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.
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
There's also a growing market
for micro hydro electricity in
developing countries. This article
is a technical over-view.
Micro hydro power is gradually
assuming the decentralized form
it once had.