Home-Built Windpower

Links to other good sites for home made windpower:-

What size of wind turbine do I need, and what can it give me?

 I am going to use some rough scans of a few tables from my book Windpower Workshop chapter 1, which will help you with the overall design of your wind machine.  I am using scans because the original files went in the sea with my computer back in '97.
 

The first table tells you how much power you can expect from a wind machine, when you  know how big it is, and how strong the wind is.

Readers in the USA should note that one metre diameter is about 3 feet, and 3 metres is ten feet.

Clearly, size matters, but windspeed matters even more.
And above all do not forget SAFETY, which must be a paramount concern.
There is a whole chapter on the subject in the book.

Wind turbines are usually designed to work best in the range 3 - 12m/s, but windspeeds as high as 12m/s are not common (everyday) occurrences, so don't expect to get such high power outputs often enough to be relied on.  It is usually a good idea to avoid very high power (high wind) operation altogether, unless you plan to use the machine for heating purposes on rare occasions.  To avoid damage in high winds, you will need a good control system which reliably protects the machine from the wind's fury.

In terms of what you can run from the wind system, the average power is more useful information.  From this average you can then work out how many Amphours of battery charge per average day you might get.

4.5m/s or ten mph is a typical average windspeed, for an open site with few obstructions.
A 2 metre diameter machine would probably give about 50 watts average output
(although it might produce 200 watts or more at times).
An average output of 50 watts may not sound much, but over a 24 hour period you can expect
50W/12V  x 24h = 100 Amp-hours of charge (on average) into a 12 volt battery.
This is sufficient to run five 'energy efficient' lamps, each using 2 amps, for ten hours.
In reality, some of the energy will be lost in the process of charging and discharging the battery,
but you get the general idea, I hope.

Once you have chosen the size of wind turbine, you need to design the blades and find or build a generator or alternator to match them.

Blade design

Your main decision will be choosing the tip speed ratio of your rotor blades.
The 'tip speed ratio' is how much faster, than the windspeed, the blade tips travel.
High tip speed ratio means more speed, low tip speed ratio needs more blades.
On the whole, high tip speed ratio is better, but not to the point where the machine becomes noisy and highly stressed.  This next diagram show four rotors, designed to run at different tip speed ratios.

The tip speed ratio will determine how fast your wind turbine will want to turn, and so it has implications for the alternator you can use.

Following through our example of the 2 metre (six foot is 1.8m) diameter machine, and choosing a tip speed ratio around 6 we find that the machine will run at about 600rpm.  This leads to the biggest problem in home-built windpower.  You will not find an alternator or generator which will give your required power (250 watts) while running at that speed. So you will either have to use gearing to change the speed, or build or adapt a special machine.  The second option is the better of the two.

Check at Windmission where you may be able to buy a purpose built permanent magnet alternator (PMG).

Or again you can use a permanent-magnet "servo" motor from a surplus store in the USA

or a 'Smart drive' washing machine motor from new zealand (see ecoinn)

or try a czech alternator at http://mgplast.web.worldonline.cz/

Alternator design

I recommend the Axial flux alternator plans (June 2005) because they contain my latest ideas.

The photo shows an alternator being assembled.  The first magnet rotor is already mounted, and the stator is being fitted.  Later a second rotor will be mounted on the four studs so that the stator is sandwiched.  The magnets in both rotors, and the stator coils, are set in polyester resin castings.  The process is easy, and requires no special tools or skills.

try Windstuffnow for an alternator recipe

A book "the homebuilt dynamo" by New Zealand author Alfred T. Forbes is available from Graham Chiu (around $US60) 
 It explains in great detail how to build your own permanent magnet alternator.  This is one fat glossy book.  

Help with finding magnets for building your own alternator here.

Finally, (last but not least!) here is a link to a free public domain on-line alternator construction manual in pdf format (2001).
I developed this design as an aid project for Intermediate Technology Development Group (ITDG) with funding from the UK government.

Other Aspects of the design

Windpower workshop does not go into the details of construction quite so deeply for any single machine, but it covers a lot of ground, including towers and how to erect them.

 
 
 

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Hugh Piggott - back to my home page..