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powered battery charging systems can be
cost-effective if the average wind speed is nine
miles per hour (mph) or more at the location of
the wind generator. If you are using wind in
combination with photovoltaic power, it may be
cost effective if good wind is available only
during part of the year. the power available
from the wind is proportional to the cube of the
wind speed. when the wind speed doubles, the
power delivered is eight times as great.
Most wind generators are designed to deliver
maximum power at a wind speed of 30 mph. At
15 mph, they will deliver about 1/8 their rated
power. A wind generator should be mounted at
least 20 feet higher than any obstruction within
300 feet to avoid turbulence. You can expect
the power output of a wind generator to decrease
roughly 3% for every 1000 feet of elevation.
That means that you'll get 70% of power at 10,000
feet elevation. |
Measuring Wind Speed
You can use either the Wind Watcher Data Logger of Kestrel
1000 Pocket Wind Meter to determine wind speed.
the Kestrel wind speed
indicator works like a speedometer, displaying current
wind speed, but does not record available wind power over
time.
the Wind Watcher monitors
historical data as well as wind speed so you can install
it and let it record for several months to get an idea if
your location is a cost effective site for a wind system.
If you measure wind speed
at ground level, you can expect about 1.5 times the wind
speed 30 feet up, which equates to about three times the
power. At 120 feet above the ground, wind speed will
be twice what is measured at ground level and power output
will be more than twice the output at 30 feet.
If you do not have a wind
gauge, you can get a rough idea of wind speed from the
table below.
| Wind
Speed (MPH) |
Wind
Effect |
| 0-1 |
Smoke
rises vertically |
| 2-3 |
Direction
of wind shown by smoke drift but not by wind vanes |
| 4-7 |
Wind
felt on face; leave rustle; ordinary wind van
moved by wind |
| 8-12 |
Leaves
and twigs in constant motion; wind extends a light
flag |
| 13-18 |
Raises
dust, loose paper; small branches are moved |
| 19-24 |
Small
trees in leave begin to sway; crested wavelets
form on inland waters |
| 25-31 |
Large
branches in motion; whistling heard in power
lines; umbrella use is difficult |
Towers
We do not recommend mounting wind generators on
roofs. thought it is possible with a wind generator
of 500 watts or less output, it will be noisy.
Larger wind generators could cause severe damage to the
building. Freestanding towers, guyed towers or guyed
poles may be used with wind generators. Wind
generators can be mounted on freestanding towers designed
for antennas. They require a large, engineered
concrete base for support, but since they do not require
guy wires, they can be installed in the smallest
space. Guyed steel truss towers, also designed for
antenna mounting, are less costly and require a large area
for guy wire placement. A tilt-up pole tower is the
most economical and the easiest to install. Wiring
and mounting of the wind generator are done before the
tower is erected. No climbing is necessary.
Steel tubing can be bought locally to save freight.
Wiring
It is important to avoid
excessive loss of power from voltage drop in wire from the
wind generator to the batteries. It is not necessary
to use a wire size that minimizes voltage drop for maximum
generator output. It will be more economical to
choose a wire size that gives a 2% voltage drop at the
average generator output for your site.
The Air403 has two wire
DC output. Use the wire loss chart here to decide on wire size.
The Whisper wind
generators have 3-phase AC output that is rectified to DC
at the control box. Wire size can be smaller on
these machines. Use a wire designed to carry the
rated current of the generator you are using, but
remember, three conductors are required. A wire
sizing chart is provided in the owners manual.
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