How to Develop a Small Hydropower Plant - Case Study Example

Hydropower Resource Analysis Hydropower resources is one of the most economical and common methods of producing electri for domestic, commercial and industrial use. It is a renewable energy that produces electricity by running the turbines with the force of water. This study is aimed at analyzing various types of turbines that are used in the generation of electricity and how it is affected by the fall and flow of water. The study also looks into the calculation of the total power production by mathematical techniques and present calculation of a case study of screw type turbine. This paper also reviews in depth about the hydroelectric scheme and discusses the methods of determining its sustainability by way of presenting methods of selecting appropriate turbines in relation to the head and flow of water source. It uses tables of generation tariffs in U.K. and shows how and what revenue is achievable with possible periods of payback of huge initial investment needed for the project. Introduction The power of water is dependent upon its pressure which is built by the height of water source. The pressure is found at the point from where water is released. The vertical distance between the water releasing point and water source such as reservoir, tank, etc. determines the water pressure. It is this elevation which is known as “Head” and measured in meters as a vertical distance. Water ‘Flow’ is the amount of water quantity or ‘volume’ in a given time. It is therefore measured as cubic meter per second (m3/s) representing volume of water and time in which it flows. The density of water and earth gravity also affects the flow of water. The density of water is commonly taken as 1000 kg/m3 and earth gravitational force is a constant having value of 9.81 m/ s3 (ESHA 2004) Pipelines are most commonly used for moving water from higher source point to a lower release point. There are many barriers in the way of water travel that reduces water distance. This includes size and shape of pipelines, friction of water with pipe material, the joints, design flow and the sides. All of these and many other factors create loss and therefore Head is always taken as net; the vertical distance is subtracted with expected loss in transit and Net Head is derived. All calculations in this paper are based on net head. The word Hydropower refers to the force of water. It is also referred mostly as hydraulic power. Generation of electricity from hydropower or hydraulic power is referred as Hydroelectric or hydraulic electricity. Figure 1 illustrates how the potential and kinetic energy in water converts to mechanical energy by rotation of turbine shaft and mechanical energy converts into electricity by generator. (ESHA 2004) Figure 1: Process of Hydroelectric Conversion (ESHA 2004) Powerhouse Powerhouse is the building that protects the entire range of electromechanical equipment from hardships of weather. Electromechanical equipment include valve or inlet gate, turbine, speed increaser, generator, control system, switchgear, condenser, protection systems, DC emergency supply, power and current transformers, etc. Figure 2 shows the Schematic View of the power house at Low Head & Figure 3 shows the Schematic View of the power house at high and medium heads. Figure 2: Power House – Low Head (ESHA 2004) Figure 3: Schematic View of a Power House – high and medium heads (ESHA 2004) Hydraulic Turbine Types and Configuration There are two different mechanisms by which potential water energy is turned into mechanical energy. The first mechanism is referred as Reaction Turbines. In Reaction Turbines water force is applied on runner blades. Water pressure decreases gradually as it travels through the turbine. Francis turbines, Kaplan turbines and propeller turbines belong to this category (ESHA 2004) The second mechanism is referred as Impulse Turbines. In Impulse Turbines kinetic energy is made by converting water pressure into high-speed jet which strikes the buckets. Periphery of runners is mounted with these buckets. Pelton turbines, Turgo turbines and Cross-flow turbines also known as Banki-Michell, belong to this category (ESHA 2004), Francis Turbines Francis Turbines as shown in Figure 4 are used mostly for medium heads ranging from 25 to 350 m having adjustable guide vanes and fixed runner blades. In this type of reaction turbines outlet is axial while admission is radial and the axis can be horizontal or vertical (ESHA 2004) Figure 4: Francis Turbine (ESHA 2004) Turbine with Horizontal Axis Vane Operating Device Runner Kaplan and Propeller turbines Kaplan and propeller turbines as shown in Figure 5 are used mostly for low heads ranging from 2 to 40 m having adjustable runner blades and guide vanes which may be fixed or not. When guide vanes and runner blades both are adjustable it is referred as ‘double-regulated’. When guide vanes are fixed it is referred as ‘single-regulated’. When runner blades are fixed it is referred as propeller turbines (ESHA 2004) Most possible configurations are allowed by Kaplan turbines based on discharge range, net head, geomorphology of the terrain and labour cost. Difference in configurations is on the basis of admission (axial, radial, or mixed) and turbine closing system (siphon or gate) and type of speed increaser (parallel gears, belt drive, right angle drive) (ESHA 2004) Figure 5: Kaplan Turbine (ESHA 2004) Double Regulated Kaplan Bulb unit derived from Kaplan turbines Kaplan Runner Pelton Turbines Pelton Turbines are impulse turbines as shown in Figure 6 which are used mostly for high heads ranging from 60 to 1000 m having one or more jets striking a wheel that carry large number of buckets on its periphery. The flow of water is controlled by a needle valve and water is issued by jet through its nozzles. The plan of the runner has axes of the nozzles. (ESHA 2004) Figure 6: Pelton Turbines (ESHA 2004) Turgo Turbines Turgo Turbines are impulse turbines as shown in Figure 7 which are used mostly for heads ranging from 50 to 250 m having one or more jets striking its runner plane at 20 degree angle. The shape of buckets is different from Pelton turbine. Runner disk receives water from one side and relieves from the other side. It can operate under a head with maximal design flow from 20% to 100% (ESHA 2004) Figure 7: Main rule of Turgo Turbines (ESHA 2004) Cross-flow Turbines Cross-flow turbines are impulse turbines as shown in Figure 8 which are used for wide range of heads ranging from 5 to 200m overlapping Pelton, Francis and Kaplan. It has one or more guide-vanes which direct water entered into the turbine. Location of guide-vanes is at runners upstream and water crosses twice before leaving the turbine. The efficiency of Cross-flow turbine is very low compared to other turbines. When power needs are defined and water is enough then it is a good alternative for rural electrification program (ESHA 2004) Figure 8: Rule of Cross Flow Turbine Power Generation and Turbine Efficiency The three most important elements in the process of hydroelectric generation are the head of water, flow of water and turbines that rotates and spins generator which produces electricity. The power is measured in ‘watts’. Figure 9 shows the mathematical representation of Power generation (ESHA 2004) Figure 9: Power Generation It can be observed in mathematical formula of power generation that the amount of power produced is directly dependent on two quantities Head and Flow; any increase in the quantity of Head or Flow will increase the power production and decrease of Head or Flow will decrease the power production. This calculation represents gross power. However in real life efficiency of turbines, water flow and generators that produce electricity vary from place to place and time to time. They are all dependent on many factors like environment, turbine size, turbine quality and water impurities. Therefore level of efficiencies such as water flow efficiency, turbine efficiency, generator efficiency, etc. represented in percentages is extremely important factor in calculating generated power (ESHA 2004) Efficiencies are ratios and it is represented by Greek small letter eta ‘ή’. For example power generating efficiency of a turbine is the ratio as shown in Figure 10 of Mechanical power of turbines to Hydraulic power of water as per international standards. (ESHA 2004) Figure 10: Efficiencies of Turbines (ESHA 2004) Turbine designs specify the maximum limit of water flow it can take. The manufactures of each and every type of turbine, provide turbine efficiency levels at different percentages of water flow from its maximum limit. This is referred as its ‘efficiency curve’. In Figure 11 an efficiency curve of screw type turbine is given which means that for any size of turbine design the turbine efficiency will be a percentage ratio of fall of useable water to the design limit of turbine. For example if a turbine design is of 2.0 m3/s, water fall of 2.0 is 100% Max flow, at 1.9 water fall it is 1.9/2.0 x100 = 95% Max flow, etc. The efficiency curve tells that at 100% efficiency level of water fall the turbine efficiency is only 86.10% (ESHA 2004) Figure 11: Efficiency Curve of Screw Type Turbine Table 1 shows that for a given usable water flow at different intervals, what will be the percentage of water flow to a 2.0 m3/s design turbine and its efficiency level derived from above curve. Power produced by turbine can be calculated by multiplying Total Power with turbine efficiency. The new equation will be as follows:- (ESHA 2004) Table 1: Use of Turbine Efficiency Curve for 2.0 m3/s Design Calculation in a case study Three tasks are done from the Screw turbine efficiency curve given in figure 11 above. In the part one “efficiency duration curve is prepared” the values of the graph were first calculated and produced in Table 1 above. The “efficiency duration curve” is produced in Figure 12. Figure 12: Task of Part I The power and energy figure for each 5% time interval is calculated in Figure 13. The maximum rated output power is 23 KWH. The total annual energy produced by this hydro is 6,044,400 KW Figure 13: Task of Part II Years m3/s m % % % KW KW count Useable flow Net head Gear & gen eff Design Efficiency Power 5 Yrs 5 2.00 1.48 88.35 100.00 86.10 22.000 963,600 10 2.00 1.51 88.35 100.00 86.10 23.000 1,007,400 15 1.81 1.52 87.42 90.50 86.20 20.000 876,000 20 1.43 1.53 87.42 71.50 86.60 16.000 700,800 25 1.15 1.54 86.48 57.50 84.60 13.000 569,400 30 0.94 1.54 86.48 47.00 82.60 10.000 438,000 35 0.76 1.55 86.48 38.00 80.60 8.000 350,400 40 0.65 1.55 85.56 32.50 80.20 7.000 306,600 45 0.54 1.55 85.56 27.00 78.70 6.000 262,800 50 0.45 1.56 85.56 22.50 76.70 5.000 219,000 55 0.38 1.56 84.63 19.00 72.40 4.000 175,200 60 0.30 1.56 84.63 15.00 60.00 2.000 87,600 65 0.24 1.56 84.63 12.00 49.40 2.000 87,600 70 0.18 1.56 83.72 9.00 0.00 0.000 0 75 0.15 1.56 83.72 7.50 0.00 0.000 0 80 0.08 1.56 82.80 4.00 0.00 0.000 0 85 0.00 1.57 0.00 0.00 0.00 0.000 0 90 0.00 1.57 0.00 0.00 0.00 0.000 0 95 0.00 1.57 0.00 0.00 0.00 0.000 0             Total 6,044,400 The annual revenue for generation Feed-in Tariff at 0.11p/KW for power produced (6,044,400 KW ) *0.11 .... ... £664,884 Add: Surplus (6,044,400KW-10000 KW) *0.03 £181,032 £845,916 Less: Annual O&M Costs £ 2,400 Annual Income £843,516 Payback period £100,00/£843,516= 0.12 years References: ESHA 2004, Guide on How to Develop a Small Hydropower Plant, viewed 12 November 2011 Read More