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.
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.
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.
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.
[note: I have edited my remarks in response to some corrections sent by email]
Adriaan has notified me of the following free reports that he has published (see below the diagram). The axial flux design has a single magnet disk, and a steel plate behind the stator coils, so the eddy current losses are pretty high (22 watts measured for an 80 watt turbine). The advantage (compared to the twin-rotor design that I use) is a a supposedly simplified construction. The magnet gluing is a potential failure point at high rpm. I have some concerns about the use of thin metal plate in the support of the blades (fatigue). These are meticulously mathematical reports which will be invaluable to the diligent student. The theoretical work is a great lesson.
Dear Hugh and others
Recently I have placed three new KD-reports, a manual and a new list of public KD-reports on my page of the website of Bidnetword: www.bidnetwork.org/en/member/adriaankragten This material can be copied for free by anybody.
KD 571 gives the description and measurements of an 8-pole, 3-phase axial flux permanent magnet generator and the calculations of the rotor and the head of the VIRYA-1.36 windmill. Manufacture of the parts and a complete set of drawings of this windmill are given in a separate manual.
KD 574 gives the description and measurements of a 6-pole, 2-phase axial flux permanent magnet generator and the calculations of the rotor of the VIRYA-1 windmill. This report also contains the drawings of the generator and the rotor. This generator is an alternative for the Nexus hub dynamo of the VIRYA-1.04 windmill which is described in an earlier public manual.
KD 340 is an older report in which rectification of the generators of the VIRYA-windmills is described. Recently a chapter about 2-phase rectification is added because this is used for the VIRYA-1 generator.
In the list of KD-reports, all public KD-reports are given. 24 KD-reports and two manuals can now be copied for free from my page on the website of Bidnetwork. I am retired now for almost three years and I no longer accept large engineering projects but through these free KD-reports I try to make that the knowledge gained by 40 years of experience with small windmills is not lost. Questions about small windmills asked by people from developing countries will be answered for free if answering takes a limited time.
PS Adriaan has also offered his replies to my comments above as follows:
Nice that you have put my message about the three new KD reports on your blog. Your comment is OK but I can say the following about it.
It’s true that there are substantial losses in the stator due to eddy currents but the copper losses in the winding at maximum power are much larger. At low powers, both the copper losses and the iron losses are low and then the generator efficiency will be rather high (I expect about 75 %). For a small windmill mounted at a low tower, enough power at low wind speeds is more important than high power at high wind speeds. The big advantage of a non rotating steel stator sheet is that you can use separate coils bolted to the front side of the stator sheet and that the wire ends can simply be guided to the rectifier by a hole in the sheet. At this moment a prototype of the VIRYA-1.36 is being built by an Indian company and they will try to measure a complete generator. Once I know the measured characteristics, I will add a chapter with these characteristics to KD 571.
It’s right that the blade is rather thin (1.5 mm) where it is connected to the armature sheet. But therefore the rotor is very flexible and this almost flattens the fluctuation of the gyroscopic moment which is typical for a 2-bladed rotor. The bending angle due to the thrust is strongly reduced by the centrifugal force in the blade and this reduces the bending stress in the blade root. The VIRYA-1.25, which has almost similar blades, has been tested for more than ten years and is still running without any problems.
V3 write:- “We run courses building small DIY wind turbines, sometimes these courses are purely educational and the turbine built on the course does not have a home to go to. We want to get these turbines generating electricity so are looking for people who would be interested in hosting a turbine or buying them from us at cost price. People living off-grid would be especially suitable. The turbine is designed by Hugh Piggott and is robust and easily maintained. We have installed many of these turbines (see the previous courses page for examples) and are happy and keen to discuss any queries so please get in touch!”
Here is footage from the presentation I made for the Windempowerment Conference in Athens last month. Actually this is a backup that was not used at the conference as I was able to make the same presentation live (and said a whole lot of different things, I think). Anyway this backup version is too long to upload as a single video so I have split it into 3 parts: Scoraig Stories, Alternator Design, and a shorter subsection: Ferrite Magnet Windmill. This last is an intro to my new 2F design document
sorry about the poor sound quality
More about windmills in the old days on Scoraig here
I am planning to hold a course here on Scoraig in April. We’ll build and test a wind turbine as usual. Accommodation is provided from Saturday 18th to Saturday 25th April 2015. These will be the arrival and departure days. The course will run for six days from 19th to 24th. Your partner may be able to find accommodation here too without attending the workshop. Please ask for details.
See photos of 2012 course (plus video) , 2013 course and 2014 course. Cost will be £700 including accommodation. I may be able to offer a limited number of student discounts if there are enough people paying full price.
Contact me for more details and to book a place. I do not plan to travel around teaching courses this year as I have mostly done over the last 12 years or so. This may be your only opportunity to be taught by me personally, although there are several other groups worldwide offering courses based on my Recipe Book or derivatives of it.