Small Wind Site Assessment
Learner Guide
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with the Alternative Technology Association and TAFE NSW Northern Sydney Institute
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(With thanks to Alicia at embark)
http://www.embark.com.au/display/public/content/Managing+wind+data
Managing wind data
Author: Alicia Webb
Contributors: Chris Blanksby, Natalie Lukies
Once you've installed your mast and have anemometers and vanes measuring wind
conditions, the logger at the base of the mast records the data. But gathering on-site wind
data doesn't stop there. You can either get a consultant to collect and store this data, or
your community group may choose to do it.
Your main tasks are to:
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collect, store and check the quality of the data
identify any damage or faults that require maintenance
carry out any necessary maintenance
carefully record any changes to the monitoring system
document an audit trail for all data
Collecting data
You'll receive data in different ways, depending on the type of logger you use. Options include:
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automatic telemetry that can email the data at specified intervals
a computer program that can automatically telephone the logger and download the data to a
specified folder
you visit the site to manually change the data cards
you visit the site and connect a computer to the logger to download data.
Whichever method you use, you should find helpful information in the logger manual, and have
technical support from the people who installed your mast. We recommend you complete a log
every time you receive data, and save the file with a clear file name.
It's important to log:
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date and time you received the data
start and finish date and time of data
next date and time you plan to retrieve data.
It's also important to note if you miss a scheduled data-retrieval date.
Storing data
It’s important you don't lose data if a computer crashes. The best way to store data is to create a
folder on a reliable computer, and create a backup (or even multiple backups) on an external hard
drive, a USB stick, or even on CD or DVD.
A good file name that keeps data in order and identifies it clearly is:
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SiteName (start date in yymmdd)_(finish date in yymmdd).txt.
As an example, if a site is called ‘Hepburn’ and data is received for the period of 4 May 2010 to 3
June 2010, the file could be stored as Hepburn_100504_100603.txt
Checking data and identifying faults
Excel is a handy tool for checking data. It's worth looking at time series plots for all instruments
in order to diagnose any breakdowns. You can make time series plots by highlighting the column
of data you wish to view, and clicking ‘insert chart’ in Excel. Selecting a line graph is best.
Anemometers
Here are some examples of anemometer time series plots, highlighting the differences between
working and faulty anemometers.
Working anemometer
An example of a time series plot of an anemometer trace. This is one month of wind data,
recorded on a fully-functioning anemometer.
There are short periods of wind speeds close to zero, but no long periods of zero wind speed,
which would tend to indicate a fault. If the instrument has failed intermittently or permanently, it
will show longer periods of zero wind speed.
Faulty anemometer
A faulty anemometer might look something like this:
The graph above has periods of zero wind speed which:
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are longer than a few hours
happen suddenly during reasonably high winds.
If wind speed data looks like this, there could be a fault with this anemometer. The fault could
be:
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malfunctioning instrument
poor electrical connection at the instrument or cable interface
malfunctioning logger (this is unlikely if other instruments are working at the time of the
fault).
Working anemometers — three anemometers on the same mast
Another way to quickly and easily check for data quality is to compare multiple anemometers to
ensure they’re tracking each other.
This plot shows the wind speed is generally faster, higher above the ground, and all three wind
speed sensors are reading similar values. It suggests the three sensors are working correctly.
Faulty anemometer — one faulty anemometer on the same mast as two working
anemometers
Here's the same graph with the 50m anemometer functioning incorrectly.
You can use this graph to confirm the periods of zero wind speed (as measured on the 50m
anemometer) happened at times when the other anemometers were measuring winds. This means
there was definitely a fault.
This graph also indicates a fault with the 50m anemometer that the time series missed. There's a
period where it's measuring wind speeds, but the measurements are too low. The short period in
the middle of the data where the blue line is below 5 m/s but the yellow and pink lines are above
5 m/s shows a fault with the 50m anemometer. Artificially low wind speed recordings can be due
to bearing friction in the instrument.
Vanes
Below are some examples of wind vane time series plots, which show the differences between
working and faulty vanes.
Working vane
A wind vane working normally will oscillate between 0 and 360 degrees. You can pick up faults
by noting if wind direction is recorded as less than zero or more than 360, or if there are long
periods of fixed direction readings. A working wind vane might look like this:
Faulty vane
For comparison, a faulty wind vane may look like this:
This plot shows periods of fixed direction readings which suggest a vane fault.
Wind vanes should also track each other over time. If they diverge, there's probably a fault.
If you suspect a fault, it is best to contact an expert. If everything looks fine, store the data away
safely as outlined above.
Other instruments
Much like the fault detection process for anemometers and vanes, you should check temperature,
humidity and pressure sensor data using a time series graph. It's important to look for:
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sudden changes
periods of fixed values
data which lies outside a reasonable range (for example, temperature values above or
below a normal, expected temperature range for the area)