Thanks for your interesting answer Andy!
I will try that as a validation of my estimation. Somehow, I'm convinced that with the measured total radiation in the three orientations, I could convert these to a total radiation on a window in any orientation. Well maybe not the total radiation, but...
So, at home I have a weatherstation which measures solar irradiation in the east, south and west in lux. I can read in these measured sensordata. From these measurements, I would like to calculate the solar irradiance on my windows. The solar energy formulas could help me with that. The work of...