What is the appropriate sample rate for measuring solar radiation?

[tinvicemp06]

I'm working on a solar radiation project. I was able to design a homemade pyranometer, yet I'm trying to establish what the sample rate should be.

After reading several pdfs I set 60 seconds as my sample rate and I have good results, I mean if I choose 10 seconds instead I just get a lot of the same results, but with 60 I'm not getting repetitive results and it's small enough to provide with information about how the parameter behaves.

I was recommended to find a theory that will support my choice, I was looking at the Nyquist theorem and it says that I should have a sampling frequency at least twice as big as the frequency of the wave I'm trying to study. The question is what's the frequency of the wave I'm trying to study?

Is it fair to say that my sampling frequency is 1/60 Hz ?

I'm pretty lost here. Thanks in advance for any guidance.

 

[mfb]

The solar radiation itself doesn't have a frequency in that sense. It will vary based on clouds and other shadows. You could measure their frequency spectrum, I guess. If there is nothing that provides shadow on a short timescale (people walking by or whatever) and a minute works well for clouds that should be fine.