Friday, 19 October 2012

Inside the Wind Turbine....

In 2009, after we returned from a spell of working overseas, I started designing and building an experimental wind turbine.

However, what with work, moving home and other commitments etc, it actually took well over two years to complete and erect the 'finished' operational unit, and during that time the basic design had also evolved significantly.

the turbine as currently configured...
The turbine has been up and running in its present location for most of this year, and so I thought we'd give you a brief description of the machine.....

The heart of any turbine is the generator.  In our case, it's a 240V DC permanent magnet motor from a machine tool, i.e. the spare motor for my lathe.  As a motor, it's rated at 1hp (say 750W).   As a generator, and given that we don't rotate it at anywhere near its rated voltage speed of 4,500 rpm, I'd say our turbine installation is around 250W maximum.

The current blade set is aluminium and was bought new on eBay, and it sweeps 1.4 metres diameter.   This replaced the home-made set I'd built, also of 1.4 m diameter, but which was constructed from PVC guttering.  This home-made set worked fine but the blades tended to flex and sing in high winds.

the old homemade bladeset & hub....

Initially, I had the blade set driving the motor directly, but later changed the design to incorporate a gear pair.  This steps up the blade speed to turn the generator faster, thus producing more voltage in lower wind speeds.  The blade shaft is mounted in its own bearing housing, independent of the motor, which allows such a gear pair to be installed.

Left-to-right: bladeset, hub bearing,
gear pair & generator

The motor saddles are mounted on studs to raise the shaft centre higher than the blade centre, to incorporate the 21:12 gearing.  The 21-tooth driving gear connected to the blades is made from 'Hostaform', an engineering plastic, and the 12-tooth driven gear keyed to the motor is from mild steel.   Mounting the motor on studs allows the gear clearance (or 'backlash') to be accurately adjusted to ensure they mesh properly.

The gear pair is covered with a transparent plastic housing, which was a 'project' box picked up on eBay for a few pounds.  This allows oil to be injected into the casing to lubricate the gears – there's just enough oil to let the blade gear teeth dip into it as they rotate.

oil within the gear casing...

The mast is from 38mm mild steel tube, and is secured to the wall of the house by brackets and car exhaust clamps.  It's also 'stayed' sideways by a piece of angle iron and front-to-back by a guy wire.   The wind in our location is predominantly from the west or south-west, so it was easy to know which side to anchor the guy wire.

mast and guys...

The smartest piece of design of the turbine is the slip ring, which I machined from aluminium bar, perspex blocks and copper sheet.  It uses a couple of carbon brushes mounted in the stator block on the mast (the brushes were from a Chinese eBay seller, just a few pounds for five pairs), to pick up the current from the copper sheet tracks mounted in the rotor.  The cabling from the stator is fed down to the workshop through the centre of the mast tube.

rubber mounts, azimuth bearing & slip-ring rotor

slip-ring rotor & stator, and masthead mounting

The slip-ring allows the entire turbine assembly to weathervane as the wind direction changes, and it can rotate continuously through 360 degrees.  Without the slip-ring, it would be necessary to limit the azimuth rotation of the turbine to stop the power cable wrapping itself around the mast.

The turbine fixing to the azimuth bearing hosuing above the slip-ring rotor is via three rubber mounts, to reduce noise and vibration transmission through the mast.

The turbine cover (fairing) was made from a couple of old plastic waste bins, and lined with thick carpet as a noise reduction measure.  The gear box casing is also surrounded by sound-deadening material, since the gears are the noisiest part of the installation.  The fairing cover is waterproof since the generator wasn't designed for outdoor use.

gearbox noise cover....

with  weather cover refitted....

The tail is made from a length of aluminium angle and a pair of cheap cutting boards.

Incidentally, and as a general remark about sourcing project materials, kitchen cutting boards are a really cheap way to get hold of sheet plastic materials.  ASDA used to sell a basic one for around 80p – I bought ten at the time, and I've still got most of them in the workshop – just try getting hold of a 6 mm thick piece of an A4-size nylon sheet for that price anywhere else.....

Originally, I had the turbine connected to a pair of 85 Ah leisure batteries via a 12V charge controller, and used them to power our 12V outside lights, but the turbine produces such a small amount of energy on average, and then only intermittently, that it's now connected to a 300W grid-tie inverter to feed directly into the household supply.  The leisure batteries are charged using our rough-and-ready 36 cell PV panel, when it's not being used in our other experiments......

The grid-tie inverter can accept inputs of between 10 to 32V, and it also includes maximum power point tracking (MPPT) circuitry which is supposed to maintain the voltage-current balance at its optimum output.  It also tries to hold the voltage down to less than 32V, but if the wind's too strong it automatically switches to the dump load, which in our case is a 12V water heater as used for making tea etc from the car's cigarette lighter socket.

In terms of performance, the wind turbine been very disappointing since the time it's been connected to the mains and we've been regularly monitoring its output.   

One thing about having such a poor summer and seeing very little sun, is that there's been very little wind too.   On the rare days when it's been bright, more often than not it's also been breezy.  However, when we've had the low clouds and long periods of very heavy rain which have characterised this summer, the rain has been prolonged simply because there hasn't been any wind to blow the clouds away.

The maximum instantaneous output we've ever had from the turbine is 172 W – we can see that maxima from our monitoring equipment.  Note, however, that this is 172 W AC, i.e. on the output side of the inverter, and probably equivalent to 200 W on the DC input side.

However, if we look at the total AC energy output since mid-May, we've produced only just over 5 kWhr, at a daily average of 30 Whr.  So, you can see why it wasn't much use to power our outside lights, which need around 450 Whr per night in the summer and 900 Whr in the winter !

On the positive side, I expect the turbine output to increase significantly through the autumn and winter as we experience higher winds much more regularly.  In fact, as I'm writing this post, the turbine is spinning very fast in a strong westerly breeze.   Additionally, of the 5 kWhr we've produced in five months, more than 10% was generated in one single 24 hour period in June, during very strong winds, which shows that if the wind blows then the turbine can produce something useful...

What can we do in the future to improve our installation ?  Well, we can perhaps increase the blade set diameter to 2.2 m (the maximum size for which planning permission is not required in the UK).  We can also mount it a little higher to catch more wind.   We could also try changing out our lathe-motor generator with something more suitable, i.e. where its rated speed is more closely matched to the speed of the bladeset.

However, these initiatives would cost money, and so I've thought about just making a larger Savonius vertical-axis turbine instead, mounted at ground level, but that's also one for the future.  Here's a sneak preview of the basic design; the frame would have chicken-wire around it to form a safety cage, if I ever get around to building it.

basic 3-D model of Savonius turbine

In the meantime, we'll continue to monitor and record the output from our existing installation, and give an update sometime next year....


  1. Brilliant stuff.

    I notice that this is quite an old post... Did you ever get around to making improvements or build the new design, or is this one still in comission?

    I did read elsewhere that home turbines were not economical but that was about premade ones. Making your own one on the cheap is just a cool idea however little output it cranks out, IMO.


    1. See this post :-

      However, although I haven't built another turbine as yet, I still haven't totally ruled it out ....