A revolutionary green energy that's switched-on (5)
I believe the answer is:
aware
'switched-on' is the definition.
(switched on can mean alert or aware)
'a revolutionary green energy' is the wordplay.
'revolutionary' says the letters should be written backwards.
'green' becomes 'raw' (both can mean naive or inexperienced).
'energy' becomes 'e' (physics symbol as in E=mc2).
'raw' back-to-front is 'war'.
'a'+'war'+'e'='AWARE'
'that's' acts as a link.
(Other definitions for aware that I've seen before include "Conscious, knowing about" , "Attentive" , "Cognisant, mindful" , "Conscious, sentient" , "Having knowledge (of fact)" .)