Daily solar PV system output analysis

We saw how the Tesla planned output compares to our own prediction using PVWatts. That is all theoretical.

Time for a reality check...how does actual output compare to what is expected from the system? 

Recall, you can extract a daily and hourly breakdown from PVWatts for the entire calender year....And, you can extract the actual system output from the Tesla app. It records about every 15 minutes.

Lets see what we get:

Here is my system output on Dec 9, 2020. It was about as sunny as you can get all day in the Denver area. So a best cast scenario. We made 19.3 kwh of energy that day.


If you download the data into the csv file, you can get the time stamped output. It's in 24-hr format. Here I highlighted two random times: 1045m and 230pm (1430 hrs) that corrrspsond to 3.2 kw and 1.6 kw total system output. Other times are shown too.

Now, we can take out our PVWatts files. In my case for East and South:
- pull the values for the same date and time
-add them together to get the total predicted system performance for that moment of the year

Here is the data for the East
and the data for the South
At 10 am, my Tesla system output was 3kw
PVWatts estimate:
535 (E)+2144 (S)=2679 W or 2.7 kw 
*System performance better than expected!
*PVWatts under estimated 

At 2 pm, my Tesla system output was 1.8 kw
PVWatts estimate:
79 (E)+1724 (S)=1803 W or 1.8 kw
*System performance exactly as expected!

System Discrepency?
Overall, this is pretty close. Better to be outperforming PVWatts though! I am not sure why the morning time is off by 10%, but that could be typical.

For sure, my assumptions are estimates.  The panel azimuth and tilt could be different. Note during the 10am time, both the East and South strings are active. Since the 2pm slot was exact, it is more likely to me an East side assumption is a bit off.

Either way, the system output appears to be right on or better than expected.

#solar #PV #Tesla #boroncarbon

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