Author Topic: Turbine on steep ridge  (Read 2090 times)

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Timbersawz

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Turbine on steep ridge
« on: July 31, 2016, 05:26:05 AM »
 I am looking at setting up a turbine with a 4m/13 foot rotor diameter on a narrow ridge (top being about 15 feet across so guying its going to be a big no) then on both sides it drops 1 metre for every 1.5 meters horizontally.

It gets plenty of wind there. a few 200kmph or 120mph storms have been recorded. (intend on lowering turbine when it looks like a big ones coming of course) 80% of wind goes over the ridge, very very little follows it. Now using this image I can see there is a "sweet" height where the wind is compressed and runs stronger, but im guessing this sweet spot changes with wind speed



My question is, what height should the tower be? Anyone have any ideas?





SparWeb

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Re: Turbine on steep ridge
« Reply #1 on: August 01, 2016, 10:24:52 PM »
Don't look at that image again.
Delete it if it's not too late.
Your first hint is what looks like a Skystream(tm) in the drawing...
I'm going to hit "Post" now and write an answer you can use in a minute.
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

SparWeb

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Re: Turbine on steep ridge
« Reply #2 on: August 01, 2016, 10:47:55 PM »
You'll have to be careful if you expect 200kph winds there.  Many WT's are not designed to withstand that.  I once saw one blow up in a 100 kph wind.

Whatever wind speed is reported by the local weather office, if you put your WT on a ridge like that, you must expect both a higher wind speed and greater turbulence than normal.  One approach is to consider the ridge an "extension" to your tower height.  Then you use the formula for estimating the increase in wind speed according to height above the average ground level in the area.  This estimate still doesn't account for the turbulence or the upward direction of the wind as it rises over the ridge.  The upward wind component does strange things to yawing and furling mechanisms.

Does the ridge have access that will allow a crane to raise the tower?  If the tower cannot be supported by guy wires, then all loads on the WT come down to the foundation in the ground.  Does the soil/rock allow this?

I don't think raising and lowering a 4-meter WT tower will be a practical response to approaching storms.  Firstly, before the peak of the storm, it's probably windy already.  Tilting down a tower on a windy day is pretty dicey.  Secondly, are you sure that you will be able to monitor the wind conditions constantly and respond quickly every time?  What if the storm comes while you're asleep?  Can you delegate the task when you aren't home?

OK,
This is probably starting off with the wrong foot.
That crappy drawing rubbed me the wrong way.
I usually have a more positive attitude!
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

Timbersawz

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Re: Turbine on steep ridge
« Reply #3 on: August 02, 2016, 05:23:14 PM »
Thanks for your post Sparweb!

 Very aware that its not going to easy on any turbine, this is whats going to dictate our choice of turbine. (any suggestions appreciated)

 We are looking at variable pitch, such as the windspot etc as they seem to have a better rate of surivability than anything else, but that comes at a price. Again any suggestions would be very welcome!

I am lucky that a mate does ground anchors for a living. so I think we can make a very strongly secured base (and can guy along the ridge line if that would be of any help), its the rest of its thats going to be tough to do.

The ridge runs between ne and nne  heading. so I could guy along that angle but that would only be 2 guys and only how the ridge line runs, I dont know if it would be any help. since the majority of winds are from the north or south

 heres the wind rose semi locally. But with all the hills and ridges its tough to know exactly how the wind flows (killed 2 weather station trying to find out so far)

https://www.niwa.co.nz/sites/niwa.co.nz/files/sites/default/files/images/0004/109921/Wind-rose--Wellington-Aero_0.png






« Last Edit: August 02, 2016, 05:38:57 PM by Timbersawz »

Timbersawz

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Re: Turbine on steep ridge
« Reply #4 on: August 02, 2016, 05:44:35 PM »
Sorry one more! thought I had included it, worthing noting this one is taken from south of a large harbour which may funnel the air slightly differently




bigrockcandymountain

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Re: Turbine on steep ridge
« Reply #5 on: August 02, 2016, 10:43:55 PM »
I was thinking about this and have a thought for you.

I would do two guy wires to the sides along the ridge.  I'd set the tower near the downwind side of the flat spot and do an angled steel pipe toward the upwind side to act as a super strong tension member for your prevailing winds.  It would act in compression for the lighter winds from the opposite direction.  It would be stiffened with some lattice between the main tower and the angled piece and would tilt up from one side being hinged at the base of the tower and base of the angle pipe.  That is a huge amount of wind to design for.  The pull out strength of the upwind anchor would be huge.  Just my 2 cents.


Timbersawz

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Re: Turbine on steep ridge
« Reply #6 on: August 03, 2016, 05:15:51 AM »
I was thinking about this and have a thought for you.

I would do two guy wires to the sides along the ridge.  I'd set the tower near the downwind side of the flat spot and do an angled steel pipe toward the upwind side to act as a super strong tension member for your prevailing winds.  It would act in compression for the lighter winds from the opposite direction.  It would be stiffened with some lattice between the main tower and the angled piece and would tilt up from one side being hinged at the base of the tower and base of the angle pipe.  That is a huge amount of wind to design for.  The pull out strength of the upwind anchor would be huge.  Just my 2 cents.

Thats great and so doable I think so long as it doesnt cause issues with resonance etc. (I dont know how but im no expert)
I wonder if it would work in tension and compression. would maybe need to be at a bigger angle than the 30 degrees that a cable does and the support should be pretty heavy duty to be sure its ridged in both forces. I do wonder, would having a second at 90 degrees to the first work to or would that create its own new issues?hmmmm
Thanks!!!
« Last Edit: August 03, 2016, 05:49:57 AM by Timbersawz »

SparWeb

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Re: Turbine on steep ridge
« Reply #7 on: August 03, 2016, 09:15:27 PM »
Wow, it's not often that I read about a site that is this daunting.
If you've already sacrificed two weather stations to Poseidon what do you think he's going to do with a wind turbine?

Whatever turbine you choose, it will probably need some modifications to harden it against a number of factors:
1) Wind gradient from the top-going tip to the bottom-going tip will cause a significant 1/rev vibration,
2) Vertical wind currents racing over the ridge will also cause a 1/rev vibration,
3) Winds following the ridge may develop eddies if there is rough terrain causing a 3/rev vibration for a 3-bladed turbine,
4) Limited guy bracing options due to the ridge.

On the other hand, the promise of strong consistent wind is undeniable.  The height of the ridge will increase the general wind speed at the turbine hub, too.  If you contact wind turbine builders and show them this wind rose, they may be enticed by the challenge.  Remember Proven?  They kept the picture of their machine in Antarctica on their website for years.  It would be a good "shakedown" trial for anyone's machine to survive your environment.

I would insist on a tower that is over-designed, and rather stubby - the penalty in tower height is made up for by the ridge height.  I don't think your site really needs towers.  By keeping the tower height low, you also give yourself a better chance of making a proper 4-point guy wire " + " pattern.  Consider maybe an " X " pattern so that there aren't 2 wires going straight down the slope of the ridge.

When storms come, you don't want to mess with the tower, but you will survive if the WT is equipped TWO of the following:
1) electric dynamic brake
2) mechanical/hydraulic brake
3) blade pitch to feather
I don't think just one of these is enough.  What if one fails?

I doubt that a WT that relies on tail furling will survive in this environment.  The size you want is already on the big side for tail furling and the conditions make it crazy.  Furling is a dynamic thing that puts a gyroscopic moment on the top of your tower and the bearings it yaws around.  The stronger the wind the stronger the torque and you have some very strong wings.  Besides, what would be the point of installing a WT that's furled 20% of the time because the wind is too high!?  I've never even considered this question before.   ???

I have been impressed by the sturdiness of my motor-conversion machine with its 2.5 meter blades but the stormy winds here rarely past 100 klicks.  I would dearly love to build a big brother and fly it in winds like yours, just for the sake of the challenge.  But any company that doesn't want to lose their shirt in warranty replacement costs will respond to you very carefully.

If you are looking at american companies, Bergey is probably your first best place to start.  Phone them up and get talking - this might not be an off-the-shelf purchase; I have heard that they still listen to their customers.  They have so many machines installed around the world this is probably a problem they've already solved.  Their Excel has a furling tail so I'm not sure this is right for you.

I'm really looking forward to what you can find and how it will work!
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

Timbersawz

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Re: Turbine on steep ridge
« Reply #8 on: August 04, 2016, 06:06:52 AM »
Oh man I have thought about this.

Amongst the toughest turbines about I have narrowed to the Windspot, (although im happy to hear suggestions) I have not heard of any failure aside from one due to modifications that lead to it shedding its blades as it was braked in high winds which defeated the variable pitch system causing the blades to not feather and take the full brunt of the wind.
 Bergeys would be well up there in survivablity terms and general quality, but dont come in the kw output we are after and I dont think they have agents in nz.
 Also considering the kingspan/proven now that I see there is an agent for them here in NZ and I know of at least 3 within 40kms of here that have survived well.

Am looking at some others to. mostly variable pitch as I think they have better chances in the really high winds, but none I have found have had the time to prove themselves yet.

Of course none are cheap but theres no point spending have the money on a machine thats going to literally get blown to bits!

Im certainly not looking at going very tall on the tower, im thinking around 10m, but really need to test the winds to find out.

I had been putting the weather stations on 7m 21 foot tree pole pruner poles, will do that with another couple at various heights and see what readings I get, need decent anemometers!





Timbersawz

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Re: Turbine on steep ridge
« Reply #9 on: August 21, 2016, 04:25:05 AM »
Thought you might like the see the last indicated windspeed of one of my deceased wind meters.

In no way at all did the wind get to that kind of speed, and the unit is cheap ($250) but it gives some idea of why it was blown to bits




you can see ones missing the main control unit and the spinner on the annemeter



Trying to make one good one out of the 2 wrecks!

SparWeb

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Re: Turbine on steep ridge
« Reply #10 on: August 28, 2016, 09:34:41 PM »
So the severed cord whipping about in the gale is what sends the 259 kph wind speed signal?

Also,
Thank you Timbersawz for preserving a long-standing Fieldlines tradition of including a dog in the photo from time to time.
It's been a long time since any of our members has had the presence of mind to compose the photos properly (including me).
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024