Added energy by revolutionary technique (5)
I believe the answer is:
extra
'added' is the definition.
(similar in meaning)
'energy by revolutionary technique' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'by' becomes 'x' (2 by 4 is 2 x 4).
'revolutionary' is a reversal indicator (letters revolve around).
'technique' becomes 'art' (I've seen this in other clues).
'art' written backwards gives 'tra'.
'e'+'x'+'tra'='EXTRA'
(Other definitions for extra that I've seen before include "Bonus; supplement" , "Player with no lines" , "Surplus to requirements" , "Not a hit certainly" , "Bolt-on" .)