Solar Cell Spectral Sensitivity
I just came across the book Solar Secrets (2014) by Peter Lindemann. It observes that most solar panels are optimized to perform on bright sunny days whereas they barely perform on cloudy days. This while there are panels that capture light of lower wavelengths and are therefore much less affected by clouds.
The author shows this in the following figure from page 17:
Here it can be seen that Amorphous Silicon (a-Si) solar panels produce energy from the 500 to 700 nm wave length range while Crystalline Silicon (c-Si) mostly produce energy from the 700 to 1100 nm wave length range. a-Si panels even perform well behind glass since the visible light is between 380 to 750 nm.