1. What is the meaning of Mega Watt ( MW ) and how is it different from units of energy ?

Capacity of a generating unit is expressed in MW. One MW is equivalent to 1000 KW. Unit of energy is Kilowatt Hr i.e. a machine of 1MW capacity running for one hour would generate 1000 Kilowatt Hr or 1000 units.

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2. What is the difference between a ‘DAM' and a ‘BARRAGE’ ?

Both the dam and barrage are barriers constructed across a river or natural water course for diverting water into a canal mainly for purposes of irrigation, water supply etc. or into a channel or a tunnel for generation of power.
In case of a barrage, its entire length across the river i.e. between the banks is provided with gates having their bottom sill near the river bed level. Thus, the storage behind the barrage is solely created by the height of the gates.
The dam on the other hand has spillway gates almost near its top level and the storage behind the dam is mainly due to the height of concrete structure and partially due to the gate height.
In both the cases, however, the number and size of gates is adequate to pass the design flood during monsoons.

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3. What is the principle of operation of Hydro-electric Power Plants?

Hydro-electric power plants capture the energy released by water falling through a vertical distance, and transform this energy into useful electricity. In general, falling water is channelled through a turbine which converts the water's energy into mechanical power. The rotation of the water turbines is transferred to a generator which produces electricity. The amount of electricity which can be generated at a hydro-electric plant is dependant upon two factors. These factors are (1) the vertical distance through which the water falls, called the "head", and (2) the flow rate, measured as volume per unit time. The electricity produced is proportional to the product of the head and the rate of flow. The following is an equation which may be used to roughly determine the amount of electricity which can be generated by a potential hydro-electric power site:

POWER (kW) = 5.9 x FLOW x HEAD

In this equation, FLOW is measured in cubic meters per second and HEAD is measured in meters.

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4. How much water and pressure is needed to run a small hydro system?

In general, the more, the better. Ideally, you need at least 3 feet of fall with a 12 gpm (gallons per minute) water flow. If you have higher fall (pressure), you can get by with much less water.

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5. How do I determine the fall at my site?

It will be easier if you have or can borrow a transit. If not, just use a line level. Start at your best possible hydro location and look along the plane of the level to a landmark (a rock, stick, another person). Walk to the landmark and repeat the process. Count how many times you did this and multiply it by the distance from the ground to your eye. This will give you the total head you have available.

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6. Once I know the total head, how do I translate this into pressure?

The basic formula is 2.31 psi (pounds per square inch) = total head. Since you know the head, just divide by 2.31 for a psi figure.

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7. Given a site with sufficient head and flow, is the biggest issue with keeping the turbine turning at a constant (or nearly constant) speed?

If there's plenty of water power available, or no way to store water uphill, varying the load on the alternator to keep the frequency constant seems to fit better than solenoid operated diverters. The Cuttyhunk windmill used to work this way, with a one-byte output from a TRS-80 controlling 8 binary-weighted 1 kW to 128kW air-cooled resistors with series switches in parallel with the alternator. Water-cooled resistors can be simpler and smaller. The control algorithm was simple: if the frequency is too high, increase the binary output count to increase the load; if frequency is too low, decrease it.

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8. How much power can I get from my hydro site?

Multiply the head (total vertical drop) by the gpm ( gallon per minute ) available by the hydro efficiency (average times .18). = Watts.

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9. What is a dependable year?

Water availability will be computed using 10 daily flows. While planning Hydro Power Projects, discharge data of the river for about 20 continuous years is taken into consideration. Unrestricted energy generation of these hydrological years is arranged in descending order and exceedance probability computed. Based on the exceedance probability, 90% & 50% dependable years are identified.
If discharge data for ‘N’ years is available, the 90% dependable year is defined as (N+1) x 0.9 year in the Table arranged in descending order.
Power planning of the project is done on the basis of annual generation of 90% and 50% dependable years.

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10. If the hydro site is located more than 300 feet from the house, is it better to use a higher voltage AC system?

If there's lots of water power available and the alternator rpm changes relatively slowly, it seems better to send well-regulated 120/240VAC, with the shunt regulator inside the house, a lightning arrestor in series, but no batteries or inverters, and use the excess power for heating water, etc. Some water wheels are more controllable than others. A Pelton wheel with no load might run 6 times faster than under full load, but other types might only run 20% faster.

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11. If you already have a utility company connection, is the primary reason for setting up a hydro system to make money with the "excess" and reduce air pollution?

Apart from reducing air pollution, water heating seems a good goal as well. It takes 2.3 kWh to boil away a gallon of water. The Cuttyhunk people had plans to heat island houses electrically with dynamic load switching as a less wasteful alternative to their desk-sized resistor bank under the windmill.

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12. What are the advantages of run of the river projects ?

A.) Storage behind the dam or barrage is just sufficient to run the power station to its full installed capacity only for about 4-5 hours during the period the discharge in the river is minimum.

B.) During monsoons, the power house runs as a peaking station for the period the river discharge is more than the design discharge required for running the power house to its full installed capacity.

C.) Due to small storage, the height of the barrage / diversion dam is low, resulting into a smaller reservoir and consequently rehabilitation and resettlement problems are minimal.

D.) Forest / Government land coming under submergence is reduced to a great extent due to a small reservoir.

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13. What is the difference between a snow fed vs a monsoon fed project?

Snow fed project – The run-off is derived from the melting of snow & glaciers.
Monsoon fed project – The run-off is derived from rainfall.

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14. What is HRT – Head Race Tunnel?

The water from reservoir enters through the Intake into the Head Race Tunnel or Power Tunnel, which runs under pressure supplying water for generation of power to the power station.

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