Volumetric Clouds Sky Ambient from 'Dark Area' GDC

Advanced Graphics Summit: Advanced Weather System for Mobile Game: ‘Dark Area’
This is a GDC Talk with some interesting ideas. One slide I can’t understand what they are talking about or how to implement it. Even after listening to the talk im still confused what they do. (Page 21, Minute 32)


NormAltitude is MaterialParameters.CloudSampleNormAltitudeInLayer in the shader code or NormAltitude in the Cloud Sample Attributes node in the material graph.
How do you get the skycolor and what exactly is the energy they are talking about? Maybe SunSkyLuminance?