45 Degree Solar Noon Day

On Oct 22, 2020 Plano, TX finally hit a solar noon angle of 44.9 degrees which would optimize the insolation angle perpendicular to the face of the majority of my solar panels on my 45 degree roof pitch (solar noon angles vary from 80.4 degrees altitude at the Jun 23 summer solstice to 33.6 degrees at the Dec 21 winter solstice). The temperature was a relatively cool 56F (one of the coolest yet in my record) which would also favor a high peak solar rate generation given the general ~200 Kwh per degree Farenheit relationship between solar generation and temperature for the 75F-95F range after accounting for the change in solar angle relative to the roof pitch.

Peak instantaneous solar generation rates around 12,000 Kwh with a 45 degree solar noon angle (same as roof pitch) and a relatively cool 56F temperature. The cooler days of fall are going to change what has been a general linear relationship.

The 11,983 Kwh clear-sky peak rate observed was high, but not the highest recorded which tend to be 12,000-12,400 Kwh. Evidently substantially cooler temperatures do not have as pronounced an effect on solar generation as the general spring-summer and summer-fall transition might suggest. The interesting spikes along the edges of clouds (most likely cloud lensing) later in the afternoon on Oct 24, 2020 were actually larger than the peak values in the clear air around noon which actually turns out to be not that unusual.

Peak solar rate of 11,983 Kwh on Oct 24, 2020 in clear air and highly anomalous 14,741 Kwh peak rate observed in between broken clouds, apparently due to cloud lensing.

Looking back at many of the scattered cloudy days that significantly drop the daily production, I am surprised to find these broken cloudy days by far and away generate the highest peak rates, sometimes a whopping 15,000 Kwh! Oct 22, 2020 (image above) shows a good example of a 14,741 Kwh anomaly that is 2,381 Kwh greater than the highest clear-air rate ever observed all year. These anomalies typically last 10-100 seconds.

I was curious to see if there were any variations in panel performance during the cloud lensing spikes. The Tigo panel by panel readout only has 1min resolution, so it is harder to resolve, but below is one of the minutes on Oct 22, 2020 that shows the high values relatively uniform on the more southward facing panels. The more westward facing panels typically peak later in the day, but during the anomaly around solar noon, they also increased consistently with the southward-facing panels. This suggests that there aren’t any strange geometries by any of the panels that explain the peak rates on cloudy days. It is likely just the energy is stronger for brief periods associated with the cloud lensing phenomena.

Looking at some of the highest values seen, here is another case where the 395W observed is close to the 400W rating of the panel:

Tigo panel-by-panel readout of 1min resolution data at 12:18pm on Oct 17, 2020 (one of the highest peak rates observed).

If I hit a peak value of 400W for the 32 panels facing southeast that would be 12,800 W, and assuming I get 290W on the southwest-facing panels at this time, that would be another 1,740W for a total of 14,540W. The highest peak rate in the 1sec Sense Solar data I have seen is 15,000 Kwh. I’ve also seen some values in Tigo greater than 400W on a panel which is also intriguing. I am curious to know more about what conditions support the really high peak solar generation rates.

Other Pages:
– Nov 14-15, 2020 cloud edge vs lensing
– Nov 12, 2020 elevated cloud lensing
– Nov 9, 2020 solar & cloud observations
– Nov 8, 2020 cloud lensing examples
– Oct 2020 solar altitude and air temperature effects on solar generation
– Sep 2020 home improvements energy savings and solar generation
– May 2020 installation and daily summary analysis