Solar Analyst - effect of the diffuse proportion on the direct insulation.

Discussion created by julian121 on Oct 17, 2011
Latest reply on Jan 25, 2012 by wicks22
Dear everyone,

I am using the Solar Analyst (ArcMap 9.3.1) to calculate the solar insulation on roofs. I have question to the effect of the diffuse proportion on direct insulation. I run the area solar radiation tool with the default settings and afterwards I increased the diffuse proportion to 0.4. The results showed that this changed the values of the diffuse radiation but not of the values of the direct insulation! That means that more clouds (higher diffuse proportion) does not affect the direct insulation in the Solar Analyst. I thought the direct plus the diffuse proportion are 1 and so higher diffuse proportion lowers the insulation of direct radiation.

In the description of the equations I could not find a connection between the diffuse proportion and the direct insulation. So it seems that the Solar Analyst does not consider the diffuse proportion in the calculation of the direct insulation.
Am I right with this assumption? If not can you please explain me the connection?

Best Regards,