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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.


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

  1. improved charging in adverse conditions
  2. 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 demonstrate full output.
  • full sun normal
    • 305w, 54% of rated, 4
  • 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.

ununsual scenarios

  • wildfire smoke - 8.98W at noon, sea level. 1.5% of rated, 1.9% of theoretical during September 2020 wildfires in Oregon.
opinion/frater_secessus/solar_harvest.txt · Last modified: 2020/10/11 19:48 (external edit)