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.
Micro Hydro Components:
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.
- Desiltingbasin : 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.
