This Savonius style wind charger reportedly produces 10-30 ma @ 2.4 vdc from 6-13 mph wind speed, which should be sufficient to trip a pilot actuated irrigation valve on occasion, with sufficient battery capacity. Just the thing to adorn the top of my vertical garden trellis!
From the page: "Ever wanted to build a wind charger but not sure where to start ? Well now you can enter the world of wind power with this mini model wind charger that produces around 75milli watts of green recycled power. Easily constructed and made of lightweight materials so particularly suited to gusty locations. This little windmill would make a nice addition to a set of solar lights, boosting their power on overcast/rainy days, simply connect the output to the batteries in the solar light.
Heres what you need:
10 X Paper Coffee cups
An old CD
Small scrap of plywood anything above 6mm thickness will do.
A stepper motor from an old printer/fax/scanner/till etc (the older the machine the better usually)
8 X 1N4001 General purpose diodes.
General purpose glue, must adhere to metal.
Miscellaneous small wires
Battery holder to suit batteries
Electrical insulation tape
Note - Not all stepper motors will work well here you must experiment!
Solder
Soldering iron.
Scissors
Sharp knife.
Hole Saw
Pen
Multimeter or ammeter (optional)
Anemometer handy too but not at all necessary."