Reply To: Help needed – Solar calculator, Solar BC boundary conditions

[AG]

These are totaly different inputs and concepts. Hope following representative schematic will make it clear:

1. Diffuse and Direct irradiation represent outer solar iradiations on outer wall of the domain. As these irradiation will enter simulation domain only through transparent walls, you will see these settings available for transparent walls only. In your case only top surfaces are exposed to sun and accordingly irradiation values are specified as you did in snapshot above. 
2. Bottom surfaces are not exposed to the sun and should have 0 value for direct and diffuse irrradiations. Read Semi-Transparent Walls for the DO Model from user manual for details. 
3. Diffuse fraction is totally different concept. Whatever radiation get reflected from surface, is it a specular or diffuse in nature that is getting defined by this. Read Semi-Transparent Walls for the DO Model completely to get full understanding of this. It is explined in detail. 
4. As you expect complete beam to get absorrbed in glass and 25% should get absorbed in ZnS glass. This gets defined by propery of material called as Absorption coefficient. You can define it differently for different bands. Read  Gray-Band Absorption Coefficient in user manual for details.