IEEE Electrification Magazine - March 2015 - 71

capacity of renewable energy sources (RESs) of
up to 10 kW. These systems usually consist of
a photovoltaic generator, whose size will
depend on the available wind resource, a
flooded lead-acid battery bank, an inverter/
charger, and possibly a diesel generator for
backing up the renewable energy system.
The small wind turbine itself requires a rectifier to feed its ac directly into the battery
bank and also a diversion load charge controller with a resistive load for diverting
excess energy when the battery bank is fully
charged. The locally manufactured small
wind turbines constructed for these applications by the global OSH community range in
rotor diameters from 1.2 to 7 m (Figure 3) and
are able to produce power from 200 W to Figure 3. A 7-m-rotor-diameter locally manufactured small wind turbine built in Kampala,
Uganda, by the Veterans Wind Power Initiative. (Source: scoraigwind.co.uk.)
4 kW, respectively, at 10-m/s wind speeds,
although rated power production is only an
estimation due to its dependence on factors such as the
cally, the hand tools consist of a chisel, a draw knife, files,
cable connection to the battery bank and the adjustment
a plane, a spoke shave, a hand saw, calipers, and a square.
of the furling tail system.
An electric plane and a chainsaw can be used to save time,
The small wind turbine is a variable-speed machine
especially for the longer blades used in larger turbines.
that consists of a three-blade wooden horizontal axis rotor
The techniques used are described in detail in the availof constant pitch angle and a coreless axial flux permanent
able construction manuals but mostly require simple
magnet generator with a double-rotor, single-stator confighand-carving skills and successive measuring throughout
uration and neodymium or ferrite magnets; it uses a
the construction process.
passive mechanical furling tail system for rotor speed reguThe axial flux permanent magnet generator has a
lation and yawing to the appropriate wind direction. A
unique topology that facilitates local manufacturing with
metal frame supports an automobile wheel hub on which
simple tools. Contrary to its radial flux counterpart,
the blades and the generator's rotor are mounted while
which consists of a cylindrical rotor and stator, the axial
also supporting the generator's stator and the furling tail.
flux generator consists of disks. This requires the manuIn addition, the metal frame provides a simple yawing
facturing of a two-dimensional (2-D) stator and rotor,
mechanism without using a bearing or brushes for conwith a thickness of a few centimeters, instead of a threenecting to the power cables running down the tower, which
dimensional (3-D) cylindrical object. The stator coils and
directly feed energy to the battery bank. The wind turbine
the rotor metal disks and magnets can be positioned in a
is usually installed on top of a tower, typically made out of
plywood mold, consisting of a base, a lid, and a middle
steel water pipes, at a height of 12 m or more, although this
part, which provides the shape and the appropriate
will depend on the location and the surrounding obstacles.
The tower is a guyed mast consisting of steel wire ropes
and four anchors in cement or bedrock and is usually
erected using a gin pole and a wire rope hoist.
The construction of the wind turbine is achieved with
simple tools that one would encounter in a rural workshop for wood and metal working and with the use of
simple techniques that do not require a skilled laborer to
perform. Most of the materials used can be sourced locally, while some specific materials like neodymium magnets
can be ordered online, which only requires an Internet
connection and a postal service within reach. The rotor
blades are usually constructed with soft wood from conifer trees, such as pine in the northern hemisphere or any
other types of trees with similar properties, including low
density and light weight, that exhibit strength in tension.
The blades are hand carved using hand tools (Figure 4)
Figure 4. A participant hand carving blades during a wind turbine
construction seminar in Ireland. (Source: eirbyte.ie.)
and sometimes power tools for faster production. SpecifiIEEE Electrific ation Magazine / March 2 0 1 5

71


http://scoraigwind.co.uk http://www.eirbyte.ie

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