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Micro
Hydro-Electric Evolution
Paul Cunningham
Since the 1970s, there have been many examples of very
small hydro machines to enter the marketplace. I am
referring to those machines which are usually used in
a battery based system, with an output of typically a
few hundred watts and usually less than 1 kW. To put
this in perspective, meeting the electrical demands of
a typical home usually requires 3-400 W continuous.
This is sufficient power to operate lights,
refrigerator freezer, washing machine and
entertainment.
Most of these
generators have used impulse turbine runners as the
hydraulic component, including Pelton, turgo, and some
cross-flow designs. Materials for these runners
include bronze, aluminium, steel and plastic. With
efficiencies of the runners alone exceeding 80%, it is
unlikely that much improvement will be possible here.
Automotive alternators
are usually used to convert the shaft power of the
runner into electricity. While this technology can
provide a cost effective means to generate power, it
is far from ideal. On the plus side, they are readily
available, cheap, simple, and the field current can be
easily varied in order to match the output of the
turbine runner with the generator. On the down side,
they usually employ carbon brushes to carry the field
current (creating a maintenance issue), the efficiency
is low (around 60%), and performance at low shaft
speeds is problematic, since most machines use direct
drive (often the speed is simply too low to achieve
desirable outputs without using belt drives, etc).
It has proven
advantageous to rewind these automotive alternators,
as the stators are usually not more than half filled
with wire. By using more wire, the efficiency can be
raised and we can now use the wire size that best
matches output to the load. However, the basic
limitations are still there, in that these alternators
were designed and evolved for automobiles, not
hydropower. Note that by combining an 80% turbine
efficiency with a 60% alternator efficiency, the best
one could hope for would be an 48% water to wire
efficiency.
It is only natural that
a machine designed for the task of residential power
generation would eventually be developed. Ideally, it
should be brushless; use permanent magnets to avoid
field losses and excitation problems; be water cooled
since all that water is only a few centimetres away;
be highly efficient; and be easily adjustable so load
matching can be facilitated by the average user.
This has now been done
with the alternator used on the Stream Engine made by
Energy Systems and Design. Neodymium magnets are used
in the rotor to maximise field strength, the
alternator and rectifier are both thermally bonded to
tile turbine housing to ensure cooling, and efficiency
is typically in the 80% range at full load. The output
is adjustable by raising or lowering the rotor which
affects its proximity to the stator in tills axial
alternator design. In this manner, turbine power can
be matched to generator output. Reconnectable windings
are used so that outputs of 12, 2.4 and 48V can be
produced front the same machines, and in some
situations, stators .arc custom wound to transmit at
120V over long distances, thereby minimising wire
losses.
An
example of a typical installation follows:
Renewable energy dealer
Harold Lunner of British Columbia, Canada, has
recently completed an installation of a Stream Engine.
The head vertical drop at this site is approximately
eight meters. The system, with two 22 mm nozzles, uses
about 10 l/s and is fed by a 150 mm pipe, 200 m long.
Output from the machine is 8.5 amps. in a nominal 48V
system, which actually operates at 54V at this current
level. This gives an output, in watts, of 459. A water
to wire efficiency of 65% is achieved.
Micro-hydro systems
have come a long way. They can produce power more cost
effectively than any other kind of renewable energy
system. It will be interesting to see what the future
brings.
Access
Paul Cunningham,
Energy Systems & Design,
P.O. Box 4557, Sussex, NB Canada E4E 5L7
Tel: (506) 433-3151
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