Anemometer Placement

[egreen]

I have a 5.5' wind turbine on a 32' tower.  I received a Inspeed Vortex anemometer for Christmas and put it on the same tower that the turbine is on (one of my favorite gifts, btw).  After assembling the anemometer I placed it about half way up the tower(~18ft).  The problem is that there are many times when I see the turbine receiving (what appears to be) alot more wind than the anemometer (turbine speeds up and anemometer slows down).  I'm guessing the wind speed difference must be because of the placement on the tower.

Will the turbulence coming off the blades even affect the anemometer measurements if the anemometer is too close to the blades?  How close to the bottom of the wind turbine blades can I place the anemometer without having it feel the affects of the turbulence that the turbine blades are creating?

Thanks

[watermanhfl]

Hi,

I have a 10' on a 45' tower.  Anemometer is at the offical 10m, 33' mark and seems to follow turbine output well.  Mine is mounted on a branch off the tower up-wind(prevailing dir) about 6" in front of blades.  I would think that as long as you are not in the 45 degree shadow of the blades there would be little affect.  Blades slow 60% of the wind but do not stop it, so spillage around blades is minor.

My experiance after 3 years anyway.

Ant

[Flux]

If you want serious measurements then you will need to mount the anemometer at blade centre height and about 2 rotor diameters upwind. Obviously this is not very practical for normal use as you need to move the thing with change of wind direction.

For comparisons with the Met office you need it at 10M ( 30ft) but for data on your turbine you want it near to blade height.

About all you can do is mount it on a branch as Ant suggests, keep it up wind in the prevailing direction and sufficiently below the blades to avoid most of the interference ( I don't really know but 6ft below the bottom of the blade tips should avoid most of it).

If this is a weather station type anemometer that samples infrequently you won't get accurate performance data wherever you mount it but it will be a good guide.

In clean air there is a significant wind gradient with height but with low towers the wind below the blades is likely way slower than that that at the top of the blades and the errors can be drastic.

Flux

[dlenox]

The least that I would want to do, is to mount the anemometer as far above the tree line as practically possible.

If nothing else mount it a couple of feet below the turbine, but extend it out away from the tower, again as far as practical.

I would be more worried about getting turbulence from the tower and not the turbine.

Dan Lenox

[imsmooth]

I have the same anemometer.  I have it a few feet below the blades on the same tower.  It gives me reasonable results.

[egreen]

Thanks for the replies everyone.

So it looks like that at the very least I need to move the anemometer up the tower to within a few feet of the blades.  It should already be far enough out from the tower and in front of the blades since I made an aluminum bracket that offsets the location of the anemometer mount by about 2 feet from the tower.  I will try moving it from where it is now at ~18' to ~26' (32' tower minus 3' for the radius of the blades minus another 3' to hopefully keep it far enough below the blades).

I really don't want to lower the tower since there's a bit of snow on the ground, so I guess I'll have to use an extension ladder and lean it on the tower to move the anemometer up that high.  I hate climbing up that high.  Even getting up on my roof make me nervous sometimes.

Dan,

I would love to be above the tree line but at 32' I'm at least 6' below the top of the closest trees.  Unfortunately I can't get above the tree line because of limited space for my tilt up tower.  I need to move to a place where the average property size is bigger than 1/4 acre.

Flux,

The sample rate of the anemometer is pretty close to real time.  It uses a cycle meter to display the wind speed.  It's pretty nice because it also keeps track of the max and avg wind speeds.  I'd like to someday use the software that Inspeed sells to log the data to my computer.