Owner`s manual

5. SYSTEM OPERATION

A. Normal Operation

The rotor of the BWC EXCEL 1 should begin to rotate when the wind speed reaches approximately 3 m/s

(7 mph). (For the first several weeks of operation, however, the start-up wind speed will be higher be-

cause the bearing seals have not worn-in.) Battery charging should commence shortly after the rotor

spins up to speed. Once turning, the rotor will continue to turn in lower wind speeds, down to approxi-

mately 2.5 m/s (6 mph).

Note

All operational wind speeds given as-

sume steady winds, sea-level altitude

and moderate temperatures. Hot

weather, high altitude, turbulence, and

gusting winds will reduce system per-

formance.

The rotor speed will increase with increasing wind speed and the system will provide a higher output.

This output increases rapidly because the energy available in the wind varies as the third power (cube) of

the wind speed. For example, if the wind speed doubles from 5 m/s (11.2 mph) to 10 m/s (22.4 m/s), the

energy in the wind increases by a factor of eight (2

= 2 x 2 x 2 = 8). One result of this relationship is that

there is very little energy available in light winds. For the average site, winds in the range of 5.5 – 9 m/s

(12 – 20 mph) will provide most of the system’s annual energy production.

B. High Winds - AutoFurl

During periods of high wind speeds the AutoFurl system will automatically protect the wind turbine. When

furled, the power output of the turbine will be significantly reduced. In winds between 13 m/s (29 mph)

and 18 m/s (40 mph) it is normal for the turbine to repeatedly furl, unfurl and then furl again. In winds

above 18 m/s (40 mph) the turbine should remain continuously furled.

AutoFurl is a simple and elegant method of providing high wind speed protection. The AutoFurl system is

based on aerodynamic forces on the rotor, gravity, and the carefully engineered geometry of the wind

turbine. As shown in Figure 4, the aerodynamic forces acting on the blades cause a thrust force pushing

back on the rotor. This force increases with increasing wind speeds.

Figure 4: AutoFurl