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TECHNICAL PAPER # 19
Christopher S. Weaver, P.E.
Theodore Alt, P.E.
Paul N. Garay
1600 Wilson Boulevard, Suite 500
Arlington, Virgnia 22209 USA
703/276-1800 . Fax: 703/243-1865
Understanding Mini-Hydroelectric Generation
Volunteers in Technical Assistance
This paper is one of a series published by Volunteers in
Assistance to provide an introduction to specific
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
They are not intended to provide construction or
details. People are urged to contact VITA or a similar
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
almost entirely by VITA Volunteer technical experts on a
voluntary basis. Some 500 volunteers were involved in the
of the first 100 titles issued, contributing approximately
5,000 hours of their time. VITA staff included Maria
and Leslie Gottschalk as editors, Julie Berman handling
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
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
control as well as in small hydroelectric systems as a
consultant. Weaver is the author of another VITA technical
Understanding Micro-Hydroelectric Generation. The reviewers
this paper are also technical experts in hydroelectricity.
Alt, P.E., is a mechanical engineer who has been in the
energy field since 1942. He has worked with the energy
and development group of the Arizona Public Service Company
the Government of Mexico's electric commission. Paul N.
associate engineer with F.M.C. Associates, has written many
papers on various aspects of water transportation and energy
VITA is a private, nonprofit organization that supports
working on technical problems in developing countries. VITA
information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to
situations. VITA maintains an international Inquiry Service,
specialized documentation center, and a computerized roster
volunteer technical consultants; manages long-term field
and publishes a variety of technical manuals and papers.
VITA Volunteer Christopher Weaver
Electricity can be generated from the power of flowing
This is called hydroelectric generation, and it can be done
that there is water and a hill or drop for it to run
an irrigation canal, where a river runs through rapids or
a waterfall, or where a dam has backed up water above the
of the river. Hydroelectric generating plants come in many
--from huge plants that produce more electricity than most
can use, to very small plants that supply electricity for a
single house. Hydroelectric plants which supply electric
the range from about 15 kilowatts to 15,000 kilowatts are
mini-hydroelectric or mini-hydro. Other phrases that mean
same thing are "small-scale hydro" and "small
Fifteen kilowatts is about the amount of power used by seven
eight houses in the industrial countries, or by a very small
manufacturing plant, or it can provide lighting and other
services for a village of 50-80 houses. Fifteen-thousand
is enough for a medium-sized town. Hydro plants which are
larger than 15,000 kilowatts are usually called "large
"conventional hydro" plants, but there is no sharp
"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,
must be designed by trained engineers. Both types of plants
also fairly expensive. Because of this, mini-hydro plants
well-suited to village-level development in most cases--a
larger organization such as a town, a collection of villages,
an industrial plant is usually needed.
Another type of hydro plant, called "micro-hydro,"
suited to village level development and local self-help
These plants are usually smaller than 15 kilowatts, and can
built by people without much special training, using mostly
materials and skills. Micro-hydro plants are usually very
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
(*) These definitions are not universally agreed on.
may use mini, micro, or small to refer to the same project.
houses and villages, but are not usually good for larger towns
industrial plants, and they cannot be interconnected with
generating plants in an electric system the way mini-hydro
large hydro plants can. Micro-hydro plants are described in
another VITA technical paper, Understanding Micro-Hydroelectric
HISTORY OF MINI-HYDRO GENERATION
Water wheels have been used since ancient times to supply
for grinding grain and other laborious tasks. The first
modern hydraulic turbines were developed in the first part
19th century by Fourneyron in France. These were further
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
invented. Edison's invention of the electric light and of
to distribute electricity occurred at about the same time,
leading to a great boom in hydroelectric development in
and North America. Until about the 1920s, most hydroelectric
developments were quite small--in the size range which is
called mini-hydro. This was for two reasons: people didn't
how to build really large dams and turbines, and the small
electric transmission systems of the time made it difficult
sell large amounts of electricity.
During the era of the 1950s and 1960s, advancing technology and
cheap oil--combined with improved long-distance electric
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
period. With the oil embargo of 1973, which has led to
increases in the cost of oil, small hydro once again appears
Many of the early plants which were abandoned in the
1950s and 1960s are now being refurbished, and many new ones
being planned. Small hydro is also well suited for
countries, and is being actively encouraged by many
and development organizations to reduce oil imports and
II. HYDROPOWER FUNDAMENTALS
This section presents a few basic facts and principles about
electric power and hydroelectric generation. Reading it will
make you into a hydroelectric engineer, but it will help you
understand how hydroelectric systems work, and what makes a
or a bad hydroelectric site. It will also help you to
your hydroelectric engineer if you decide to hire one.
Power is defined as an amount of energy divided by the time
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
One kilowatt is equal to 1,000 watts. Power is also measured
horsepower. one horsepower equals 746 watts.
Two other quantities that are important in talking about
power are the electric current and the voltage. Electric
can be thought of as the amount of electricity flowing
wire (like the amount of water flowing through a pipe),
voltage can be thought of as a measure of how much force is
needed to push the current. Current is measured in amperes,
amps for short, while voltage is measured in volts. The
power (in watts) is equal to the product of the current and
voltage, so that a current of 1 amp with a voltage of 100
would give a power of (1 x 100) = 100 watts.
Two types of electricity are commonly used. Alternating
(AC) electricity is generated in a way that makes it change
(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
Large electric power systems and many small ones use
current, in order to be able to use transformers to change
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
AC can be converted into DC using a device called a
while DC can be changed into AC using an inverter.
Almost all mini-hydroelectric systems produce alternating
in the same way as large electric power systems located in
cities. In these systems, the voltage and frequency of the
produced are carefully controlled to keep them constant.
Adding more load to an operating power system (such as by
on more lights) tends to slow the generators down, which
the voltage and the frequency to drop. Conversely, shutting
lights will reduce the load, permitting the generator to run
faster. These systems must have some kind of an automatic
which detects when the speed changes, and takes action (such
letting more water into a turbine) to bring the generators
up to the right speed. These controls are expensive, and
micro-hydro systems don't have them.
Electrical equipment is rated in terms of the voltage and
type of current it is designed for, and the nominal amount
power it can produce (for a generator) or use (for things
consume electricity, such as motors and light bulbs). A
with a rating of 5 kilowatts (KW) at 100 volts is designed
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
must be equal to the amount of power being used by the
equipment connected to it. The voltage ratings and type of
(DC or AC) used for the electrical equipment should
always be the same as the voltage and type of electricity
supplied. If you connect a device rated for one voltage to a
at another voltage, it almost certainly will not work, and
device is very likely to be damaged. The same is true of
AC devices to DC. However, many DC devices such as light
bulbs and motors can also be used with AC, if the voltage
are the same.
The amount of energy produced in a generator or used by an
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
one second. One joule is a very small amount of energy, so
commonly use units like megajoules (one megajoule is one
joules) or kilowatt-hours (abbreviated KWH). A kilowatt hour
equal to one kilowatt provided for one hour, which is 3.6
joules. As an example, a 50-KW generator, if it ran at full
for one hour, would produce produce 50 KWH of electric
If it ran for two hours, it would produce 100 KWH.
Mechanical power is the force that causes machinery and
things to move. The engine of a car produces mechanical
and so does an electric motor. Mechanical power can easily
converted into electrical power (this is what a generator
and electrical power can be converted back to mechanical
(this is done by an electric motor). Mechanical and
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
energy, because of where it is situated. This potential
measured in terms of the "head," which is the
from the water level at the top of the drop to the water
the bottom. Figure 1 shows how head is measured.
In natural streams, the potential energy or head of the
dissipated by friction against the stream bed as the water
downhill, or by turbulence at the bottom. However, if we put
a smooth pipe from the top to the bottom to reduce friction,
then put in a water turbine at the bottom, we can use the
the water to turn the turbine and produce mechanical power.
amount of power we can theoretically get is given by:
[P.sub.th] = F x H x 9.807
where [P.sub.th] is the theoretical power output in watts,
F is the rate
of flow of water through the pipe in liters
H is the head
in meters, and
9.807 is the
conversion factor that accounts for the force of
on the water.
However, turbines and generators are not perfectly
the amount of electric power we can actually get from a
plant with a given head and flow rate is less than
This amount is given by:
[P.sub.act] = [P.sub.th] x [E.sub.t] x [E.sub.g] x [E.sub.s]
where [P.sub.act] is the actual useful power output from the
the efficiency of the turbine,
the efficiency of the generator, and
the efficiency of the rest of the electrical system.
Efficiencies are always less than 1.0. Typically, [E.sub.t]
0.85 for turbines from a specialized manufacturer, 0.6 to
pumps used as turbines, and 0.5 to 0.7 for locally-built
turbines: [E.sub.g] is usually 0.9 or more, for most kinds
[E.sub.s]will be about 0.95, unless you are transmitting
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 =
watts, or 98.07 KW. With a turbine efficiency of 0.85, a
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
power, or 71.27 KW. The rest would be lost due to
in the system.
III. MINI-HYDROELECTRIC SYSTEMS
Figure 2 is a sketch of a typical mini-hydroelectric system,
showing the major components.
The water is backed up behind a dam (as shown) or some
structure, where it enters the penstock (the pipe leading to
turbine). It passes through the turbine, forcing the turbine
turn, and the turbine then turns the electric generator. The
water then passes out through the draft tube into the
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,
tube, tailrace, power house, and so forth are called the
works. The generator, transformer, and circuit breaker are
referred to collectively as the electrical gear. The
gear also includes many controls, switches, and safety
which are not shown in Figure 2.
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
might require building an access road to the site, a dam,
penstock, powerhouse, draft tube, tailrace, and various
other items, at a cost of several million U.S. dollars. On
other hand, a mini-hydro plant to go into an existing
system might require only a power house, a short penstock,
draft tube, with a correspondingly lower cost.
Civil works are the most variable portion of a hydro plant's
--they can account for anywhere from about 15 to more than
percent of the total. Be careful not to underestimate their
--many of the things that are needed may not be obvious to
without experience in the area. The construction of dams and
similar structures can be astonishingly expensive.
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A hydraulic turbine is a machine that converts the head or
energy in water into mechanical energy (also called work),
which is used to turn a shaft. There are a number of
kinds of hydraulic turbines--some of the more common types
shown in Figure 3. Except for the crossflow (also called the
Michell or Banki turbine), all hydraulic turbines for mini-
large hydro generation are high-technology items which must
built by a specialized manufacturer.
In response to the increasing interest in small hydro, a
of manufacturers have recently begun to come out with
turbines for small hydroelectric plants.
Since each turbine
does not need to be individually designed and built, this
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
than a third of that of a specially-made turbine.
lower cost must be balanced against a lower efficiency,
reduce the total power output and increase the cost per
from the plant.
Selecting the right turbine is one of the most important
designing a hydroelectic facility, and should be done by a
engineer in consultation with the turbine manufacturer.
choice of turbine is affected by many considerations,
the available head and flow, whether the plant will need to
operate at part-load, whether it will be necessary for the
to regulate the voltage and frequency in the electric
type of generator to be used, and the cost of the turbine,
generator, and other parts of the plant.
The electrical gear for a mini-hydro plant consists of the
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
is to trip the circuit breaker (and thus disconnect the
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
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
three-phase electric motor).
They are simple, reliable, more
efficient, and much less expensive than synchronous
of similar size, but they need to be connected to a larger
system containing one or more synchronous generators in
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
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,
generators can also control the system frequency, voltage,
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
for this reason, and at least one generator in any isolated
electrical system must be of the synchronous type.
USES FOR MINI-HYDRO PLANTS
Almost all mini-hydro plants supply electric power as their
product. In the
past, hydro turbines were sometimes used directly
to drive large machinery, but except for micro-hydro, this
very rare. Where the
plants differ is in what kind of system they
supply electricity to, what the alternative sources of
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
is enough water to run it.
The power generated by the hydro plant
does not have to be generated by some other (usually
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
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
water supply systems, since the water flows in these systems
needed for other purposes, and cannot be changed to match
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
addition, the system is able to count on the plant to help
meet the peak electric demand.
Unless the water supply is very
reliable, this will require that the plant have a reservoir
storing water, in order to make sure that it will be
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
only generator on the system, or where it accounts for a
fraction of the system's generating capacity.
This will usually
be the case in small, isolated power systems which are not
to a national or regional electric transmission network.
Obviously, power from such a plant needs to be very
which will require either a very reliable water source or a
and reservoir. In
addition, this kind of plant will need to be
able to adjust the amount of power it produces to match the
on the system, and will need to be able to regulate the
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
how reliable its water supply is and what kind of system it
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
but the cost of the alternative--diesel-electric
likely to be even higher.
Even in a large utility system, firm
capacity is almost always more valuable than fuel-saving
since the utility will not have to maintain its other
to fill in for the hydro plant if it is unable to generate.
SKILLS REQUIRED TO DESIGN, BUILD, OPERATE, AND MAINTAIN A
Designing and building a mini-hydro plant is a complex
and most aspects of it are best left to experts in the
skills and expertise required to design the plant include
and hydraulic engineering, mechanical engineering, electric
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
During the construction stage, the major skills required are
those related to construction of the civil works:
engineering, heavy-equipment operation, concrete
masonry construction, and so forth.
Skills in electrical construction
and power-system installation will also be needed.
installation of the turbine-generator and its control
will also require highly-skilled mechanical and electrical
The operation and maintenance of a mini-hydro system are
less demanding than its design and construction.
plant requires only an understanding of how the plant
what is normal, and what requires special action to
requires a basic understanding of mechanics and electricity,
along with specific training in the operation of the
system installed at the plant.
This training is normally supplied
by the same organization that oversees the building of the
Maintaining a hydro plant requires the same skills needed
operating it, along with a general familiarity with
and skill in using ordinary tools such as wrenches and
The level of basic skill required is about the same as is
by an auto mechanic.
In addition, the plant maintenance person
will need specialized training in maintenance procedures for
particular plant being maintained.
This training is also usually
supplied by the organization that oversees the building of
COST OF MINI-HYDRO GENERATION
The cost of building a mini-hydro power plant is highly
on the specific circumstances--whether there is already a
dam at the site, how much civil work will be needed, the
difficulty of access, the level of sophistication of the
needed, and so forth.
A recent study of small-hydro potential at
existing structures in the U.S. came up with cost estimates
$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
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
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
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
of this range, while complicated or very low-head projects
would approach the upper end.
IV. COMPARING THE ALTERNATIVES
Before deciding to build a mini-hydro plant (or any other
electric generating plant), it is wise to carefully evaluate
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.
The person may want to provide electric
power to an area
where there is
no electric service at present.
The person may want to generate his or her
own power (or
power for a
town, employer, cooperative, etc.), instead of
from a national or regional electric utility.
The person may have a good hydro site and
want to develop
it in order to
sell the power to an electric utility.
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
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,
invest the money in some other profitable investment.
cases are easy to analyze--if you know the price you will
pay for power or the price the utility will pay you for your
power, and the approximate cost of the hydro plant, you can
the rate of return on your investment with the rate of
you can get elsewhere.
The section below on "Choosing
the Right Technology" gives some pointers on how to do
In the first and the fourth cases, the major alternative to
building a mini-hydro plant will usually be to build some
kind of generating plant.
Depending on the situation, there may
be a large number of different kinds of generating plants
look attractive. The
decision as to which technology to use
should be based on many factors, including: (1) the
cost of generating electricity using each technology; (2)
consideration of the social and environmental costs and
benefits created by each technology; (3) the risk of delays
cost overruns and (4) the amount and timing of power demand.
Some of the important kinds of electric generating plants
both large utilities and isolated electric systems are
the next subsection.
The following subsection describes some of
the special advantages of mini-hydro technology as compared
the others. The
points discussed in Section V, "Choosing the
Right Technology" are also applicable to these cases.
ELECTRIC GENERATION TECHNOLOGIES
Table 1 contains a list of the major types of conventional
alternative electric generation technologies, along with
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
country with similar economic conditions and topography.
Table 1. A
Comparison of Electric Generation Technologies
Type of Technology
For Isolated Systems
generator Most commonly
generator Cheaper to buy than
hydro but uses more
plant More expensive to
requires no fuel and less
generator Requires strong,
Very expensive, except in
For Large Interconnected Utilities (grid)
hydroelectric plant Usually the
if an appropriate site is
plant Expensive fuel makes this
(oil or natural
gas-fired) very expensive to run.
plant Less costly to run than
or gas-fired plants due to
cheaper fuel, but more expensive
to build, plus there are
gas-turbine plant Very cheap to
buy, but expensive
(oil or natural
gas-fired) to run due to low
and high fuel cost.
reactor Feasible only in
plants, and frequently very
generator Not suitable for
plants Feasibility depends
and other conditions, but
often good feasibility.
plant, Requires a large,
supply of biomass. May have
ADVANTAGES OF MINI-HYDROELECTRIC GENERATION
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
most important advantages for developing countries are
Cost--Hydro plants usually cost more to build than plants
make electricity by burning coal, oil, or natural gas; but
they are built, the energy to run them is free, while
generating plants must pay for their fuel.
The hydro plant is
also inflation-proof, while the cost of fuel for other
Hydro plants also last longer than most
other kinds of generating plants.
Rapid Construction--Smaller projects such as mini-hydro
can be built more quickly, and can thus be built and
electricity long before large hydro plant or most kinds of
means faster development, less interest
paid on construction loans, and quicker benefits to the
There is also much less risk of long delays in construction
cost overruns, and a reduced risk of ordering an expensive
far in advance, then finding out that it isn't needed after
Local Self-Sufficiency--as a renewable resource, hydropower
not depend on imported oil, coal, or uranium; and it is much
dependent on foreign experts and technology than other kinds
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
a national electrification project, and without depending on
supplies which may be unreliable and expensive to get.
Appropriate Technology--Compared to other means of
electricity, mini-hydro is labor-intensive and suited to
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
Most other kinds of generating plants require much more
skilled labor, which must be imported at great expense from
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Beneficial Side-Effects--Small-hydroelectric development is
accompanied by other beneficial developments such as
water-supply and sanitation, fishing, and fish-farming.
of the electric power generated can often make the
between a practical, profitable project and one which is too
Environmental and Social Impact--Since small-hydro
occurs on a much smaller scale, most of the bad
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,
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
V. CHOOSING THE
A choice between mini-hydro and some other generating
or some other source of electricity, should be based
mainly on economics--which option will cost less in the long
The best way to calculate this is to calculate the
present value of the life-cycle cost for each alternative.
Present value is a way of measuring how much something (such
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
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
a year, and have the $100 plus the interest on the $100 at
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,
at 10 percent per year.
The present value of any amount of money to be received at
future time can be calculated from the following formula:
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
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
In general, it should be the same as the best rate that you
earn in some other equally risky investment.
If you would need to
borrow the money for the plant, then the discount rate
at least as great as the interest rate on the borrowed
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
you simply add up the discounted present values of the costs
each year that the system would last, and subtract out the
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
to allow for future increases in price, especially in the
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
of money. These
might include the lost production from farmland
covered by a hydro reservoir, downtime and expense due to
on an unreliable power source, lost profits from money
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
Similarly, if you are planning to substitute your own power
the utility's, you will need to know how much you will save
power over the life of the plant, which means that you must
to predict the utility's rates.
BUILDING A MINI-HYDRO PLANT
The major steps in planning, designing, and building a
plant are listed below.
In the sections that follow, a few tips
are given on how to carry out those steps.
Select a promising site.
Gather as much information about the site as
Do a "pre-feasibility" study to
determine whether the site
further investigation. If not, drop the
go back to Step
Carry out a full-scale feasibility study.
If the feasibility
unfavorable, drop the project or go back to
Arrange financing for the project, and agree
on any necessary
with the electric utility.
Have a consulting engineering firm draw up
designs and specifications
reservoir, dam, penstocks, power plant,
Issue a request for proposals to build the
plant, select a
draw up a contract for construction.
Arrange for construction management.
Have the plant built.
10. Test the
operation of the plant.
11. Operate the
Steps 1 and 2 in this process are ones you can do yourself,
with very little technical background. Step 3, the
study, requires some technical background, but not as much
you might think.
Several books listed in the Suggested Reading
List can help you with this. A few tips on how to carry out
steps are presented below.
Steps 4 through 10 are highly technical, and unless you have
strong background and experience in the area these are best
to the management of professional consultants. Such
expertise is expensive, but it is usually much more
to have professional help.
If a consultant prevents just one
serious mistake in the project, he will have paid for his
ten times over! Step
11, operating the plant, will normally be
done by you, or by someone you hire. You should be sure that
training on the plant's operation is included in the
for its construction.
Site Selection--Before you can even begin to decide whether
build a mini-hydro plant, you will need to know where you
to build it. In other words, you must pick out a site. The
should have a steady supply of water, and a significant
drop--the more the better.
The cost per kilowatt increases for
low head plants, for low flow, and for plants where a great
of civil works must be constructed.
In a preexisting dam with
reliable flow, a head of as little as one meter might be
exploiting, since most of the civil works would already be
On the other hand, a completely unimproved site might need a
of as much as 50 meters to be worth exploiting.
Gathering Data--Once you have picked out a promising site,
should try to find out as much as possible about it.
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
Who must give permission to build a dam, or to install a
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
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
the river for washing)?
You should try to think of as many questions
as possible, then try to find answers to them.
way, you will be able to find out about any major problems
you invest a lot of time and money in the site.
All of these
questions will need to be answered during the feasibility
anyway, so you can save on consulting fees by answering them
Pre-feasibility Study--Before making a definite commitment
but the very smallest mini-hydro projects, you will need to
in the help of professional hydro engineering consultants
full-scale feasibility study, which will generally include
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
this kind. Such
studies are quite expensive (from U.S.$5,000 to
this reason, it is important to carry out a
"pre-feasibility" study, in which you make a very
of the cost of the plant, the amount of power to be
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
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,
university professor of engineering, or a professional
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
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
FOR MORE INFORMATION
The Suggested Reading List at the back of this technical
describes a number of useful books and reports that can
more general information, as well as some that give specific
directions for evaluating a potential hydro site.
the manufacturers of small hydroelectric equipment, listed
end of this paper, may be able to provide information and
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
amount of power you want to generate.
Many organizations may be able to provide information or
to you in evaluating a small hydroelectric site.
places you should check with are the local electric utility
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
may be able to help.
If there is a government agency which is
concerned with rivers, dams, navigation, or similar areas,
will probably be a good source of information, and you will
to contact it anyway to find out what legal restrictions
may be. Another good
source may be in the departments of civil
engineering, mechanical engineering, or agricultural
at a nearby university or technical institute.
Finally, VITA and
other international organizations may be able to provide
technical assistance, or both in some cases.
SUGGESTED READING LIST
International Water Power and Dam Construction, Business
Ltd. Oakfield House, Perrymount Road, Haywards
RH16 3DH, Great Britain.
This is an excellent source of information on everything to
with all forms of hydropower.
They run frequent articles on
aspects of mini-hydro, and have devoted several special
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
BOOKS AND REPORTS
Feasibility Studies For Small Scale Hydropower Additions: A
Manual from the
U.S. Army Corps of Engineers. Available
the U.S. Army
Corps of Engineers, Institute for Water Resources,
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
numerous pictures and drawings, and the glossary
help somewhat to make the text more understandable, but it
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
or other water works are already there, and it is aimed at
in the U.S. However,
it can be adapted to local conditions.
Low-Cost Development of Small Water Power Sites by Hans
VITA, c/o Publisher's Service Inc., 80 South
Alexandria, Virginia 22304 USA.
This book was written in 1967, so it is somewhat dated.
aimed mainly at people interested in micro-hydro.
However, it is
still an excellent, understandable guide to assessing a
site, determining head and flow, etc., and includes a good
of low-technology hydro schemes.
Reading this book is a
good first step for the beginner.
Simplified Methodology For Economic Screening of Potential
Small-Capacity Hydroelectric Sites, prepared by Tudor
Company. Available as report EPRI
Power Research Institute, Research Reports Center,
P.O. Box 50490,
Palo Alto, California 94303 USA.
This report is intended for people without experience in
but with some technical background in electric
shows you how to come up with reasonable estimates of the
of power available, the value of the power, and the cost of
hydroelectric project at a given site, so that you can
whether it is worthwhile to call in consultants to do a
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
Available as Bulletin 211 from the state of
Department of Water Resources, P.O. Box 388,
California 95802 USA. Price is $15.00
report and its
appendixes (be sure to specify that you want
California has a similar climate to many developing
large agricultural sector, and extensive irrigation.
is actively encouraging mini-hydro development.
and its appendixes describe 70 possible mini-hydro projects,
with a summary of the characteristics, advantages,
estimated cost to construct, and cost of power produced at
site. The cost
estimates and technology are up-to-date, so this
is a very good source of numbers to compare with your
The large number and variety of projects described may also
to suggest ideas.
Like the Corps of Engineers' report, however,
it deals only with adding hydro to present water
which would require new dams are not covered.
MANUFACTURERS AND DISTRIBUTORS
Allis-Chalmers Fluid Products Co.
Hydro Turbine Division
York, Pennsylvania 17405
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
5346 Moquito Lake Rd.
Deming, Washington 98224
C-E/Neyrpic Hydro Power, Inc.
969 High Ridget Rd.
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
129 Glover Ave.
Norwalk, Connecticut 06856
General Electric Co.
Small Hydroelectric Operation
One River Rd.
Bldg. 4, Rm. 305
Schenectady, New York 12345
701 Placentia Ave.
Costa Mesa, California 92627
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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
organization also sells wind generators and photovoltaic
systems, and many low-voltage DC appliances.
is an excellent introduction to low-voltage power
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
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
Barber Hydraulic Turbine Division of Marsh Engineering
P.O. Box 340
Port Colborne, Ontario L3K 5W1 Canada
Canbar Products Ltd.
P.O. Box 280
China National Machinery Company
People's Republic of China
(Contact the Chinese embassy in your country for
Dependable Turbines Inc.
#7, 3005 Murray St.
Rue General Mangin, BP 75
38041, Grenoble Cedex
P.O. Box 425
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