diffuse shading factor for fixed tilted array

[pvsj]

When I create a PV array with a 30 degree tilt in the scene creator and then generate the shading table, the diffuse factor is zero. Why? I thought the diffuse shading model with an isotropic shading model over the entire skydome? Should'nt there be some loss when considering a tilted array?

[André Mermoud]

For a tilted plane, the isotropic diffuse component is indeed evaluated as the irradiances coming from the "orange slice" between the collector plane and the horizontal plane.

The result of this integral may be calculated explicitely, it gives DiffPl = DiffHor * (1 + Cos(tilt)) / 2.

This evaluation is done in the transposition model (see especially the Hay model).

Now the shading factor is a corrective effect due to the shading of objects. If you don't have shading objects, you don't have any shading factor.

[pvsj]

Thanks for the clarification Andre...I was looking at the diffuse shading factor independent of the irradiation model which already accounts for the shading "behind" a tilted array as labeled in your shading table.