QUESTION:

How can I turn off the surface subdivision (objects) after a cumulative insolation calculation has been done, so that I can only see the colour values and not the grid ?

ANSWER:

Firstly, a surface subdivision is not the analysis grid. This is important, as you can't turn the grid off and still see the colours, but you can turn of the subdivided objects and see the colours.

Go to the Display Menu » Object Attribute Values » Display Colours, once you have done a cumulative insolation calculation to turn the colours on -- then just hide the zone that contains the objects to remove them from the display.