Here is a compilation of essays on ‘Small Hydro Power Plants’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Small Hydro Power Plants’ especially written for school and college students.
Essay on Small Hydro Power Plants
Essay Contents:
- Essay on the Introduction to Small Hydro Power Plants
- Essay on the Indian Situation of Small Hydro Power Plants
- Essay on the Determination of Net Electric Power Output of a Hydroelectric Power Plant
- Essay on the Current Energy of Floating Water
- Essay on the Types of Small Hydro Power Plants
- Essay on the Hydraulic Machines Used for Small Hydro Power Plants
- Essay on the Floating Type Micro Hydro Power Plant
- Essay on the Economic Considerations for Small Hydro Power Plants
Essay # 1. Introduction to Small Hydro Power Plants:
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The utilization of hydro energy to operate agricultural and industrial devices is one of the oldest and widespread techniques of human achievement. Hydraulic rams were used to raise water for lift irrigation and drinking purposes. Water mills had been used to generate mechanical power to drive irrigation pumps, machine tools and small electric generators. The Himalayan Mill is well known in the mountain areas from Afghanistan to Burma which is mostly used for grinding grains.
China has developed 1200 MW of power by small hydel projects by creating water heads of about 5m along the rivers. Chinese model is difficult to develop in India due to different topography. The current number of operational small hydro power plants is 90,000 in China, 10500 in USA, 5300 in Japan, 2600 in Switzerland, 1300 in Austria.
Essay # 2. Indian Situation of Small Hydro Power Plants:
As we come down the hills, the available head decreases and equipment costs go up. Most of our rivers flow through flat terrains which can be harnessed to produce hydropower. The large potential of hydro energy available from flowing water in the rivers and irrigation canals, however, still remains untapped.
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Generating power on a small scale from low and ultra-low head drops of 3 to 20 meters has not been an economic proportion because of the high civil and equipment costs as well as high operating cost to be incurred per unit of power generated. The situation is further deteriorated by very low load factors in rural areas.
The modern high technologies do not adapt to rural ecology. An energy production technique based on renewable source and appropriate technology which can be take care by trained local people for its operation and maintenance problems is ideally suited. Only appropriate technology involving local resources, manpower and raw materials can ensure environmental harmony and sustainability of the development.
Hydropower, available free of cost in the form of flowing water, is an important, pollution free, renewable source of energy. Contrary to large size hydroelectric power stations, small hydro power plants have a very low, if any, impact on the environment. These can be integrated with irrigation, fish breeding and drinking water supply schemes. A potential of 15000 MW capacities has been identified out which 1398 MW of actual potential has been already exploited.
Essay # 3. Determination of Net Electric Power Output of a Hydroelectric Power Plant:
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Hydroelectric power stations harness the kinetic energy of water flow. This energy is produced from the potential energy of water flowing down due to height difference created by a dam or a slope.
The net electric power output of a hydroelectric power plant is given by:
P = ρQgHƞo
= ρQgHƞTƞgƞTr
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Where
P = Electric power output in [W]
ρ = Density of water, [kg/m3]
Q = water flow rate in turbine, [m3/s]
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g = Gravitational acceleration [9.81m/s2]
H = net useful water head, [m]
ƞo = overall efficiency of hydropower plant,
ƞT = Turbine efficiency [0.85 – 0.95]
ƞG = Generator efficiency [0.95 – 0.99]
ƞTr = Transformer efficiency [0.92 – 0.98]
Example:
Determine the net power output of a small hydroelectric power plant using a Pelton turbine if water flow rate is 2m3/s and the plant has an overall efficiency of 82%. Water is delivered to the turbine from a height of 300 m. The density of water is 1000 kg/m3.
Solution:
ρ = 1000 kg/m3
Q = 2m3/s
H = 300m
ƞo = 0.82
P = pQgHƞo
= 1000 × 2 × 9.81 × 300 × 0.82 × 10-6 MW
= 4.8265 MW.
Essay #
4. Current Energy of Floating Water:
Special ‘zero’ head turbines operating on kinetic energy of flowing water in rivers and irrigation canals can be used to harness huge river current energy.
The current energy of flowing water may be expressed as:
P = ½ AV3ƞ
Where,
P = Power generated (W)
A= Embarrassing area Runner (m2)
V = Water current speed [m/s]
ƞ = Efficiency of runner [0.5 to 0.85]
The efficiency depends upon the type of runner. The relation between river current speed for a turbine with swept are of and rotor efficiency of 25% is shown in Fig. 5.1.
Essay # 5. Types of Small Hydro Power Plants:
The small hydro power plants can be classified according to the size of the hydro turbine.
1. Micro Hydel Projects:
Micro Hydel Projects of capacity 50 to 100 kW.
Example:
A micro hydro power plant with a propeller type turbine with a power output of 50 kW at a head of 10m and water flow rate of 0.8 mVs.
2. Mini Hydel Projects:
Mini Hydel Projects of capacity range 100 kW to 1000 kW.
Example:
A mini hydro power plant with Francis turbine with a power output of 750 kW at a head of 25m and water flow rate of 0.4 m3/s.
3. Small Hydel Projects:
Small Hydel Projects capacity range of 2MW to 15 MW.
Example:
A small hydro power plant with Pelton turbine with a power output of 3 MW at a head of 400 m and water flow rate of 0.9m3/s.
Small hydel projects can be completed in four to five years, mini and micro projects in three years provided civil works of irrigation projects are already completed. Water released for irrigation only is used and power can be generated for 6 to 7 months a year.
Essay # 6. Hydraulic Machines Used for Small Hydro Power Plants:
Various hydraulic machines used for small hydro power plants are:
1. Hydro Turbines:
Two types of hydro turbines are used in power plants:
(i) Impulse Turbine:
It utilizes the kinetic energy of a high velocity water jet which strikes the buckets on blades mounted on a shaft. The kinetic energy of water jet is converted into mechanical energy of rotation of shafts. The impulse turbine with tangential water flow (Pelton turbine) is used for very high water heads as shown in Table 5.1.
(ii) Reaction Turbines:
The reaction turbines develop power utilizing both pressure energy and kinetic energy of water. The blades of a reaction turbine are totally immersed in the flow of water and the energy of the water is converted into shaft work.
The reaction turbines are Francis turbines with radial water flow and Kaplan turbines with axial water flow.
The schematic representation of various hydro turbines is given is Fig. 5.2 and the efficiency curves are given in Fig. 5.3. The type of turbine for a site is selected on the basis of available head. In case of overlapping the type of turbine selection is decided from efficiency curves. Pelton turbine has more efficiency but is more suitable for constant load operation. For variable loads, Francis and Kaplan turbines are suited as these have flat efficiency curves.
2. Himalaya Mill:
It is a vertical shaft, horizontal runner hydraulic turbine used for driving grain mills. The wooden radial blades are attached to a boss fitted into a wooden or steel shaft. The water is fed through open wooden channel. It produces about 0.35 kW of shaft power with a water head of 1 m. There are about 10,000 such mills scattered in the hilly areas from Afghanistan to Burma producing power equivalent of about 45,000 kWh daily.
The horizontal water wheel can be improved in performance to raise its efficiency substantially. The improved wheel can be used in a small scale industrial park as a prime mover for flour mills, thrashers, rice husking machines, vertical lathe, circular saw, trip hammer, small electrical generator, carpet loom, etc.
The vertical lathe can be used by the craftsmen to produce wooden vessels and trip hammers for embossed copper vessels. The saw mill can be used by carpenters. All these machines can be employed together to meet the local needs for production of domestic and agricultural implements and packing boxes for the export of fruits and other products.
The Himalaya Mill can also be developed into an efficient and modern Pelton turbine using metallic buckets filted to a vertical shaft supported or roller bearings. The water can be directed onto the buckets through adjustable nozzle from piping system collecting water from natural streams existing abundantly in the hilly areas. The stopping of turbine can be achieved through manual brakes and load/speed regulation by the nozzle. The output of the machines can be standardised at 5 to 10 kW. The mill can be designed and manufactured locally in the small-scale industry park.
The tail race water can be re-circulated by lifting it with a hydraulic ram for irrigation purposes.
3. Hydraulic Ram:
Hydraulic ram is a contrivance to raise a part of large amount of water available at some height, to a greater height. This can be employed in hilly areas where some natural source of water like a spring or a stream is available at some altitude. Work done by a large quantity of water in falling through a small height is used to raise a small part of it to a greater height. Action of water hummer makes it feasible.
No external power is, therefore, required to work this machine. Other attractions are- negligible amount of maintenance and supervision costs, continuous operation, high efficiency, quiet operation and possibility of automatic adjustment of water supply .The lift-able volume diminishes asymptotically with lifting height. In case of medium lifting height, the hydraulic ram operates with efficiency absolutely comparable to a piston pump of the same performance.
As the hydraulic ram does not need a driving unit it is to be considered as ideal for lift irrigation and drinking water for hilly areas where the supply in fossil energy carriers or electricity is problematic. The hydraulic ram operates with water streams of 1 to 40 m3s and fall heads of 1.5 to 30 m and with lifting heights up to 300 m. Hydraulic ram is a simple and rugged device for operating irrigation schemes. This can be easily assembled from local materials.
4. Poncelet Water Wheel:
In ancient times, floating mills were used in Germany on large rivers such as Rhine to drive electric generators and machine tools. A vertical undershot water wheel consisting of a horizontal shaft and radial blades fixed to it was fitted on the side of a barge which was either moored to the bank or firmly anchored in the stream.
A smaller barge was used to support the other end of the shaft. The hulls of the barges were built with local materials. The efficiencies realised were very low, in the range of 20 to 30% because of bad blade geometry (straight radial blades).
Poncelet water wheel is an improvement on the straight blades of undershot water wheel, which has suitable curvature. Water strikes the vanes practically without shock (inlet vane angle 15°) and drives it by impulse. Water is discharged from the blades almost vertically downwards. The efficiencies achieved are 55 to 65%.
The main drawback of such machines is low power output for a given size and weight because at any instant only a small part of it is actually in the water being driven by the current while the rest of the machine is idle.
5. Darrieus Turbine Rotor:
Darrieus turbine rotor is similar to modern vertical-axis wind turbine which was first introduced in France by G.J.M. Darrieus in 1920’s. Its configuration consists of four hydrofoil blades which rotate at much higher speed than the water current speed.
The speed of rotation is primarily dependent upon the machine overall dimensions. It has relatively low starting torque. Because of simplicity of the blade design and because they are relatively thin, blade fabrication costs are low. They require no pitch control for synchronous applications.
Two prototypes have been developed by Intermediate Technology Development Group, London as shown in Fig. 5.4. The blades can be made out of timber of fabricated from steel, ferro-cement or glass fibre. The expected performance is shown in fig. 5.1.
Prototype (a):
Vertical axis rotor 13.5 rpm in 1 m/s current. Power takes off above surface. Swept area 3.75 m2
Prototype (b):
Horizontal axis rotor 32 rpm in 1 m/s current. Powers take off under water. Swept area 3.75 m2.
Essay # 7. Floating Type Micro Hydro Power Plant:
The floating type micro hydro power plants are suitable for use in situations where there is no “head” of water available and are designed to extract kinetic energy from a river or canal water current. Therefore, appropriate sites are along the banks of large rivers or on irrigation canals.
As the energy flux depends upon the cube of water velocity, the latter must be as large as possible. The depth of water required for a 4m2 runner is at least 2.5m.
(i) Hydraulic Machines:
The Darrieus turbine rotor is a low speed machine. It is a low solidity device which is completely submerged during operation and this, together with its high efficiency (above 50%) means that a rotor of moderate size and modest material content can extract useful amounts of energy from current speeds as low as 1 m/s (2 knots).
The mechanical energy obtained can be used for running irrigation pumps, small electric generators and small compressors for cold storages and ice mills. The small cold storages in hilly areas are necessary to store potatoes and other perishable goods to get better returns. Ice mill can be used to chill and store milk before it is sent to bigger collection centres.
The electricity generated is required to light the houses, schools, community centres and to operate TV sets and other domestic devices. All these measures can improve the wealth of the village multifold and raise the standard of living of the local population which will arrest their migration to big cities.
A turbine with swept area of and rotor efficiency of 25% can give an output of 8 kW at a water current speed of only 2 m/s.
In plain areas, irrigation canals are expected to be an important area of application for floating type micro hydro power plants. In a large canal, like in a river the turbine rotor could be mounted on a pontoon, whereas on a small canal it might be cheaper to mount the rotor under a bridge or beam over the canal. The power output from the rotor could be increased by shaping the canal banks to form a venturi in order to increase the local water velocity through the rotor.
(ii) Installation:
The appropriate sites for floating type micro hydro power plants are along the banks of large rivers or on irrigation canals. The pontoon carrying the turbine, generator and transmission system can float on two rows of barges or oil drums under which wooden keels are affixed. The site requirements are shown in fig. 5.5.
The mooring details are shown in Fig. 5.6. The mooring cable arrangement protects the rotor against submerged or semi-submerged objects striking the blades. The cable can be adjusted with a winch to ensure sufficient angle of the keels to the current direction so that water side thrust on the keels keeps the pontoon at a sufficient distance from the bank.
(iii) Auxiliaries and Controls:
The rotational speed of Darriens turbine is very low- 13.5 rpm for vertical axis and 32 rpm for horizontal axis turbines. For Poncelet turbine, the peripheral velocity of runner is about half of water current speed. Therefore, multistage belt drives or gear boxes are needed to increase the speed of generator shaft to about 950 rpm.
Permanent magnet alternator or induction generators are preferred over synchronous generators. In order to reduce equipment costs, the conventional mechanical or hydro-mechanical speed governor should be dispensed with the inertia of rotor being small; there is a problem of instability in power supply quality.
The above problems can be solved by the use of a flywheel which can ensure stable power supply and can shave-off power demand fluctuations. A flywheel designed for this purpose can be accelerated to extremely high speeds without any risk of breaking apart.
It can be made from concentric rings of quartz fibre as windings, the rings being fitted over one another and close gaps filled with an elastic substance to keep the plies of the rims together. The flywheel is coupled to a generator and enclosed in a sealed evacuated casing to reduce wind-age losses. The device operates as a generator when power demand on the system grows and as an electric motor when it is time to accumulate energy.
Essay # 8. Economic Considerations for Small Hydro Power Plants:
Bharat Heavy Electricals Ltd. Haridwar and Bhopal plants, Jyoti Limited, Baroda have the capacity to manufacture small hydro turbines as per Table 5.1. Himalaya Mills, Hydraulic Rams and Floating Mills can be designed, manufactured and installed using local materials and skills. Independent small hydel projects become very costly due to heavy civil costs involved. The cost may be Rs. 18000 per kW installed.
Therefore such projects become viable if planned as multiple purpose use of water including irrigation and power generation. As we come down the hills, the available head decreases and equipment costs go up. For example, the cost of one hydro set of horizontal tubular design of 3.2 kW capacities operating at a head of 3 m may be Rs. 1.20 lakhs, i.e., Rs. 40,000 per kW installed.
The civil costs are site specific but taking 30% of equipment cost, the total installed cost will be a high value of Rs. 52,000 per kW installed. Even though the schemes are costlier but the cost of 1 kWh will be less than from pumped hydroelectric power plant as water is essentially free and other running cost components of operation and maintenance are very low.