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Wind power

Product analysis: A small wind-powered system

The market
The market for small-scale electricity generation is huge. In Sri Lanka alone, around 45% of households are not on the mains. However, the winds are only consistent enough in the north west and south east of the island for a wind-powered system to work.

The market is also limited by cost. It would take people about five to six years of savings from buying kerosene and taking batteries into town to be recharged to pay for a wind-powered system. However, Practical Action is working with a local credit organisation to offer cheap loans for buying a wind system.

Technical specification

The stator contains six coils of copper wire, cast in fibreglass resin. This stator casting is mounted onto the spine; it does not move.

The magnet rotors are mounted on bearings, which turn the shaft. The rear rotor is behind the stator, and enclosed within it. The front one is on the outside, fixed to the rear one with long studs which pass through the hole in the stator.

The turbine's rotor blades are also mounted on these same studs. When they turn they also turn the magnet rotors and move the magnet passed the coils. Magnetic flux passes from one rotor to the other through the stator. This moving magnet flux is what produces the electric current.

Wires from the coils take electricity to the rectifier, which changes the AC to DC for charging the battery.

There is a load controller to make sure there is an even flow of current through the battery to protect it from damage and keep the voltage within safe limits.

Generator: Permanent Magnet Generator (PMG)
Generator capacity: 250W
Cut-in wind speed: 3m/s
Cut-off wind speed: 14m/s
Rated wind speed: 9m/s
Direction control: hinged vane system
Diameter of rotor: 2m
Number of blades: two or three
Magnets eight: 50x50x20mm; eight 50x50x10mm
Tower height: 11m
Load controlling system: 330W ballast resistor
Automobile battery: 12V
AC output (from inverter): 230V, 50Hz

Product function
The wind-powered system generates electricity, with battery storage, for use in homes. .

The wind machines blades are made from epoxy resin reinforced with glass fibres. The generator housing is steel and glass fibre reinforced plastic. The tower is made from mild steel that has been painted or galvanised. It is fastened to steel plates that are set in concrete. The six stays are made from steel wire and are fastened to steel pegs that are also set in concrete.

A commercial fibreglass manufacturer makes the blades. A blade form was made from wood. This was used to cast an aluminium version, which was then used to make a mould. All of the other components are made in Udaya Hettigodas workshop in Colombo, the capital city of Sri Lanka.

Ten people can assemble the whole unit on site in about two hours. The blades, generator and vane are assembled and fixed on top of the pole. The flanges welded to the base of the pole are bolted to the steel plates set in concrete, and the whole assembly is hauled up and fixed in place by the stays.

Electricity is safer and cleaner to use than kerosene. The low voltage (just 12V) is safe. Having more light in the home can help to reduce the risk of accidents.

The small wind-powered system is easy to install and requires little maintenance. The whole assembly can be lowered to the ground if access is needed for repairs, and so on.

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Practical Action - Technology challenging povertyEuropean Commission - Department for International Development

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