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Report 2 (of 5): Stream
Line, Kenya
Introduction
The absence of electric power greatly
constrains a community's ability to generate income
and provide local services. Decentralised energy options
using local resources, such as wind, biogas, solar
power and hydro power, offer many advantages for meeting
the needs of rural populations. Development of one
or more renewable energy options can improves both
of these aspects of community life
Since the early 1990s, pico-hydro
has been used to deliver electricity and mechanical
power to remote mountainous areas of the world. Pico-hydro
projects are hydroelectric schemes with a power generation
capacity of up to 5 kilowatts (kW). The energy in
water flowing down a slope is converted into electrical
energy. Pico-hydro schemes have low power outputs,
but require little water and are simple to install.
They typically provide energy for lighting and battery
charging.
Experts from the Energy Programme
of ITDG East Africa, based in Kenya, in collaboration
with Nottingham Trent University in the UK are working
to develop the pico-hydro power sector in Kenya. The
project demonstrates that pico-hydro technology is
a sustainable and affordable technology for community
electrification. Contributing to the establishment
of hydro power infrastructure in rural Kenya and sub-Saharan
Africa as a whole, the project benefits two rural
communities in Kirinyaga District, central Kenya.
Water Power
The flow of water in rivers and streams
is a potential source of energy. Hydro power is a
very clean source of energy. It relies on a natural,
non-polluting and renewable resource. Traditional
water-wheels, used for providing energy for milling
and pumping, have been superseded by modern turbines
that are compact, highly efficient and capable of
turning at high speed.
Hydro power has many advantages, including:
- Power is usually available continuously
on demand.
- It is a concentrated energy source.
- The energy available is predictable.
- No fuel and limited maintenance
are required, so running costs are low compared
with diesel power.
- It is a long-lasting and robust
technology; systems can last for 50 years or more
without major new investments.
Micro-hydro is the term used for technologies
that convert energy in flowing water to direct-drive
shaft power or to electricity generation on a very
small scale. Ranging from a few hundred watts for
battery charging or food processing applications up
to 100 kW, micro-hydro provides power for small communities
and rural industry in remote areas away from grid
electricity. Hydro power that produces a maximum electrical
output of 5 kW is called pico-hydro.
Pico-hydro Power
Recent innovations in pico-hydro technology
have made it a source of power for some of the poorest
and most remote regions in the world. It is a versatile
power source as it can produce alternating current
(AC) electricity, enabling standard appliances to
be used, and it can be distributed to a whole village.
It is used to power light bulbs, radios, televisions,
refrigerators and food processors. It offers communities
an alternative to the use of hazardous and expensive
kerosene for lighting households, schools and businesses.
Mechanical power can also be used with some designs
to operate workshop tools and grain mills.
Pico-hydro has a number of advantages
over larger systems.
- Smaller water flows are required
and there are many more sites that are suitable.
- It is easier to establish and maintain
agreements regarding ownership, payments, operation,
maintenance and water rights, as the units only
supply power for a small number of households.
- Even in countries with extensive
grid electrification, pico-hydro can be suitable
for the many small, remote communities for which
grid extension would be extremely expensive and
not practical.
- Locally manufactured systems can
be produced that have much lower long- term costs
per kilowatt than solar, wind and diesel systems.
Pico-hydro in Kenya
Kathamba and Thima, in the Kirinyaga
District of Kenya, are the recipients of a pico-hydro
scheme, the first of its kind in Africa, thanks to
ITDG East Africa and Nottingham Trent University's
Pico Hydro Unit. The success of the project is due
to the availability of trained people and the support
given by the local communities.
In Kathamba during the wet season,
the spring produces 8 litres of water per second,
generating approximately 1.7 kW to 2 kW of power.
This is distributed to more than 30 households, with
another 35 homes awaiting connection. The scheme in
Thima covers 66 households. Each 'package' consists
of light units and a socket for which users pay between
US$55 and $75 to be connected to electricity. Fuel
costs have dramatically reduced, with money saved
each month on kerosene and dry cell batteries.
Powerhouse and community in Ndundu Village, Thima
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Eric Mucharia and family at home watching TV
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How Does it Work?
Water is diverted down a pipe, called
the penstock, to fall through a vertical height or
head, in order to gather energy. The lower end of
the penstock is attached to a turbine that is turned
by the energy in the falling water. As the turbine
spins, it can be connected either directly to machines
such as mills and presses or to a generator to provide
electrical power for a small grid or battery charging.
The amount of energy available is directly related
to the volume of water flowing down the penstock and
the height, through which it falls. The greater the
volume of water and the greater the height, the more
energy can be harnessed.
Figure 1. Components of a Pico-hydro System ©
Maher and Smith, 2001
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There are eight main components to
a pico-hydro system:
- Water supply
The source of water is a stream or an irrigation
channel. Small amounts of water can also be diverted
from rivers. It is important that the source of
water is reliable and not needed by anyone else.
Springs make excellent sources as they do not dry
up in dry weather and are usually clean, which stops
silt building up in the system.
- Forebay tank
Water is fed into a forebay tank. This is often
enlarged to form a small reservoir. This can be
useful if the water available is not enough during
the dry season.
- Penstock pipe
Water flows from the forebay tank or reservoir down
a long pipe called the penstock. At the end of the
penstock water comes out of a nozzle as a high-
pressure jet. A drop or head of at least 20 metres
is recommended and means that the amount of water
needed to produce enough power for the basic needs
of a village is quite small.
- Turbine and generator
The power in the jet, or hydro power, is transmitted
to a turbine runner that changes it into mechanical
power. The runner has blades or buckets that cause
it to rotate when struck by the water. The turbine
is a general name that refers to the runner, nozzle
and surrounding case. The runner typically spins
1500 times every minute. The turbine is attached
to a generator. This converts rotating power into
electrical power. This is how water flowing in a
small stream can become electricity.
- Electronic controller
An electronic controller is connected to the generator.
This matches the electrical power that is produced
to the electrical loads that are connected, and
stops the voltage from changing as devices are switched
on and off.
An electronic load controller
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- Mechanical load
The mechanical load is a machine connected to the
turbine shaft using a pulley system so that power
can be drawn directly from the turbine. The rotating
force of the turbine runner can be used to turn
equipment such as grain mills or woodwork machinery.
Approximately 10 per cent of the mechanical power
is lost in the pulley system but it is still an
efficient way of using the power as none is lost
in the generator or electric motor.
- Distribution system
The distribution system connects the electricity
supply from the generator to the houses or schools.
This is often one of the most expensive parts of
the system.
- Electrical loads
Electrical loads are usually connected inside houses.
This is a general name given to any device that
uses the electricity generated. The type of loads
connected to a pico-hydro scheme depends largely
on the amount of power generated. Using the power
wisely can add more benefits. Special lights such
a fluorescent bulbs, for example, use less power
and so more lights can be connected to the same
generator.
After passing through the whole system,
water is normally returned to a stream or river below
the powerhouse.
Planning a Pico-hydro Scheme
It is important to conduct a feasibility
study in a proposed area to determine what is required
to implement a pico-hydro project for village electrification.
Overview: Establish the demand,
willingness to pay, local ability to manage a scheme,
and grid electricity available or planned.
Location: A suitable geographical location
for a pico-hydro scheme is one with steep rivers that
have an all-year flow.
Demand survey: Estimate the number of houses
within 1km (approximately two- thirds of a mile) from
the water supply and those who are willing to pay.
A 1km radius is the distance that electricity can
most easily be transmitted.
Power estimate: The head and flow rate should
both be measured to determine the possible power output
and to help in choosing equipment.
Cost and availability: Estimate the size of
generator needed to meet the energy demand, based
on the head, flow and power outputs of available equipment.
Typically, the higher the head the lower the cost
per installed kilowatt. A typical system may cost
approximately US$3,000 per kilowatt. The initial investment
is high, but running costs, mostly maintenance, are
low because there is no need to buy fuel.
Viability: Comparing the likely annual income
with capital cost gives a rough guide to financial
viability. If the annual income is less than 10 per
cent of the capital cost, the project is not viable.
If it is 10-25 per cent the scheme could be possible.
If the annual income is more than 25 per cent, then
the scheme is viable.
Head and flow: Decide on a suitable combination
of head and flow to produce the required power. Assumptions
should be made on the system efficiency, but if in
doubt, assume an overall efficiency (water power to
electrical power) of 45 per cent.
Village meeting: Present the findings of the
survey to the community at an open meeting. Local
government staff and local development organisations
should be encouraged to attend.
Other steps: A number of other steps need to
be taken, including a detailed site survey, finalising
power output, producing a scale map and scheme layout,
a detailed costing, consumer contracts for electricity
supply and organising finance. Once this has been
done the scheme can get under way. Ordering materials,
installation and training can all be undertaken.
Measuring Power and Efficiency:
Power
- Power is measured in Watts (W) or kilowatts (kW). There are 1000 W in 1 kW.
- Pico hydro power has a maximum electrical power output of 5 kW.
- There are three types of power when referring to a hydro project; water or hydraulic power, mechanical power and electrical power.
- Hydraulic power will always be more than mechanical and electrical power because as power is converted from one form to another, some is lost at each stage of the process. See diagram below.
- Up to 30% of power is lost in the penstock when water comes into contact with the walls of the pipe. This friction slows down the water, hence losing power.
- The biggest loss usually occurs when the jet of water hits the turbine runner. This should be approximately 30% on a well designed system.
- Approximately a further 20-30% will be lost in the generator when the mechanical power is converted into electricity.
Efficiency
- Efficiency describes how well power is converted into from one form to another.
- A turbine with an efficiency of 70% will convert 70% of the hydraulic power into mechanical power, with 30% being lost.
- System efficiency is the combined efficiency of all processes together.
- The system efficiency for electricity generation using pico hydro is typically between 40% - 50%.
Example
If there is found to be 2.8 kW of hydraulic power in a small stream, the electricity that could be expected is:
2.8 x 45% = 2.8 x 0.45 = 1.26 kW
Calculating hydraulic power
The hydraulic power in a stream can is calculated when the Head and the Flow have been measured. The formula for calculating hydraulic power is:
Power = Head (metres) x Flow (litres per second) x 9.81
Example
If the head = 60 m and the flow = 10 l/s then:
Power = 60 x 10 x 9.81 = 5886 watts or 5.9 kW
The pico-hydro project in Kenya has
proven that this technology is both sustainable and
affordable. Utilising a small spring to generate electricity,
the communities of Kathamba and Thima now watch TV,
listen to the radio and children can do homework at
night knowing this technology is environmentally friendly.
Money saved on buying kerosene and batteries can be
used for other things, including children's education.
All photos © ITDG/Zul
For further Information, please contact:
ITDG East Africa
P.O. Box 39493
Nairobi
Kenya
Tel: +00 254 2 719313
Fax: +00 254 2 710083
E-mail: itkenya@itdg.or.ke
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The Pico Hydro Network
Micro-Hydro Centre
Dept of Electrical and Electronic Engineering
Nottingham Trent University
Burton Street
Nottingham NG1 4BU
United Kingdom
Tel: +44 (0)115 8482 031
Fax: +44 (0)115 948 6567
E-Mail: n.smith@ntu.ac.uk
Website: www.eee.ntu.ac.uk/research/microhydro/picosite/
The department also publishes
a newsletter, Pico Hydro. |
Further reading
Pico Hydro for Village Power: A
Practical Manual for Schemes up to 5 kW in Hilly Areas
Phillip Maher and Nigel Smith
Free, Nottingham Trent University, 2001. Also available
in Spanish.
This manual helps to overcome some of the problems
of pico-hydro implementation by providing clear instructions
for design and installation of schemes on a local
level. Designs are recommended that emphasise simplicity,
low maintenance and long-life expectancy. The manual
is aimed at everyone interested in pico-hydro or rural
electrification. It is particularly intended for those
who are thinking about this technology for the first
time and perhaps looking to implement such a scheme
locally, for 'first time' engineers.
The Pico Power Pack: Fabrication
and Assembly Instructions
Phillip Maher
Free, Nottingham Trent University, 2001
The Pico Power Pack is a design of water-powered turbine
and generator unit that can be installed in regions
where there is a head or drop of at least 20 metres.
The pack is aimed at manufacturers to stimulate local
production of recommended designs and increase availability.
This manual is a complementary publication to Pico
Hydro for Village Power.
Water Power for a Village Business
Adam Harvey and Nigel Smith
Free, Nottingham Trent University, 2001
Provides initial advice and ideas to help explore
opportunities for harnessing power from streams and
rivers. It contains information on a range of applications
for water power, illustrated case studies and an introduction
to estimating the power potential of a stream.
These manuals can be obtained for
free by joining the Pico Hydro Network from the website
or by contacting them directly.
Books available from ITDG Development
Bookshop
Micro-Hydro Design Manual
Adam Harvey
This book has grown from Intermediate Technology's
field experience with micro- hydro installations and
covers operation and maintenance, commissioning, electrical
power, induction generators, electronic controllers,
management and energy surveys.
£39.95, ITDG Publishing, 1993, ISBN: 1853391034
The Micro-hydro Pelton Turbine
Manual: Design, manufacture and installation for small-scale
hydropower
Jeremy Thake
The Micro-hydro Pelton Turbine Manual is written to
enble the reader to design and manufacture Pelton
turbines with capacities from a few hundred Watts
to around 100kw, though much of the information is
relevant for larger units too. Aimed at readers with
a general engineering workshop background, the emphasis
is on simple technology, so that the turbines can
be made in small workshops with basic engineering
facilities. More advanced processes are discussed
for those with access to better manufacturing facilities.
As well as detailing all the important aspects of
design, the book covers basic theory, turbine selection,
manufacture, installation, testing and problem solving.
£25.95, ITDG Publishing, 2000, ISBN: 1853394602
Pumps as Turbines: A Users Guide
Arthur Williams
A practical handbook on the use of standard pump units
as a low-cost alternative to conventional turbines
for electricity generation in remote locations. For
engineers and technicians designing and installing
small water-power schemes.
£9.95, ITDG Publishing, 1995, ISBN: 1853392855
Websites
http://www.microhydropower.net/
Micro-hydro website
http://www.brit-hydro.cwc.net/
The British Hydropower Association
resum.ises.org/cgi-bin/resum/resum.py?showproject&PHVietnam
Summary of pico-hydro in Vietnam.
http://www.lightuptheworld.org/
The aim of Light Up the World is to introduce poor
rural people of all countries to a safe, simple, healthy,
affordable and reliable form of home lighting using
pedal generators, pico-hydro and solar photovoltaic
power sources. Has project information on installing
pico-hydro in Nepal.
This document is an output from
a project funded by the UK Department for International
Development (DFID) and the European Commission (EC)
for the benefit of developing countries. The views
expressed are not necessarily those of DFID or the
EC.
Acknowledgements
ITDG would like to thank Nottingham
Trent University for providing the original material
on pico-hydro, particularly Pico Hydro for Village
Power: A Practical Manual for Schemes up to 5 kW in
Hilly Areas by Phillip Maher and Nigel Smith, from
which this information is drawn.
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