I want to log these to evaluate a site for wind power. Do I need a computer connected to the anemometer to do this?
No. Standalone, without any other equipment attached, the anemometer
logs speed and direction distributions. These data can be used with the
proposed wind turbine's power curve to gain a good estimate of the
site's
potential. You only need to attach a computer to the anemometer serial
port to retrieve the data, so you can either take a laptop to the site
from time to time, or take the anemometer (depowered if you wish)
elsewhere
to retrieve the data.
We suggest you reset the log(by holding down the anemometer pushbutton
for more than 5 seconds) each time you read the data. To ensure the log
counters don't overflow you should reset it at least once each year.
Will this thing play havoc with my radio reception or be upset by my transmitter?
We can only give you limited qualitative answers, as no formal testing has been done. The general answer is that it probably won't be a problem, but if you are running high power then you may need to use a metal case for the display unit and bypassing on incoming leads.
The display and main boards were in a plastic case when the
following
were determined.
- You can detect the microcontroller clock signal at 3.6864 MHz using
a communications receiver with its antenna less than a metre or two
from
the anemometer main board.
- You can detect broadband LED display switching noise up to about
10 MHz using a communications receiver with its antenna less than about
100 mm from the anemometer main board, and using a broadcast AM or FM
radio
less than about 50 mm from the main board.
- A 1 watt 144 MHz transmission has no effect on the anemometer when
the transmitter antenna is held next to the sensor lead.
How is it that on the page about the principle you say a direction accuracy of 1.5 degrees, but elsewhere say this anemometer will only give +/- 5 degrees?
The 1.5 degree figure was from tests using a precision machine-made sensor with excellent bearings, a photoplotted chopper disk and optics with a 1/4 mm diameter aperture, and using more sophisticated microcontroller software than is possible in the code space available in the PIC.
I put the sensor in front of a fan to do some direction accuracy tests. Both direction and speed measurements fluctuated too much to get any useful results.
The airflow from a fan is wildly turbulent so the anemometer readings should fluctuate. Tie a 300 mm length of wool to the centre of the fan guard and try and decide the air flow direction!
You can do a useful direction accuracy test with a fan if:
- The fan diameter is 300 mm or more.
- You place the sensor so the centre of the spider is on the axis of
the fan and two to three fan diameters away from it.
- You place a ramp at least a fan diameter wide, made from a flat sheet
of plywood or similar, from just beneath the fan to just under the
bottom
of the cups. This ramp straightens the airflow somewhat in the vicinity
of the cups and allows useful readings.
- You only rotate the sensor body, keeping its axis in a fixed
position.
How long do the bearings last?
It depends, mainly on how windy the site is.
We've had this PTFE-bearing design outside in Melbourne, Australia for more than five years so far. There's more clearance in the main bearing now than there was when new, but the anemometer is still functioning correctly. There is no noticeable wear in the thrust bearing. We expect these bearings will last some years yet at this location. The PTFE bearing seems more durable than the ball bearings we used in some of our early sensors.
Your mileage may vary.
I use these units for stand-alone logging for potential wind power sites. Can I omit the display LEDs to increase battery life?
Yes. This nearly doubles battery life.
With the display, eight alkaline D cells last typically 40 days.
Without
the display the same last typically 70 days.
Six of the seven lines to the LED array must be switched to disable all
the LEDs.
Lantern batteries or a
lead
acid with a small solar panel may be more cost effective for protracted
logging.
The different varieties of 78L05 regulators (U1) have different
quiescent currents and dropout voltages. Using an ultra-low quiescient
current, low dropout device (eg. LM2936Z-5) increases battery life
about 40%.
Wind power site assessment using average wind speed
I am looking for a simple amemometer for on-site wind evaluation. The requirement is for a complete unit to generate average wind speed data over long term sampling periods.
While our unit logs data from which average wind speed can be derived, average wind speed is of little value in estimating a site's energy potential. The reason is that wind power is proportional to the cube of speed. For a full explanation of why average is inappropriate please see "Computing Wind Turbine Energy Output - The Average Bottle Fallacy " on the "Guided Tour on Wind Energy" from the Danish Wind Turbine Manufacturers Association.
The DIY Rotorvane anemometer logs wind speed distribution, so the
gross
error described in this document can be avoided and a much more
realistic
figure for power calculated.
The anemometer logs distributions, not actual data points, so time
to overflow depends on the wind regime.
The short answer to your question is that (except in extraordinary,
extremely unlikely wind regimes) no distribution bin will overflow
in less than a year.
The longer answer is that it depends on the variability in the wind
speed and direction and on the average wind speed.
One speed bin is incremented each 10 minutes. The time before overflow
of
any one bin depends on how these increments are distributed amongst the
20 speed bins.
If the speed is constant, and so the same speed bin is incremented each
10 minutes, then that speed bin will overflow (reach 65536) after 455
days.
If the wind speed varies a little so that two speed bins are
incremented equally frequently, then those speed bins will overflow
after 455 x 2 ie. 910 days.
If the wind speed varies a little more so that three speed bins are
incremented equally frequently, then those speed bins will overflow
after 455 x 3 ie. 1365 days.
One direction bin is incremented each (approx) 3.2 km of distance run.
The
time before overflow of any one bin depends on both the wind speed and
on how these increments are distributed amongst the eight direction
bins.
If the direction is constant and so the same direction bin is
incremented each 3.2 km of distance run, and the average wind speed is
10 knots, then that direction bin will overflow after 455 days.
If the direction varies a little and so two direction bins are
incremented equally frequently, and the average wind speed is 10 knots,
then those direction bins will overflow after 910 days.
If the direction varies a little and so two direction bins are
incremented equally frequently, and the average wind speed is 20 knots,
then those direction bins will overflow after 455 days.
Will lightning damage the anemometer?
They're unaffected by activity in the general area. We'd expect a direct hit on the sensor or mast to damage the anemometer and any equipment connected to it.
Since we've experienced no lightning-induced malfunctions and have
had only one reported to us, the following suggestions are
essentially speculative:
- Connecting the thrust bearing screw to a ground stake may divert
minor discharges
- Passing the downlead through a ferrite toroid (as used for EMI
reduction)
may reduce risk to the on-ground equipment
- Optoisolation in the serial port connection may protect attached
equipment
An optical fiber sensor and downlead are best if the risk of strike is significant.
A mast at risk of lightning strike should have an air termination at
the highest point and a suitable conductor from
this to an adequate earth. Lightning protection is a complex subject
and authoritative guidance should be sought if the threat is
significant.
- fully built units
- all the parts on the Parts List including those not usually
included
in the Kit
- just the following parts, not the complete Kit
- the PIC source code or object code
No.
However, we do supply individual parts if necessary as warranty
replacements,
and as support for existing units if there are no alternative
suppliers.
Is this suitable as my first electronics construction project?
No.
We describe it as intermediate level of difficulty if built from one of
our Kits, and advanced level otherwise. You need to have
proved your soldering skills, be able to read resistor colour codes and
capacitor number codes, and be able to track down any construction
errors
such as solder bridges you may form between tracks.
Where do I get the other parts?
You probably shouldn't be building this anemometer if you need to
ask
this.
Try your local electronics hobbyist shops, Farnell,
Digikey or Mouser
for the electronic parts and hardware and plumbing suppliers for the
remainder.
Do I get a printed manual, country of origin statement, commercial/pro forma invoice, .... with the Kit?
No.
All the necessary technical documentation is on this web site.
The Insurance form attached to the Kit package provides content
description,
value and weight information, along with a declaration that the
contents
do not contain prohibited or dangerous items. This is sufficient for
for
US, Canadian, EU and Australasian customs. If you reside elsewhere and
have doubts, please contact your Customs to determine if this is
sufficient
information for them before you order a Kit.
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