Geco Insolation - Cumulative errors?

Hi all,

I originally had posted this on the main discussion board but it more correctly belongs here.

I'm currently running a grasshopper script to calculate the insolation levels on a vertical screen. I'm trying to work out what the effects would be if the wall became heliotropic - following the sun.

What I want to do is calculate the insolation levels per hour and add them up for a total daily insolation level.

When I compare the cumulative total through geco, it is different to the individuals added up.

Example:

6am-7am: 3052 Wh/m2

7am-8am: 4513 Wh/m2

However, 6am-8am: 5804 Wh/m2 (should this not be 3052+4513?)

I've attached my GH file for anybody interested...

Perhaps I've made a huge incorrect assumption somewhere but I feel the model is properly set up.

Z