solar yield in overcast conditions

Over the past few years I’d estimated that my system puts out about

  • 25-33% of normal max in bright overcast

  • 20% in overcast

  • 10% in dark overcast

It was guesswork, but then I saw this article that gave lux for various sky conditions.

I plugged the values into a spreadsheet to convert the lux into theoretical max yield for a 100w panel:

[caption id=”” align=”alignnone” width=”295”] should be “lux” not “lumens”[/caption]

That lines up pretty closely with my observations.