better control is achieved with hydraulic system. 13

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Francis turbine may be mounted with vertical or horizontal shafts. Vertical mounting allows a smaller plan area and permits a deeper setting of the turbine with respect to tailwater elevation. Generator cost for vertical units are higher than for horizontal units because of the need for a larger thrust bearing. Horizontal units are often more economical for applications where standard horizontal generators are available.

Francis turbine drawing - Photo Credit: B Fouress Pvt Ltd

Horizontal Francis turbine- Wikipedia Francis turbine - Photo Credit: Global Hydro Energy Hydrolink s.r.o.

Advantages of Francis turbine are: • Variation in the operating head can be easily controlled in Francis turbine • The ratio of maximum and minimum operating head can be even be two in the case of Francis turbine • The operating head can be utilized even when the variation in the tail water level is relatively large when compared to the total load • The size of the runner, generator and power house required is small and economical if the Francis turbine is used instead of Pelton wheel for the same power generation.

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• The mechanical efficiency of the Pelton wheel decreases faster with wear than Francis turbine Disadvantages of Francis turbine are: • Water which is not clean can cause very rapid wear in high head Francis turbine. In passing through the guide vanes and cover facings, it can quickly reduce overall efficiency of the turbine by several percentages. The effect is much more serious in turbines of smaller diameter than in larger ones. • The inspection and overhaul of a Francis Turbine is much more difficult job than that of the equivalent Pelton turbine. • Cavitation is an ever present danger in Francis Turbine as well as in all the reaction turbines. The raising of the power house floor level to reduce the danger of flooding may be followed by the endless cavitation troubles. • If there is a possibility of running below the 50% load for long time, the Francis will not loose efficiency but cavitation danger will become more serious. • Difficult to maintain/clean. • The water hammer effect with the Francis turbine is more difficult to reduce compared with action turbines. Propeller turbines A propeller turbine is one having a usually runner with four, five or six blades in which the water passes trough the runner in an axial direction with respect to the shaft. The pitch of the blades may be fixed or movable. Principal components consist of water supply case, guide vanes, a runner and a draft tube. The efficiency of a typical blade Propeller turbine forms a sharp peak, more abrupt than a Francis turbine curve. For variable pitch blade units the peak efficiency occurs at different outputs depending on the blade setting. An envelope of the efficiency curves over the range of blade pitch settings forms the variable pitch efficiency curve. This efficiency curve is broad and flat. Fixed blade units are less costly than variable pitch blade turbines; however, the power operating ranges are more limited. Propeller turbines may be operated at power outputs with flows from 40 to 105 percent of the rated flow. The Kaplan turbine has adjustable runner blades and may or may not have adjustable guide-vanes. If both blades and guide-vanes are adjustable, the turbine is a "full Kaplan" and double-regulated. "Semi-Kaplan" features fixed guide-vanes and are single-regulated. Unregulated propeller turbines, in which both the guide-vanes and runner blades are fixed, are used when both flow and head remain essentially constant. Conversely,

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the double-regulated Kaplan, is a vertical/horizontal axis machine with a spiral casing and inlet casing, and a radial wicket-gate configuration. Full Kaplan turbine may operate with flows from 25 to 105 percent of rated flow with very high efficiency. In the case of adjustable blades and fixed gates high efficiency zone is from 40 to 105 percent of the rated flow. At propeller turbines with fixed blades and adjustable guide vanes there is a sharp drop in efficiency below the 70 percent of rated flow. Head range for satisfactory operation is from 60 to 140 percent of design head. Efficiency loss at higher heads drops 2 to 5 percentage points below peak efficiency at design head and as much as 15 percentage points at lower heads. The conventional propeller or Kaplan turbines are mounted with a vertical shaft. The vertical units are equipped with a guide vane assembly which is usually actuated by hydraulic servomotors. Variable pitch units are equipped with a cam mechanism to coordinate the pitch of the blade with gate position and head. The advantages and disadvantages discussed above with regard to vertical versus horizontal settings for Francis turbines apply also to propeller turbines. The water supply case is generally concrete. Either an open flume or a closed conduit type of construction may be used. At higher heads the turbine shaft length becomes excessive. Also open flume construction is disadvantageous with regard to maintenance cost. Tubular turbines. Tubular or tube turbines are horizontal or slant mounted units with propeller runners. The generators are located outside of the water passageway. Tube turbines are available equipped with fixed or variable pitch runners and with fixed or adjustable guide vanes. Performance characteristics of a tube turbine are similar to the performance characteristics discussed for propeller turbines. The efficiency of a tube turbine can be one or two percent higher than for a vertical propeller turbine of the same size since the water passageway has less change in direction. Tube turbines can be connected either to the generator or to a sped increaser. The speed increaser would allow the use of a higher speed generator, typically 900 or 1200 rpm, instead of a generator operating at turbine speed. The choice to utilize a speed increaser is an economic decision. Speed increaser lower the overall plant efficiency by about one or two percent. This loss of efficiency and the cost of the speed increaser must be compared to the reduction in cost for the smaller generator. The required civil features are different for horizontal units than for vertical units. Horizontally mounted tube turbines require more floor area than vertically mounted units. The area required may be lessened by slant mounting, however, additional turbine costs are incurred as a larger axial thrust bearing is required. Excavation and powerhouse height for a horizontal unit is less than that required for a vertical unit. 16

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Bulb turbines. Bulb turbines are horizontal units which have propeller runners directly connected to the generator. The generator is enclosed in a water-tight enclosure (bulb) located in the turbine water passageway. The bulb turbine is available with fixed or variable pitch blades and with or without guide vane mechanism. Performance characteristics are similar to the vertical and tube type turbines previously discussed. The bulb turbine will have an improved efficiency of approximately two percent over a vertical unit and one percent over a tube unit because of straight water passageway. Maintenance time due to accessibility, however, may be grater for either the vertical or the tube type turbines. Rim type turbines. A rim type turbine is one in which the generator rotor is mounted on the periphery of the turbine runner blades. The turbine has been developed by Escher Wyss Ltd. of Zurich, Switzerland and given name “Straflo”. Straflo turbines are axial turbines with the generator outside of the water channel, connected to the periphery or rim of the runner. This outer rim of the turbine is fitted with seal lips, which are lubricated by a small amount of water designed to permanently leak from the system. The initial designs had fixed runner blades while subsequent designs had adjustable runner blades. These Straflo rim generator units find a wide application in tidal power plants.

Kaplan turbine - Photo Credit Zeco

Kaplan runner- Photo Credit TBHIC

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The patented VA Tech Hydro Straflo Matrix turbines have been adapted to small hydro applications. They have the following improvements and features over the traditional large size and capacity: permanent magnet technology, reduced dimensions. Permanent magnets allow synchronous operation without slip rings and excitation systems. As no electricity is transferred to the rotor, water can flow through the air gap between the rotor and stator allowing for a very efficient generator cooling. Additionally, this eliminates the main drawback of the traditional Straflo turbines, where the sealing of the generator at a large diameter led to some problems. The Straflo™ technology has the feature that the turbine runner also serves as support for the generator rotor and both components turn in the flow as a single unit. The resulting compact dimensions render the turbine even more efficient and offer significant advantages if confined space is a factor.

Construction of vertical Kaplan turbine

Bulb turbines- Photo Credit Hydrotu

Straflo turbine- Photo Credit: Andritz hydro Tubular turbine 18

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Advantages of Propeller turbines • Good adaptation to varying flow rates. The efficiency curve of full Kaplan turbine remains flat for over the wide load range • The frictional losses passing through the blades considerably lower due to small number of blades used in Kaplan Turbine • Can be used in a low head situation, leading to lower cost of penstock/piping • Turbines with highest efficiency Disadvantages of the Propeller turbines • • • • •

Single regulated does not easily adapt to varying head Requires a high flow rate Difficult to maintain/clean Runner blades/guide vanes must be adjusted based on flow rate Expensive to design, manufacture, and install Impulse turbines

An impulse turbine is one having one or more free jets discharging into an aerated space and impinging on the buckets of a runner. Efficiencies are often 90 percent and above. Pelton Turbines Pelton turbines are designed with a number of cup-shaped components connected around the circumference of a runner that is in turn connected to a central hub. Nozzles are positioned all around the runner, and they inject water into these cups, which change the potential energy of the water into kinetic energy by pushing the turbine's wheel around. Pelton turbines may include different generations of the same cup-and-wheel apparatus, each an iteration of which creates a greater level of energy efficiency. Single nozzle Pelton turbine has a very flat efficiency curve and may be operated down to loads of 20 percent of rated capacity with good efficiency. For multi nozzle units, the range is even broader because the number of operating jets can be varied. Control of turbine is maintained by hydraulically operated nozzles in each jet. In addition, a jet deflector is provided for emergency shut down. The deflector diverts the water jet from the buckets to the wall of the pit liner. This feature provides surge protection for the penstock without the need for a pressure release valve because load can be rapidly removed from the generator without changing the flow rate. Runners on the modern impulse turbine are a one-piece casting. Runners with individually attached buckets have proved to be less dependable and, on occasion, have

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broken away from the wheel causing severe damage to powerhouse. Integral cast runners are difficult to cast, costly and require long delivery times. However, maintenance cost for an impulse turbines are less than for a reaction turbine as they are free of cavitation problems. Excessive silt or sand in the water however, will cause more wear on the runner of an impulse turbine than on the runner of most reaction turbines. Draft tubes are not required for impulse turbines. The runner must be located above maximum tailwater to permit operation at atmospheric pressure. This requirement exacts an additional head loss for an impulse turbine not required by a reaction turbine. Pelton turbine may be mounted horizontally or vertically. The additional floor space required for the horizontal setting can be compensated with lower generator costs on single nozzle units in the lower capacity sizes. Vertical units require less floor space and are often used for large capacity multi nozzle units. Turgo Turbines The Turgo impulse turbine was invented and patented by Mr. Eric Crewdson, in 1919. Further improvements in 1936 and 1962, complete with patents, enabled the runner to operate faster and with a higher efficiency across a broad flow range. The Turgo impulse design is a high capacity, medium head, free jet impulse turbine. Instead of the jet striking the centre the bucket at a right angle and splitting into two the jet on the Turgo enters the runner at an acute angle, passes through the wheel, and discharges from the other side. The runner is designed to pass a large diameter jet of water relative to the mean diameter, thus giving the turbine a high specific speed for an impulse design. Being of a simple construction the Turgo design requires minimal maintenance. Bearings are designed to absorb worst case scenario loads, and run at runaway speed for a designed period of time, – even though the Turgo is designed to protect itself from an overspeed condition. Being an impulse technology and having deflectors installed, the Turgo can instantly protect the penstock from surge pressures during a loss of load condition. Turgo’s are particularly well suited, and popular, for energy recovery in water treatment plants and we have options available for use with potable water to specifically suit that application. Crossflow Turbines Crossflow water turbines are designed with many trough-shaped blades in a radial arrangement around a cylinder-shaped runner. They are tapered at the water inlet as well as the blades' ends to ensure that the water flows as smoothly as possible. Crossflow turbines have only two nozzles, which shoot water at a 45-degree angle to the blades, thus converting the force into kinetic energy. A controlling mechanism regulates the flow of the water out of the nozzle. These turbines are drum-shaped. The water in these turbines

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actually passes through the blades twice, once from the outside of the blades to the inside, and another time from the inside to the outside. Crossflow turbines can usually handle a greater amount of water flow than Pelton turbines. They are also sometimes referred to as Michell-Banki or Ossberger turbines.

Pelton turbine

Pelton runner A Crossflow turbine may best be described as an impulse turbine with partial air admission. Performance characteristics of this turbine are to an impulse turbine, and consist of a flat efficiency curve over a wide range of flow and head conditions. The wide range is accomplished by use of a guide vane at the entrance which directs the flow to a limited portion of the runner depending on the flow. This operation is similar to operation of multi jet impulse turbine. Peak efficiency of the Crossflow turbine is less than that of other turbine types previously discussed. Guaranteed maximum efficiency is 83 percent and expected peak efficiency is 85 percent. In some cases Crossflow turbines are equipped with a conical draft tube creating a pressure below atmosphere in the turbine chamber. Therefore the difference between the turbine centerline elevation and the tailwater is not lost to an Crossflow turbine as is the case for an impulse turbine. Air is admitted into the chamber through an adjustable air inlet valve used to control the pressure. Crossflow turbines are free from cavitation, but are susceptible to wear when excessive silt or sand particles are in the water. Runners are self-cleaning and, in general, maintenance is less complex than for the other types of turbines. Floor space requirements 21

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are more than for the other turbine types, but less complex structure is required and a saving cost might be realized.

Cross flow turbine- Photo Credit CINK

Five nozzles Pelton turbine

Cross flow turbine- Photo Credit CINK

Cross section of Pelton turbine

Turgo turbine- Photo Credit Glikes

Turgo turbine with two nozzles

Turgo turbine runner

Cross flow turbine runner 22

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Advantages of impulse turbines Impulse turbines are generally more suitable for micro-hydro applications compared with reaction turbines because they have the following advantages: • greater tolerance of sand and other particles in the water, • better access to working parts, • no pressure seals around the shaft, • easier to fabricate and maintain, • better part-flow efficiency. Disadvantages of the Propeller turbines • The major disadvantage of impulse turbines is that they are mostly unsuitable for lowhead sites because of their low specific speeds too great an increase in speed would be required of the transmission to enable coupling to a standard alternator. • The crossflow, Turgo and multi-jet Pelton are suitable at medium heads. Multi-jet Pelton turbines have the disadvantage of additional complexity due to the branched manifold and extra valves. • Main disadvantage of Cross flow turbine is lower efficiency compared to the reaction turbines at rated flow. Application range of reaction and impulse turbines

Typical range chart of turbines

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PART II Analysis of innovative types of turbines (Arcimedian screw turbine, VLH Turbine, Hoped pelton etc.) and their advantages as compared with conventional turbines Low head turbines Previous analyzes have shown that there is no adequate solution for hydropower plants with a very small head. Also most conventional turbine is not fish friendly. In a further study some innovative solutions are analyzed that can solve these problems. “Head”

refers to the elevation difference between the water levels upstream and downstream of a hydroelectric power plant. As with small hydro, there is not a standard accepted definition of low head hydro. In many jurisdictions, projects with a head of 1.5 to 5 m are considered to be low head. Generally, projects with a head under 1.5 or 2 m are not viable with traditional technology. New technologies are being developed to take advantage of these small water elevation changes, but they generally rely on the kinetic energy in the streamflow as opposed to the potential energy due to hydraulic head. As with larger hydropower developments, low head hydropower site layouts can vary dramatically from one to another. The development relies on the natural topography of the region in order to take advantage of differences in water elevation to provide head on the plant. This means that there can be tremendous variation in the civil works between sites. Caution must, therefore, be used when making generalizations about low head hydro sites; what applies to one site may not apply to another. However, some broad generalizations can be made. There are several advantages to low head hydro over other generation types. While not all will apply to a given site, some of the advantages include the following: • generally smaller impounded reservoir area than for large hydro sites. This reduces both the environmental impact of the projects and associated mitigation costs. • many low head hydro projects are ROR (run of river) hydro projects. This is thought to reduce both the environmental impact of the projects and the associated mitigation costs. • there are a large number of existing low head dams and hydraulic structures for flood control and water supply or irrigation. Many of these are suitable for development of low head hydro. This can significantly reduce the capital investment required to

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develop a hydro station and reduce environmental mitigation and monitoring costs due to reduced environmental impacts. • diversification of the energy supply is a goal of many governments. Encouraging the development of low head hydro sites can help to meet this goal. • development of low head hydro sites can also:  provide short-term economic benefits for local communities during construction  improve water access and navigation in headpondsenhance sport fishing opportunities in headponds  enhance access for resource users to previously inaccessible areas  benefit also including income and jobs for community members. There are also some disadvantages associated with low head hydro developments over other generation types. Again, not all will apply to a given site. Some potential disadvantages include the following: • Generally, small and low head hydro have limited or no control over when energy is available for generation. Small reservoirs mean that very little water can be stored to be used for generation to follow demand. ROR sites are even more limited; they must generate when water is available with no seasonal storage allowed. Depending on the Power Purchase Agreement, this inability to follow the load can reduce revenues because water cannot be stored for generation during peak demand periods. This in turn would make the project as a whole less economically viable. • The major disadvantage of low head hydro projects is the project economics. Many of the costs associated with developing a site do not scale down linearly from large to small projects; meaning that on a per megawatt basis, small projects can be far more expensive than large developments. The size and cost of water conveyance structures and electromechanical equipment required for a hydroelectric project depends largely on the flow rate. The larger electromechanical equipment also requires larger powerhouse facilities. This results in construction costs increasing exponentially as the head decreases, imparting a much larger cost per installed kilowatt to a low head hydro development. There are, however, some new technologies being developed to circumvent this problem. For example, if a turbine/generator set is placed directly in a stream, with little structural works required, the high cost of the large electromechanical works can be balanced by a reduced need for structural works. Turbine blades and hydraulic passages are optimized for certain velocities, therefore, for higher flows the turbine dimensions must increase. Not only is the relative cost of the 25

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turbine higher at low heads, but the generator cost is also higher. Because low head turbines are associated with high flows and low rotational speeds, the runaway speeds are about 3 times the rated speed, and runaway flows are 2 to 2.5 times the rated flow. Direct-driven low speed generators with large rotor diameters are subject to high centrifugal forces at such high runaway speeds, resulting in use of more material to resist the internal stress. This means that low head electromechanical equipment gives less power for a unit weight of material and, hence, that generators for low head schemes are generally more expensive. Another factor that can significantly affect power generation of low head schemes is the relatively high variation in head when the tailwater level rises during periods of high river flows. For a plant with 3 m of head, a rise of 1.5 m in tailwater level significantly reduces the head on the plant. This has a two-fold effect: • The head available for generation is reduced by 50%. • The minimum discharge is reduced due to a lack of driving head. Typically, these factors can combine to result in a 65% loss in power production. Each low head hydro scheme needs a detailed analysis to find an optimal and most economic solution keeping in view the hydrology, site topography, civil structures, the connected load or grid system, environmental factors, and constraints on transportation. Very low head hydropower technologies developed within the last few decades. Difficulties in conducting this review arise as the vast majority of sources of information are commercial, only publishing favorable or optimistic data and predictions. Whilst magazine articles and internet blogs discussing most of the technologies exist, they do not present independently verified data. Many novel hydropower machines exist ranging from patented ideas, operational prototypes, and in the case of just one machine at this time, a commercially established product. What is presented is a selection of the concepts which are considered to potentially be technically and economically viable, covering most of the approaches to exploiting very low head hydropower. Head, flow and efficiency values provided by the manufacturers are quoted but not verified. Claims regarding cost or environmental credentials are omitted. This review does not include large free stream kinetic energy converters designed for large scale tidal energy conversion, or ideas that are considered to be technically or economically unviable.

Archimedes Screw The Archimedes Screw is an ancient machine for pumping water from a lower level to a higher one. It is traditionally credited to Archimedes who lived between 287 B.C. and 212 26

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B.C. In recent years, the Archimedes Screw has been installed as a hydropower machine, instead lowering the water and generating power. This turbine consists of a rotating screw supported within a trough by bearings at each end, with a gearbox and generator situated in the control house. The water is lowered within cells which form between the blades and the trough. Analyses of the geometry and parameters including blade pitch have been conducted for the Archimedes Screw. This is mostly from the perspective of its utilisation as a pump, and its “performance” is based upon the volume of water lifted per rotation. Limited investigation into the efficiency of the Archimedes Screw as a pump has been conducted by initially assuming 100% efficiency from which losses, including leakage, sources of friction and turbulence are deducted. The only work investigating the Archimedes Screw operating as a hydropower machine is a recent Master's dissertation by Harkin (2007). This work was conducted to investigate the relationship between efficiency and angle of inclination. It was conducted using scale model testing, and secondly a mathematical analysis was conducted, resulting in the power output equation. It is important to note that it has been derived based on an analysis of hydrostatic pressure acting upon the Archimedes Screw. The equation has been derived as an initial attempt to estimate the power output of Archimedes Screws, however the author concludes that whilst the results are of the correct magnitude, the equation requires further development. To date, the Archimedes Screw is becoming the most commercially successful of the contemporary low head hydropower machines. Dozens of units have been installed in recent times, the main manufacturers being ANDRITZ Atro GmbH (formerly Ritz-Atro GmbH), REHART Group, GESS-CZ s.r.o., Mann Power Consulting Ltd… The maximum flow rate through an Archimedean screw is determined by the screw diameter. The smallest screws are just 1 metre diameter and can pass 250 litres / second, then they increase in 250 mm steps all of the way up to 5 metres in diameter with a maximum flow rate of around 14.5 m3/s. The 5 metre maximum is really based on practical delivery restrictions, and in many cases 3 metres is the maximum diameter that can be delivered to a site. If there is more flow available, multiple screws can be installed in parallel. A series of new Archimedean screw turbines are designed for low heads, in the range of 1 to 10m, with flow rates between 0.1 to 15m3/s and for inclination angle, between 22 and 40 degrees from the horizontal. For greater heads a cascade of two or more similar energy spiral rotors could give an efficient hydropower solution. The Archimedean spiral turbine rotors showed the efficiencies between 78 and 83%, making these an interesting alternative for turbines in low head hydropower applications. 27

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Some of manufacturers are claimed that efficiency can be up to 90% for the largest diameter machines. Similar to traditional waterwheels, the filling ratio of the cells is less than one. The machines on the market are currently run at constant speed, the filling ratio increasing with flow rate. The main parts of an Archimedean screw used as a hydro generator are shown below. The actual screw is below the upper bearing. The helical screw or ‘flights’ are made from rolled flat steel plate that is then welded to a central steel core. Most Archimedean screws have three flights, or three separate helices winding around the central core. Archimedean screws typically rotate at around 26 rpm, so the top of the screw connects to a gearbox to increase the rotational speed to between 750 and 1500 rpm to make it compatible with standard generators. Even though they rotate relatively slowly Archimedean screws can splash water around, though this is reduced significantly by the use of a splash guard. Archimedean screws are normally set at an angle of 22 degrees from horizontal, which is the optimum for the most cost-effective installations. There is scope to adjusting the angle slightly if the site requires it (to fit into a particular space for example).

Efficiency of Archimedes screw turbine-Photo credit Renewables first

The best Archimedean screws are variable-speed in operation, which means that the rotational speed of the screw can be increased or decreased depending on the flow rate available in the river. This is much better than having a fixed-speed screw and varying the flow rate through an automated sluice, which creates high head losses and impacts the overall system efficiency. Variable-speed screws are also quieter in operation and don’t suffer from “back slap” at the discharge-end of the screw.

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A typical efficiency curve for a good quality variable-speed Archimedean screw is shown on previous figure. This is the mechanical efficiency, so doesn’t include the gearbox, generator and inverter losses (these are approximately 15% on in total). It’s worth noting that there are some Archimedean screw suppliers that “over sell” the efficiency of screws, so be careful when comparing performance. A lower claimed efficiency may not be because a particular screw is inferior; it could just be that the supplier is more honest! Good quality Archimedean screws have a design life of 30 years, and this can be extended with a major overhaul which includes re-tipping the screw flights. A significant advantage of Archimedean screws is their debris tolerance. Due to the relatively large dimensions of the screw’s flights and slow rotational speed, relatively large debris can pass through unhindered and without damaging the screw and certainly all small debris such as leaves can pass through without any problems at all. This means that fine screens are not required at the intake to the screw and they can manage with course screens with 100 or 150 mm bar-spacing. This leads to relatively modest amounts of debris build-up on the course screen and removes the requirement for (expensive) automatic intake screen cleaners which are normally required on larger low-head hydropower systems. The low rotational speed and large flow-passage dimensions of Archimedean screws also allow fish to pass downstream through the screw in relative safety. Archimedean screws are often touted as “fish friendly” hydro turbines, which they undoubtedly are. In non-screw hydro systems this just means well designed intake screens and fish passes / by passes would be required. Note that if upstream fish passage is required at an Archimedean screw site, a fish pass will be required. The final advantage of the Archimedean Screw is simplified civil engineering works and foundations. Because screws don’t have draft tubes or discharge sumps, it means that the depth of any concrete works on the downstream-side of the screw is relatively shallow, which reduces construction costs. The civil works are also relatively simple, the main part being the load-bearing foundations underneath the upper and lower bearings. In softer ground conditions the load-bearing foundations can be piled.

Installed Archimedes turbine Efficiency of Archimedes screw turbine-Photo credit Andritz

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Typical installation of Archimedes screw turbine

• • • • • • • • •

• • • • •

Advantages of Archimedes screw Very cost-effective compared with turbines and water wheels Better efficiency with partial loads than comparable water sheels and turbines Simple to use, install and maintain No complex excavations Durable bearings thanks to low speed Robust, wear-resistant and reliable Fine screen not required; resistant to flotsam and compatible with fish Can be used with a head as low as 1 metre and flow as little as 0,1m³/s Screws can be coated with the highly wear-resistant "nanoseal" ceramic composite material Disadvantages of Archimedes screw Change of head during the year and the consequent changes in production Requires high flow rates Maintenance of lower bearing is difficult Low rpm require gearbox and this reduce the efficiency For high efficiency Archimedean screws need variable-speed in operation

VLH-Very Low Head Turbine The Very Low head Turbine is a novel form of Kaplan turbine that operates without complex inlet and outlet structures. It consists of a large diameter runner installed at 45 degrees to the vertical within a concrete shroud, extending from the channel bed up to the free water surface. The runner is directly connected to a submerged permanent magnet 30

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generator, and operates at variable speed to maximize its operational efficiency at a given flow. Trials of the first prototype turbine commenced in March 2007 and were presented at the 2008 Hidroenergia Conference. The grid connected and fully commissioned turbine consists of a 4.5m diameter runner, and operates with a nominal head, flow, and electrical power output of 2.5m, 22.5m3/s and 438kW respectively. It operates with a hydraulic efficiency of 85% at nominal flow, reducing to 50% at 20% of nominal flow. The stated intention of the manufacturer is to provide five standardized designs with runner diameters between 3.55m and 5.6m, suitable for head differences between 1.4m and 2.8m, and flow rates between 10m3/s and 30m3/s. The manufacturer claims that the Very Low Head Turbine would only become economical for installations above 100kW. The VLH is not a specific site designed turbine but a family of turbines. The VLH is an axial turbine with 8 blades. It's a double regulated turbine with Kaplan runner blades and its variable speed generator. The fixed distributor has 18 wicket gates with three flat bars inserted between each of them as a trash rack and structural stiffener. An automatic rotary trash rack cleaner is incorporated to the turbine. The position of the blade's axis has been calculated in order to get a closing force for every operating condition. Since it's a self-closing machine, there is no need to install a gate as a closing system. The VLH's bloc is slanted and can be positioned between 30° and 50° from vertical axis. This characteristic is sites dependent, as per head and downstream configuration. Fish friendliness characteristics of the VLH were design according to a biological study. Roche ltd., a consulting group in Québec, has been mandated to identify and quantified criteria to meet in order to make this turbine acceptable for relevant species and size of fish. Ten parameters have been identified. Eight of them are quantitative, the remaining two are qualitative.

VLH turbine-Photo credit MJ2 Technologies

VLH turbine efficiency

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Peripheral velocity of the runner has to be lower than 12 m/s: VLH will range from 4.5 m/s to 9.3 m/s, depending of head and operating conditions. Absolute pressure in the turbine has to be higher than 40% of upstream pressure: 94 kPa is the minimal absolute pressure in the turbine according to CFD simulations. Maximum pressure gradient has to be lower than 550 kPa/s: 80 kPa/s is the maximum value according to CFD simulations. Maximum velocity gradient through shear zones has to be less than 180m/s/m: 10 m/s/m is the maximum value according to CFD simulations. Maximum tip gap has to be 2 mm: the largest VLH (5.6 m) is expected to have 4.5 mm. Optimum turbine efficiency has to be better than 85%: the performance measured on model for the VLH was 86%.

Example of installation of VLH turbine-Photo credit Novatech-Lowatt turbines

Finally, considering spawning run concern, the absolute velocity at inlet and outlet of the turbine is species dependent. A range of 0 m/s to 3.4 m/s is recommended, higher velocities being reachable for salmonid only.

• • • • • • • •

Advantages of VLH turbine Fitted for Hydro Power sites with heads lower than 3.2 m Integrated Variable Speed Turbo Generator for Very Low Head sites Standard Range of product with 5 Turbine Runner Diameter Sizes from 3.5 up to 5.6 m diameter Simplified and cost saving Civil Work infrastructure Fish Friendly Turbine. Allows Profitable harnessing of very low head sites thanks to optimized reduced Civil Work Costs High Performances, high efficiency and production capacity thanks to variable speed generation, and high efficiency runner performances. Fish friendly turbine confirmed by tests with living salmons and eels, very low mortality of fishes migrating through the working turbine. 32

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• High Visual integration, submersed turbogenerator set. • Completely Silent and Vibration less functioning can be installed in urban areas

• • • •

Disadvantages of VLH turbine Change of head during the year and the consequent changes in production Requires high flow rates Requires very wide channel Special generator increase the price

The HydroEngineTM The hydroEngine™ combines the simplicity,low cost, and freedom from cavitation of impulse turbines in a compact, easy-to-install package comparable in size and power output to more expensive Kaplan-type turbines. The device is well suited to low head hydropower applications because, due to its unique mechanical configuration, it can pass large flows at low heads, while maintaining high shaft speeds. The hydroEngine™ is a unique 2-stage axial flow hydraulic machine optimized for low head large flow hydroelectric generation. Water, conveyed in a pipe or penstock, enters the hydroEngine™ and first encounters a cascade of fixed foils, called guide vanes, which direct flow into the first cascade of moving blades. After passing over the moving blades, the water flows through a second cascade of guide vanes, and finally, passes through a second cascade of moving blades. The guide vanes inside the hydroEngine™ adjust pitch automatically, allowing for direct control of flow rate, while keeping the machine’s efficiency high across a wide range of flows.

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Principle of work and operating range-photo credit Natel Energy, Inc

HydroEngines™ are currently available in several sizes, from 50-500 kW, operating at up to 6 meters of head. The SLH10 is rated to a maximum power of 50 kW at 6 meters of net head, passing 1.1 3 m /s. The SLH100 is rated to a maximum power of 500 kW at 6 meters of net head, passing 10.1 m3/s. To optimize profitability, projects should be designed such that installed SLH’s will operate near its maximum flow capacity, given the available net head. The hydroEngineTM maintains high efficiency across a wide range of operating flows. Internal guide vanes, similar to wicket gates, control the rate of flow while keeping efficiency high.

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Configuring the hydroEngine™ system-photo credit Natel Energy, Inc

To determine the efficiency curve of an SLH unit at a particular site, the figure of efficiency can be utilized. Peak hydraulic efficiency is about 78%. Using its internal guide vanes, the engine can modulate flow rates to values both greater than and less than the peak-efficiency flow rate (Q*). At certain heads, the machine is capable of operating at flow rates up to 120% the peak-efficiency flow rate. At these larger flow rates, the engine will produce more power (and generate more revenue), but the efficiency will be slightly lower than its peak value. The flow rate can also be reduced to a value as low as 20% of peak-efficiency flow before the efficiency falls below 60% of its peak value. The hydroEngineTM is delivered to the project site as a compact unit, fully assembled and factory tested. Commissioning time and cost are reduced as installation into the prepared powerhouse can be accomplished in a simple operation. In most gravity-head situations (run-of-river or in-dam), the following guidelines are recommended: Intake should be placed a minimum of 1 pipe diameter below the upper pool, to avoid ingestion of air. Draft tube outlet must be submerged at all times of expected operation. It is recommended to submerge the upper edge of the draft tube outlet a minimum of 12 inches, or 1/4 draft tube outlet height, below the lower pool surface. The hydroEngine™ allows for reduction in civil works cost because it is not at risk for cavitation. In most cases the hydroEngineTM can be situated above the lower pool, reducing the need for excavation. In addition, the hydroEngineTM can be placed in a small vault, with all control and electrical equipment on a higher floor, further reducing civil works costs.

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The SLH can be easily installed in low-pressure pipeline settings. For example, it can be integrated as an energy-recovery device in parallel with pressure-reducing valves. For the most efficient performance, the divergence angle on the engine’s outlet should not exceed 10 degrees.

Types of installation- photo credit Natel Energy, Inc

The hydroEngine™ can be integrated into any kind of low head hydropower setting, including in-conduit, run-of-river, in-dam, and directly in pipelines. Where possible, the run-of-river approach is favored, as it provides inherently more protection from debris, allows straightforward maintenance when necessary, and has less impact on the main water channel during construction. For any application except for in-pipe flows, it is critical to properly design the plant trashrack to screen debris, while minimizing maintenance and head losses. Placing the trashrack at an angle to the main stream flow, can allow most floating debris to passively bypass the plant. The trashrack can be additionally protected by an upstream float or boom. Drop structures and check-drop structures represent ideal opportunities for energy recovery. Power plants built on irrigation drops with Natel hydroEngines™ generate clean energy and profits with only small modifications to the existing infrastructure. Natel generally recommends the “run-of-river” configuration for irrigation drop-structure energy recovery projects. This type of design ensures that the normal function of the drop will never be compromised by power plant operation.

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PART III Economic appraisal and analysis of small hydropower plants (methods for determining the economic and financial feasibility of hydropower projects, presentation of basic tools for economic analysis, financial and cash flow analysis; methods for determining the costs and benefits). Energy Generation Economics An investment in a small hydropower scheme entails a certain number of expenses, extended over the project life, and procures some revenues also distributed over the same period. The expenses include a fixed component - the capital cost, insurance, taxes other than the income taxes, etc- and a variable component -operation and maintenance expenses. From an economic viewpoint, a hydropower plant differs from a conventional thermal plant; because its initial investment cost per kW is much higher but the operating costs are extremely low, since there is no need to pay for fuel. The economics of hydropower installations are a very complicated discipline into which many decades of research and knowledge are applied. Included in the conventional analysis of costs and revenues are detailed trends and estimates over time in costs, revenues, interest rates, flow duration curves and even government policy. At its most basic level, if electricity is sold to the distribution network, the revenue is a function of the number of Kilowatt hours (kWh) generated. The costs encountered come from many sources and are specific for each project and site. These include the costs of design, land acquisition, planning approval, construction, installation, connection to the national grid, abstraction licenses from the government agencies, maintenance and more. General observations made are that the specific cost, the investment cost per kW of installed capacity, increases with decreasing flow capacity and head as shown in Figure. The result is that using standard turbine technology; low head installations are not as favorable as high head installations. Installations below 3m head or 100kW are not attractive. These values are of course dependent on the price that can be earned per kWh and available grants, which are subject to change. It is also observed that the specific cost for low head sites can be reduced by using simpler technology and using as few units per site as possible. The economic feasibility of a small hydro development is provided by a favorable combination of site topography, hydrology, location and market conditions. Economic feasibility is the most important aspect influencing the development of a waterpower site. If a site is not economically justifiable, the political, environmental and social issues, which in many ways affect the cost, become moot points.

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Installation cost per kW of Capacity in function of head

Economic feasibility is based on three factors: the costs of construction and operation, the revenue for energy produced, and the required return on investment. The first two factors are highly variable, depending greatly on the location of the site. The third, the required return, depends on the developer. A government-owned utility will have different expectations than an independent power producer. With these influences on the economics of a waterpower development, every site is unique, and because of different expectations, one developer may find a site to be an encouraging investment while another will not. Because of this variability, this report cannot address the issue of whether any of the sites are viable or not; it is up to the waterpower developer to determine if a site meets financial objectives through detailed specific study of the potential revenue, engineering, construction, environmental, social, regulatory and financing aspects of the project. It is important to note that, for the waterpower sector specifically, cost and revenue estimations for projects must be premised on assessments of the risks and factors that can affect the ultimate project viability. Factors such as the length of approvals processes, and the availability of water for generation (hydrologic variability), are often out of the direct control of the developer. For the reasons stated above, in order to facilitate this market assessment of low head hydro, it is necessary to make only broad estimations for the potential range of costs.

Low Head Hydro Costs Civil Works A waterpower development requires civil and environmental works and electromechanical equipment as well as transmission and interconnection to the power grid. 38

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For greenfield sites, the costs of the civil, environmental, and transmission works can be anywhere from 50% to 70% of the of the total development costs. A variety of books and manuals have been published in recent years that explain the construction and environmental requirements of waterpower facilities for the nonspecialist, so details of these facilities will not be discussed in this report. The typical civil and environmental works for a greenfield waterpower site will include: • diversion dam or weir, with  embankment or concrete structure to divert water for power  spillway to release floodwaters  gates or valves to release in-stream flow needs  fish passage (upstream and downstream) • water passage for power, with  intake with trashrack and gate  excavated canal, underground tunnel and/or penstock  valves/gates at turbine entrance/exit, for maintenance  tailrace at exit • powerhouse for turbine, mechanical, and electrical equipment • environmental mitigation. Dam construction can be extremely costly. Generally with new dam construction, there is also a significant amount of work and cost involved with the mitigation of environmental impacts. These two costs render most greenfield sites unviable. Thus, it is far more economic to develop waterpower at an existing site that is close to existing transmission lines. There are a large number of existing sites that have low head hydro potential. These include sluice gates, irrigation canals, drinking water pressure release valves and municipal wastewater outfalls, as well as sites in numerous rivers with existing dams. For a waterpower development with this existing infrastructure, the major civil costs are typically reduced to just the water passage for power and the powerhouse, with minimal works for environmental mitigation. While still significant, these costs are generally very small when compared to the cost of new dam construction. By eliminating the need to construct a new dam and the environmental works that accompany it, many sites become more economically viable. Electromechanical The electromechanical equipment includes the turbine, generator, and control systems. It is well known that the costs for low head sites are relatively high because the required electromechanical equipment is large and the associated water passages are large. The cost of a Kaplan turbine for a design head of 6 m is approximately 84%higher than the cost for a design head of 30 m.

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Thus, in order to achieve the same return on investment under the same revenue conditions, a low head site must have either: • a significantly higher plant factor (more water for generation) than a site with intermediate head, or • the other costs (civil, etc) must be significantly reduced by installing at a existing dam. Transmission and Interconnection The cost of delivering the generated energy to the consumer can also be a major cost barrier to the development of a site. There are many sites that would be feasible if the site was located close to a demand center or grid connection. There are two reasons why long transmission distances become a concern: • The cost of building the transmission line, for distances less than 15 km can be approximately 10% of the development cost for a low head hydro site. • There is also a cost associated with lost energy, as described below. The present means of power transmission is by wires strung on poles or towers. The wires have resistance to the flow of electricity which is directly proportional to the length of the line and inversely proportional to the cross-sectional area of the wires. This resistance causes a loss of power, and therefore a loss of revenue. Thus, the decision on how much to spend on the capital cost for a transmission line is based on a cost-benefit analysis of the construction cost versus the loss of revenue. Less money spent on the transmission line (i.e., smaller wires) results in more loss of revenue, in fact the use of wires which are too small can result in a net present value of lost revenue exceeding the capital cost of the transmission line. The total cost (capital plus loss of revenue) gets very high for transmitting electricity over long distances. The capital costs and revenue losses of transmission apply equally to any type of power generation and are, therefore, a barrier to development of any power source that is not close to a demand or grid connection. Estimation of Low Head Hydro Costs As discussed in previous section, the civil works make up a significant portion of the overall project costs and can vary dramatically depending on the site. Developing a greenfield site is generally very expensive when compared to adding hydropower capacity to an existing dam. Many existing dams have existing infrastructure that can be utilized by the hydropower development, which can significantly reduce the cost of the civil work required to develop the site. For this reason, costs were developed separately for greenfield sites and existing dams. It is well known that turbine costs per kilowatt of installed capacity decrease as the size of a project increases. This holds true for other aspects of hydropower as well.

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The cost of civil works, including construction of the powerhouse, water passage and potentially dam construction, decrease on a per kilowatt basis as project sizes increase. Therefore, low head hydro costs were developed for projects that fall in specified ranges of installed capacity. The estimated cost ranges for greenfield sites and the average cost for developments at existing dams are listed in Table 1. Table 1: Estimated Capital Cost for Low Head and Small Hydro Development

Estimated Capital Cost Per Kilowatt of Installed Capacity

Low Head Hydro

Small Hydro

0 to 0.5 MW

0.5 to 2 MW

Greenfield Sites

€2,500 to €4,800

€2,200 to €4,500

Existing Dams

€2,300 to €4,500

€2,000 to €4,000

Greenfield Sites

€2,200 to €4,500

€2,000 to €4,000

Existing Dams

€2,000 to €4,000

€1,500 to €3,000

These costs include transmission for short distances and are based on close proximity to labour markets and material supplies, and easy site access. For comparison purposes, estimated capital costs for conventional small hydro developments are also included in Table 1. More recent figures from ESTIR, show investment costs specific to small hydro and scheme kW size (but does not relate to head). These costs have quite a range and are shown in.

These figures suggest that in the smaller kW range end investment costs can be as high as 6000 €/kW in extreme cases. However, as a cost estimate is essential for economic analysis, it is necessary as a second step, to make a preliminary design including the principal 41

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components of the scheme. Based on this design, budget prices for the materials can be obtained from suppliers. Such prices cannot be considered as firm prices until specifications and delivery dates have been provided. This will come later, during the actual design and procurement process. The approximate breakdown of the low head hydro project costs are listed in Table 2. These are highly dependent on project site and are included for illustration purposes only. As can be noted, all costs are larger for greenfield sites except for the electromechanical costs. These remain relatively constant regardless of the site. (The proportion of electromechanical cost is higher for existing sites because the overall project costs are lower, not because the absolute electromechanical costs are higher.) Table 2 Estimated Capital Cost Breakdown for Low Head Hydro Developments Civil

Electromechanical

Transmission

Engineering and Approvals

Greenfield Sites

45%

35%

8%

12%

Existing Dams

25%

53%

12%

10%

Regional cost variations for hydropower developments were also explored. However, the variability in hydropower development costs for most regions were very small when compared to the variability due to the uniqueness of each development.

Methods of economic evaluation While the payback period method is the easiest to calculate most accountants would prefer to look at the net present value and the internal rate of return. These methods take into consideration the greatest number of factors, and in particular, they are designed to allow for the time value of money. When comparing the investments of different projects the easiest method is to compare the ratio of the total investment to the power installed or the ratio of the total investment to the annual energy produced for each project. This criterion does not determine the profitability of a given scheme because the revenue is not taken into account and constitutes a first evaluation criterion. Static methods Payback method The payback method determines the number of years required for the invested capital to be offset by resulting benefits. The required number of years is termed the payback, recovery, or break-even period.

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The calculation is as follows: Payback period =

investment cos t net annual revenue

The measure is usually neglecting the opportunity cost of capital. The opportunity cost of capital is the return that could be earned by using resources for an alternative investment purpose rather than for the purpose at hand. Investment costs are usually defined as first costs (civil works, electrical and hydro mechanical equipment) and benefits are the resulting net yearly revenues expected from selling the electricity produced, after deducting the operation and maintenance costs, at constant value money. The payback ratio should not exceed 7 years if the small hydro project is to be considered profitable. However, the payback does not allow the selection from different technical solutions for the same installation or choosing among several projects that may be developed by the same promoter. In fact it does not consider cash flows beyond the payback period and thus does not measure the efficiency of the investment over its entire life. Under the payback method of analysis, projects or purchases with shorter payback periods rank higher than those with longer paybacks do. The theory is that projects with shorter paybacks are more liquid, and thus represent less of a risk. For the investor, when using this method is more advisable to accept projects that recover the investment and if there is a choice, select the project, which pays back soonest. This method is simple to use but it is attractive if liquidity is an issue but does not explicitly allow for the “time value of money” for investors. Return on investment method The return on investment (ROI) calculates average annual benefits, net of yearly costs, such as depreciation, as a percentage of the original book value of the investment. The calculation is as follows: = ROI

net annual revenue − depreciation ×100 investment cos t

For purposes of this formula, depreciation is calculated very simply, using the straightline method: Depreciation =

cos t − salvage value operational life

Using ROI can give you a quick estimate of the project's net profits, and can provide a basis for comparing several different projects. Under this method of analysis, returns for the 43

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project's entire useful life are considered (unlike the payback period method, which considers only the period that it takes to recoup the original investment). However, the ROI method uses income data rather than cash flow and it completely ignores the time value of money. To get around this problem, the net present value of the project, as well as its internal rate of return should be considered. Dynamic methods These methods of financial analysis take into account total costs and benefits over the life of the investment and the timing of cash flows. Net Present Value (NPV) method NPV is a method of ranking investment proposals. The net present value is equal to the present value of future returns, discounted at the marginal cost of capital, minus the present value of the cost of the investment. The difference between revenues and expenses, both discounted at a fixed, periodic interest rate, is the net present value (NPV) of the investment, and is summarized by the following steps: 1. Calculation of expected free cash flows (often per year) that result out of the investment 2. Subtract /discount for the cost of capital (an interest rate to adjust for time and risk) giving the Present Value 3. Subtract the initial investments giving the Net Present Value (NPV) Therefore, net present value is an amount that expresses how much value an investment will result in, in today’s monetary terms. Measuring all cash flows over time back towards the current point in present time does this. A project should only be considered if the NPV results in a positive amount. The formula for calculating NPV, assuming that the cash flows occur at equal time intervals and that the first cash flows occur at the end of the first period, and subsequent cash flow occurs at the ends of subsequent periods, is as follows: = NPV

i =n

∑ i =1

Ri − ( I i + Oi + M i )

(1 + r )

i

+ Vr

where: I i -investment in period i Ri -revenues in period i Oi -operating costs in period i M i -maintenance costs in period i Vr -residual value of the investment over its lifetime, where equipment lifetime exceeds the plant working life 44

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r -periodic discount rate, where the period is a quarter, the periodic rate is ¼ of the annual

rate n -number of lifetime periods e.g. years, quarters, months ets. The calculation is usually done for a period of thirty years, because due to the discounting techniques used in this method; both revenues and expenses become negligible after a larger number of years. Different projects may be classified in order of decreasing NPV. Projects where NPV is negative will be rejected, since that means their discounted benefits during the lifetime of the project are insufficient to cover the initial costs. Among projects with positive NPV, the best ones will be those with greater NPV. The NPV results are quite sensitive to the discount rate, and failure to select the appropriate rate may alter or even reverse the efficiency ranking of projects. Since changing the discount rate can change the outcome of the evaluation, the rate use should be considered carefully. For a private developer, the discount rate will be such that will allow him to choose between investing on a small hydro project or keep his saving in the bank. This discount rate, depending on the inflation rate, usually varies between 5% and 12%. The method does not distinguish between projects with high investment costs promising a certain profit, from another that produces the same profit but needs a lower investment, as both have the same NPV. Hence a project requiring €1 000 000 in present value and promises €1 100 000 profit shows the same NPV as another one with a € 100 000 investment and promises € 200 000 profit (both in present value). Both projects will show a € 100 000 NPV, but the first one requires an investment ten times higher than the second does. There has been some debate regarding the use of a constant discount rate when calculating the NPV. Recent economic theory suggests the use of a declining discount rate is more appropriate for longer-term projects – those with a life-span over thirty years and in particular infrastructure projects. Examples of these could be climate change prevention, construction of power plant and the investment in long-term infrastructure such as roads and railways. Taking Climate Change as an illustrative example, mitigation costs are incurred now with the benefits of reduced emissions only becoming apparent in the distant future. When using a constant discount rate these benefits are discounted to virtually zero providing little incentive, however the declining discount rate places a greater emphasis on the future benefits. In summary, correct use of a declining discount rate places greater emphasis on costs and benefits in the distant future. Investment opportunities with a stream of benefits accruing over a long project lifetime therefore appear more attractive.

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Benefit-Cost ratio The benefit-cost method compares the present value of the plant benefits and investment on a ratio basis. It compares the revenue flows with the expenses flow. Projects with a ratio of less than 1 are generally discarded. Mathematically the Rb/c is as follows: n Rn Rb / c =

∑ (1 + r )

n

0

n

I n + M n + On

∑ (1 + r )

n

0

where parameters are the same as stated in. Internal Rate of Return method The internal rate of return (IRR) method of analysing a major project allows consideration of the time value of money. Essentially, it determines the interest rate that is equivalent to the Euro returns expected from the project. Once the rate is known, it can be compared to the rates that could be earned by investing the money in other projects or investments. If the internal rate of return is less than the cost of borrowing used to fund your project, the project will clearly be a money-loser. However, usually a developer will insist that in order to be acceptable, a project must be expected to earn an IRR that is at least several percentage points higher than the cost of borrowing. This is to compensate for the risk, time, and trouble associated with the project. The criterion for selection between different alternatives is normally to choose the investment with the highest rate of return. A process of trial and error, whereby the net cash flow is computed for various discount rates until its value is reduced to zero, usually calculates the rate of the return. Electronic spreadsheets use a series of approximations to calculate the internal rate of return. The following examples illustrate how to apply the above-mentioned methods to a hypothetical small hydropower scheme: Mathematical formulations to estimate the cost trends of the most important elements of the plant The following mathematical equations are based on the hydroelectric minicentral´s manual published by the Institute for Energy Diversification (IDEA): = CA

(100h

2

+ 800 ) l

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C A -cost of weir (€) h - weir height (m) l - weir longitude (m)

= COT 9000Qe0.75 + 3500

COT -cost of intake (€) Qe - nominal flow rate (m3/s) Excavated rock:

= Cc Ground path:

= Cc

( 200Q

+ 10 ) l

( 70Q

+ 50 ) l

0.45 e

0.55 e

Cc -cost of channel (€) Qe - nominal flow rate (m3/s) l - length of channel (m)

= Ccc 11000Qe0.945 + 2500 Cc -cost of forebay (€) Qe - nominal flow rate (m3/s) = CTf

( aQ

b e

+ c)l

Cc -cost of penstock (€) Qe - nominal flow rate (m3/s) a, b, c - approximation coefficients l - length of penstock (m)

a b c

Hu<100m 400 0.45 140

Hu=100m 350 0.53 200

Hu=200m 350 0.65 220

Hu=500m 550 0.75 220

Hu=800m 800 0.78 220

CEC = 100000 H u0.046Qe0.25

CEC -cost of central building (€) H u - net head (m) Qe - nominal flow rate (m3/s) 47

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CT = aH ubQec

CT -cost of turbine (€) H u - net head (m) Qe - nominal flow rate (m3/s) a, b, c - coefficients for typical turbines

a b c

Pelton 130000 0.25 0.45

Francis 100000 0.2 0.5

Kaplan 100000 0.2 0.4

Cost of cross flow turbine CTO = (160H u1.6 + 60000 ) Qe0.8 + 35000

Cost of cross flow turbine includes asynchronous generator and the multiplier gearbox Synchronous generator: −P   CG 500000 1 − e 6500  =  

Asynchronous generator: −P   = CG 400000 1 − e 6500   

CG -cost of generator (€) P - nominal power of generator (kW) Transformer: −P   = 200000 1 − e 6000  + 2500 CTrafo  

CTrafo -cost of transformer (€) P - nominal power of transformer (kW) Electrical system:

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  1   CSE 200000 1 + = P     21−    1 + e  3600  

CSE -cost of general electrical system (€) P - total power (kW) Power line:

C = L

( ax + b ) l

CL -cost of power line (€) x - degree of terrain difficulty l - length of power line (km) Power line a b

10kV 1200 12000

35kV 1400 13000

100kV 1700 16000

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PART IV Environmental influences of small hydropower plants (for all small hydropower developments with special emphasize on Archimedian screw schemes). Social issues linked with small hydropower plants From a scientific perspective, environmental studies are complex because of the many interactions in the ecosystem. When human societies interact with the environment, the complexity increases because different groups attach different values to environmental costs and benefits. Like all extraction of natural resources, the harnessing of rivers affects the natural and social environment. Some of the impacts may be regarded as positive; others are negative and severe. Some impacts are immediate, whereas others are lingering, perhaps appearing after several years. The important question, however, is the severity of the negative impacts and how these can be reduced or mitigated. The aspect of ecological succession is also of great interest. Through history, the ecosystems have changed, as a result of sudden disasters or more gradual adjustments to the prevailing weather conditions. Any change in the physico-chemical conditions seems to trigger processes that establish a new ecological equilibrium that matches the new ambient situation. Under natural conditions environmental change is probably more common than constancy. Ecological winners and losers, therefore, are found in natural systems as well as those created by man. Even if the "fuel" of a hydropower project is water and as such renewable, the projects are often quite controversial since the construction and operation directly influences the river systems, whereby the adverse impacts become direct and visible. The benefits, like avoidance of polluting emissions that would have been the unavoidable outcome of other electricity generating options is, however, less easily observed. Access to water and water resources management will be a very important environmental and social global challenge in the new century, because water is unevenly distributed and there are regional deficits. Dam construction and transfer of rivers and water abstraction are elements in most water management systems. The lessons learned from past hydropower projects may be of great value in future water resources management systems. If a regional water resources master plan or management system is available, then the development of hydropower resources could also contribute to an improved water supply for other uses.

Sources of environmental and social impacts Main physical impacts: Air and water temperature, drainage from construction work, flood frequency, flow regime, groundwater level, heavy metals, oxygen content, sedimentation, transport of elements and matter, and turbidity or suspended solids. 50

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Main biological impacts: Fauna (aquatic and terrestrial - birds, insects, mammals), fish communities, fish migration, fisheries (fish stocking), flora (aquatic and terrestrial), mercury (in fish), and red-listed species (both aquatic and terrestrial). Main socio-economic impacts: Access roads, agriculture, fisheries (fish stocking), forestry, indigenous people, landscape appreciation, recreational areas, resettlement, rock tips, schools, social intrusion, tourism employment, transportation, and water supply. Establishment of reservoirs The main parameters deciding the impacts related to the establishment of a reservoir are the reservoir level, the size and depth of the reservoir, the water-level fluctuations (especially the drawdown zone, the hydrological management regime, and optimum compensation flows, including what is commonly referred to as minimum flows), water turnover time, etc. These parameters will vary greatly in significance related to the climatic and geographical zone in which the reservoir is established. For example erosion, sedimentation and siltation usually be very important aspects in many areas. Social issues may become very important when large reservoirs are established in densely populated areas where the land areas to be flooded have been extensively used for agriculture, grazing, or human settlements with various infrastructures, or where the areas have other cultural, scientific, aesthetic or emotional values attached to them. In addition to the lost infrastructure and cultural values, this will often involve involuntary resettlement and disruptions of social networks. On the other hand, a reservoir might also create new habitats for different kinds of game and fish, recreational potential for fishing, tourism and so on. Other potential positive spin-offs, in addition to the extra supplies of electricity, are related to the possible combination of hydropower development with irrigation schemes, water supply, improved navigational possibilities and flood control. Impounding of reservoirs usually results in a reduction in the downstream water flow for a few months and in some cases up to several years depending on the hydrology and the size of the reservoir. The increase in water level after impounding is usually one of the greatest impacts of a hydropower project as it involves flooding of land and a total change of the ecosystem. This will mainly affect the aquatic life in general, and migrating fish in particular, but also the terrestrial life in the surrounding land areas to be impounded and the ecotone between the terrestrial areas and the running river. Hydraulic management Hydraulic management modifies the flow pattern downstream and could be very important for the local ecosystem as well as for the local perceptions of the project. Hydraulic management related to minimum flows, optimum compensation flows, daily fluctuations and periods of flooding are usually the most important. 51

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Usually the hydraulic management will have a profound impact on the ecological characteristics of fauna and flora in the reservoir area as well as downstream, particularly in the reservoir and along the riverbanks. Other human activities can also be directly affected by changes in the downstream water regime, like reductions in the water flow of waterfalls and rapids, security risks for riparian owners and users, restrictions in traditional activities for the local population, limited access to water, etc. Furthermore, the change in hydrology and in sedimentation will often have a profound impact on the rich estuary ecosystems where fresh water meets the sea, including impacts on areas with fish spawning, sea fisheries, fish, clam and shrimp farming, and agriculture on estuarine flood plains. Hydroelectric development involves major modifications of the environment. However, some of these modifications are reversible. The negative effects can be minimized with well-adapted projects and suitable site selections and could make hydroelectricity more attractive as compared to other means of electricity production. Some types of hydropower structures are more suitable for a given environment than others, and it is therefore important that environmental considerations are incorporated from the very start of the planning phase. Today, certain mitigation measures are known to be effective in reducing various impacts on the environment and on social issues. There are also various ways of compensating for impacts that are not possible to mitigate, or impacts that can be mitigated only to a limited degree. Some of the main mitigation and compensation measures related to physical impacts of hydropower development may be summarised as follows: Climatic conditions Parameters like temperature, wind, precipitation, humidity, fog and greenhouse gas emissions could have effects on the local climate. Some of the changes in such parameters arising as a result of a hydropower project are often difficult to distinguish from annual climatic fluctuations. However, some of the induced modifications to the local climate may be permanent. In our climate area, extensive deforestation as a direct or indirect effect of hydropower development may result in the local climate to become less humid, also impacting the level of precipitation and e.g. agricultural activities. Generally, the most effective mitigation measures in relation to climatic change involve a careful evaluation of the relevant parameters before site selection and technical solutions are decided upon. Hydrology A major part of the more serious impacts connected to hydropower development, regardless of geographical area or climatic zone, is related to changes in the natural hydrology of the actual watershed and watercourses. Mitigation measures can be 52

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implemented to ameliorate negative effects on water quality as well as water quantity. Key words in mitigation measures related to impacts on water quantity include the selection of an appropriate type of regulation, adequate minimum flows (”optimum compensation flows”), reservoir management procedures, etc Regarding water quality, main mitigation efforts might include design measures for keeping contaminants away from watercourses, aeration, provisions of weirs or rapids, flushing programmes, reservoir intake position and depth, removal of vegetation and soils in impounded areas, implementation of an effective sewage treatment. Sedimentation Dams will usually retain sediments, resulting in various problems like dam siltation, increased downstream erosion, and profound changes in the physical, chemical and biological characteristics of the estuary. This might indirectly affect groundwater levels and the whole biotic environment of the watershed, with subsequent effects on agriculture and fisheries. Common mitigation measures include flood management, sand traps and silt fences, flushing programs, upstream reservoirs and cofferdams, intake design to enable sediment bypass, controlled dredging, physical bank stabilization, revegetation of erosive slopes, watershed land use programs to prevent reservoir sedimentation, etc.

Biological impacts - mitigation and compensation measures With respect to hydroelectric power projects, the main potential sources of impacts on biological parameters are considered to be: • Loss or creation of terrestrial and aquatic habitats • Modification of water quality • Regulation of streamflow downstream from dams • Flood control • Obstacle of a dam to the migration of fish • Introduction and dispersal of species Lots of various mitigation and compensation measures have been developed to ameliorate negative effects on the biotic life. Some important key-words here will include fish ladders and fishways or other by-pass facilities to aid migration, technical designs to minimize aquatic life mortality, minimum flows during critical periods for aquatic life, water level management to mitigate effects of drawdown, protection or reestablishment or improvement of habitats for endangered species, scheduling of work which disturbs wildlife only during non-sensitive time periods, development of forest, wildlife and watershed management and monitoring plans, revegetation programmes, etc.

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Socio-economic impacts - mitigation and compensation measures The socio-economic impacts could be addressed under three categories: Land use, economic impacts and social impacts. Land use Changes to land use are generally a consequence of submergence of large areas, permanent modifications to upstream and downstream water levels and water flows, and other types of induced development associated with regulation flows and the creation of large reservoirs. Important mitigation measures here include the establishment of local or regional development plans as well as resource management and monitoring programmes (also to avoid or reduce land use conflicts) emergency preparedness and warning procedures on sudden flow variations, establishment of alternative areas for agriculture and fisheries for local people, clean water supply, irrigation, planning to minimise farm, forest and other resources loss, maximizing recovery of valuable resources prior to inundation, etc. Economic impacts Economic impacts may both come as direct effects of induced land use changes, or indirectly by the availability of electricity supply or by altered infrastructure in the area. In a strict economic sense, the area will have no net economic development unless the project’s direct and indirect benefits are larger than their direct and indirect costs, including environmental and social benefits and costs. Important mitigation measures within this area include various job opportunities in the construction phase as well as in the operation phase, including indirect spin-offs as a result of changed infrastructure and availability of electricity, establishment of various new job opportunities, relevant training programmes, improvement of municipal infrastructure (medical, social, communication), promotion of tourism, etc. Social impacts The majority of social impacts caused by hydropower projects are often related to forced resettlement, disruption of social infrastructure and networks, and changes in job opportunities. Impacts on aesthetic, cultural, archaeological or scientific values might also be included here. Important mitigation measures within this area include establishment of local or regional development funds and programmes, careful planning of resettlement if is needed, establishment of acceptable procedures to solve social problems, monetary compensation 54

BULGARIA – SERBIA IPA CROSS-BORDER PROGRAMME 2007CB16IPO006 2011-2-229 Reclaiming Rivers for Implementation of Vital and Environment – Friendly Renewable Energy Source - RIVERS

or compensations in kind, re-establishment of reserved land or provisions of alternatives, protection or relocation of cultural heritage features, protection of areas with important landscape features, etc. Recommendations The following recommendations should be generally implemented in hydropower development. • • • • • • • • • • • • • • • • • • • • • •

Award work and supply contracts to local companies Minimum flows, optimum compensation flows Local recreational and community facilities Sufficient financial compensation (agriculture land, forestry land etc.) Traffic regulation for construction vehicles Train and hire local workers for project work Water supply for irrigation Erosion prevention and control Fish protection (creation of spawning areas) General fish population management Long term data sets for fish population and detailed knowledge of fish biology Good communication/co-operation with the local authorities Minimizing soil contamination and loss of soil due to inundation Removing of floating peat and debris Funds to society to "repair"/minimise impacts on natural resources Landscape adjustment by clearing of shorelines Agreements between the corporation and the indigenous people to protect their way of life Protecting or mitigating changes to aboriginal land use, cultural heritage, archaeological resources Cooperation with local and national authorities regarding historical monuments etc Protection, replacement and control of vegetation (cleaning of construction areas, landscape adjustment, revegetation, use of selected seeds) Sedimentation prevention and control Using local people in the construction work as much as possible

Bearing in mind previous facts the turbine considered for the small weirs explored in this report is the Archimedean screw. There are several reasons for this choice... • The Archimedean Screw is designated as ‘fish friendly’. It, and the Waterwheel, are accepted by the Environment Agency as being the least harmful to fish of all the turbine types. Scientific evidence (Fish Monitoring and Live Fish Trials Phase 1, Sept 55

BULGARIA – SERBIA IPA CROSS-BORDER PROGRAMME 2007CB16IPO006 2011-2-229 Reclaiming Rivers for Implementation of Vital and Environment – Friendly Renewable Energy Source - RIVERS

2007 and Phase 2, April 2008, Fishtek Consulting, monitored by the Environment Agency) shows the safe passage of fish down the screw whilst it is operational. The Archimedean Screw and the Waterwheel operate at normal atmospheric pressure whilst other turbines – for instance the Kaplan – operate by forcing water at high pressure into the system. In addition, the screw turns at a low velocity of approx 28 rpm. This, together with the operation of the turbine under normal atmospheric pressure, enables the safe passage of fish through the system. • There are few moving parts, so less parts to get damaged and go wrong. Water flows from the top and out from the bottom, transferring its potential energy to the screw by rotating it at a constant velocity. The top of the screw is coupled to a gearbox which drives a generator via a belt. A quite simple building will need to be constructed. • Clearly, by taking a given volume of water out of a river, there will be an impact upon the natural ecology of the river bed. A large depletion distance (distance between where the water leaves a river to enter a hydro system and where the water goes back into the river) may therefore compromise the ecology of the river bed. The smaller the depleted distance, the less impact there will be upon the fish and wildlife ecology. The Archimedean screw has the lowest depletion rate because it is placed alongside a river weir – the water enters the system from just above the weir and returns to the river just below the weir. Whilst more traditional turbines such as the Kaplan can also be placed alongside the weir, the Kaplan does not have the advantage of being considered ‘fish friendly’. • Visibility – because the Archimedean Screw is visible, there is an educational benefit to this type of turbine. It can be readily viewed whilst in operation and the linkage between the turning motion and the generation of electricity is immediately obvious. The educational aspect of the Archimedean screw ought not to be underestimated. The Kaplan system is inside the power house and cannot therefore be viewed.

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BULGARIA – SERBIA IPA CROSS-BORDER PROGRAMME 2007CB16IPO006 2011-2-229 Reclaiming Rivers for Implementation of Vital and Environment – Friendly Renewable Energy Source - RIVERS

Literature 1. C.C. Warnick, Hydropower Engineering, ISBN 0-13/448498-3, Prentice-Hall, 1984. 2. Chris Rorres, THE TURN OF THE SCREW: OPTIMAL DESIGN OF AN ARCHIMEDES SCREW, Journal of Hydraulic Engineering, Vol. 126, No. 1, January, 2000. 3. Snezhana Bozhinova, Veronika Hecht, Dimitar Kisliakov , Gerald Muller, Silke Schneiderm Energy Hydropower converters with head differences below 2.5m, http://dx.doi.org/10.1680/ener.11.00037 4. Internet sources: http://www.andritz.com/oi-andritz-atro-gmbh http://www.spaansbabcock.com/products_en_applications/screw_generators.aspx http://www.renewablesfirst.co.uk/hydro-learning-centre/archimedean-screw/ www.vlh-turbine.com www.natelenergy.com/

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