EFFICIENCY ANALYSES FOR SMALL HYDRO POWER PLANT WITH FRANCIS TURBINE

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1 EFFICIENCY ANALYSES FOR SMALL HYDRO POWER PLANT WITH FRANCIS TURBINE Xhevat Berisha 1, Bukurije Hoxha 2 and Drilon Meha 3 1,2,3 Department of Thermotechnics and Renewable Energy, Faculty of Mechanical Engineering Pristina, Kosovo Abstract The focus of this paper describes the designing procedure of Small hydro power plant implemented in Lepenci River, Kosovo. For normal operation of the Small hydro power plant, there must be done measurements of the river basin annually water flow, hydraulic net head of water, to calculate sustainability of water flow, flow duration curve, flow rate, configuration units depending on flow rate etc. The choice of the turbine was made depending on head and flow rate of water from which has resulted in the installation of Francis turbines that have fit better those conditions. The head losses in penstock are estimated to be in the percentage (%) of the hydraulic gross head, depending on the length of the penstock, its diameter, sustainability of flow rate and its velocity. Since the water flow, it's not stable enough for production 10 MW electricity from one turbine, in this case, are proposed to installing three Francis turbines. In this case, one Francis turbine will take part with 13.33%, flow rate 1.2 m 3 /s and power 1.34 MW, and two Francis turbines with 43.33%, flow rate 3.9 m 3 /s and power 4.36 MW for each. This paper aims to determine the best efficiency of Small hydro power plant SHPP Lepenci with three turbines during operation depending on rated discharge per unit. Keywords Francis turbine, efficiency, biodiversity, water flow, head, power, sustainability I. INTRODUCTION Hydro power as a primary renewable energy source is extracted or captured directly from the environment and is converted into other useful secondary forms of energy, usually as electrical energy, to promote the normal operation of different activities. Secondary energy sources can be used, for demands in transportation, infrastructure, residential, industrial and commercial sectors, education, healthcare, etc. Hydro power plants tend to achieve longer economic lives (50 years or longer) than fuel-fired power production. The sale of hydroelectricity may cover the construction costs after 5-8 years of full operation [1]. The water streaming down from higher to lower levels consists of potential energy in itself because of its altitude which is converted into kinetic energy while flowing downhill. The gravitational force near the Earth s surface varies very little with the height z (m) and is equal to the mass m (kg) multiplied by the gravitational acceleration, g (m/s 2 ). As much higher the height z (m) to be more potential energy is produced, respectively more electricity in our case. Hydro power is a renewable source of energy because it is renewed continuously in a natural way. It eliminates the use of fossil fuels and hence the carbon dioxide emission. It is called Small hydro power plant (ab. SHPP) because its capacity is up to 10 MW [2]. Small hydro power plants can generate between 100 kw to 10 MW power when they installed across rivers and streams. Moreover, energy from the water is available day and night, so it has advantages over other renewable energy sources. Other benefits when evaluating cost factors, hydro power shows the comparison of the lowest cost of electricity across all the dominant fossil fuel and renewable energy sources. Figure 1 shows the relatively low price of hydro regarding maintenance, operations, and fuel costs when compared with other electricity sources and across a full project lifetime. DOI: /IJMTER ARBMD 155

2 Figure 1. The comparison of low cost of electricity for various power and energy efficiency options, /kwh Electrical power produced in a small hydro power plant generated when water flow hit a wheel or turbine to convert potential energy of water into mechanical energy of rotation, Figure 2. Figure 2. Schematic diagram of small hydro power plant The interaction between the fluid and runner blades results in a torque applied to the runner. The runner is connected to the driving shaft to drive an electric generator [3], [4]. A study, which investigates the designing and construction of small hydro power plant in Kosovo, was analyzed by [4]. Within the aim of that paper, detailed design and install of a small hydro power plant were done, at a recreational center in the village Sllakovc, Kosovo, financed by the European Union. That small hydro power plant consisted of water intake, penstock, hydro turbine, control system, and powerhouse. The synchronous generator was connected directly to the turbine to convert mechanical energy into electrical energy. Similar studies, which analyzed construction and operation of small and micro hydro power plants, were performed by [5], [6], [7] and [8]. The first Small hydro power plant in Kosovo was built in the town of Prizren in 1929 with an output power of 160 kw. Another hydro power plant was installed, in Mitrovica on the Iber River in 1930 [9]. II. HYDROLOGICAL ANALYSIS OF THE LEPENCI RIVER 2.1. Hydrological data for river basin The Lepenci river basin is located, in the south-eastern location of Kosovo. The surface of this river basin up to the connection with Vardar river near Skopje is F = km², and the length is L = 85.0 km. In the territory of Kosovo, the river basin has a surface of F = 622 km2 at the Hani All rights Reserved 156

3 Elezit station and a length of L = 52 km. The main branch of the Lepenci River is the Nerodima River which has its source in the Nerodima Mountains. The Nerodima river has a basin area of F = 224 km2 and a length of L = 32 km, and it discharges on average 1.0 m3/s to Lepenci River. The main contributor to the Lepenci River is the snow and the mixed snow-rain regime, called a nivopluvial regime of the alpine type [10]. Almost in all cases, the annual maximum flow is observed in the spring period, mainly April May, but even June has considerable streams. Thus the mountainous region of Lepenci has a typical snow regime. In this area, during the period April-June passes almost 50% of the annual flow. The effect of the snow is observed even during the warm time of the year, August-September when the precipitation is nearly absent. The Lepenci River has a flow of 2-3 m³/s as a result of underground water. To make possible construction of SHPP Lepenci the flow rate measurements were calculated based on an analogy with the measured data at the Hani I Elezit station. This data was available for the period from 1975 up to After the calculations, it was created a time series for 15 years. Based on this data have been calculated the mean monthly flows for Hani I Elezit station, which, are presented in Table 1. Table 1. Monthly flows, SPHH Lepenci at Hani I Elezit Q, m3/s Year Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. Nov. Dec. Sum Average Minimum Maximum Source: Kosovo Environmental Protection Agency, Kosovo Hydro-Meteorological Institute Flow series and flow duration curve The SHPP Lepenci is located on the Lepenci River between the villages Vica to the north and Drajkovce to the south at the elevation 710 m above sea level. The basin area up to the axis of the intake is km². Based on our calculations the module for this input should be taken as 22 l/s/km², and as a result, the mean flow for the intake of SHPP Lepenci is 4.76 m³/s. Also, the mean monthly flows at Hani I Elezit have transformed through a coefficient, which is equal to 0.449, to the mean flow of Lepenci River. The results of calculations are presented in Figure 3. Since this study deals with the calculation of various parameters for the designing of small hydro power plants, it is of great importance to analysis the flow duration curve of daily flows, which expresses the frequency of occurrence of a specific discharge during the year. The mean flow gives an idea of stream s power potential. Flow duration curve can be produced at different times as well as for the particular time of the year. In Figure 4, are plotted flow duration curves for average flow 4.76 m³/s for the year with a probability of exceedance 25%, 50%, and 75%. This presents the flow duration curve available for generation of the SHPP Lepenci. The average flow rate value is estimated to be 4.76 m³/s, and the flow with a 50 % probability of exceedance is 3.47 m³/s. As for the plant rated flow of 10.0 m³/s, the probability of exceedance is 10.0 %. Similar conclusions can be drawn, for other flow rate percentages. Figure 3. Monthly flows for SHPP All rights Reserved 157

4 [11]: where: Figure 4. Flow duration curves for daily flows, SHPP Lepenci Mathematically, the flow series available for the project generation can be written as follows QGeneration GWater Intake QBiodiversity (1) Q Generation (m 3 /s) Daily flow available for generation, Q Water Intake (m 3 /s) Daily flow at Lepenci water intake, Q Biodiversity = 0.3 m 3 /s maintained all year at the weir site Flow requirements for biodiversity In order, to protect the biodiversity in 8 km river stretch where the natural flows will be, reduced, a minimum In-stream Flow Requirement (IFR) is to be, maintained. The method is based on hydrological values and refers to the minimum mean flow (MNQ) in the river. The reserved flow calculated when applying these techniques is 20% of MNQ. The IFR for SHPP Lepenci is set 20%, of the minimum annual mean discharge. From the hydrological data provided at water intake at Lepenci has resulted that IFR value is 0.3 m3/s for 20% of 1.48 m³/s. This flow must be spilt in the river at all times at the weir site Estimation of maximum flows Regarding the maximum flows with different probabilities at the intake of SHPP Lepenci has also been used the analogy with the maximum water flows for Lepenci River at Hani I Elezit station. To convert the maximum flows to the ones at the intake axis has been used the following equation [12]: where: Q 1 1 Q2 A2 A (2) Q 1 [m 3 /s] - calculated flow Q 2 [m 3 /s] - flow of the available data A 1 [m 2 ] - basin surface at the intake of SHPP Lepenci A 2 [m 2 ] - basin surface at Hani I Elezit station η = 0.8 for A<100 km² and η = 0.5 for A>100 All rights Reserved 158

5 Table 2. Maximum flows with different probabilities Q (m 3 /s), SHPP Lepenci Axis Area (km 2 Return period in years ) Hani I Elezit SHPP Lepenci Source: Kosovo Environmental Protection Agency, Kosovo Hydro-Meteorological Institute III. TECHNICAL ANALYSIS OF THE SHHP LEPENCI 3.1. Evaluation of the net head Head losses were evaluated using the hydraulic configuration as shown in the drawings. The evaluation included all frictional and singular losses from the intake entrance (including the trash rack) up to the draft tube exits, including the butterfly valve at the entrance of the units Local and pressure losses The pressure losses, which occur due to change speed, direction, the quantity of fluid, the system piping components (except straight tubes) are called local pressure losses and are included in the equation by the coefficient k l [12]: 2 w Hl ki (3) 2g where: w (m/s) - velocity of fluid flow; g (m/s 2 ) - acceleration of gravity, and k l (-) - the coefficient of local pressure losses. The numerical values of the losses coefficient for various components (elbows, valves, inlet, and outlet) are experimentally determined Longitudinal pressure losses Longitudinal losses are due to the friction of the fluid flow with the inner walls of penstock and their analytical description is made through the equation given by Darcy-Weisbach: 2 l w H f f (4) d 2g where: f (-) - is the coefficient of friction between the wall of inner penstock and the flowing fluid, d (m) - the diameter of the penstock, l (m) - the length of the penstock. The total pressure energy losses that arise in the penstock are written as follow: H H H los l f (5) The coefficient of friction f (-) The non-dimensional number of Reynolds is used to determine the fluid flow regime during tubes, hence by Streeter, V. L., Wylie, E. B. [12]: w d R e (6) where: ρ (kg/m 3 ) - fluid density, µ (Pa s) - dynamic viscosity of the fluid. For laminar flow, the number of Reynolds is Re 2400 the coefficient of friction is not dependent on the roughness of the tube, but only by the Reynolds All rights Reserved 159

6 64 f (7) Re For the turbulent flow, the coefficient of friction is determined by the empirical equation given by Colebrook [12]: 1 / d log (8) f 3.7 Re f - is the characteristic of the roughness of the inner walls of the penstock. For smooth tubes, the coefficient of friction is determined according to Blasius equation [12]: f (turbulent, =0) (9) 0.25 R e The average water level at the forebay is m. The elevation of the water level at the weir in tailrace is m. Therefore, the hydraulic gross head is m for the rated flow of 10.0 m³/s. The total head losses are estimated, to 20.3 m, and the derived net head is therefore m or about 14.6 % of the whole available gross head of m (707.9 m m).the length of the penstock is 7.82 km, with d in = 2100 mm and d out = 2200 mm. It consists of glass fibers and brings water to the houses where the turbines are installed. Figure 5. Head loss curve estimated for various flows Near to this house, the penstock is divided into three tubes, two with a diameter of d T3.9 = 1400 mm and one with a diameter of d T1.2 = 800 mm respectively. As a result, hydraulic head loss calculations and thus, the hydraulic net head available for energy generation, vary according to the amount of discharge directed towards the turbines. The hydraulic losses for various flows from the forebay up to the draft tube exit at the powerhouse are shown by a curve (Figure 5). This curve was input into the energy production model Calculation of power output All hydro power plants depend on water flow rate and net head of water. These two parameters determine the power that can be captured by a hydro turbine. Other parameters have little effect on the overall production of power from the hydro power plant. The output power generation from the hydro turbine (P out ), can be estimated by the following expression [12]: P ρ g H Q η η (10) out n t g where are: P out [W] - power output ρ [kg/m 3 ] - water density g [m/s 2 ] - gravity acceleration constant H n (m) - net downward water height, t (%) - the maximum efficiency of hydro turbine ( t = 0.93), g (%) - generator efficiency (g = All rights Reserved 160

7 3.3. Calculation of the specific speed The specific speed is a dimensionless parameter associated with a given group of turbines at maximum efficiency with known values of angular velocity ω, head net H, and power output P out. It constitutes a reliable criterion for selection of turbine type and dimension. The specific speed is given by equation: T P out // g H 5 4 n (11) where, ω [rad/s] - angular velocity. A preliminary selection of appropriate type of turbine for given installation is based on specific speed ω T. For presented analysis, the specific speed was found to be ω T = 1.5 and this range determines the selection of Francis turbine. Table 3. Specific speed ω T given from different authors Author Pelton Francis Mixed flow Axial flow Potter (1977) Douglas (1995) also higher - Shames (1992) also higher - Another equation, which is used for calculation of the specific speed of turbine, is given with expression: N P N s T 5 / 4 out H n (12) where is: N [rpm] - turbine s rotation speed H n [m] - net head P out [kw] - power output. From the above-mentioned equation, the specific speeds of different turbines based on the book of Fluid Mechanics are given by Arora (2005). Table 4. Turbine selection characteristics Nor. Range of head (m) Specific speed Ns Type of Turbine Propeller and Kaplan Francis low speed Francis high speed Pelton 4 nozzles Pelton 2 nozzles Pelton 1 nozzle 3.4. Turbines and auxiliaries Francis turbine It covers a wide range of specific speed from Ns = 70 to 340 corresponding to high head and low head respectively. Table 3 and Table 4 present the zone of specific speed for different turbines [10]. The turbine power output has been established to be 10 MW. Given the available head, the rated flow was set at 9.0 m3/s. The choice of the runner type is mainly based on the availability of flow rate and net head. From Table 3 and Table 4 it can be seen that for a flow rate of SHPP Lepenci a Francis turbine type has been selected as it offers a high efficiency, and ensures the optimal use of the available water flow. Due to the wide flow fluctuations, this hydro power is designed to be a run-ofthe-river type because it does not require a reservoir to power the turbine [5] and for this study, three units were All rights Reserved 161

8 Each unit can operate between 30 % and 100 % of their design flow and therefore will be able to pass 0.36 m3/s to 3.9 m3/s each. Horizontal axis turbines were selected as they produce lower civil works costs than a vertical configuration and also, they are more straightforward to install and maintain. Table 5 presents the general turbine characteristics. Table 5. Turbine characteristics of SHPP Lepenci Number of units 2 +1 Rated discharge per unit 2 x 3.9 m 3 /s + 1 x 1.2 m 3 /s Total rated discharge 9 m3/s Gross head m Rated net head m Rated power per unit 2 x 4.36 MW + 1 x 1.34 MW Turbine setting Hs m above tail water Total installed capacity 10 MW Figure 6. Power output vs mass flow Each unit is equipped, with a regulating system. The regulating system has included the pumps, reservoir, sump tank, command cabinets and all necessary instrumentation for automatic operation. The oil pressure system is equipped, with an auxiliary pumping unit which was able to compensate for the losses in the servomotors of the wicket gates as well as for the losses in the turbine inlet valves Turbine and generator efficiencies and unit operation range The provided turbine efficiency curves are used for predicting the energy performance for all different suppliers Jinlun, Wasserkraft, Gugler, and Global Hydro, which are analyzed, and it was chosen the Wasserkraft supplier. Figure 7. Turbine and generator efficiency, All rights Reserved 162

9 The lower limit of guaranteed turbine performances varies from manufacturers from 20 % to 40 %. Figure 7 shows the turbine and generator efficiencies for the selected supplier, Wasserkraft. The analysis has shown that flow rate 10.0 (m³/s) is suitable to provide a maximum power output of MW. Three horizontal Francis turbines were selected, Unit 1 (4.33 m³/s), Unit 2 (4.33 m³/s), Unit 3 (1.33 m³/s), and each unit can operate between 20 % and 100 % of their design flow and therefore will be able to pass 0.27 m³/s to 4.33 m³/s each. The overall plant efficiency curve is shown in Figure 8 with the blue curve. Figure 8. Overall efficiency curve of SHPP Lepenci for various turbine configurations Figure 8. shows the overall efficiency of the small hydro power plant for various turbine Configurations with a certain percentage of general production of energy. From the expression of power output, it can conclude that the power output from the hydro power plant is dependent only on the parameter of overall efficiency. Therefore, to achieve the highest value of power generation, analyses were made for different cases of participation of various turbine configurations in the production of electricity. The analysis was released for three operating units with participation in general production: 1 x 1.34 MW (13.33 %) and 2 x 4.36 MW (43.33 %), as shown in Figure 8. These units of operation for Small hydro power plant Lepenci has been shown to be suitable when it has small flow rates of m3/s, and the flow values approaching the design conditions 7-10 m3/s. In these cases, this method of connection has very high amounts of produced power, and in other instances in which the water flow which is brought to the SHPP Lepenci is between the values m3/s and 5-6 m3/s from the diagram are seen several dropping fluctuations of overall efficiency, specifically of the power produced. IV. CONCLUSION Knowing the operating conditions of the system as the average water flow of 4.6 m3/s and the hydraulic net disposable of water m has resulted that the Francis turbine that best suits these conditions. Both from the tables and the calculations in the software are the turbine Francis for which the average annual output power had the highest value of all other turbines. As a result of substantial fluctuations in flow rates, it was seen reasonable to install three Francis turbines that produce power with lower flow rates. Because of the feasibility of the installation, if only one turbine of Francis would have been installed, the average value of the produced energy would be as half of 10 MW generated by three turbines. The project has a plant flow of 10.0 m³/s that was imposed to provide a maximum power output of MW. Three horizontal Francis turbines were selected, Unit 1 (4.33 m³/s), Unit 2 (4.33 m³/s), Unit 3 (1.33 m³/s), and each unit can operate between 20 % and 100 % of their design flow and therefore will be able to pass 0.27 m³/s to 4.33 m³/s each. Furthermore, from the last diagram, it is seen how the mode of connection of turbine units in SHPP operation reaches the highest values of produced power. From this analysis, it has All rights Reserved 163

10 that the unit with 1.34 MW (13.33 %), 4.36 MW (43.33 %) and 4.36 MW (43.33 %) has the highest value of overall efficiency. This means that there is a higher value of the power produced, so in this way, the operation of this unit to the current Small hydro power plant installed in Lepenci River is selected. The use of renewable energy sources (RES) respectively Small hydro power plants as a national interest by contributing to the realization of the country s overall energy policy objectives, enhancing the security of energy supply, promoting investments in the energy sector, developing energy market and ensuring environmental protection [13]. REFERENCES [1] F.R. Forsund, Hydro power economics, Resource Economics at the Department of Economics, University of Oslo, [2] Energy Regulatory Office, V_810_2016 The Feed - in Tariffs for generation of electricity from Renewable Energy Sources, [3] P. Celso, Layman's guidebook on how to develop a small hydro site. Published by the European Small Hydro power Association (ESHA), Second edition, Belgium, June, [4] Sh. Lajqi, N. Lajqi, B. Hamidi, Design and Construction of Mini Hydro power Plant with Propeller Turbine, International Journal of Contemporary ENERGY, vol. 2 (1), pp. 1-13, 2016, DOI: /ce [5] M.A.R.Mohibullah, A.H. MohdIqbal, Basic design aspects of micro-hydro-power plant and its potential development in Malaysia, National Power and Energy Conference (PECon) Proceedings, Kuala Lumpur, Malaysia, [6] B.A. Nasir, Design Considerations of Micro-hydro-electric Power Plant, Energy Procedia, vol. 50, pp , 2014, Elsevier, doi: /j.egypro [7] P. Adhikar, U. Budhathoki, S.R. Timilsina, S. Manandhar, T.R. Bajracharya, A Study on Developing Pico Propeller Turbine for Low Head Micro Hydro power Plants in Nepal, Journal of the Institute of Engineering, vol. 9 (1), pp 36 53, 2013, [8] J. Delson, V. Lini, G. Renjini, Design of small hydro electric project using tailrace extension scheme, International Journal of Advanced Research in Electrical and Electronics Engineering, vol. 3 (1), ISSN_NO: [9] Sh. Lajqi, Xh. Fejzullahu, N. Lajqi, H. Hajdini, Analysis of the Mini Turgo Hydro Turbine Performance for Different Working Regimes, International Journal of Contemporary ENERGY, vol. 3 (1), pp. 1-8, 2017, DOI: /ce [10] A.C. Santos, M.M. Portela, A. Rinaldo and B. Schaefli, Inference of analytical flow duration curves in Swiss alpine environments, Hydrology Earth System. Science, Manuscript under [11] ESHA: Guide on How to Develop a Small Hydro power Plant, European Small Hydro Power Association, power_plant.pdf [12] V.L.Streeter, E.B. Wylie, Fluid Mechanics. First SI Metric Edition, McGraw-Hill Book Company, [13] Ministry of Economic Development, (2016), Energy Strategy of the Republic of Kosovo , All rights Reserved 164