Theoretical Hydropower Output

“Work volume per 1 second (J/s)” when the water of discharge Q (m3 /sec) drops from
the height of H(m) is shown as the following equation.

The above-mentioned equation shows that the lager “Q” (discharge) and the higher “H” (head)
is, the bigger “P” (power output) is. “Q” (discharge) mainly depends on catchment area at intake
point and an amount of rainfall in the catchment, while “H” (head) depends on topographical
conditions such as riverbed slope.

Practical Hydropower Output
No power conversion system can deliver as much useful power as it absorbs –some power is
lost by the system itself in the form of friction, heating, noise, etc.

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What’s Catchment Area

The volume of the river flow or discharge depends on the catchment area and the volume of
rainfall. Figure 1.5-1 shows how the rainfall is divided on both sides (A and B) of the watershed.
For example, there is an existing Hydropower Plant at A-side, the rainfall at B-side cannot be
used for power generation at this Hydropower Plant. Therefore, the catchment area of a
proposed hydropower plant should be known at the first step of the study of hydro scheme.

The dashed-dotted lines in Figure 1.5-2 indicate the watershed of Point-A. The catchment area
is the area enclosed by dashed-dotted lines.

In Figure 1.5-2, the arrows indicate the flows of rainwater. The rainwater in the catchment area
at point A, such as blue arrows in the figure, will eventually flow down through point A, while
the rainwater outside of the catchment area, such as red arrows in the figure, will not pass
through point A.

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Concept of Hydro Power

Energy of a falling stone depends on a height and the weight of the stone. The higher the
position of the stone is and the heavier the stone is, the larger its energy is. Just like the energy
of a falling stone, energy of hydropower depends on the height or a drop in height (referred to as
‘Head’) and weight of the water or “discharge” as shown in Figure 1.2-1.

A hydro scheme requires both water flow and a drop in height or ‘Head’ to produce useful
power. The power conversion absorbs power in the form of head and discharge, and delivering
power in the form of electricity or mechanical shaft power as shown in Figure 1.2-2

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Background and Purpose of the Manual for Feasibility Study on Micro-Hydro Development

Usually, Micro/Small-Hydropower is used in the rural electrification and does not necessarily
supply electricity to the national grid. They are utilized in isolated and off-grid villages for
decentralized electrification.
There is an increasing need in many developing countries for rural electrification purposely to
provide illumination at night and to support livelihood projects. Also, the government is faced
with the high costs of extending electricity grids. Often, Micro/Small-Hydro system offers an
economical option or alternative to grid extension. The high cost of transmission lines and the
very low load factor in the rural areas contributes to the non-viability of the grid extension
scheme. On the contrary, Micro/Small-Hydro schemes can be managed by the local people and
smaller organizations. It is hoped that this Manual will provide people with appropriate
knowledge and skills in carrying out feasibility studies on micro/small-hydropower
development.
The flow of micro/small- hydropower development is generally shown in Figure 1.1-1. Of all
the stages, stages from “Potential Site Identification” to “Designing Stage” (except detailed
design) are covered by a feasibility study”. This manual was described basically in line with this
flow.

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