Measuring Wind Speed
You can use one of the measuring devices on
page 25 to determine wind speed. The NRG Wind Totalizer acts like an odometer in a car, giving you the total wind passage over time.
Average wind speed is calculated by the user by
dividing the miles of wind passage by the number
of hours the machine has been running. This unit can be installed and checked weekly or monthly. If you are patient, you can measure for a year or two and get a good idea of your potential power availability. Both the Dwyer and Kestrel wind speed indicators work like a speedometer, displaying current wind speed, but neither records any information for future reference. The Dwyer and NRG can be mounted on a tower to give you an idea of wind speed where the generator will be located.
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; leaves rustle; ordinary wind vane 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 leaf begin to sway; crested wavelets form on inland waters. |
25-31 |
Large branches in motion; whistling heard in power lines; umbrella use is difficult. |
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Towers
We do not recommend mounting wind generators on roofs. Though 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. The four or five inch 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 on page 61 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. If wire size required is too costly, compare the price of a Whisper HVT machine, which has a 240 VAC output that is stepped down to battery charging voltage. This results in significantly smaller wire size, which will usually more than offset the extra cost of this machine. Call for details.
For wind power products click here.
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