My first Mill - Newbie in UK - Spain

[(unknown)]

I have been lurking here for a short while and was determined not to ask any stupid questions as all the answers are already here.  But now my head just hurts.  Sorry . . I tried really, really hard!

I live in the UK and have a remote off-grid property in Northern Spain.  I am building my project in the UK for use in Spain.  Unfortunately, I have little experience of the prevailing wind conditions at the deployment site.

My existing system comprises two 6 V 560 Ah lead acid batteries connected in series into a 1000 W 240 V inverter which I charge using the 50 A alternator fitted to my car.  My electrical demands are small - one 11 W bulb and a 60 W TV or lower power radio a few hours most days.  I have an 850 W microwave but used it only once before realizing it is too power hungry.  In practice I fire the car up for half an hour or so every few days and then I'm good to go.  I suspect I am using no more than 500 WH per day.

I have built many virtual wind generators, the 7 ft and 10 ft Volvo hub based otherpower designs and I even put together an imaginary 10 ft mill using the current "No Volvos were Hurt in the Making of this Machine" design.  Before I pick up a real piece of metal though I decided I better get something - anything - working in the real world, hence the acquisition of the Reebok RT1000 Treadmill motor I just bought:

Specifications: 2.25 HP Continuous duty at 230 Vdc, 9.5 A.  Speed is not specified so I powered the motor with a 9 Vdc supply and observed rotation speed of 210 rpm - 23 rpm per Volt. Approx 5366 rpm at rated supply voltage.  A search on google turned up other motors for this same treadmill rated at a different voltage but at 6000 rpm.  I therefore assume my motor is a 6000 rpm device, requiring 26 rpm per Volt.

I -think- my two 6 V batteries will start charging at 6.5 V (150 rpm) or 13 V (300 rpm) depending on configuration.  Series connection would be inconvenient but possible (I would need two sets of batteries and would have to disconnect and reconfigure them regularly).  

I also think I understand that in any given wind using any design of blades where cutin speed is exceeded the higher voltage battery load will receive more power than the other.  I do not fully understand this mechanism though.

I came in here with a question ... I'm sure . . . oh yes.  Blades ... given that I am not sure about the wind my rotor may see what might be a first try on PVC blade design to best guarantee charging my 12 V battery bank with 3.5 kWH per week, assuming a cut in speed of 300 rpm?  I have see three different pvc designs on these pages - one is a 2-blade design cut from a single length of pipe, one comprises 3 or 5 blades with a simple profile resembling a wood saw and a third aesthetically brilliant design (http://www.otherpower.com/images/scimages/6863/PVC_blades.jpg) has a sweeping bulge near the root - this resembles the shape of the huge commercial rotors I see.  Which might suit my purpose?

I have also seen diffent PVC pipe diameters mentioned.   To make a blade of a given width "W" I could use a pipe with a diameter as small as "W" (a semi-circular profile) or any larger diameter, giving a shallower attack.  What is best?  Some seem to be 90 degrees, allowing the cutting of four blades from a single pipe.  What would be the effect of cutting three blades of 120 degrees from a pipe?  What does that pretty bulge do for the blade?  

Thanks in Advance.

Mal

[wooferhound]

You shouldn't make a Pipe blade that is more than 90 degrees, If you do then the leading edge starts wrapping around into the oncoming wind.

[tanner0441]

Hi

Would you get more from solar PV in spain, I would think the sun shines more than the wind blows, and it looks less intrusive and attract less interest when your not there.

Brian

[Mal Farrelle]

Thank you - that makes sense.  What do you think of the blades I referred to in my posting, in the photo there is a bulge where there appears to be a greater than 90 degree pipe angle.  I love how it looks but am not sure what it does!

I have cut some model blades out of a cardboard tube.  There are three obvious ways to arange them on a hub - what are the implications of the following different configurations (and is any of them ideal):

1. the three leading edges converging at the centre of the hub.
   
   
2. the three trailing edges converging at the centre of the hub.
   
   
3. the centre lines of the blades converging at the centre of the hub.

   
   
   

Thinking of testing different blade designs - would an efficient blade design cause a motor to draw more, less or an indeterminate current compared with a less efficient blade when spinning at a given speed on a bench?  I guess that would be too much of a gift :-)

Thanks all!

Mal

[Mal Farrelle]

During some (probably most) days yes.  Probably not at night time :-)

[CG]

Mal, you might like to look at my gutter blades on this site, I can't give you a link because I am on a public library computer and using Explorer 6, which I think the IT department has blocked the trick of highlighting the address, cutting and pasting way of linking. Just look for gutter blades in my postings.

PV guttering is ok for small turbines, I have gone up to one meter diameter on mine, you might be able to push it up it a little bit more, but not much more. But I have to tell you I have yet to generate any electricity, I am grid tied and do not have the need as you do - neccesity being the mother of all kicks up the arse. I have had very few blades breaking, but then they were only turning their own weight, so there has been very little strain on them, but guttering is a cheap way to practice cutting your blades. At the moment I have a very small turbine, with blades only .25 of a meter long, but it has been up for a very long time. The blades are a different shape to the ones in the picture, less narrow.

Best of luck with your turbine, whatever blade you use.

[ptitchard]

Mal,

I am not a blade expert but will hopefully answer your question correctly"What does that pretty bulge do for the blade?"

The bulge at the root end provides more torque to start the blades turning. The reason it is close to the hub and not the tips is to do with drag. Because the more surface area you present to the wind the more drag it produces and as the root is travelling slower than the tips this is the most effective position to increase the blade width and produce the lowest drag.

If you are a helicopter buff you will notice that some blades like the EH101 Merlin, have the bulge at the tips. As these are being powered it increases the lift at the tips of the blade. Unfortunatly as wind turbine blades are completely different this idea is not directly transferrable to wind turbines.

I wish you luck on your new project and would suggest a combination of wind and solar as in Spain I am sure the solar would be more reliable.

[Mal Farrelle]

Perfect, thanks for the great blade explanation.  

I will indeed implement a wind + solar solution.  A single 100 W solar panel would probably be all I need right now but I do love windmills. I was in the vast minority who appreciated the new turbine when it appeared and dominated the skyline near me in Reading, UK.  I now have a site where I can build my own - and they will give me some electricity too!

I also intend to build some solar water heaters - and when I get time to I will try to figure out how I can extract energy from hot water when I actually don't need hot water (Spain in August - Hot water is about the last thing I will be needing!).

All the best,

Mal

[Rover]

Plesae don't take this the wrong way but I think you will hard pressed to get a guranteed 3.5 Kwh/week out of the motor. I'm playing with a 2hp motor now, 2500 rpm/90vdc/21 amp.

The volt/rpm ratio is about the same as yours , around 26-27 rpm volt. Although the numbers are close, when I bench test as a generator, my cut in is about 400 rpm.

You would have to have very constant, high winds with fast blades (pvc blades may not be fast enough, mine never where, but I'm not the best pvc blade maker) to achieve your goal.

I just got tickled when mine produced 14 amps at 12.5 volts in 15-20mph winds - but thats under 200 w, but it is what I expected. And that was a peak reading, continuous output is far far different.