Do talk about source of energy (5)
I believe the answer is:
cheat
'do' is the definition.
(I've seen this before)
'talk about source of energy' is the wordplay.
'talk' becomes 'chat' (I've seen this before**).
'about' means one lot of letters goes inside another.
'source of' suggests taking the first letters.
The initial letter of 'energy' is 'e'.
'chat' placed around 'e' is 'CHEAT'.
(Other definitions for cheat that I've seen before include "Swindler - crib" , "Con" , "fleece" , "Rogue" , "Deceitful person" .)