====== patterns in solar harvest ======



===== unscientific terms =====


  * **Rated** = the actual panel rating in watts under lab conditions
  * **MPPT theoretical** = 82% of rated, allowing for 5% DC-DC losses and 13% temperature derating at 70deg F ambient.

In my case, Rated is 570w and MPPT theoretical is 467w.





===== observations =====

Overpaneled configurations (relatively high panel watt to battery Ah ratio) tend have two main features:

  - improved charging in adverse conditions
  - //apparent// low output in normal conditions  - this occurs because the batteries are typically in Absorption with battery charging demand dropping by solar noon;  there is rarely an opportunity to [[http://bdp.mousetrap.net/index.php/2020/07/17/mythtesting-higher-voltage-for-additional-yield-in-the-mornings/|demonstrate full output]].  


  * full sun normal 
    * 305w, 54% of rated
  * bright sun through thin / cirrus clouds, shadows thrown
    * 312w at 11am, sea level.  55% of rated, 67% of theoretical. 
  * bright overcast, sun is completely occluded but too bright to look at comfortably, no open sky, no shadows - 25% of rated, 67% of theoretical
        * 150w spiking to 200w in light rain (26-31% of rated, 33-44% of theoretical mppt)
  * overcast, can look at sun's assumed position - 20% of rated
      * 125w, 22% of rated
      * 100w, 18% of rated
      * 75w, 13% of rated
  * dark overcast, cannot locate sun - 10% of rated
  * exceptionally low yield - less than 5% of rated
      * thunderstorms, typically 10W, less than 2% of rated.

===== correlation with available direct light =====

This is harder to grasp and compute, but increases accuracy by factoring in location, time, etc.((It cannot account for //indirect// light by refraction, reflection,etc. The contribution of indirect light is considered to be +15% in clear skies.))

  -  find solar zenith angle with app or calculator
  -  derive cosine of the above; this is the percentage of direct sunlight landing on a flat surface
  -  multiply this value by panel wattage
  - the result is the theoretical direct light available at that time/place under clear skies.((since MPPT-based system losses typically are -15% and indirect lighting is +15%, an MPPT-based system might make this direct-light power level under clear skies.)) 

I have observed the following cosine-based direct light percentages:

  * clear skies:   98% of theoretical direct sun
  * bright overcast skies (shadows thrown):  82% of theoretical direct sun
  * overcast: 58% of theoretical direct sun









===== ununsual scenarios =====





    * exceptionally high yield, 90% of rated 
        * [[http://img.mousetrap.net/2020/Screenshot_20200222-114332.jpg|519w at in February in Quartzsite @ noon]], ~500' elevation.  91% of rated, 114% of theoretical.  I've seen 500w+ out of 570w rarely, maybe 3x in two years off grid so far.((before I increased array to 750w))
    * wildfire smoke - [[http://img.mousetrap.net/2020/Screenshot_20200908-122938.jpg|8.98W at noon]], sea level.  1.5% of rated, 1.9% of theoretical during September 2020 wildfires in Oregon.