Forum Discussion
finding deviations from the mean
Valentinaampuero So I go the sample files (May-Nov of 2021). I am attaching the Nov data here. In this file I added a tab (DailyAvg) where I calculate the average for every :15 sec slot for each panel across all the days recorded. I then calculate the average (col LED) and std (col LEE) for each :15sec slot and added conditional formatting to highlight all the spots <1std (orange) and <2 std (red). Finally at the bottom I did a count for how many times that particular panel was found to be <1 STD and <2 STD on average. I hope this might be helpful and can be a template for the other months. Maybe even collate these summary counts across months for even better indicator of performance across the year.
That said, about 1/2 of them will be less than the mean (sort of by definition but not exactly). So you need to define a better metric. Maybe less than 1 or 2 STD less than the mean or use functions like PERCENTILE or QUARTILE or RANK to help. But also need to determine if you want average values and how to average. As you noted the output will increase and decrease throughout the day and the location of some may be better than others. Should you be looking at the average for a day across the set or maybe look at the average for a month for the SAME one a year ago and see how much it dropped and in comparison to how much all the others have dropped because any given month may be more or less sunny.
mtarler thank you for your answer.
I agree with you that there will be multiple below average current values which does not mean that all those PV panels are shaded. Those whose value is considerably below average (thank you very much for the suggestion to incorporate the standard deviation) would be those that are shaded.
I am analyzing the values every 15 minutes, ie.
7:00
7:15
7:30
7:45
8:00
etc.
In this way I will be able to have a daily, then monthly, and finally annual trend, understanding that the position of the sun and the angle of incidence of solar radiation has seasonal variation so that the modules that receive shade in summer may not be the same as in winter.
- any chance you can attach the document or give a link to it in sharepoint or dropbox or something.