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Micro hydro power is gradually assuming the decentralized form it once had.

Water power predates the use of electricity. At one time hydro power was
employed on many sites in Europe and North America. It was primarily used
to grind grain where water had a vertical drop of more than a few feet and
sufficient flow. Less common, but of no less importance, was the use of
hydro to provide shaft power for textile plants, sawmills and other
manufacturing operations.

Over time thousands of small mills were replaced by centrally-generated
electric power. Many major hydroelectric projects were developed using large
dams, generating several megaWatts of power. In many areas, hydro electric
power is still used on a small scale and is arguably the most cost-effective
form of energy.

Renewable energy sources such as wind and solar are being scaled up from
residential to electric utility size. In contrast, hydro power is being scaled
down to residential size. The small machines are similar in most ways to the
large ones except for their scale.

Micro hydro turbine generator siting
A hydro system is much more site-specific than a wind or photovoltaic (PV --
solar electric) system. A sufficient quantity of falling water must be available.

The vertical distance the water falls is called head and is usually measured in
feet, meters, or units of pressure.

The quantity of water is called flow and is measured in gallons per minute
(gpm), cubic feet per second (cfs), or liters per second (I/s).

More head is usually better because the system uses less water and the
equipment can be smaller. The turbine also runs at a higher speed. At very
high heads, pipe pressure ratings and pipe joint integrity become problematic.

Since power is the product of head and flow, more flow is required at lower
head to generate the same power level. More flow is better, even if not all of
it is used, since more water can remain in the stream for environmental
benefits.

A simple equation estimates output power for a system with 53% efficiency,
which is representative of most micro hydro systems:

Net Head* (feet) x Flow (US gpm) / 10: Output (Watts)

* Net head is the pressure available after subtracting losses from pipe
friction. Most hydro systems are limited in output capacity by stream
conditions. That is, they cannot be expanded indefinitely like a wind or PV
system. This means that the sizing procedure may be based on site
conditions rather than power needs.

The size and/or type of system components may vary greatly from site to
site. System capacity may be dictated by specific circumstances (e.g., water
dries up in the summer).

If insufficient potential is available to generate the power necessary to
operate the average load, you must use appliances that are more energy
efficient and/or add other forms of generation equipment to the system.
Hybrid wind/PV/hydro systems are very successful and the energy sources
complement each other.

The micro hydro turbine generator system described here are called "run of
river"; i.e. water not stored behind a dam. Only an impoundment of sufficient
size to direct the water into the pipeline is required.

Power is generated at a constant rate; if not used, it is stored in batteries or
sent to a shunt load. Therefore, there is little environmental impact since
minimal water is used. There is also much less regulatory complication.
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Micro Hydro Turbine Generator: Part I   
Part II: System Types    Part III: System Components    System
Components cont.
Micro hydro turbine
generators
are making a
comeback for electricity
generation in homes.

Increasing numbers of small
hydro systems are being
installed in remote sites in
North America.

There's also a growing
market for micro hydro
electricity in developing
countries. This article is a
technical over-view
.