Conscious of a conflict over energy (5)
I believe the answer is:
aware
'conscious of' is the definition.
(being conscious means being aware of something)
'a conflict over energy' is the wordplay.
'conflict' becomes 'war' (war is a kind of conflict).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'energy' becomes 'e' (physics symbol as in E=mc2).
'a'+'war'+'e'='AWARE'
(Other definitions for aware that I've seen before include "fly" , "Conscious, sentient" , "Knowing (of something)" , "Attentive" , "Having knowledge or realisation" .)