movable support for wind turbine - suggestions? (cricket sightscreen?)

[Harry Davis]

Hi, I'm planning to erect a wind turbine in my garden in Scotland, with hub about 3.2m high and turbine diameter 1.8m. It won't be grid-tied. Rather than bothering my local council, I won't be applying for planning permission or a building warrant, which is OK if it's not a permanent structure and doesn't cause a nuisance for anyone. Installation won't be MCS certified.

I'll need to make sure it's not a permanent structure. Rather than argue the toss about how to describe a tilting pole, I've decided to make the whole thing genuinely movable in an unambiguous sense, and mount it on some sort of trailer. This will also enable me to transport it to my sister's place fairly easily, for when I'm away from home, which I usually am for a few months each year.

I don't currently possess a trailer.

Has anyone got any suggestions about what sort of structure I will need? I've had a look at a cricket sightscreen, which looks as though it would be ideal once the slats are removed. Galvanised; erectable and dismantlable with a spanner; presents a small surface to the wind; and has long outriggers for stability. Unfortunately the things seem to cost getting on for £1000, whereas for basically a metal frame and two axles with a wheel on each end, I was hoping I could get away with spending a lot less.

Any ideas?

Thanks in advance.

Harold

[brass monkey]

I don't wish to put a dampener on your project but I suspect you'd be wasting your time, effort and cash. Or do you intend to store this energy somehow?

[brass monkey]

A friend of mine built something of similar size and managed to get a few watts out of a car alternator with it. Admittedly it was a Heath-Robinson affair using the drum pulley from a washing machine, but fairly useless.

[Chris J Dixon]

I'm having difficulty in seeing what makes this project worth doing.

If you must, you might consider using water containers to ballast your trailer when in use - much easier to transport empty.

A recent report somebody here linked to showed some turbines mounted on the tops of tower blocks. So as not to penetrate the roof, they simply had a large metal framework on which were laid paving slabs to hold it in place.

Chris

[Martin Brown]

Why not install it as a very beefy flagpole base foundation with locking pins and guy rope anchor points to hold it steady?

That way when the turbine is on it you have a good rigid structure and when it isn't you can have a flagpole in your garden.

If anyone complains you can undo two bolts and fold it down.

I would think very carefully about the wind loading acting on a 3m lever when it is in storm force ten winds first.

Why are you doing this? It doesn't sound remotely cost effective.

[Harry Davis]

"brass monkey" wrote in news:4f8f5bca$0$10356$c3e8da3$ [e-mail]:

Er yes. No need to take the mickey!

Car alternators on their own give too few RPM per volt. You need about

13.5V to start charging 12V batteries. This is presumably why he used a pulley, which reduces efficiency. Bus alternators are better. Better still are treadmill motors, where you can get 13.5V at lower RPM and not need a pulley. Helps of course if you're in a windy area, as I am. I'll be buying a turbine, though. There'll be more of a problem with high winds rather than slow winds. The vane will furl when the wind's too strong. You might be surprised at what can be achieved.

Harold

[Harry Davis]

Martin Brown wrote in news:y8Pjr.9599$ [e-mail]:

I'd love to do it that way, but would be a bit scared that the council would think I was playing the system. That's fine in England, but not so fine in the Highlands of Scotland, unfortunately.

7.5cm tubular steel; structure similar to scaffolding. I'm thinking the problem reduces to anchorage.

Partly for fun, partly to reduce outgoings. Total cost likely to be less than £1000. High average wind speed. Wouldn't surprise me if I get well over 1kWh per day. It won't be grid-tied. I'm thinking of a DC network in the house, plus an inverter for a few things that need AC.

Harold

[Harry Davis]

Chris J Dixon wrote in news: [e-mail]:

That's a good idea

Interesting, given that it must have had to withstand strong winds at that height.

I'm sure concrete will have to be involved somewhere, e.g. guying the trailer to embedded posts as well as weighting it down?

Harold

[The Natural Philosopher]

It doesn't matter what motor you use: the power output of a one meter and a bit windmill can not exceed the Betz limit value of the free energy in the wind at any given windspeed.

And small windmills have an extra problem: they operate in the bundary layer where wind speeds are already lower.

If a 100meter diameter windmill is somewhere around the 3MW mark averaging at best 1MW, then a one meter windmill is at best going to be

300W. averaging around 100W. In reality you are going to be seeing (in the ground effect) more like half that - 50-150W.

Frankly a good cyclist can generate more.

RPM/volt is irrelevant if you use an inverter - you simply exchange volts for amps.

And is in any case easy to change by rewinding with more turns of thinner wire.

And the best motors to use are custom made model aircraft motors with neodymium permanent magnets.

e.g.

rewind that with fine wire and get the KV down to 50RPM/V and you should be seeing 12V or more in a light breeze..at a few hundred mA.

[Harry Davis]

The Natural Philosopher wrote in news:jmoj84$qqh$ [e-mail]:

True that you can't beat the Betz limit, but I'm not confident enough to do electrical work on motors, and there's a big difference between a car alternator which needs 750rpm to produce 13.5Volt and a treadmill motor which requires 300rpm.

Can you explain what a boundary layer is. I'm not familiar with the term.

That's what I figured too. It's very windy where I am, so I expect that sort of average 24 hours per day, so well over 1kWh per day, probably closer to 2kWh. That'll suit me fine.

They'd want wages, though :-)

Not sure I follow what this would mean in practice. Are you saying control the charge to a steady voltage of say 3V to be fed into a 3V to (whatever) inverter??

Many thanks for the link - I will have a look at this. But 600RPM in a light breeze?

Harold

[newshound]

Two thoughts. One is that I can't see that this is much of a return on the investment. The other is that have you thought about what the wind loading is going to be?

I had a field shelter for horses picked up and turned over by winds in the south of England. (I thought it was adequately held down by screw-in ground anchors, but it wasn't).

[The Natural Philosopher]

Ok. its really used more often the other way around, in terms of aircraft moving through the air..it refers to the layer of air that is next to the aircraft which is NOT still - it gets disturbed by the passage of the aircraft through it - in the same way wind high up - above 150ft - tends to be relatively steady (barring thermal activity).

Down near the ground its disturbed by the ground especially by sticky-up things - moorland wind and sea winds are better - but around trees hedges and houses there is a layer of rolling turbulence that any pilot knows about where the wind is on average lower than higher up. And bumpy too.

Large wind turbines aim to get as much above that as they can, but of course they can't do that entirely - and indeed its one of the larger sources of stress and vibration - the lower blade cuts through that layer and experiences less and more variable wind, leading to asymmetrical loading on the turbine tower and main bearings and variable stresses that lead to subsonic vibration - that and the wake turbulence passing the tower causing a thump are the main sources of the extremely disturbing (but airbrushed out of A weighted noise measurements used by developers) low frequency noise the things produce. Coupled directly into the ground as a sort of continuous seismicity...you can't hear it and you cant keep it out of houses either. But you can feel it..and it is hugely disturbing.

Nope. take whatever power there is an up convert to a steady charge suitable for e.hg. battery charging.

the basic idea.

So you can use something in the 5-30V area to give a steady 14v or so to charge a lead acid, and then a standard UPS type inverter to get your 240V.

I would think so with a decent blade design.

You want to keep tip speeds below 200mph or so top whack (90m/s) so that

28 revs a second or 1700 rpm.

to get 1/3rd of that in a modest breeze would be about right. Not sure what effective pitch you would need to get that, but its in the ballpark of a normal microlight sort of prop.

BUT its all a complete waste of money compared with being 'on grid' Id use it to charge a caravan maybe on a windy moor, but seriously - 20p of electricity a day? 70 quid a year?

For several thousand outlay? You probably lose 50% of that driving te trailer 20 miles in terms of extra fuel..

Its obviously fun and interesting to do, but in terms of saving fuel and lowering emissions its as useless as it is at saving money. Which sums up all renewable energy pretty neatly really.

[The Natural Philosopher]

you can calc the wind loading from the peak power at a given windspeed really.

i.e. work out what force at 50mph equals a kilowatt.

[Jeremy Nicoll - news posts]

Are you suggesting having the turbine on a gymbal / pivot in the middle? If not, how will it turn to face the changing wind direction?

[Tim Streater]

So in short what you're saying is, wind turbines cause earthquakes. Only they're continuous rather than just infrequent.

[Harry Davis]

The Natural Philosopher wrote in news:jmophr$87v$ [e-mail]:

Thanks for this explanation. I am in a very windy area, 600m from the sea, peat moorland for miles all round. The prevailing wind is northwesterly, coming in from the sea, perpendicular to the coast. People who move here soon find out what windchill is! I haven't collected enough data about windspeed yet, but I'm expecting an average figure varying from 15-25mph.

That's a very interesting piece of kit. I've been hanging around various 'windhead' places on the web, and I reckon quite a lot of people don't know about that device, which isn't very expensive and easily fixes the problem of not getting enough RPM per volt to produce voltage capable of charging

12V batteries on the other side of a charge controller. Thanks very much for the heads-up on this. With a high-voltage low-max-RPM motor, it makes much more sense to use one of these than gearing.

You sound as though you have aeronautics experience.

Are the windheads right to say that RPM varies roughly as the cube of windspeed?

I' m beginning to think I could get 2-3 times my expected 1.5kWh per day.

Here's the turbine I am thinking of buying:

manufacturer claims 1.1kW in a 35mph wind. Got my pinch of salt at the ready, but half that would be great.

Harold

[Harry Davis]

Jeremy Nicoll - news posts wrote in news: [e-mail]:

Yes - fix a mast going up from the middle, as long as it needs to be.

Harry

[brass monkey]

How would you be storing this, Harold?

[The Natural Philosopher]

Model ones, yes, a lot. Designed more than a few. And the power trains (electric) this is similar, in reverse.

no. its not that simple. in theory if the prop is running right it varies as winsdpeed, but the torque varies as the speed so power varies as the square

But variable pitch makes things a bit odder

more like 300-400W its almost impossible to get the nameplate power..when wind gets that strong chances are its gusting as well.

well if you think its worth $1000...

[brass monkey]

Here's an idea, it solves the storage problem and does away with the windmill too ;) Bear with me. You get yourself a BFO naval gun, you'd prolly pick one up from the guvmint for a couple of quid (they're scrapping enough ships). Point it skywards and arrange for it to hoik up a BFO weight say 40 feet along a rack using a ratchet. As the BFO weight slowly returns to earth it spins up a generator. I'm still working on the maths *ahem* but hey, maybe 2 BFO bangs a day and you're in biz and all it costs is black powder ;) I'm not taking the piss, honestly. Good luck with the project.