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a wind machine is proportional to the wind speed cubed. The significance of stronger winds is
noticed immediately.
A 20mph wind will get the smallest commercial electrical generator working, producing about
100 watts of electricity. About a 30mph wind will be required for a car generator or alternator to
start charging a 12-volt car battery.
It is up to the user to decide if it is worthwhile to build an S-rotor for winds of less than 20mph if
stronger winds are rare in the area.Unlike horizontal-axis wind machines, S-rotors will begin
turning in very low-speed winds but will produce only small amounts of usable power at those
low speeds.
It is not possible to give a precise formula for the power available at the generator or a pump
because the friction and transmission losses are largely dependent on the design and accuracy of
manufacture of the rotor. Since the rotor is intrinsically not very powerful, friction losses due to
bad bearings and transmission losses could absorb most of the available power.Therefore, proper
construction and excellent fitting of the bearings is most important.
It is very important to establish the following before attempting to build any wind machine:
Availability of wind. Find how often wind comes, its intensity, and its annual patterns.This
information can generally be gotten from the nearest meteorological station. An alternative and
more accurate method is to use an anemometer (wind speed measuring instrument) to measure
wind speeds on a chosen site for a period of perhaps one year.
Intended use of the windmill.
pumping water for household use
generating electricity
other applications
Choice of a suitable site.The choice of site will of course depend upon the intended use of the
windmill. Then it is very important to select a location that will allow the windmill maximum
exposure to wind, i.e., to get maximum power.
The top of a gently sloping hill with no trees, bushes or other obstructions to the wind is ideal.
However, if the windmill is to be used for pumping water, often the most likely place for a well
is the bottom rather than the top of the hill, or even in the vicinity of buildings where the water
will be used. If the site is sheltered from the prevailing winds by buildings, trees or other
obstacles, it would be quite unsuitable for a windmill unless it is built on top of a tall tower or
on top of a building itself.If this is the choice, then the windmill must clear the tallest obstacle by
a minimum of about 10'(3m).
If the rotor is to be used for charging batteries, the top of a nearby hill, clear of obstructions,
would seem to be a logical choice.
Take into account that power will be lost when transmitted over a distance, and locate the rotor
as close as possible to the place where the, power will be used.
At almost any site, the higher the windmill is mounted, the stronger the winds will be.The
benefits of extra power should be compared against additional costs of a tower or a support