maintenance sur une petite éolienne

Maintenance sur la petite éolienne Colibri sur l’ecosite d’Eurre. Projet fait en co-opération avec le Greta sur le projet RET.

 

This Colibri machine design is based on my approach, using an axial flux alternator.  You can see some details of the fabrication here.

New Tripalium website

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scoraigwind.com is back online

My old homepage at scoraigwind.com is back up, after falling over a couple of weeks back. Thanks to the guys at Otherpower for hosting it for me over the last ten years. Thanks also to Irishsolar (eirbyte) for hosting this .co.uk site.  I am bringing both sites together at Irishsolar now.  I can recommend Irishsolar for domains, hosting and wordpress sites powered by renewables.

The old site dates back to the 1990s and is frankly a bit of a mess, which is why all the new stuff tends to be on this wordpress site instead.  But there are some good galleries of pictures of courses over the last 15 years and various other miscellaneous gems.  See the contents link for an over-view.  And somehow Google still likes to point people to my old site.

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Wiring loss in 3 phase wind systems

Here is a piece I did about AC and DC in 1999.  It explains why DC wiring is slightly more efficient than 3-phase AC wiring where the AC is feeding a rectifier (rather than grid AC which is at  higher voltage).  One way to understand why AC is less efficient is to notice that Ac current is intermittent, only using the wire part of the time, whereas DC uses it all the time.  So for the same peak voltage, DC is going to work better.

There is some confusion about how to calculate losses in the cables of a 3 phase wind system.  If the 3 wires are feeding a rectifier, charging a battery, then the current in the cables is dominated by the need to supply DC at battery voltage to the load.

The cables may change, but the current tends to remain constant.

 LOSS

Paul Gipe’s question 

What is the power lost in conductors from a 850 Watt permanent-magnet, three-phase alternator feeding a diode bridge rectifier delivering a nominal 24 VDC to a battery bank. The rpm, voltage, and current of the three-phase alternator varies with wind speed. There are three cables (conductors) between the wind turbine’s alternator and the diode bridge. There are two conductors from the diode bridge to the batteries. The conductors are #8 AWG with an AC resistance of 0.78 Ohms/1000 feet. There is 150 feet from the wind turbine to the diode bridge, and an insignificant distance from the diode bridge to the batteries.

The DC current is found by dividing watts by volts.  this gives 850/24 = 35 amps.

If you want to analyse situation mathematically, current in each conductor is 35 amps for 2/3 of the time.  The rms current in each conductor is therefore (2/3)^.5=0.82 times 35 amps = 29 amps (rms).  Resistance of each conductor is 0.78 times the cable run of 150/1000 feet,  giving  0.117 ohms.

Power loss is I^2*0.117

which is 2/3*35^2*0.117

which is 1/3*35^2*.234 for each conductor

which is 35^2*.234=287W in total.

This is a 34% loss!

An easier way to analyse the situation (which also give the same answer) is to say that at any given instant the DC current 35 amps is flowing around a circuit path with resistance equal to 0.78*(cable run in feet/1000).  Cable run is 300 feet for the full circuit.

Finally I should point out that the above is strictly only true if the internal loss is small.  As loss increases, the situation becomes much more complex, since more than 2 wires will start to conduct at once during the changeover.  But the above answer will be accurate enough for practical purposes, given that we are arguing about such large differences in our answers.

Hugh

October 1999

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Assessment of locally manufactured small wind turbines as an appropriate technology for the electrification of the Caribbean Coast of Nicaragua

This paper spells out the many hard lessons that were learned by blueEnergy in their effort to bring locally manufactured wind energy to remote villages on the Caribbean coast.  It should be read by anyone setting out to use my wind turbine designs for a tropical maritime local electrification project.

ABSTRACT HERE        FULL PDF HERE

I have always been inspired by blueEnergy’s principle of “sticking around” which I feel is the downfall of so many aid projects: here today and gone tomorrow.  But unfortunately, as you can read, there were numerous factors lined up against the success of using locally manufactured small wind in this situation – not least of which is the lack of wind.  No amount of enthusiasm and dedication can compensate for a low windspeed site.

Corrosion issues have been the biggest potential weakness in my published designs, and these are also spelled out.  Inexperienced workers, remote locations, lightning damage etc make for poor reliability and high cost in relation to the relatively simple and ever cheaper PV generated power.

See also video about How to encourage wind energy in Tanzania: NGO or private company?

Posted in developing world, People | Leave a comment

Hornet wind turbine next door

After the storm destroyed the Ampair 100 that was on this mast, a neighbour bought a Hornet from http://windgenerator.org.uk/  This is the 8-blade 1250 watt version.  Apparently it has been seen producing 1251 watts into a 24 volt battery “in the bottom of a valley”.  Which I assume would be about 40 amps and 30 volts.  However this is one on Scoraig is connected to a 12-volt system.

The Hornets are made by Hydrogenappliances in the USA and are a bit similar to the products of Missouri Wind and Solar (see below).  Converted car alternators and tiny composite blades.  The 28″ long blades look like copies of the AIR machine’s high speed blades but on the Hornet the alternator is stiff to turn so they use them in large numbers to get enough torque to spin in low winds, and this somewhat defeats the low solidity.  Furthermore they recommend cutting this tips off to get more power (?)

Having said all of that it’s an affordable little unit and when I went to look at it in a good stiff breeze it was purring along producing a respectable 50-100 watt output.  Let’s see how long it lasts.

Posted in products/technical, Scoraig, UK small wind scene | 6 Comments

back in action after storm

Perceptive readers will have noticed the little red graph on the right plunge to zero after the big wind we had on 9th January.  This was due to my AWP windmill plunging to the ground with a broken alternator shaft.  Yesterday I was pleased to get it back in action.

This would have happened a lot sooner if I had not had a lot of neighbours’ windmills to fix as well.  Out of 35 windmills up and running on the night of the storm, roughly 25% failed, many of them pretty catastrophically.  It’s almost exactly ten years since the last big wind like this which had a similar effect.

Most of the wind turbines ran through the night unscathed.  Some had the short circuit brake on.  It’s interesting that the failure rate of the braked turbines was slightly higher than the failure rate of those that were left running.  Failure rate of commercially manufactured turbines (Ampair, Proven) was similar to or higher than local manufactured ones.

Posted in products/technical, Scoraig | 2 Comments

Missouri video

I mostly like everything that people do with small wind turbines, especially hands-on and do-it-yourself, so I got excited to discover Missouri Wind and Solar, and I watched this video that I found on the home page with interest.

Unfortunately I was a bit disappointed as there was almost nothing the Jeff said that could begin to agree with.  Here are just some of the main points of disagreement.  If anyone wants to chime in and explain what Jeff was thinking of I would be grateful but to be honest I am afraid I just don’t get it :-(

  • AC versus DC transmission in cables.  At 4.40 Jeff states that “3-phase AC output, you can simply use an extension cord and run it 200 feet with literally no loss whatsoever.”  In fact the 3-phase AC cable supplying a rectifier has to carry the same current as the DC cables that follow after, but the difference is that they are only working part time.  So you need 3 wires the same size as the two DC ones would be to achieve the same efficiency.  I wonder if Jeff has tried putting 50 amps of AC down his extension cord, or maybe not.  I mostly use AC transmission and my rule of thumb is that for the same voltage you need the same wire size for AC as you do for DC (to have the same power losses).
  • Solid core wiring.  At 6.50 Jeff says to never use solid core wiring for DC current.  I think he has some garbled idea about skin effect however this only affects AC current, and at low frequencies it would only be significant at huge wire sizes having solid cores 3/4″ or more thick.  solid core wire will work fine for AC or DC.  Often stranded wire is easier to work with but weight for weight they have the same resistance.  the coils in the alternator are wound with solid core wires.  I use both types of wire on AC and on DC.
  • Seven blades will start at lower windspeeds.  AT 8.50 Jeff contends that 3-bladed wind turbines cannot start in low winds whereas machines with multiple blades can start at lower windspeeds.  In fact the start-up depends also on the friction in the seals, the losses in the stator core, and above all upon the diameter of the blades.  Blade diameter matters more than blade number, and this is not something Jeff mentions at all.  You can use more blades to get more torque (at lower rpm) to overcome friction etc (and to sell more blades), but the key to low wind performance is large blade diameter (longer blades to catch more wind).  A multi-blade will turn slowly in low winds but there is no real power to be had from small rotors in low winds, and the rpm is too low as well.
  • Odd numbers of blades.  At 10.40 things get really bizarre when Jeff tells us that blade rotors need to have odd number of blades.  I wonder if he ever heard of the old Dutch windmills with 4 blades? 2-bladers have their issues with vibration which you can read about elsewhere but they are faster than 3-bladers.  For many years (1970s and 80s) when I needed maximum rpm speed I only made 2-bladers.  3-bladers run more smoothly and if you don’t have excessive friction or a tiny diameter then 3 is all you need.  Odd or even makes no difference.
  • Blade pitch and stall.  At 14.30 Jeff tells us about aluminum blades with coarse pitch.  He claims that “at 15 mph these blades will throw themselves out of the wind and stall”.  In fact the coarse pitch is a good strategy for a low speed, high torque blade rotor.  If you combine the large pitch of these blades with the large blade number that Jeff uses (to achieve the low wind start-up) then you would get the best result for an efficient low speed rotor, suitable for pumping water etc.  The problem is not “stall” in this case but simply coarse pitch which limits rpm.  Rpm in relation to windspeed is determined by “tip speed ratio” and these aluminum blades are designed to work at low tip speed ratio so they need a very slow generator to work well.  Stall however is the opposite problem, when high speed rotors (with a flat pitch angle and fewer blades) have too much load torque holding them back so they cannot achieve their best (high) tip speed in relation to the wind.  Best results are achieved with larger diameter blades (with high tip speed ratio) and a good understanding of how to match the generator load to what the blades can do over a range of windspeeds.  There is not much sign of these lessons being learned, unfortunately.
  • Towers at 17.40 we learn that “Most wind turbines fit on an inch and a half pipe”.  This confirms that Jeff’s experience is pretty much limited to the world of vehicle alternator wind turbines with diminutive blade rotors that can’t produce more than a few amps (or he would have already set fire to his extension cords).
  • 18.10 “you can simply take a pipe, stick it in the ground, concrete it in up to twenty feet” yikes!  that would get bent over pretty quickly where I live!  You need to put guys on the tower, fairly close up to the tips of the blades so as to support the pipe.  That is if you are generating serious power output.

I won’t get into my comments on the missouri wind and solar controllers here.  I have just touched above on a few of the problems I have with Jeff’s instruction material.  I hate to be negative about this, and I have no wish to start a big argument, but I can’t really leave this stuff out there without challenging it.

Posted in People, Video links, wind systems tutorial | 45 Comments

Hugh Piggott Wind Turbine Components

V3 have been building my turbines for over 8 years and are able to provide full bespoke kits or separate components.

Bespoke kits comprise a set of three hand-carved blades, alternator and mounting. The turbines can be installed as a grid-tie or to charge a battery bank and can come as 12V, 24V, 48V or higher voltages for use with grid tie inverters.

Each component of the kit is also available separately.

Blades, stator, magnet disks, mounting with tail.

Posted in construction, People, UK small wind scene | Leave a comment

We have power up!

Hi Hugh,
We have power up ! Some pics from the initial switch on. (The plumbing is not ready for the immersion so air dumps in use now). The system was ‘right on the money’ as far as the calculations go. There was over 1 bar reading on the pressure gauge, even when running with four nozzles. We are using only about a third of the water flowing down the stream right now, (there has been quite a lot of rain, but this is more or less the normal winter level). We see around 7 amps on the meter when dumping is in progress, at about 60 volts, so around 420 watts. I haven’t read the the amps accurately, going on the analogue meter you sent.
I am sure we could get a lot more from the system if necessary, but for now it will be plenty until Michael works out using some of the 240 volts with washing machine, fridge, and water heating.

The only thing we didn’t like was the fact the Turgo is quite noisy. Michael’s house is exceptionally quiet, miles from a road, and minimal ambient noise from the inhabitants. We could hear it from the house, even though it is at least 100m away. Michael was not really bothered by it, but I suspect he will want to enclose it with something to damp the sound, longer term. He plans a roof over it anyway. Any ideas on the best solutions  ? I suggested some sound attenuating foam.

It was very satisfying, and have to repeat our earlier thanks for all your advice and input.

Cheers
Bobby

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Great result …and pics

Hello Hugh,

Now the festivities are over I want to report back on our Powerspout and
Midnight Classic installation.  It’s incredible!  The generator has not
been used once this winter.  We are making around 250 watts 24/7 with
the small nozzles which is enough to fulfil our needs along with our
solar……….. even the recording studio.  If we do need more I know
we can fit the larger nozzles.  So once again I´d like to thank you for
all your help.  I am attaching pics of the installation.  Please could
you pass these on to Powerspout.

Best wishes,

Richard

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