There´re a few things you should look in a wind logger:
- Able to record wind direction into a minimum of 16 bins (or wind directions, like NNE, SWW, etc)
- Able to store historical data of the wind. It is not enough just the average wind speed for a month or for a year (read below)
- Record average wind speed at least once per minute for smale scale wind turbines
- Good to measure two anemometers at once at different heights
- Standard deviation to find out the wind fluctuations
- Data storage: Where and how is it stored
The Logic Energy LeWL wind speed logger and anemometer meets all this specifications:
- No need for computer to log data, everything is logged into a PC compatible SD card
- No computer crashes -> No data lost
- All data held in non volatile memory (SD card) so no data is lost when replacing the batteries
- SD card can hold up to 20 years of data
- Able to monitor two anemometer at once + wind vane (with self North finder)
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- No need for special software, just remove SD card an put it on your PC, ready to open with any spreadsheet program
Over the years working with small scale wind turbines, wind data, finding best wind turbine for a site, etc... We have been asked many times very similar questions. Here is the summary of what you should know about wind loggers, anemometers and how to find out estimated energy production for a wind turbine.
Why do I need a wind logger?
By taking a decision on buying a wind turbine and just knowing your monthly or annual average wind speed, you may be taking a gamble. Small scale wind turbines power production change very rapidly on gusty winds and one minute they may be generating very little and the next they are at full power.
The only way to find out how much time your wind turbine will be producing power is to look into how many hours of good wind your site has. Good wind can be anything above 4.5 m/s (meters per seconds), however you really want to go into the 6 m/s to start producing some good energy.
I have been ask to find out the average wind speed at my site and found wind loggers that give me only the average wind speed over time. Why do I need a LeWL wind logger that stores historical data? Is it not the same?
No, not really. An average wind speed is going to give you only a rough idea of how windy it has been over a period of time but is not going to give you the real potential for the wind turbine. With just the average wind speed you need to apply what is called a "weibull distribution" that is going to predict how many hours the wind is going to be blowing at different wind speeds. Now, this is a little bit of guessing, a little bit of experience, having seen the site, and a bit of statistics. When you use the LeWL wind logger, you are not predicting nor guessing. The data you store is real and it has a date and a time stamp with it. This is going to make possible to find out exactly how many hours the wind blows at different wind speeds on your site. Let´s have a look at this chart, both of them belong to the same site. One is giving a wind probability based on Weibull distribution and the other based on real data logged with the LeWL wind logger. Both average wind speed of 3.5 m/s.
The chart below shows on the horizontal axis the wind speed in meters per second and on the vertical axis the wind probability per wind speed. In the case of the LeWL (Real data) there´s no probability, just real data!!
With the predicted data we found that we have a 12% probability of wind at 6m/s but with the real data, it shows only 6.5%. This seems bat news at first but look at the higher end of the wind speed: 10m/s, 12m/s, ... these are the short of wind speeds that usually wind turbines work best and have their higher efficiency!! So far so good, but how does this relate to energy production?
We find the numbers of hours the wind has been blowing a different wind speeds for both sets of data (Real data and Weibull). With the total number of hours at different wind speeds, we put them together with the typical power curve supplied by any wind turbine manufacturer, and we find very different values: Data collected with the LeWL: 1,492kWh in one month Data estimated using Weibull: 1,086kWh in one month You see the difference between known real data from your site and guessing it? And in this case it has been a possitive approach but what about if it is the other way around? What about if we estimate more energy than really it is available on the site? Definetly it is well worth to know the real potential of your site before investing on a wind turbine. But... 1,500kWh per month is not a lot is it?
Well, all depends of the size of the wind turbine and the wind at your site. In this particular case the site is not extremelly good but is not too bad either and would require further time logging as this is just one month. The data used for the power curve is real data from a wind turbine manufacturer, however we cannot give the name away for privacy records.
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