Do you have a good wind site?
Wind 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 you have good wind 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.

Measuring Wind Speed
You can use one of the measuring devices in this section to determine wind speed. The NRG Wind Totalizer acts like an odomet er 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. The Dwyer and Kestrel wind speed indicators are both like a speedometer, displaying wind speed at the time you are looking at it, but it does not record 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.

Towers
We do not recommend mounting wind generators on roofs. Though it is possible with wind generators 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, but 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.