djkav currently WW only caters for a single array. So what most of us do is take a fudged combined average based on expected peak, and that gets close enough for the most part.
In your case, you might say your summer peak is S(10 x 0.45) + N(10 x 0.45 x 0.75) = 7.9kW.
If you get shading, and the solar calculation is important to you, you may need to adjust the peak a little during the winter.
I've got E/W with a total capacity of 7.6kW but, in reality it only reaches 6kW in summer. For winter I change this to 5kW to allow for some shading.
