One can calculate the amount of insolation that strikes a PV module by using insolation on a surface aligned normal to the sunlight and using the cosine function on the angle from the solar normal to module's normal. But, that said, I think there may be more to it because of the various tricks that the manufacturers use in making the face of the modules to reduce reflection loses. Question: Does anyone have a data on acceptance angle? Especially on the SP75, but others as well.

Hi Gordon,

The Cosine function is fairly close. It is a little lower than the cosine function at steep angles due to reflection but that is somewhat compensated for by light coming from the rest of the sky.

Ron