THE WALSH RIVER MICRO-HYDRO SYSTEM
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The Walsh River range of Micro-hydro turbines
are designed especially for home use.
Planetary Power developed the Walsh River
Micro-hydro system in 1991 to provide reliable
low-head micro-hydro power for its own facility on
the Walsh River in Far North Queensland. This prototype
turbine is used to generate electricity and pump water
- it is able to do both continuously and simultaneously,
and from it has developed the range of Walsh River
Micro-hydro systems.
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These systems provide cost effective and environmentally
friendly micro-hydro power for low head sites,
ranging from less than 1 meter up to 8 meters
The Turbine
The turbine is of the Banki-crossflow type consisting
of a cylindrical, horizontal axis 18 blade runner, intake
nozzle, exit draught tube and housing. The turbine is available
in two sizes: LH6-180 has a runner 270mm dia. and 180mm
wide LH6-300 has a runner 270mm dia. and 300mm wide The
runners are made of epoxy coated mild steel and are of all
welded construction. The intake nozzle is designed to accept
water entering via a 150mm dia. UPVC penstock (ie inlet
pipe). The LH6-300 has a double entry, allowing a penstock
made up of two pipes, side by side.
The penstock needs to be of sufficient length to develop
adequate head, and is usually between 2 metres and 50 metres
long.
In normal operation the turbine sits just above the tail
pond into which the water is discharged. The water exits
via a draught tube, which ideally descends into the tail
pond itself. If rising water levels submerge the turbine,
no harm results. The turbine will continue to operate when
partially submerged, although it will stop when completely
submerged, automatically restarting when the water level
drops.
Electricity Generation
The WALSH RIVER MICRO-HYDRO SYSTEM is usually supplied
as a complete package ready to generate electricity once
assembled. It comprises: either the LH6-180 or LH6-300 turbine
a permanent magnet DC generator micro-hydro controller frame,
belt, pulley and other auxiliary items The turbine needs
to be anchored in a protective part of the stream bed. Usually
it is bolted to concrete footings.
The generator is mounted, either above the turbine on a
1.2m high tower, or separately on the stream bank. Power
is transmitted from the turbine to the generator using a
cog belt and pulleys. The output of the generator is then
transmitted to the controller, which forms part of the switchboard
located at the house, near the battery bank. The controller
provides the battery with a continuous and regulated charge.
The output voltage of the controller is switch selectable
to accommodate any type of battery. The most common type
of battery is the wet cell lead acid at 12V, 24V or 48V.
An inverter, connected directly to the battery is used to
provide mains quality 240V power for lighting and other
loads.
Water Pumping
The turbine can also be used to pump water, either as a
stand alone operation or as an adjunct to electricity generation.
One system currently operating pumps water to a head of
100 metres, another pumps 40,000 litres/day to 20 metres
head. PERFORMANCE The performance of the turbine, both for
electricity generation and pumping water depends on the
head and flow rate. Once these are known the output can
be estimated using Figs. 1 & 2.
The head is the difference in height between the intake
and the turbine and includes an allowance [of between 5%
and 30% depending on the site] for intake and penstock friction
losses. The WALSH RIVER MICRO-HYDRO SYSTEM is designed
for heads in the 1 metre to 3 metre range. It will however
operate at lower heads, with 70cm being the practical lower
limit for electricity generation and 50cm the lower limit
for water pumping. The LH6-180 turbine will also operate
at heads greater than 3 metres, the upper limit being 8
metres.
The flow rate is the rate at which water flows through
the turbine. It is usually limited by the flow rate of the
stream, however the penstock and the turbine itself can
also be limiting factors.
For the LH6-180 turbine, the maximum flow possible is 18.5
litre/sec for a head of 1 metre, rising to 26 litre/sec
for 2 metres head and 32 litre/sec for a 3 metre head.
For the LH6-300 turbine the corresponding values are: 31
litre/sec, 43 litre/sec and 53 litre/sec. The turbines have
an adjustable nozzle to accommodate variable flow rates.
The flow can drop to as little as one third of the maximum
flow rate with little reduction in efficiency. This is a
feature for which Banki-crossflow turbines are noted.
A Typical Micro Hydro Site
A typical low head micro-hydro site has the following parts:
A diversion weir is a small dam or weir to divert
water into a penstock. The penstock is the pipe that
carries the water to the turbine inlet. The turbine
is the machine that extracts power from the water. Water
exits the turbine via a draught tube into a tail
pond or tail race. At the entrance to the penstock
is an area to trap sand and debris called a forebay.The
trash rack is located at the forebay to prevent debris and
small animals being sucked in.
Collectively, all parts of the installation upstream of
the turbine are called the headworks. The turbine is coupled
to the generator cause it to rotate and thus generate
electricity which is then transmitted via the transmission
line to dwelling, workshop or wherever power is needed.
The transmission line can be above ground or underground
depending on site and environmental considerations. Transmission
over several hundred metres is usually practical although
once the distance exceeds about 300 metres the cost becomes
quite significant
Assessing a Site for Micro Hydro
Assessing the suitability of a site takes time and care.
It is important. You may invest a lot of money on the basis
of your understanding of a stream. You need to spend time
with your watercourse and get to know it so you can find
the best site for your turbine and its headworks. As already
noted the key factors that determine the output potential
of a turbine are the head and flow rate and once these are
known the performance curves can be used as a guide to how
much power you could expect to be generated.
The head is the difference in height between the turbine
and the intake of the penstock. It can be measured in any
one of several ways, for example by using a measuring staff
and sight level or for low heads a water hose level is suitable.
The flow rate of the stream can be measured directly, for
example by seeing how long it takes to fill a 10 litre bucket
or indirectly by using a notched weir.
The weir method is useful for all stream sizes. A weir
is built across the stream to cause the water to flow through
a notch of known dimensions. Sometimes a natural rock formation
will resemble a weir and will channel most of the stream
through a narrow gap resembling a notch. The depth of the
water flowing through the notch is measured and this is
converted to a flow rate using tables published for the
purpose. Usually the notches are triangular or rectangular.
Care for the Environment
All the water diverted through a turbine is quickly returned
to the stream and assuming that some water is allowed to
remain flowing in the original watercourse, the environmental
impact of a micro-hydro site is minimal. The use of a WALSH
RIVER MICRO-HYDRO SYSTEM keeps about one ton of CO2
out of the atmosphere per year.
The local generation of power also saves the cost of distributing
mains electricity and/or petroleum and the related infrastructure.
These costs are not currently considered in environmental
assessments as they are borne by the community at large
whether or not it uses mains electricity. Any project that
reduces Australia's CO2 emissions helps to meet our international
treaty commitments.These national contributions need to
be recognised and rewarded appropriately.
WALSH RIVER turbines are manufactured locally out
of mostly Australian parts generating local employment.
The staff at Planetary Power are available to assist
you with the calculations and evaluation of potential
sites.
A site assessment service is available. We will
inspect the site, take the relevant measurements and produce
a written report describing:- the site's potential to generate
power, its potential to meet the expected loads, design
considerations and options. The report also will include
a system design proposal and development cost estimates.
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