Good question. Here are the performance charts I developed in 2020.
I built a datalogger to collect my own data. I bench-tested the generator before installing it in the wind turbine, and one of the checks on the datalog that I did before accepting its data was to verify that it was recording values consistent with the original bench test. You can see the data below collected from 3 separate logging runs in 2019. The reason they are different is because the battery voltage was substantially lower on the 20th (green dots). I measured this during my bench tests so I confirmed this, too.
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In the next graph below, the wind power values (red line) are basic calculations based on the wind power law. For the datalogs used for my performance evaluation, I included data from my weather station for wind speeds and barometric pressure (and air density). The output power relative to wind speed is found by just crossing the measured power with the speed at that moment. But that hides the complexity of the calculation because using the raw data to do that would lead to a ridiculous and useless hash of dots. To get reasonable averages, I needed hours of data to be collected, even though the data was sampled and recorded by the datalogger every 10 seconds or so.
To manage all of this data, I binned the data in 1-minute chunks, and tried to use statistical methods consistent among the data reduction that the weather station uses (automatically, which I can't control or change) and the data from my datalogger.
Note that the "input power" curve is created by cross-referencing the bench test data, where I collected the generator's input and output power measurements. All of the in-situ values of wind turbine output power were correlated to the bench-tested input power values.
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The wind speed and associated turbine rotor speed data allow for a fairly direct calculation of Tip Speed Ratio (TSR). When I started collecting datalogs of my wind turbine over a decade ago, I began to learn that the things people like to say about TSR is often inaccurate, sometimes misleading. I went back to basics with some fluid dynamics textbooks and confirmed that TSR
should do this with increasing wind speed. I had designed my wooden blades for TSR=5, so I guess I hit it right on.
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Finally here is the number we're all happy to see, the Coefficient of Performance of the wind turbine (Cp). Really happy with the results when I was able to demonstrate this. Note also that the peak CP coincides with the actual measured TSR matching the as-designed TSR of the wooden blades. After many tries, I seem to have gotten it right. It was a satisfying pay-off for 15 years of learning and experimenting.