| 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. |
| 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. |
| 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. |
| 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. |
|
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. |
| 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. |
| 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. |
|
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. |
| 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. |
| 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. |
| 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. |
| 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. |
| 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. |
| 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. |
