Home-Built Windpower
updated February 2006
hugh@scoraigwind.co.uk
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:-
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.
Document Outline
