Proven 2.5 kW
In the Falkland Islands there are around 100 remote homes and farms with no access to the power grid. In 1996, a renewable energy program was launched by the Falkland Islands Development Corporation and there are now more than 60 power systems in operation that use Proven wind turbines
The Proven range was originally chosen because of its rugged construction and ability to survive consistent high-speed winds, the average annual wind in the Falklands being in excess of 8.5 m/s.
Low operating speed
Small commercial wind turbines operating at relatively high rotation rates usually have a short lifetime and those that do not fail outright, suffer rapid leading edge blade erosion, therefore requiring regular blade repair or replacement.
The relatively low operating speed of the Proven was considered as a factor that would improve its chances of long-term success. This has been substantiated as some Proven wind turbines have now been in operation for 10 years.
The Proven wind turbine is a downwind horizontal axis type. The rotor is constructed from 3 polypropylene blades each with 2 spring-loaded hinges at the blade root. This assembly is referred to as a Zebedee hinge and comprises an inner hinge (angled at 90 degrees) and an outer hinge (angled at 45 degrees).
The two hinges work together to effectively twist the blade as an automatic passive blade pitch and power control system. The system is normally set to give a low angle of attack for easy starting at low wind speeds. As the turbine accelerates, centrifugal force causes the hinges to open. This flattens the blade, increasing the angle of attack to the relative airflow.
The centrifugal force and therefore the pitch both increase with rotor speed. In high winds, the wind force on the blades overcomes the spring tension and the rotor disk cones, both stalling the blades and reducing the effective rotor disk area and therefore power output. An increase in shaft torque will cause the blades to oppose the action of the centrifugal force which will tend to close the hinges, decreasing the angle of attack.
The spring tension is factory-set to run at a maximum operating speed of 300 rpm (5 rev/s) at the rated 12 m/s wind speed and above. Wear at the spring mountings and loss of elasticity of the springs in use can cause stalling and coning to commence at lower wind speeds, reducing the maximum power output of the turbine.
The Proven wind turbine is a variable-speed three-phase permanent magnet alternator and consists of 4 pole pairs rotating within 24 stator coils. Each coil nominally produces 30 volts and eight coils per phase are arranged during manufacture in series and parallel combinations to produce wind turbines generating 24, 48, 120 or 240 volts.
The neutral is not accessible as a common point on production machines. The rating of 300 rpm with a 4 pole pairs generator produces a line frequency of 20 Hz.
Port Louis is an historic part of the Falklands and the last person to engage in any scientific work here was probably Charles Darwin in the 19th Century.
The choice of suitable sites for small wind turbines is usually limited by the cost of the heavy-duty power cable needed to carry the turbine power output to the charge controller and battery. Most of the turbines are sited within 100 metres of the powerhouse, which contains the battery bank, diesel generator, power inverter and wind turbine charge control panel.
Turbine siting is always a compromise and can result in less than ideal winds. To reduce DC power losses in the power cables, most turbines in the Falklands operate at 48 V (50-60 A) but a few operate at 24 V (100-120 A).
The Port Louis WT2500 wind turbine was designed to generate 2.5 kW at 48 volts in a 12 m/s wind and is 110 metres from the powerhouse on a slight rise of land to the north west of the buildings.
It has been sited so that is relatively unobstructed from the prevailing westerly winds. However, being relatively low to the ground on the standard 6.5 metre mast, the turbine receives more buffeting and turbulence than if it were mounted higher.
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