Help Siting A New VP2

[mopac01]

I've just finished a solar array installation.  It's visible in the attached photo.  I'm now considering a small wind turbine.  But first I want to track exactly what wind I receive at my site before proceeding.  I've just ordered a VP2 (6152).  I'm planning on mounting the anemometer on the eave at the peak of my pole barn with a 6332 wireless anemometer transmitter.  The peak of the barn (2 story since it has a hayloft) should be around 24' off the ground.  So question 1 - How high above the peak/what length pole should I use for the anemometer?

In the attached photo the subpanel box for the solar array is visible.  This is 4' high.  It is surrounded on 3 sides by grass.  (The 4th side is a few inches from my daughter's playhouse.)  I'm considering down the road adding a 7747 daytime fan aspirated shield kit and using a Radio Shack adapter to make it 24 hour.  I'm also considering next fall adding a 7720 rain collector heater.  So having the rest of the ISS (minus the anemometer) mounted next to an electric subpanel would seem like a good idea.  I'm thinking of using u-bolts to mount a pole with the ISS on the south side of the subpanel (south is facing towards the solar panels in the photo).  So question 2 - Does that sound like a fairly good spot to mount the ISS and how much higher above the subpanel box (which is 4' high) would you suggest?  (I'd be positioning the ISS on the pole so it was over the grass and not the top of the subpanel box.)  The subpanel box is made of steel.

Thanks for the help.  I'm brand new to all of this.

[jerryg]

The recommended height for the anny is 33 feet so that would be a target to shoot for but you would want to get it up off the roof enough to keep the roof from causing errors in your readings. As far as the iss is concered i would get it far enough away from the panel so heat would not cause an error in you readings do to internal heat in the panel or build up of heat from the sun shinning on it. When the wind hits the sides of the barn and the angled roof it will set up all kinds of weird air currents that could give false readings.

[SlowModem]

Nice going on the solar.  I wish I could afford it.

Here's a link to everything you every wanted to know about sensor placement and then some:

http://www.comptus.com/PDF/CWOP_Guide.pdf

[Skywatch]

Jerry is right about the height of 33Ft. If pole mounted you might want to use guy wires. if mounted on a roof you can use a tri-pod sold at Radioshack. Just keep the anny at least 7 Ft off the peak of the roof. Keep the ISS 5 ft off the ground for accurate temperature humidity and rain data.

Also for the use of solar energy at a future date you might consider investing in the solar radiation sensor (6450).

Anyway hope everything works well.

[dalecoy]

In this particular case, I totally disagree about the 33ft mounting height.

... I'm now considering a small wind turbine.  But first I want to track exactly what wind I receive at my site before proceeding.  I've just ordered a VP2 (6152). 

You should mount the anemometer (temporarily) at the same location and height that you would mount your wind turbine.  Terrain and structures (as well as height) influence the amount of wind. 

[SlowModem]

In this particular case, I totally disagree about the 33ft mounting height.

... I'm now considering a small wind turbine.  But first I want to track exactly what wind I receive at my site before proceeding.  I've just ordered a VP2 (6152). 

You should mount the anemometer (temporarily) at the same location and height that you would mount your wind turbine.  Terrain and structures (as well as height) influence the amount of wind. 

I was thinking that myself.  For a specific application, the data gathered needs to be specific, too.

[d_l]

After comparing results from my anemometer mounted on a flag pole with the results from my neighbor's anemometer mounted 8-10' above his garage's ridge line, I'm now convinced that mounting an anemometer above the roof or even on the gable of the roof will give anomalously high wind speeds.  I guess that is okay if you want to report the highest wind speeds for your neighborhood, but you probably want to measure realistic wind speeds that exist away from your barn unless you are planning to mount the turbine on the ridge line of the barn.

You might read over this PDF from the Danish Wind Industry Association: http://www.motiva.fi/myllarin_tuulivoima/windpower%20web/en/tour/wres/shear.htm

[mopac01]

So, do you have the anemometer mounted at the top of the flag pole or on the side of it some feet from the top? 

Do you see any sort of "derate factor" between your readings and your neighbors that would indicate a somewhat stable variance between the two over time?

[d_l]

I recently installed a second anemometer on top of a telescoping flagpole at 26 ft. to get closer to "true" 10m wind readings.  My primary anemometer has been set at 12 ft. for ET calculation purposes. 

I used a telescoping flag pole to be able to easily service the anemometer if it needed it.  A long tilt-up pole would have been much, much cheaper than the flag pole, but I didn't think I could handle that that much weight.  The aluminum flag pole only weighs about 21 lbs.  Although it is the strongest flag pole of its type made, it did sway 12-18 inches in high winds (+40 mph) because of play in the telescoping joints.  I don't think this affected the wind speeds much, but then I mounted a Davis temp/hum sensor on top of it too.  So I ended up guy wiring the pole for complete stability.

I only have several months of wind data to compare to my neighbor's VP2 and the relationship is complicated.  Basically the two anemometers are very close in height, but when the wind is blowing so that it is running up the roof slope, his wind speeds and gusts are something like 15-25% higher than mine.  When the winds are more parallel to the roof ridge line, then his readings are more like +/- 10% of mine.

The link I posted will enable you to estimate your local roughness length and estimate the wind speed increase at various heights above your site.  I've done that for the three anemometers that I watch.  The differences between my two anemometers usually agree well with the estimates, but my neighbor's speeds often seem as if his anemometer was mounted much higher than it really is.  This reflects the speed up of the wind as it passes over his roof.

[mopac01]

Well, one difference my barn might have over your neighbor's house is size.  I would venture to bet your neighbor has much more roof at his ridge line than my barn will.  I wonder how much that might play into it.  Just to give you an idea, I've attached a drawing of my barn.  The anemometer would be mounted on the eave of the center section.  At the ridge this is 20.9' off the ground.  I was thinking about a 10' pole above the ridge line.  That center section of roof will be 12' wide and and 24' long along the ridge. 

[Skywatch]

I only have several months of wind data to compare to my neighbor's VP2 and the relationship is complicated.  Basically the two anemometers are very close in height, but when the wind is blowing so that it is running up the roof slope, his wind speeds and gusts are something like 15-25% higher than mine.  When the winds are more parallel to the roof ridge line, then his readings are more like +/- 10% of mine.

The link I posted will enable you to estimate your local roughness length and estimate the wind speed increase at various heights above your site.  I've done that for the three anemometers that I watch.  The differences between my two anemometers usually agree well with the estimates, but my neighbor's speeds often seem as if his anemometer was mounted much higher than it really is.  This reflects the speed up of the wind as it passes over his roof.

The Venturi effect I think this is. My neighboring station on Wunderground is this way too. Mounted only 1 Ft above the chiminy cover and this is on the side of the house below the apex of the roof in a corner. Always 10 MPH above everyone else. If you do roof mount it, 7-10 Ft above the peak of the roof or the highest point on the house to avoid these wind errors.

[Skywatch]

Well, one difference my barn might have over your neighbor's house is size.  I would venture to bet your neighbor has much more roof at his ridge line than my barn will.  I wonder how much that might play into it.  Just to give you an idea, I've attached a drawing of my barn.  The anemometer would be mounted on the eave of the center section.  At the ridge this is 20.9' off the ground.  I was thinking about a 10' pole above the ridge line.  That center section of roof will be 12' wide and and 24' long along the ridge. 

Sounds about right.

[dalecoy]

Well, one difference my barn might have over your neighbor's house is size.  I would venture to bet your neighbor has much more roof at his ridge line than my barn will.  I wonder how much that might play into it.  Just to give you an idea, I've attached a drawing of my barn.  The anemometer would be mounted on the eave of the center section.  At the ridge this is 20.9' off the ground.  I was thinking about a 10' pole above the ridge line.  That center section of roof will be 12' wide and and 24' long along the ridge. 

So, you are saying that you would mount your wind turbine about 10 ft. above your barn roof?

[mopac01]

Dale,

Yes - if you look at the drawing of my barn earlier in this thread, I'm planning on putting it right in the middle of that 2-story center section.  The pole would be 10' higher than the ridge of the roof on that center section with the anemometer on top of it.  Looking at that drawing of the barn the center section is 12' wide and the barn is 24' deep.   The first floor of the barn is 36' wide - 12' wide stalls on each side of a 12' wide center aisle.  That center aisle is the only part that's 2 stories tall.  (The overhangs on each side for the horses to get out of the weather are each 10' wide.)

[dalecoy]

Dale,

Yes - if you look at the drawing of my barn earlier in this thread, I'm planning on putting it right in the middle of that 2-story center section.  The pole would be 10' higher than the ridge of the roof on that center section with the anemometer on top of it.  Looking at that drawing of the barn the center section is 12' wide and the barn is 24' deep.   The first floor of the barn is 36' wide - 12' wide stalls on each side of a 12' wide center aisle.  That center aisle is the only part that's 2 stories tall.  (The overhangs on each side for the horses to get out of the weather are each 10' wide.)

But I asked:
So, you are saying that you would mount your wind turbine about 10 ft. above your barn roof?

Or, maybe you are saying that you had already firmly decided to mount the anemometer on the barn roof, and it makes no difference where you might mount the wind turbine?

It's fine to mount your anemometer on the barn roof, and you will be correctly measuring the wind at the location of the anemometer.

[mopac01]

Dale,

I'm sorry.  I misread.  No, if I install a wind turbine it would be mounted on a 50' pole about 75'-100' feet from the barn.  But I didn't think it practical to try to mount an anemometer 50' up and didn't want to get into putting guy wires up since this is in a pasture area where I have horses.  I don't think the horses would be at risk from a substantial pole supporting a turbine, but I'm pretty sure they'd cut themselves or otherwise interfere with guy wires. 

It was easy to get reasonable numbers on solar irradiation on which to forecast a payback on the solar arrays I installed, even without site specific sensor readings on solar irradiation.  Wind is so much more site specific that taking readings on my own seems the only way to get a good handle on whether a wind turbine would pay off for me.  With a pole 10' above the ridge line of the barn, that would put the anemometer about 30' off the ground.  I would expect the wind to be no weaker 50' off the ground than at 30' and most likely would be stronger.  If the wind looks like it's reasonable for a financial payback on the turbine at 30' then I'd feel like I had a "conservative comfort factor" in my estimate and I'd proceed.  This would be after keeping records for 18-24 months before making a decision.  But if the roof of the barn causes eddies that spikes the readings of the anemometer 10' above the roof wildly high then I might be risking a bad decision on completely inaccurate numbers.  If I could be +-10% at 30' off the ground with the pole 10' above the 20' roof ridge compared to a 30' pole sitting in the field by itself then I'd think I'd have a shot at not overestimating the wind at 50'.    It's all about not wildly overestimating.   If I have conservative numbers and they make financial sense and the actual wind speed turns out higher, than so much the better.  The inverse could be a very bad investment.

[smorris]

Well, one difference my barn might have over your neighbor's house is size.  I would venture to bet your neighbor has much more roof at his ridge line than my barn will.  I wonder how much that might play into it.  Just to give you an idea, I've attached a drawing of my barn.  The anemometer would be mounted on the eave of the center section.  At the ridge this is 20.9' off the ground.  I was thinking about a 10' pole above the ridge line.  That center section of roof will be 12' wide and and 24' long along the ridge.

Dale's correct in that the best way to get the wind profile for your turbine will be to put the anemometer at the height and location you expect the turbine to be. But I understand your expectation that the wind for a turbine will be, if anything, higher than on your barn. If that's the route you take, you will be in a similar situation as my setup. I used the Radio Shack tripod and 10 foot mast on top of my second story, putting it about 33-35 feet AGL. That's the highest I could get it without resorting to a flagpole or guy wires.

[mopac01]

Steve,

Thanks for the reply.  Your photo looks a little like what I'll have with the 10' pole on top of a second story roof next to a single story roof. (See the diagram of the barn I'm building earlier in the thread.) 

You don't have any other anemometers in your area that you compare your readings to do you?  I'm just curious if you have any idea what sort of % error the mounting above the roof line might be introducing.

The solar looks soooooo much simpler now that I'm investigating a turbine.  No moving parts on the arrays, easy charts available for expected solar irradiation for my area, low to no maintenance.  Maybe I need to rethink the whole turbine thing.  But I'll say that I've never paid much attention to the weather until my electrical generation became so influenced by it.  I'm much more tuned into it now.

[smorris]

You don't have any other anemometers in your area that you compare your readings to do you?  I'm just curious if you have any idea what sort of % error the mounting above the roof line might be introducing.

There's a few around, but I don't know how they are sited. Here's my WU page that shows a bunch of "local" ones at the bottom, string with the closest and up to about 20 miles away.
http://www.wunderground.com/cgi-bin/findweather/getForecast?query=44011&sp=KOHAVON11

And my MADIS shows me right on with direction, but a little low on speed. By the satellite view at the top, you can see that I have trees to the west I had to get above. I'm sure they still have some bearing on my wind speed, and that's the prevailing direction. So I expect my reading is slightly low.
http://weather.gladstonefamily.net/site/D8454

I looked at a small wind turbine a couple of years ago, but we really can't justify it here based on the regional wind map. Meanwhile, the town I live in has restricted wind turbines to commercial businesses only on the other side of a nearby highway. Makes no sense, since I'm semi-rural. If I knew it would justify itself, I'd probably challenge the restriction, seeing as there's state and federal rebates and tax incentives to use wind turbines.

Good luck with your setup
Steve

[d_l]

Well, one difference my barn might have over your neighbor's house is size.  I would venture to bet your neighbor has much more roof at his ridge line than my barn will.  I wonder how much that might play into it.  Just to give you an idea, I've attached a drawing of my barn.  The anemometer would be mounted on the eave of the center section.  At the ridge this is 20.9' off the ground.  I was thinking about a 10' pole above the ridge line.  That center section of roof will be 12' wide and and 24' long along the ridge.  

Even if you mount on the end gable of the center section, I still think you would see some anomalous increase in wind speed and some turbulence as the wind moved over your roof from certain directions.  Many years ago, I had an anemometer on my gable about 4-5 ft above the roof line.  I haven't recorded any where near the peak winds with my new anemometers as I did so frequently with that old Digitar.  I think that set up was still seeing a wind speed boost.

I agree with Dale that measurements of wind speed above your barn should only be expected to be accurate for that location.

I've read papers proposing to place small windmills along the ridge line of buildings such as barns to take advantage of the speed increase of the wind there.  The authors never addressed the increased stresses such an installation would place on the entire building.  

If you were surveying a site for a commercial wind mill, you would erect a tower with anemometers at multiple heights so that you could measure your local surface roughness for all compass directions.  You could probably do something like that on your survey with two anemometers on a pole at say ~10 and ~30 ft heights.

[dalecoy]

... if I install a wind turbine it would be mounted on a 50' pole about 75'-100' feet from the barn.  But I didn't think it practical to try to mount an anemometer 50' up and didn't want to get into putting guy wires up since this is in a pasture area where I have horses. 

If I were getting a VP2 to (initially) find out about wind conditions, as accurately as "practical", I would consider mounting it in an area away from structures.  If it fits your farm, consider getting a 20-ft substantial pipe (fence pole or whatever), set it on the ground next to an existing secure fence post and strap or bolt it to the post.  Mount the VP2 ISS up about 8 or 10 ft. (above where the horses can reach), and put the anemometer at the top of the pole. 

A.  Yes, neither the ISS (temp/humidity/rain) nor the anemometer are at "correct" height, but close enough.  And wind at 50 ft. will be higher than 20 ft., so you'll be "safesided" with your data.

B.  Just to feel better, pick a location that's "line of sight" to where you'll put the console.  But transmission distances of a 200 feet  or more aren't going to be a problem.

C.  Note that there's 40 ft of cable between the ISS and the anemometer, so you could mount the ISS at "correct" height outside the fence if the livestock can't bother it.

D.  For the record, neither my anemometer nor my rain gauge are mounted at "correct" locations - but I'm quite content that they accurately measure the conditions where they are located.

[mopac01]

Dale,

I like your idea of strapping a pole to a fence post.  I'm having the pasture fenced for the horses and the guy who is doing the fencing will be putting in substantial corner posts with bracing to support the high tensile hotcoat that will be strung for the fence.  So that might be just the ticket for sturdiness and getting away from the roof.  A 20' pole should be close to the top of the barn.  (Barn roof ridge is 20.9' but all the ground generally slopes away from the barn and will lose a few feet.) 

However, relative to the ISS.  Check up at the beginning of the thread where I posted a picture of the 4' tall cabinet that houses the solar array subpanel.  There's nothing in the cabinet but a 200amp subpanel, which shouldn't really generate any heat of it's own.  But the cabinet is steel so could be subject to some thermal heating.  What's your opinion about that location?  The only reason I think that might be better than mounting the ISS 8'-10' on the fence pole is that I can tap into that cabinet subpanel to power an electric heater for the rain gauge and an adapter to convert a solar powered fan aspirated shield to 24 hour.  (You can't get the battery back up aspirated shield for the VP2 after the fact.  And I didn't order it initially.)  I already ordered the wireless anemometer transmitter, so the anemometer doesn't have to be where the ISS is.

[dalecoy]

Oh, I had totally missed the mention of the wireless anemometer.  That helps a lot.

Yes, I think mounting the ISS above the grass very near that electrical cabinet would be great.  Perhaps just a bit above that level - 5 ft. or so.  Having nearby electrical power is ideal for the rain gauge heater, and I am a big "fan" of powering the "daytime FARS" from an AC adapter. 

[Skywatch]

The way Dalecoy described the setup is kinda how I have mine setup. How high or strong is the fence post you would use? In most cases the fence post idea is what I'd recommend. However in my area I've seen 25 mph winds take out fence posts that were lose, old, weak, or not installed correctly without anything being attached. Now again I doubt that's the case here but I'd cheak it out. Even with the anemometer and anny transmitter being lighter they can still put some strain on the post if any of the cases I mentioned above are present.

[mopac01]

Well, that's the nice part of my situation - both the barn and fencing haven't been built yet.   But both contractors are in place and should start in the next week or two.  So I have some control over how things might be done to accommodate my anemometer. 

The fence will be 4 high tension white plastic coated steel wires.  So the posts will have to be substantial to handle the tension.  The posts will probably be about 4' high.  I'll see if I can find an example to post.

What size diameter and schedule (thickness) of pipe do you think I'd need with 4' of solid fence post support to go up 30' and support just the Davis anemometer without swaying all over the place?