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                         TECHNICAL PAPER # 19
                      Christopher S. Weaver, P.E.
                        Technical Reviewers
                          Theodore Alt, P.E.
                             Paul N. Garay
                           Published By
                   1600 Wilson Boulevard, Suite 500
                     Arlington, Virgnia 22209 USA
                 Tel: 703/276-1800 . Fax: 703/243-1865
            Understanding Mini-Hydroelectric Generation
                        ISBN: 0-86619-218-2
            [C]1985, Volunteers in Technical Assistance
This paper is one of a series published by Volunteers in Technical
Assistance to provide an introduction to specific state-of-the-art
technologies of interest to people in developing countries.
The papers are intended to be used as guidelines to help
people choose technologies that are suitable to their situations.
They are not intended to provide construction or implementation
details. People are urged to contact VITA or a similar organization
for further information and technical assistance if they
find that a particular technology seems to meet their needs.
The papers in the series were written, reviewed, and illustrated
almost entirely by VITA Volunteer technical experts on a purely
voluntary basis. Some 500 volunteers were involved in the production
of the first 100 titles issued, contributing approximately
5,000 hours of their time. VITA staff included Maria Giannuzzi
and Leslie Gottschalk as editors, Julie Berman handling typesetting
and layout, and Margaret Crouch as project manager.
The author of this paper, Christopher S. Weaver, P.E., is a
senior engineer with Energy and Resource Consultants, an interdisciplinary
consulting firm in Boulder, Colorado. He is a registered
Professional Engineer, and has worked in the areas of
electric-utility planning, solar energy, cogeneration, and air-pollution
control as well as in small hydroelectric systems as a
consultant. Weaver is the author of another VITA technical paper,
Understanding Micro-Hydroelectric Generation. The reviewers of
this paper are also technical experts in hydroelectricity. Theodore
Alt, P.E., is a mechanical engineer who has been in the
energy field since 1942. He has worked with the energy research
and development group of the Arizona Public Service Company and
the Government of Mexico's electric commission. Paul N. Garay, an
associate engineer with F.M.C. Associates, has written many
papers on various aspects of water transportation and energy uses
of water.
VITA is a private, nonprofit organization that supports people
working on technical problems in developing countries. VITA offers
information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to their
situations. VITA maintains an international Inquiry Service, a
specialized documentation center, and a computerized roster of
volunteer technical consultants; manages long-term field projects;
and publishes a variety of technical manuals and papers.
               by VITA Volunteer Christopher Weaver
Electricity can be generated from the power of flowing water.
This is called hydroelectric generation, and it can be done anywhere
that there is water and a hill or drop for it to run down--in
an irrigation canal, where a river runs through rapids or over
a waterfall, or where a dam has backed up water above the level
of the river. Hydroelectric generating plants come in many sizes
--from huge plants that produce more electricity than most countries
can use, to very small plants that supply electricity for a
single house. Hydroelectric plants which supply electric power in
the range from about 15 kilowatts to 15,000 kilowatts are called
mini-hydroelectric or mini-hydro. Other phrases that mean the
same thing are "small-scale hydro" and "small hydro."(*)
Fifteen kilowatts is about the amount of power used by seven or
eight houses in the industrial countries, or by a very small
manufacturing plant, or it can provide lighting and other basic
services for a village of 50-80 houses. Fifteen-thousand kilowatts
is enough for a medium-sized town. Hydro plants which are
larger than 15,000 kilowatts are usually called "large hydro" or
"conventional hydro" plants, but there is no sharp line dividing
"mini-hydro" from "large hydro." All mini-hydro and large hydroelectric
plants use similar machinery, and work in the same way.
Plants of either type need specially manufactured machinery, and
must be designed by trained engineers. Both types of plants are
also fairly expensive. Because of this, mini-hydro plants are not
well-suited to village-level development in most cases--a
larger organization such as a town, a collection of villages, or
an industrial plant is usually needed.
Another type of hydro plant, called "micro-hydro," is better
suited to village level development and local self-help projects.
These plants are usually smaller than 15 kilowatts, and can be
built by people without much special training, using mostly local
materials and skills. Micro-hydro plants are usually very low
in cost, but they are less efficient, and the quality of the
electricity is not as good. Micro-hydro plants are suited to
running lights, small motors, and electric cookers in isolated
(*) These definitions are not universally agreed on. Different authors
may use mini, micro, or small to refer to the same project.
houses and villages, but are not usually good for larger towns or
industrial plants, and they cannot be interconnected with other
generating plants in an electric system the way mini-hydro and
large hydro plants can. Micro-hydro plants are described in
another VITA technical paper, Understanding Micro-Hydroelectric
Water wheels have been used since ancient times to supply power
for grinding grain and other laborious tasks. The first
modern hydraulic turbines were developed in the first part of the
19th century by Fourneyron in France. These were further developed
by a number of researchers during the middle of the century,
so that by 1890 most of the types of turbines now in use had been
invented. Edison's invention of the electric light and of ways
to distribute electricity occurred at about the same time,
leading to a great boom in hydroelectric development in Europe
and North America. Until about the 1920s, most hydroelectric
developments were quite small--in the size range which is now
called mini-hydro. This was for two reasons: people didn't know
how to build really large dams and turbines, and the small
electric transmission systems of the time made it difficult to
sell large amounts of electricity.
During the era of the 1950s and 1960s, advancing technology and
cheap oil--combined with improved long-distance electric transmission--made
it possible to sell electricity cheaper than the
earlier small hydro plants could make it. Hundreds of small
hydroelectric facilities were abandoned or dismantled during this
period. With the oil embargo of 1973, which has led to enormous
increases in the cost of oil, small hydro once again appears competitive.
Many of the early plants which were abandoned in the
1950s and 1960s are now being refurbished, and many new ones are
being planned. Small hydro is also well suited for developing
countries, and is being actively encouraged by many governments
and development organizations to reduce oil imports and encourage
This section presents a few basic facts and principles about
electric power and hydroelectric generation. Reading it will not
make you into a hydroelectric engineer, but it will help you
understand how hydroelectric systems work, and what makes a good
or a bad hydroelectric site. It will also help you to understand
your hydroelectric engineer if you decide to hire one.
Electric Power
Power is defined as an amount of energy divided by the time it
takes to supply the energy, or in other words as the rate at
which energy is delivered. Power is measured in units called
watts, or (for large amounts of power) in units of kilowatts.
One kilowatt is equal to 1,000 watts. Power is also measured in
horsepower. one horsepower equals 746 watts.
Two other quantities that are important in talking about electric
power are the electric current and the voltage. Electric current
can be thought of as the amount of electricity flowing through a
wire (like the amount of water flowing through a pipe), while
voltage can be thought of as a measure of how much force is
needed to push the current. Current is measured in amperes, or
amps for short, while voltage is measured in volts. The electric
power (in watts) is equal to the product of the current and the
voltage, so that a current of 1 amp with a voltage of 100 volts
would give a power of (1 x 100) = 100 watts.
Two types of electricity are commonly used. Alternating current
(AC) electricity is generated in a way that makes it change directions
(alternate) many times each second. The number of times
it changes direction is called the frequency. Direct current
(DC) electricity does not change directions; it always flows the
same way.
Large electric power systems and many small ones use alternating
current, in order to be able to use transformers to change voltages
up and down. Transformers will not work with direct current.
On the other hand, batteries can produce only DC, so small
electric systems which use batteries generally use DC current.
AC can be converted into DC using a device called a rectifier,
while DC can be changed into AC using an inverter.
Almost all mini-hydroelectric systems produce alternating current,
in the same way as large electric power systems located in
cities. In these systems, the voltage and frequency of the electricity
produced are carefully controlled to keep them constant.
Adding more load to an operating power system (such as by turning
on more lights) tends to slow the generators down, which causes
the voltage and the frequency to drop. Conversely, shutting off
lights will reduce the load, permitting the generator to run
faster. These systems must have some kind of an automatic control
which detects when the speed changes, and takes action (such as
letting more water into a turbine) to bring the generators back
up to the right speed. These controls are expensive, and most
micro-hydro systems don't have them.
Electrical equipment is rated in terms of the voltage and the
type of current it is designed for, and the nominal amount of
power it can produce (for a generator) or use (for things that
consume electricity, such as motors and light bulbs). A generator
with a rating of 5 kilowatts (KW) at 100 volts is designed to
produce 50 amperes at 100 volts at full load, which is 5,000
watts or 5 KW. The same generator could also produce smaller
amounts of power. The amount of power put out by the generator
must be equal to the amount of power being used by the electrical
equipment connected to it. The voltage ratings and type of electricity
(DC or AC) used for the electrical equipment should
always be the same as the voltage and type of electricity being
supplied. If you connect a device rated for one voltage to a wire
at another voltage, it almost certainly will not work, and the
device is very likely to be damaged. The same is true of connecting
AC devices to DC. However, many DC devices such as light
bulbs and motors can also be used with AC, if the voltage ratings
are the same.
The amount of energy produced in a generator or used by an electrical
machine can be calculated by multiplying the amount of
power used by the length of time that it is used. Energy is
measured in units of joules--one joule is equal to one watt times
one second. One joule is a very small amount of energy, so we
commonly use units like megajoules (one megajoule is one million
joules) or kilowatt-hours (abbreviated KWH). A kilowatt hour is
equal to one kilowatt provided for one hour, which is 3.6 million
joules. As an example, a 50-KW generator, if it ran at full load
for one hour, would produce produce 50 KWH of electric energy.
If it ran for two hours, it would produce 100 KWH.
Mechanical Power
Mechanical power is the force that causes machinery and other
things to move. The engine of a car produces mechanical power,
and so does an electric motor. Mechanical power can easily be
converted into electrical power (this is what a generator does),
and electrical power can be converted back to mechanical power
(this is done by an electric motor). Mechanical and electrical
power are measured in the same units--watts and kilowatts.
Head, Flow Rate, and Power Output
Water at the top of a hill or drop has energy, called potential
energy, because of where it is situated. This potential energy is
measured in terms of the "head," which is the vertical distance
from the water level at the top of the drop to the water level at
the bottom. Figure 1 shows how head is measured.

umh1x5.gif (600x600)

In natural streams, the potential energy or head of the water is
dissipated by friction against the stream bed as the water flows
downhill, or by turbulence at the bottom. However, if we put in
a smooth pipe from the top to the bottom to reduce friction, and
then put in a water turbine at the bottom, we can use the head in
the water to turn the turbine and produce mechanical power. The
amount of power we can theoretically get is given by:
              [] = F x H x 9.807    (Equation 1)
where [] is the theoretical power output in watts,
        F is the rate of flow of water through the pipe in liters
            per second,
        H is the head in meters, and
  9.807 is the conversion factor that accounts for the force of
            gravity on the water.
However, turbines and generators are not perfectly efficient, so
the amount of electric power we can actually get from a micro-hydro
plant with a given head and flow rate is less than [].
This amount is given by:
              [P.sub.act] = [] x [E.sub.t] x [E.sub.g] x [E.sub.s]   (Equation 2)
where [P.sub.act] is the actual useful power output from the plant,
        [E.sub.t] is the efficiency of the turbine,
        [E.sub.g] is the efficiency of the generator, and
        [E.sub.s] is the efficiency of the rest of the electrical system.
Efficiencies are always less than 1.0. Typically, [E.sub.t] is about
0.85 for turbines from a specialized manufacturer, 0.6 to 0.8 for
pumps used as turbines, and 0.5 to 0.7 for locally-built cross-flow
turbines: [E.sub.g] is usually 0.9 or more, for most kinds of generators.
[E.sub.s]will be about 0.95, unless you are transmitting power
a great distance.
Thus, a flow of 1,000 liters per second, with a head of 10
meters, could theoretically produce 1,000 x 10 x 9.807 = 9,8070
watts, or 98.07 KW. With a turbine efficiency of 0.85, a generator
efficiency of 0.9, and a system efficiency of 0.95, we would
actually get 98,070 x 0.85 x 0.9 x 0.95 = 71,270 watts of useful
power, or 71.27 KW. The rest would be lost due to inefficiencies
in the system.
Figure 2 is a sketch of a typical mini-hydroelectric system,

umh2x7.gif (600x600)

showing the major components.
The water is backed up behind a dam (as shown) or some diversion
structure, where it enters the penstock (the pipe leading to the
turbine). It passes through the turbine, forcing the turbine to
turn, and the turbine then turns the electric generator. The
water then passes out through the draft tube into the tailrace,
and then back into the river. Electricity from the generator
goes to the transformer, where it is raised in voltage,
and then out through a circuit breaker to the power line.
The structural parts of the hydro plant--the dam, penstock, draft
tube, tailrace, power house, and so forth are called the civil
works. The generator, transformer, and circuit breaker are often
referred to collectively as the electrical gear. The electrical
gear also includes many controls, switches, and safety devices
which are not shown in Figure 2.
Civil Works
The civil works needed for a given mini-hydro plant will depend
very strongly on the exact circumstances at the site. In the
worst case, generating power at a completely undeveloped site
might require building an access road to the site, a dam, spillways,
penstock, powerhouse, draft tube, tailrace, and various
other items, at a cost of several million U.S. dollars. On the
other hand, a mini-hydro plant to go into an existing irrigation
system might require only a power house, a short penstock, and a
draft tube, with a correspondingly lower cost.
Civil works are the most variable portion of a hydro plant's cost
--they can account for anywhere from about 15 to more than 75
percent of the total. Be careful not to underestimate their cost
--many of the things that are needed may not be obvious to people
without experience in the area. The construction of dams and
similar structures can be astonishingly expensive.
Hydraulic Turbines
A hydraulic turbine is a machine that converts the head or potential
energy in water into mechanical energy (also called work),
which is used to turn a shaft. There are a number of different
kinds of hydraulic turbines--some of the more common types are
shown in Figure 3. Except for the crossflow (also called the

umh3x90.gif (600x600)

Michell or Banki turbine), all hydraulic turbines for mini- or
large hydro generation are high-technology items which must be
built by a specialized manufacturer.
In response to the increasing interest in small hydro, a number
of manufacturers have recently begun to come out with standardized
turbines for small hydroelectric plants.   Since each turbine
does not need to be individually designed and built, this reduces
the turbine's cost significantly.   It is also possible to use
rotating water pumps as hydraulic turbines.   Since these pumps
are mass-produced in great quantities, their cost can be less
than a third of that of a specially-made turbine.   However, this
lower cost must be balanced against a lower efficiency, which can
reduce the total power output and increase the cost per kilowatt
from the plant.
Selecting the right turbine is one of the most important parts of
designing a hydroelectic facility, and should be done by a qualified
engineer in consultation with the turbine manufacturer.   The
choice of turbine is affected by many considerations, including
the available head and flow, whether the plant will need to
operate at part-load, whether it will be necessary for the plant
to regulate the voltage and frequency in the electric system, the
type of generator to be used, and the cost of the turbine, the
generator, and other parts of the plant.
Electrical Gear
The electrical gear for a mini-hydro plant consists of the generator
and the machinery to connect the generator to a powerline.
In most cases, this machinery includes a transformer, a
circuit breaker, and a number of protective relays, whose function
is to trip the circuit breaker (and thus disconnect the generator
from the power line) if anything goes wrong with either
the plant or the electrical system it's connected to.
There are two main types of generators for use with mini-hydro
plants.  The first type is the synchronous generator, while the
second is called the induction generator.   An induction generator
is the same thing as an induction motor (the most common kind of
three-phase electric motor).   They are simple, reliable, more
efficient, and much less expensive than synchronous generators
of similar size, but they need to be connected to a larger power
system containing one or more synchronous generators in order to
work.  This is because the induction motor gets the power it needs
to energize its magnets from the power system itself.
Synchronous generators are more expensive and are harder to
interface to the power system, but they can operate independently
of the system when necessary.   This is because synchronous generators
provide the power to energize their magnets themselves,
rather than depending on the system.   By controlling the timing
and degree of energization, and their own rotation rate, these
generators can also control the system frequency, voltage, and
power factor.  (Don't worry if you don't understand these technical
terms, just take it for granted that these are things that
need to be controlled).  All generators in large hydro plants and
other large electric generating plants are synchronous generators
for this reason, and at least one generator in any isolated
electrical system must be of the synchronous type.
Almost all mini-hydro plants supply electric power as their only
product.  In the past, hydro turbines were sometimes used directly
to drive large machinery, but except for micro-hydro, this is now
very rare.  Where the plants differ is in what kind of system they
supply electricity to, what the alternative sources of generation
are, and how reliable and well-controlled the power from the
plant needs to be.
Hydro plants are used in three major ways.   The simplest way is
for the plant to be used to save fuel for an electric system
that has other thermal electric generators.   In this arrangement,
the hydro plant is turned on and generates power whenever there
is enough water to run it.  The power generated by the hydro plant
does not have to be generated by some other (usually oil-burning)
generating station, so the utility saves on fuel and
money.  This type of plant is usually cheap and simple to build,
since no water storage is needed, and elaborate controls are not
necessary.  Plants of this kind are sometimes called "run-of-river"
plants.  This is usually the only kind of generation
that is acceptable for plants in irrigation systems and municipal
water supply systems, since the water flows in these systems are
needed for other purposes, and cannot be changed to match the
generating needs.
A second way of using a mini-hydro plant is to provide firm
capacity to a large electric system.   In this case, the hydro
plant is still used to generate power and to save fuel, but in
addition, the system is able to count on the plant to help it
meet the peak electric demand.   Unless the water supply is very
reliable, this will require that the plant have a reservoir for
storing water, in order to make sure that it will be available
when it is needed.  Since this type of plant will always be connected
to a large system with other generators, however, the
plant itself can have simple controls.
The most demanding role for a mini-hydro plant is when it is the
only generator on the system, or where it accounts for a large
fraction of the system's generating capacity.   This will usually
be the case in small, isolated power systems which are not connected
to a national or regional electric transmission network.
Obviously, power from such a plant needs to be very reliable,
which will require either a very reliable water source or a dam
and reservoir.  In addition, this kind of plant will need to be
able to adjust the amount of power it produces to match the load
on the system, and will need to be able to regulate the system
voltage, frequency, and power factor.   This will require complicated
and expensive controls, and may require a more complicated
kind of turbine as well.
The type of generation a plant is to do is determined mostly by
how reliable its water supply is and what kind of system it is
connected to.  As discussed above, this can have major effects on
the design of the plant, and on its cost.   The type of generation
also affects the value of the power produced by the plant.  In an
isolated system, for instance, the cost per KWH from a hydro
plant might be high (due to the extra controls and so forth),
but the cost of the alternative--diesel-electric generation--is
likely to be even higher.  Even in a large utility system, firm
capacity is almost always more valuable than fuel-saving generation,
since the utility will not have to maintain its other generators
to fill in for the hydro plant if it is unable to generate.
Designing and building a mini-hydro plant is a complex operation,
and most aspects of it are best left to experts in the area.  The
skills and expertise required to design the plant include civil
and hydraulic engineering, mechanical engineering, electric power
system engineering, hydrological expertise, map-making, and
drafting skills.  In addition, some knowledge of planning and
financing for energy projects will be needed in designing an
mini-hydro plant.
During the construction stage, the major skills required are
those related to construction of the civil works: construction
engineering, heavy-equipment operation, concrete construction,
masonry construction, and so forth.   Skills in electrical construction
and power-system installation will also be needed.   The
installation of the turbine-generator and its control systems
will also require highly-skilled mechanical and electrical workers.
The operation and maintenance of a mini-hydro system are much
less demanding than its design and construction.   Operating the
plant requires only an understanding of how the plant operates,
what is normal, and what requires special action to correct.  This
requires a basic understanding of mechanics and electricity,
along with specific training in the operation of the particular
system installed at the plant.   This training is normally supplied
by the same organization that oversees the building of the plant.
Maintaining a hydro plant requires the same skills needed for
operating it, along with a general familiarity with machinery,
and skill in using ordinary tools such as wrenches and hoists.
The level of basic skill required is about the same as is needed
by an auto mechanic.  In addition, the plant maintenance person
will need specialized training in maintenance procedures for the
particular plant being maintained.   This training is also usually
supplied by the organization that oversees the building of the
The cost of building a mini-hydro power plant is highly dependent
on the specific circumstances--whether there is already a
dam at the site, how much civil work will be needed, the ease or
difficulty of access, the level of sophistication of the controls
needed, and so forth.  A recent study of small-hydro potential at
existing structures in the U.S. came up with cost estimates of
$1,500 to $4,000 per kilowatt (in 1984 U.S $) for mini-hydro
plants over about 500 KW, and from $2,000 to $6,000 per KW for
those under 500 KW.  Allowing for lower costs of local construction,
and the fact that most of the best hydro sites in the
U.S. have already been used, the comparable costs in a developing
country might be from $1,000 to $4,000 per KW for units
above 500 KW and from $1,500 to $6,000 per KW for units below
that.  This would result in costs of $500,000 to $2,000,000 for
a 500 KW plant, and of $75,000 to $300,000 for one of 50 KW.
Simple projects with moderately high head, so that extensive
civil works would not be needed, would fall toward the lower end
of this range, while complicated or very low-head projects
would approach the upper end.
Before deciding to build a mini-hydro plant (or any other kind of
electric generating plant), it is wise to carefully evaluate all
of the alternatives.  The alternatives that are available will
depend on your situation, and on why you are interested in a
mini-hydro plant.  In general, people who are interested in building
a mini-hydro plant fall into one of four categories.
  1.   The person may want to provide electric power to an area
      where there is no electric service at present.
  2.   The person may want to generate his or her own power (or
      power for a town, employer, cooperative, etc.), instead of
      buying power from a national or regional electric utility.
  3.   The person may have a good hydro site and want to develop
      it in order to sell the power to an electric utility.
  4.   The person is an employee of an electric utility and wants
      to develop a hydro site to provide additional capacity or to
      save on fuel for generation.
In cases two and three, the major alternative to building a mini-hydro
plant is usually to do nothing at all--in case 2, to
continue buying power from the utility, and in both cases, to
invest the money in some other profitable investment.   These
cases are easy to analyze--if you know the price you will have to
pay for power or the price the utility will pay you for your
power, and the approximate cost of the hydro plant, you can compare
the rate of return on your investment with the rate of return
you can get elsewhere.   The section below on "Choosing
the Right Technology" gives some pointers on how to do this.
In the first and the fourth cases, the major alternative to
building a mini-hydro plant will usually be to build some other
kind of generating plant.  Depending on the situation, there may
be a large number of different kinds of generating plants that
look attractive.  The decision as to which technology to use
should be based on many factors, including: (1) the long-term
cost of generating electricity using each technology; (2) appropriate
consideration of the social and environmental costs and
benefits created by each technology; (3) the risk of delays or
cost overruns and (4) the amount and timing of power demand.
Some of the important kinds of electric generating plants for
both large utilities and isolated electric systems are listed in
the next subsection.  The following subsection describes some of
the special advantages of mini-hydro technology as compared with
the others.  The points discussed in Section V, "Choosing the
Right Technology" are also applicable to these cases.
Table 1 contains a list of the major types of conventional and
alternative electric generation technologies, along with some
comments on the applicability and cost of each.   Costs for electric
generating plants vary greatly from year to year, country to
country, and plant to plant.   For this reason, no specific cost
figures are given.  In order to compare the cost of mini-hydro
with other alternative sources of generation, you should use
recent cost estimates for similar plants in your country, or in a
country with similar economic conditions and topography.
Table 1.  A Comparison of Electric Generation Technologies
Type of Technology                       Comments
For Isolated Systems
  Conventional Systems
  Diesel generator                Most commonly used approach.
  Gas-turbine generator           Cheaper to buy than diesel or
  (oil-fired)                      hydro but uses more fuel/KWH
                                  than diesel.
  Mini-hydro plant                More expensive to build, but
                                  requires no fuel and less
  Wind-turbine generator          Requires strong, steady wind.
  Photovoltaics                    Very expensive, except in small
For Large Interconnected Utilities (grid)
    Large hydroelectric plant     Usually the lowest-cost choice
                                  if an appropriate site is
    Steam-electric plant          Expensive fuel makes this
    (oil or natural gas-fired)    very expensive to run.
    Steam-electric plant          Less costly to run than oil
    (coal-fired)                   or gas-fired plants due to
                                  cheaper fuel, but more expensive
                                  to build, plus there are
                                  environmental concerns.
    Simple gas-turbine plant      Very cheap to buy, but expensive
    (oil or natural gas-fired)    to run due to low efficiency
                                  and high fuel cost.
    Nuclear reactor               Feasible only in very large
                                  plants, and frequently very
    Wind-turbine generator        Not suitable for base-load power.
    Mini-hydro plants             Feasibility depends on site
                                  and other conditions, but
                                  often good feasibility.
    Steam electric plant,         Requires a large, dependable
     biomass-fired                supply of biomass.  May have
                                  engineering and/or environmental
If properly used in a good site, small-scale hydroelectric
generation has many advantages over most of the conventional
means of electrical generation listed in Table 1. Some of the
most important advantages for developing countries are listed
Cost--Hydro plants usually cost more to build than plants that
make electricity by burning coal, oil, or natural gas; but once
they are built, the energy to run them is free, while thermal
generating plants must pay for their fuel.   The hydro plant is
also inflation-proof, while the cost of fuel for other plants has
increased enormously.  Hydro plants also last longer than most
other kinds of generating plants.
Rapid Construction--Smaller projects such as mini-hydro plants
can be built more quickly, and can thus be built and providing
electricity long before large hydro plant or most kinds of fuel-burning
generators.  This means faster development, less interest
paid on construction loans, and quicker benefits to the country.
There is also much less risk of long delays in construction with
cost overruns, and a reduced risk of ordering an expensive plant
far in advance, then finding out that it isn't needed after all.
Local Self-Sufficiency--as a renewable resource, hydropower does
not depend on imported oil, coal, or uranium; and it is much less
dependent on foreign experts and technology than other kinds of
electric generation.  Mini-hydro plants can promote self-sufficiency
within a country--if necessary, a town, a cooperative, or
an industry can build its own electric plant, without waiting for
a national electrification project, and without depending on fuel
supplies which may be unreliable and expensive to get.
Appropriate Technology--Compared to other means of generating
electricity, mini-hydro is labor-intensive and suited to operation
by local people.  Although the initial cost of the plant can
be quite high, a good part of this cost comes from on-site
construction, which can provide jobs and training to local residents.
Most other kinds of generating plants require much more
skilled labor, which must be imported at great expense from the
industrial countries.
Beneficial Side-Effects--Small-hydroelectric development is often
accompanied by other beneficial developments such as irrigation,
water-supply and sanitation, fishing, and fish-farming.   The value
of the electric power generated can often make the difference
between a practical, profitable project and one which is too expensive.
Environmental and Social Impact--Since small-hydro development
occurs on a much smaller scale, most of the bad environmental and
social effects of large energy-development projects are eliminated
or greatly reduced.  In many cases, the social consequences of
small hydro (such as jobs, training, community cooperation, opportunity
for small manufacturing development) are highly beneficial,
and well-designed small-hydro projects should not have any
serious environmental problems.   However, some plants using storage
reservoirs may flood a large amount of farm land or other
valuable land.
A choice between mini-hydro and some other generating technology,
or some other source of electricity, should be based
mainly on economics--which option will cost less in the long run?
The best way to calculate this is to calculate the discounted
present value of the life-cycle cost for each alternative.
Present value is a way of measuring how much something (such as
an amount of money) which will be received in the future, is
worth right now.  For instance, if someone promised to give you
$100 in one year, that would be worth less than if he were to
give it to you right away.  This is because, if you had the $100
now, you could put it in the bank or loan it out at interest for
a year, and have the $100 plus the interest on the $100 at the
end of the year.  If the interest rate were 10 percent, you could
loan $90.91 for a year and get back $100.   Thus, the present value
of $100 one year from now is $90.91.   The interest rate used in
computing the present value is called the discount rate, and
$90.91 is the present value of $100 one year from now, discounted
at 10 percent per year.
The present value of any amount of money to be received at any
future time can be calculated from the following formula:
          P =       M
                [(1 + i).sup.n]
where P is the present value
      M is the amount of money to be received in the future
      i is the discount rate, expressed as a decimal fraction per
             unit of time (for instance, 0.10 per year)
      n is the number of units of time in the future the money is
             to be received.
The discount rate you should use will depend on your situation.
In general, it should be the same as the best rate that you could
earn in some other equally risky investment.   If you would need to
borrow the money for the plant, then the discount rate should be
at least as great as the interest rate on the borrowed money, and
probably higher, since there is some risk involved.   It is also
important that the units of time be consistent.   If n is expressed
in years, then i must be in fractions per year; if n is in
months, then i must be in fractions per month.
To calculate the discounted present value of the life-cycle cost,
you simply add up the discounted present values of the costs in
each year that the system would last, and subtract out the present
value of any payments you would receive during the life of
the system.  If you are not sure how to do this, any accountant,
or any good book on accounting should be able to help you.
In calculating the costs of each option, you should be careful
to allow for future increases in price, especially in the price
of oil.  Inflation will probably also increase the cost of electricity
purchased from a utility, operation and maintenance, and
most other recurring costs.  You should also be sure to count any
"hidden" costs--costs which do not result in an immediate outlay
of money.  These might include the lost production from farmland
covered by a hydro reservoir, downtime and expense due to depending
on an unreliable power source, lost profits from money invested
in a power plant that could have been invested elsewhere,
and other factors.
If you are planning to sell power to an electric utility, it
will be necessary to determine how much the utility will be
willing to pay (and whether it will even be willing to buy the
Similarly, if you are planning to substitute your own power for
the utility's, you will need to know how much you will save on
power over the life of the plant, which means that you must try
to predict the utility's rates.
The major steps in planning, designing, and building a mini-hydro
plant are listed below.  In the sections that follow, a few tips
are given on how to carry out those steps.
  1.   Select a promising site.
  2.   Gather as much information about the site as possible.
  3.   Do a "pre-feasibility" study to determine whether the site
      is worth further investigation.  If not, drop the project or
      go back to Step 1.
  4.   Carry out a full-scale feasibility study.   If the feasibility
      study is unfavorable, drop the project or go back to
      Step 1.
  5.   Arrange financing for the project, and agree on any necessary
      arrangements with the electric utility.
  6.   Have a consulting engineering firm draw up designs and specifications
      for the reservoir, dam, penstocks, power plant,
      and switch yard.
  7.   Issue a request for proposals to build the plant, select a
      contractor, and draw up a contract for construction.
  8.   Arrange for construction management.
  9.   Have the plant built.
10.  Test the operation of the plant.
11.  Operate the plant.
Steps 1 and 2 in this process are ones you can do yourself, even
with very little technical background. Step 3, the pre-feasibility
study, requires some technical background, but not as much as
you might think.  Several books listed in the Suggested Reading
List can help you with this. A few tips on how to carry out these
steps are presented below.
Steps 4 through 10 are highly technical, and unless you have a
strong background and experience in the area these are best left
to the management of professional consultants. Such professional
expertise is expensive, but it is usually much more expensive not
to have professional help.  If a consultant prevents just one
serious mistake in the project, he will have paid for his fees
ten times over!  Step 11, operating the plant, will normally be
done by you, or by someone you hire. You should be sure that adequate
training on the plant's operation is included in the contract
for its construction.
Site Selection--Before you can even begin to decide whether to
build a mini-hydro plant, you will need to know where you want
to build it. In other words, you must pick out a site. The site
should have a steady supply of water, and a significant vertical
drop--the more the better.  The cost per kilowatt increases for
low head plants, for low flow, and for plants where a great deal
of civil works must be constructed.   In a preexisting dam with
reliable flow, a head of as little as one meter might be worth
exploiting, since most of the civil works would already be built.
On the other hand, a completely unimproved site might need a head
of as much as 50 meters to be worth exploiting.
Gathering Data--Once you have picked out a promising site, you
should try to find out as much as possible about it.   Exactly how
much head is available?  What are the minimum and maximum flow
rate, and when do these occur?   How much power can be generated
with these flow rates?  How much water would we need to store for
the dry season?  Can we store water at all?  Who owns the land?
Who must give permission to build a dam, or to install a power
plant at an existing dam?  Where are the nearest power lines?
How long an extension to the power lines would be needed to
reach the site?  What arrangements must be made with the electric
utility (if any) to sell them power, or to generate in parallel
with them?  What would the environmental effects of a mini-hydro
plant be?  Are there people who would be harmed by building a
plant at that site (for instance, fishermen, or people who use
the river for washing)?  You should try to think of as many questions
as possible, then try to find answers to them.   In this
way, you will be able to find out about any major problems before
you invest a lot of time and money in the site.   All of these
questions will need to be answered during the feasibility study
anyway, so you can save on consulting fees by answering them
Pre-feasibility Study--Before making a definite commitment to any
but the very smallest mini-hydro projects, you will need to call
in the help of professional hydro engineering consultants for a
full-scale feasibility study, which will generally include the
preliminary design and costing for the plant.   This will be necessary
both to ensure that there are no unsuspected problems with
the site, and to obtain financing.   Few banks or other sources of
funding will provide money without a professionally done study of
this kind.  Such studies are quite expensive (from U.S.$5,000 to
U.S.$50,000).  For this reason, it is important to carry out a
"pre-feasibility" study, in which you make a very rough estimate
of the cost of the plant, the amount of power to be generated,
and the value of that power.   Only if this pre-feasibility study
is favorable should you proceed with the full study.
If you are technically inclined, you can probably carry out this
pre-feasibility study yourself, with the help of one of the
guides listed at the end of this paper.   Otherwise, you should try
to find a local consultant, such as an practicing engineer, a
university professor of engineering, or a professional consulting
firm to assist you.  In some cases, VITA or other development-promotion
organizations may also be able to provide assistance
for a pre-feasibility study.   A reasonably detailed study should
not take more than three to five days of a consultant's time,
depending on the size of the site and the complexity of the
issues.  You should allow considerably longer if you are planning
to carry it out yourself (unless you have considerable
related experience).
The Suggested Reading List at the back of this technical paper
describes a number of useful books and reports that can provide
more general information, as well as some that give specific
directions for evaluating a potential hydro site.   In addition,
the manufacturers of small hydroelectric equipment, listed at the
end of this paper, may be able to provide information and additional
references.  Before contacting manufacturers about a specific
site, you should first find out (at least approximately)
the head, and either the minimum and maximum flow rates or the
amount of power you want to generate.
Many organizations may be able to provide information or assistance
to you in evaluating a small hydroelectric site.   The first
places you should check with are the local electric utility and
the local irrigation authority or other organization that is
concerned with dams and canals.   These organizations will probably
employ engineers knowledgeable in the area, and may be able
to refer you to consultants, government agencies, or others who
may be able to help.  If there is a government agency which is
concerned with rivers, dams, navigation, or similar areas, it
will probably be a good source of information, and you will need
to contact it anyway to find out what legal restrictions there
may be.  Another good source may be in the departments of civil
engineering, mechanical engineering, or agricultural engineering
at a nearby university or technical institute.   Finally, VITA and
other international organizations may be able to provide information,
technical assistance, or both in some cases.
                      SUGGESTED READING LIST
International Water Power and Dam Construction, Business Press
     International, Ltd. Oakfield House, Perrymount Road, Haywards
     Heath, Sussex RH16 3DH, Great Britain.
This is an excellent source of information on everything to do
with all forms of hydropower.   They run frequent articles on
aspects of mini-hydro, and have devoted several special issues to
the topic.  Their advertisements also serve as a good directory
to engineers, manufacturers, and consultants in the field.
Alternative Sources of Energy, Alternative Sources of Energy
     Inc., 107 S. Central Ave., Milaca, Minnesota 56353 USA.
Issue No. 68, July/August 1984, is a special issue on hydropower.
Feasibility Studies For Small Scale Hydropower Additions: A Guide
     Manual from the U.S. Army Corps of Engineers.  Available from
     the U.S. Army Corps of Engineers, Institute for Water Resources,
     Kingman Building, Fort Belvoir, Virginia 22060 USA.
This book is intended to help someone decide whether a hydro
site is worth a full-scale feasibility study.   The book would also
be a big help in doing the full-scale study.   It is much more
detailed than the EPRI report below, and is somewhat harder to
understand.  The numerous pictures and drawings, and the glossary
help somewhat to make the text more understandable, but it can be
slow work going through it.  Nonetheless, if you have the time and
some technical background, this is the book to use.   It has two
major limitations--it is intended mostly for sites where the dam
or other water works are already there, and it is aimed at conditions
in the U.S.  However, it can be adapted to local conditions.
Low-Cost Development of Small Water Power Sites by Hans Hamm.
     Available from VITA, c/o Publisher's Service Inc., 80 South
     Early Street, Alexandria, Virginia 22304 USA.
This book was written in 1967, so it is somewhat dated.   It is
aimed mainly at people interested in micro-hydro.   However, it is
still an excellent, understandable guide to assessing a hydro
site, determining head and flow, etc., and includes a good discussion
of low-technology hydro schemes.   Reading this book is a
good first step for the beginner.
Simplified Methodology For Economic Screening of Potential Low-Head
Small-Capacity Hydroelectric Sites, prepared by Tudor
     Engineering Company.  Available as report EPRI EM-1679 from
     the Electric Power Research Institute, Research Reports Center,
     P.O. Box 50490, Palo Alto, California 94303 USA.
This report is intended for people without experience in hydro,
but with some technical background in electric generation.  It
shows you how to come up with reasonable estimates of the amount
of power available, the value of the power, and the cost of a
hydroelectric project at a given site, so that you can decide
whether it is worthwhile to call in consultants to do a full-scale
feasibility study.  It concentrates on the larger mini-hydro
sites (above 500 KW).  It is aimed at people in the U.S.,
so you may need to adapt it somewhat to local conditions.
Small Hydroelectric Potential At Existing Hydraulic Structures in
     California.   Available as Bulletin 211 from the state of
     California, Department of Water Resources, P.O. Box 388,
     Sacramento, California 95802 USA.  Price is $15.00 for the
     report and its appendixes (be sure to specify that you want
     the appendixes).
California has a similar climate to many developing countries, a
large agricultural sector, and extensive irrigation.   The government
is actively encouraging mini-hydro development.   This report
and its appendixes describe 70 possible mini-hydro projects,
with a summary of the characteristics, advantages, disadvantages,
estimated cost to construct, and cost of power produced at each
site.  The cost estimates and technology are up-to-date, so this
is a very good source of numbers to compare with your estimates.
The large number and variety of projects described may also help
to suggest ideas.  Like the Corps of Engineers' report, however,
it deals only with adding hydro to present water works--projects
which would require new dams are not covered.
Allis-Chalmers Fluid Products Co.
Hydro Turbine Division
Box 712
York, Pennsylvania 17405
Arbanas Industries
24 Hill St.
Xenia, Ohio 45385
Axel Johnson Engineering
666 Howard Street
San Francisco, California 94105
Bouvier Hydropower Inc.
12 Bayard Lane
Suffern, New York 10901
BBC Brown Boveri Corp.
1460 Livingston Ave.
North Brunswick, New Jersey 08902
Canyon Industries
5346 Moquito Lake Rd.
Deming, Washington 98224
C-E/Neyrpic Hydro Power, Inc.
969 High Ridget Rd.
Box 3834
Stamford, Connecticut 06905
Elektra Power Corp.
744 San Antonio Rd.
Palo Alto, California 94303
Essex Development Associates
110 Tremont St.
Boston, Massachusetts 02108
Fairbanks Mill Contracting
North Danville Village
St. Johnsbury, Vermont 05819
Flygt Corporation
129 Glover Ave.
Norwalk, Connecticut 06856
General Electric Co.
Small Hydroelectric Operation
One River Rd.
Bldg. 4, Rm. 305
Schenectady, New York 12345
Generation Unlimited
701 Placentia Ave.
Costa Mesa, California 92627
Hayward Tyler Pump Co.
P.O. Box 492
80 Industrial Pkwy
Burlington, Vermont 05402
Hydro-Tech Systems, Inc.
P.O. Box 82
Chattaroy, Washington 99003
Hydro Watt Systems, Inc.
146 Siglun Rd.
Coos Bay, Oregon 97420
International Power Machinery Co.
833-835 Terminal Tower
Cleveland, Ohio 44113
The James Leffel Company
426 East Street
Springfield, Ohio 45501
Layne & Bowler, Inc.
P.O. Box 8097
Memphis, Tennessee 38108
Mini Hydro Co.
110 East 9th St.
Los Angeles, California 90079
Micro Hydro, Inc.
P.O. Box 1016
Idaho Falls, Idaho 83401
New Found Power Co., Inc.
P.O. Box 576
Hope Valley, Rhode Island 02832
Northwest Energy Systems
P.O. Box 925
Malone, Washington 98559
Oriental Engineering and Supply Co.
251 High St.
Palo Alto, California 94301
Philip C. Ellis
RD 7, Box 125
Reading, Pennsylvania 19606
Real Goods Trading Company, Inc.
308 East Perkins Street
Ukiah, California 95482
    (This organization also sells wind generators and photovoltaic
systems, and many low-voltage DC appliances.   Their catalog
is an excellent introduction to low-voltage power generation.)
162 Battery St.
Burlington, Vermont 05401
Small Hydro East
Star Route 240
Bethel, Maine 04217
Sunny Brook Hydro
P.O. Box 424
Lost Nation Rd.
Lancaster, New Hampshire 03584
Ted Miller Associates
2140 S. Ivanhoe
Denver, Colorado 80222
Worthington Group, McGraw-Edison Company
Box 91
Tarrytown, Maryland 21787
    (Worthington is a pump company that has done a lot of work on
using its pumps as turbines.)
Atlas Polar Company, Ltd.
Hercules Hydrorake Division
P.O. Box 160, Station O
Toronto, Ontario
Barber Hydraulic Turbine Division of Marsh Engineering Limited
P.O. Box 340
Port Colborne, Ontario L3K 5W1 Canada
Canbar Products Ltd.
P.O. Box 280
Waterloo, Ontario
China National Machinery Company
People's Republic of China
(Contact the Chinese embassy in your country for information.)
Dependable Turbines Inc.
#7, 3005 Murray St.
Port Moody
British Columbia
Rue General Mangin, BP 75
38041, Grenoble Cedex
P.O. Box 425
D-8832 Weissenberg/Bavaria
West Germany