Home-Built Windpower

updated February 2006

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This page is designed to help those who plan to build their own wind turbine. I hope you find it useful.
Some of it is getting a bit dated - especially the stuff about brakedrums.

I have been teaching

workshop courses

in wind generator construction, here in Scotland and also in the USA and

Wales.
I am not offering these in 2006 due to pressure of other work.
See my

courses pages

for many stories and pictures of homebrew windpower.

Details of how to buy my

books

on home built wind turbines

Links

to other good sites for home made windpower:-

http://www.otherpower.com

Windstuffnow

Chuck Morrison's site

Andy Little's site

Dave Allender

Windmill plans and courses from Peru

eco-inn windpower course in New Zealand

Otherpower's discussion board

is full of fast moving action on the windmill building front with pictures.

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

Before you do anything else, you have to know how much power your windturbine is likely to produce and make sure that the

speed of the rotor blades matches the speed of the alternator (or whatever produces the electricity). If you fail, and the alternator is

too fast or the rotor too slow, for example, then you will not produce any power.

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

To design the blades, may find it useful to study some notes I have put on the web at another site:-

a short course in

blade design

I prepared for the Centre for Alternative Technology.

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.

Here are some on-line guides to the detail of how I make blades:

●

blade design spreadsheet (free for download)

●

Detailed instructions for making a set of blades,

to run at tip speed ratio 5.5 or thereabouts.

●

Colour pictures of the blade carving process

●

Chuck Morrison

has produced a set of templates for carving blades according to my books.

●

Wind stuff now blade design software

(based on my ideas)

●

Notes on where to get suitable wood for carving blades in the USA

There is also a guide to fibreglass blade manufacture on my

download page

I edited the document but I did not write it - I do not have experience with making fibreglass blades myself.

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.

Finding a suitable alternator....

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.

There is plenty of advice on the subject in Windpower Workshop (1997),

and I have also produced older plans (2000) for building a low speed alternator from the brakedrum hub of a small truck or van.

However these are no longer for sale.

The brakedrum alternator has quite a good power/speed characteristic for small windpower as shown in the graphs below:-

For people who are still building the brakedrum machine, I have prepared an

update page

with some questions answered.

See my

workshop courses page

for the latest stuff and lots of good pictures of homebrew stuff happening.

My

Axial flux alternator

plans are much easier to use because the parts are easier to find and the stator is easier to

assemble.

More help for homebuilders at

www.otherpower.com

wind alternators

Check out the

www.fieldlines.com

postings for otherpower Monday sessions like

this

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.

Click on the image above to contact Phil.

Other Aspects of the design

Control is very important. Your wind turbine needs controls to prevent it from overspeeding in gales. I use a furling tail

arrangement. Later I shall post an explanation for this but meanwhile you will have to buy one of my books.

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.

For details of

how to buy my books

please follow this link.

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Hugh Piggott - back to my home page..