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LECTURE NOTES

Wind Characteristics and Resource Assessment

Niall McMahon ©

Wind Rose

Just to re-cap. The wind speed and wind direction are recorded at regular intervals, e.g. every 1 second, like this:

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| Time (seconds) | Speed (m/s) | Direction (degrees from north) |
-----------------------------------------------------------------
| 01             | 5.0         | 220                            |
| 02             | 5.2         | 221                            |
| 03             | 5.1         | 225                            |
| 04             | 4.9         | 223                            |
| 05             | 5.0         | 222                            |
| 06             | 5.0         | 220                            |
| ...                                                           |
-----------------------------------------------------------------

... for a long time!

Then the wind speeds and wind directions are averaged over, say, 1-minute or ten minute intervals. Say it's 10 minutes:

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| time (minutes) | speed (m/s) | direction (degrees from north) |
-----------------------------------------------------------------
| 10             | 5.0         | 221                            |
| 20             | 6.0         | 225                            |
| 30             | 4.0         | 223                            |
| 40             | 3.0         | 090                            |
| 50             | 3.0         | 220                            |
| 60             | 1.0         | 005                            |
| 70             | 1.0         | 355                            |
| ...                                                           |
-----------------------------------------------------------------

... for a long time!

Then plot the wind rose. Divide a circle up into sectors, say 22.5 degrees each. So, 16 sectors. The first is centred on north (top). Then you simply count the number of data points in sector 1 (two in the example above, at 60 and 70 minutes - 5 degrees and 355 degrees) and do this for all the data points. Imagine that we do this for a year's worth of data; we end up with something like:

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| Sector | Percentage of Total Number of Data Points            |
-----------------------------------------------------------------
| #1     | 3.8%                                                 |
| #2     | 1.9%                                                 |
... etc.
-----------------------------------------------------------------

Then you draw the wind rose on the circle ... the length of the "arms" associated with each sector corresponds to the % above, i.e. the number of data points in that sector.


Shared by BREEZE Software under the GNU Free Documentation License, Version 1.2.

You can also add colours to the arms to show how wind speeds are distributed within the sector.

Legals

Please see here.

Most material © Niall McMahon. See legals and disambiguation for more detail. Don't forget that opinions expressed here are not necessarily shared by others, including my employers.