User experience with evacuated tube water heating

Nathan Jowett asked me to publish his article that he wrote about his solar hot water system.  I have to agree with him that evacuated tubes are brilliant, having had my own system for fifteen years now.

Nathan’s Article V3.0

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Kragten update again

Dear Hugh

I have written a new report KD 723 which can be copied for free from my website: at the menu KD reports. The title of this report is: “Ideas about an 18-pole, 2-phase permanent magnet generator using the housing of a 6-pole asynchronous motor frame size 100 for driving a 0.55 kW motor of  a centrifugal pump”. In chapter 6, an alternative 6-pole armature is described which can be used in combination with the standard 6-pole, 3-phase winding.
Adriaan Kragten
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New Kragten paper on asynchronous motor conversion

Report KD 718 can be copied for free from my website: at the men KD-reports. The title of this report is: “Ideas about a 16-pole, 3-phase permanent magnet generator using the housing and winding of a 4-pole asynchronous motor frame size 100”.

This report describes a way how to modify a standard 4-pole, 3-phase asynchronous motor such that it can be used as a PM-generator for a wind turbine for 24 V or 48 V battery charging. Manufacture of the new armature is rather easy as the magnet grooves are wide and shallow and in parallel to the armature axis. The magnet costs are low as only a rather small magnet volume is used. Mechanically the armature has sixteen poles but physically it has four poles and therefore it can work together with the standard winding of a 4-pole motor. The flow pattern is given in figure 2. The armature pole angle is 2.5° larger than twice the stator pole angle and the fluctuation of the sticking torque is therefore almost flattened. A front and a side view of the armature and the stator is given in figure 1.
Adriaan Kragten”
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Upcoming workshops with Jonathan in Germany and Austria

Windrad Selbstbau Workshops  

Baue mit uns ein Windrad. Voll funktionsfähig, nach dem weltweit bewährten Piggott Design.

Die einfache Anwendung nachhaltiger Technologie steht im Mittelpunkt des Workshops.

 An einem Workshop teilnehmen

 Einen Workshop veranstalten


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Some of the owner-installed Powerspout turbines that I supplied over the last twelve months

Bear in mind that the turbines are freshly installed and working so the setup is a bit rough in some cases. Most owners will do a bit more work around and about or even build a shed although this is not necessary for protection against the rain. These turbines happen to all be in the British Isles.

Most of my sales are to people who do the work themselves, so I spend plenty of time explaining stuff. I love it. Especially when I get to see pictures.

This PLT in England was expected to produce 548W but kicking out 720W off grid.
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F-series wind turbine manual available soon from Jonathan

Here is a link to find out more and keep in touch with Jonathan.
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New chapter 9 in Kragten’s public report KD 341

Adriaan writes:

“Dear Hugh
I have added a new chapter 9 in my public report KD 341 which may interest you. The title of this chapter 9 is: “Voltage generation in a coil”. This chapter also contains three pictures of a small 8-pole axial flux PM-generator which show how you go from the ideal coil shape to a shape which is easier to manufacture and contains more copper. KD 341 can be copied for free from my website: at the menu KD-reports.
Adriaan Kragten”

It’s comforting to see that the coil shape arrived (below) at is similar to the ones I use in the F- series alternator designs, where I pack in the maximum number of ferrite magnets into the disk. With my Recipe designs for NdFeB magnets I used larger disks relatively and therefore a different coil shape.

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An up-to-date list of UK sources of materials for my wind turbine projects

My most recent wind turbine plans are dated 2014, and I don’t really make enough sales to justify updating them now but the list of UK suppliers at the back of my Recipe Book is out of date for sure. Often the best supplier will be a local one, but I will offer a list of suppliers below in case this is useful.


Neodymium Blocks 46mm x 30mm x 10mm thick from Spider Magnetics These are grade N35 which is not particularly strong, but it is hard to find this size neo magnet these days. Powermagnetstore have N40 which is better for keeping the rpm down, but the cost is somewhat higher. You can get N42 from First4magnets but the cost is almost double the cost of the N35 ones. Thanks to Adriaan for pointing out Enesmagnets in Poland who can offer 50 x 25 x 12 magnets in N38 which should work well with the Recipes.

Ferrite Magnet 50 x 50 x 20mm thick (C8 Grade 3) as used in my 2F turbines
First4magnets have them.
Ferrite Magnets 75x50x20 Y30 as used in my larger 3F, 4F etc
Magnethandel in Germany have these.
Enes have 75 X 50 X 20 / F30 – Ferrite Magnet

Winding wire

I buy my winding wire in 20kg reels from EC wire.
For smaller deals, here is an ebay supplier I found quite easily.

Resins, Vinyl Ester, Epoxy etc

East Coast Fibreglass
These suppliers also offer the glass cloth you need for reinforcing the resin castings

Steel disks

Find a local workshop that offers profile cutting services. Bear in mind that it will be much cheaper to buy a larger batch if possible (shared with friends?). I like to get them sent to be galvanized on their way to me. Another option is to get them powder coated but I don’t find this lasts so long in my maritime environment. It is possible to cut your own disks using a grinder (a big polygon works OK). Harder to get a precise result this way.

Trailer hubs

There are several online suppliers.
Trailertek offer stub axles and hubs for small turbines around 2m diameter
(beware of the seal behind the bearings which will not last due to thrust of the wind, so safer to remove this seal)
and also some nice solutions for bigger machines at low cost.
I have also used AutoW for hubs and they offer cheap options.
Towsure are a good option too.
You may wish to replace the bearings with decent ones such as SKF or other major brands.

I hope this helps. If anyone needs further advice please contact me at [email protected]

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F series wind turbine designs

My wind turbine designs in recent years have used ferrite magnets and the naming system is based on “F” for ferrite (or ceramic) magnets, preceded by number denoting the diameter in metres. Hence the 2F is my 2012 design ferrite using ferrite magnets with 2 metre blade diameter and it is the only one that is available as a finished document for sale as hard copy or ebook. I have also built 3F, 4F and several 3.6F machines and I have a designs for a 1.2, 2.4 and 5F. Details of these models are available to people who contact me and ask for them in person.

16 pole version of the 2F – magnet rotors in the moulds

I first started building ferrite magnet machines around 1991. I produced designs for various geometries including the radial flux “Brakedrum windmill plans” and African Wind Power 3.6m turbine in Zimbabwe (AWP), and the axial flux design for ITDG/Practical Action machines in Sri Lank and Peru around 1999-2000.

Here is a detailed design document for this generation of axial flux design. In those days these magnets were expensive. This illustration below (from 2001) shows the layout with the magnets quite widely spaced. The logic was that they were costly and this layout gave me the best best “bang for my (magnet) buck”. These magnet rotors have proved extremely reliable but the power output is low, around 100-200W maximum. Good long term energy producers though.

In 2001 I got my first taste of NdFeB magnets or “neos” at a Workshop in the USA. The magnets were provided by Otherpower and they were very strong and very shiny. For the next ten years my designs were all based on these sexy new magnets. This culminated (2009) in the Recipe Book series of designs that have become very popular worldwide, leading to the creation of the Windempowerment network. Unlike the older ferrite designs they had much higher power/weight ratio, made possible by the very powerful neo magnets.

Corrosion issues in NdFeB magnets on Scoraig – The casting has been cut open for repair.

There are many machines built using these magnets, and they work well, but one persistent issue here on Scoraig (with our maritime climate) has been corrosion of the magnets. Inside their shiny coating they are extremely vulnerable to corrosion, which causes them to swell up. The resin casting fails to protect against this. When the corrosion starts at the back of the magnet (as in the above photo) the whole casting swells up and rubs on the stator. Some or all of the magnets eventually need to be replaced. Upgrading to galvanised disks helped a bit. Sometimes the issue can be dealt with for a few years using oil and grease to protect the magnets, but eventually there is a costly repair. It’s disappointing, and it has turned me back to using ferrite magnets that are immune to any kind of corrosion.

By 2012 the cost of ferrite magnets had fallen dramatically compared to the turn of the century. This enabled me to use a new approach of “throwing magnets” at the problem and so to maximise the flux in the air gap I crowded the rotor with big thick magnets, trying to fill the space. This is the opposite to my previous philosophy of trying to get the most power from the magnets I had (spaced sparsely on a large disk). Nowadays I try to get as many magnets onto the disk as I can. The optimum coil shape has also consequently changed from square with a large hole, to triangular with a small hole in the middle.

4F coils in the stator
4F magnet rotor

The result of this new approach is that the performance of this new generation of ferrite alternators is much closer to the equivalent sized neo alternator than one would expect, given the much less powerful magnet type. This chart compares the magnet rotor diameters. The F series are slightly larger but they produce roughly the same power output at the same rpm as the NdFeB magnet equivalents. (The 3.6F is a bit higher power than the neo one.)

Posted in construction, ferrite magnets, my own projects, Scoraig, Uncategorized | Tagged , , | 2 Comments

Jon Leary’s performance study of Scoraig wind turbines published

The long awaited final version of Jon’s study based on data he collected here in 2012-2014 has finally been published and is free to read or download here courtesy of Wind Engineering.

An important conclusion is the the table in the Recipe Book that shows the anticipated energy yields for various site windspeeds was (amazingly) not too grossly misleading. “Piggott’s estimates for the annual energy yields of his Recipe Book machines are an accurate prediction of their average real-world performance (+5/−20%). However, the performance of individual machines can be significantly above or below this (+70/−51%). These deviations are sometimes intentional, where reliability is prioritised over power performance, but often unintentional.”

Jon had already given me the basic data, much of which has been available on a page on this blog since 2015. The page complements his article in many ways, giving some more detail of the individual turbines’ performance.

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