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The Pedley
Wheel charitable trust, based in the UK, has re-evaluated
the water wheel and introduced it into the low head
micro-hydro market, producing AC electricity by using
modem high-geared motors as generators. Water wheels
have been successfully installed in two villages in
Sri Lanka, and work is currently underway on three more
projects.
Background
The origins
of the water wheel can be traced back over 2500 years,
but it was a Roman engineer named Vitruvius who is credited
with inventing the overshot water wheel some 2000 years
ago. The design was progressively refined, and by the
early 19th century most of Europe was dependent on the
water wheel for power. Wheels of up to 20m in diameter
formed the cornerstone of early industry, and even early
steam power was used for pumping water, frequently from
mines, to supply working wheels.
Water wheels
are essentially gravity-driven and are therefore slow
moving (traditional wheels only rotate at between 4
and 12 rpm). The lack of strong and reliable gearing
systems, coupled with the advent of steam power and
the introduction of higher speed water turbines, rapidly
led to the demise of the water wheel. By the turn of
the 20th century, all but a few were redundant. Those
which remained simply ground corn, pumped water or carried
out simple mechanical functions requiring slow speed
and high torque.
More than
a century after the last great
wheels were built, the first Pedley wheel was constructed
as part of an educational project at an environmental
awareness centre in the UK. This original wheel, built
in 1991, now forms the basis of an electricity-generating
system, while also providing a facility for direct mechanical
power.
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Simple
design
Modem micro
hydro turbines are ideal for operating under medium
or high heads (more than 5m). At lower heads (between
2 and 5m), such small turbines can be uneconomic and
inefficient. It is here that the Pedley wheel can offer
a cheap and reliable solution, especially for the many
small villages in the developing world, where grid connection
is either very costly or simply not available.
The Pedley
wheel system has been refined over the past few years,
and is now efficient and robust. The wheel, which can
have a diameter of between 2 and 3.5m, is simple enough
for local manufacture in the developing world, and ancillary
equipment, if not locally available, can readily be
imported off-the-shelf. Simple civil works (a water
channel to and from the wheel and concrete foundations)
can be constructed to standard specifications using
local labour. With no requirement for trash screens,
operation and maintenance is cheap and straightforward.
The bridge
between the slowmoving water wheel and the 1600 rpm
required to generate AC electricity is made by incorporating
a modern, highly geared electric motor running as a
generator. A typical installation can deliver up to
5 kW of electricity, although a higher output is feasible
if the head and flow will allow for it. One of the most
significant design improvements has been the incorporation
of a Rexnord-Hansen parallel-geared motor coupled directly
on to the water wheel shaft. This eliminates the need
for additional couplings and supports, resulting in
a simplified, more costeffective installation.
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Sri Lankan
installations
The Sri Lankan
village of Lower Amanawela, some 460m above sea level,
was the first community outside the UK to benefit from
a Pedley Wheel installation. When it was constructed
in March 1998 it caused great interest among the local
people, mainly because there is very little history
of water wheel technology in the region.
A 5m head
between two paddy field irrigation channels is used
to drive the 3.5m wheel, thus minimizing the required
civil works. The system develops 2.75 kW` of AC power,
which is transmitted to 24 houses. The power is used
for lighting, water heating, ironing, battery charging
and a variety of other applications, including 15 colour
televisions.
The Village
Electricity Consumers' Society manages and maintains
the system, maximizing the use of power by using a rota
system. Each household is allocated a low-peak slot,
during which they can increase their domestic power
consumption beyond the 100 W available during high-peak
periods.
The second
Sri Lankan installation is in the village of Seaforth,
an ex-colonial tea plantation at el. 600 m. The Pedley
wheel was commissioned in November 2000, and is located
below the outflow pipe from a nearby 10 kW Pelton turbine.
It uses this 'second-hand' water, augmented with water
from a nearby river, to produce 2.5 kW from its 2.25
m-diameter wheel. A further 20 houses, as well as the
village community centre and school, are now receiving
electricity, and there are plans for the establishment
of a computer training centre.
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Future
prospects
The success
of these installations has led to three more village
projects in Sri Lanka being given the go-ahead, assisted
by external funding from the British High Commission,
Rotary International and other small trusts. Civil works
are currently well underway at the three sites, which
have heads of around 4m and minimum flows of 200 l/s.
Commissioning should be completed by November this year,
with each wheel expected to produce around 4.5 kW, which
is enough to provide power for between 35 and 45 houses
per village.
These are
genuine low-head sites, where no other comparable generating
system could operate. Thus the Pedley Wheel will bring
electricity to an increasing number of Sri Lankan homes
which would otherwise not be able to enjoy the many
benefits electricity can provide.
The Pedley
Wheel Trust hopes to provide a continuing UK facility
for the design and construction of water wheels. Students
from UMIST (University of Manchester Institute of Science
and Technology) are currently carrying out research
into improved control systems for use with the Pedley
wheel, and the Trust is now looking for suitable locations
for demonstration projects elsewhere in the developing
world.
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