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Hydro power is available in a range of sizes from a few
hundred watts to over 10GW. At the low end of the spectrum, small hydro
power can be divided into three categories. The definitions of the categories
vary, but are broadly: micro (less than 100kW), mini (100kW-1MW) and small
(1MW-10MW) hydro.
Micro-hydro systems are generally stand-alone systems, ie they are not
connected to the electricity grid.
Micro-hydro systems operate by diverting part of the river flow through
a penstock (or pipe) and a turbine, which drives a generator to produce
electricity. The water then flows back into the river through a civil
construction known as the tail race. Micro-hydro systems are mostly "run
of the river" systems, which allow the river flow to continue. This
is preferable from an environmental point of view as seasonal river flow
patterns downstream are not affected and there is no flooding of valleys
upstream of the system. A further implication is that the power output
of the system is not determined by controlling the flow of the river,
but instead the turbine operates when there is water flow and at an output
governed by the flow. This means that a complex mechanical governor system
is not required, which reduces costs and maintenance requirements. The
systems can be built locally at low cost, and the simplicity gives rise
to better long-term reliability. However, the disadvantage is that water
is not carried over from rainy to dry season. In addition, the excess
power generated is wasted unless an electrical storage system is installed,
or a suitable ‘off-peak’ use is found. In general cases the
excess power thus generated I used to for heating purposes or to charge
the battery using an inverter scheme.
Micro-hydro systems are particularly suitable as remote
area power supplies for rural and isolated communities, as an economic
alternative to extending the electricity grid. The systems provide a source
of cheap, independent and continuous power, without degrading the environment.
The basic components can be briefly described:
• Intake: This
is where the water from the river/spring is diverted from its main course
(River).
• Weir: A weir is used to divert water through an opening in the
riverside (the intake opening) into an open channel. The Weir is site
specific and sometimes may require some civil construction work. At some
sites using boulders and stones available we can facilitate the weir.
• Channel: leads
the water from the intake to the forebay tank in some cases or to the
head of the penstock. This too is site specific. Usually a forebay tank
helps us to maintain the output power constant.
• Desilting basin :
This is a small tank designed to desilt the water. There may be many desilting
tanks along the channel. This facilitates water without silt to flow into
the forebay tank.
• Forebay Tank:
Water from the headrace flows to this tank at the head of the penstock.
Here it collects and serves as a buffer to control sudden flow and pressure
variations. The tank should be designed to hold the volume of water needed
to operate the turbine-generator for the number of hours the system operates.
Measures such as trash rake/wire mesh are needed to prevent silt, leaves
and other debris from entering the pipeline.
• Penstock:
This is the pipeline supplying water from the forebay to the turbine.
It should be well supported every 15 - 20 feet for Mild Steel / Cast Iron
Pipes or be buried under a thin layer of soil to protect it from physical
damage and also from corossion. The pipeline can be of PVC too depending
on the site conditions.
• Turbine: This
is the mechanical device that rotates when driven by water issuing from
pipes. There are several kinds of turbines that can be used, e.g. Pelton
wheel, cross flow turbines, pumps as turbines and standard reaction turbines.
Each kind of site is suited to a particular kind of turbine. Therefore
the choice of turbine is site-specific.
• Generator:
Electricity is generated when the turbine drives the generator. There
are basically two kinds of generators that can be used for AC power. Regular
Synchronous Generators are the simplest option, but in the lower ranges
of power (<10kW) it may be difficult to source them. In this case,
three phase induction motors can be used in reverse as generators with
the help of a capacitor bank.
• Governor:
This device ensures that the generator is not affected when the load on
it changes. It can be hydraulic, in which case the flow of water is regulated
when the load changes; or electronic, in which case ballast or dump load
is activated when the load changes. The type of governor used depends
on the generator. In electronic control, the synchronous generator requires
an Electronic Load Controller (ELC) whereas with an induction generator,
Induction Generator Controller (IGC) is required.
• Distribution System:
The electricity generated in the power house is supplied to the house
holds through local grids. This consists of weather proof Aluminium cables
as conductors and locally available wooden poles as electric posts.
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