Energy making one blow one's top (5)
I believe the answer is:
gusto
'energy' is the definition.
(I've seen this before)
'blow one's top' is the wordplay.
'blow' becomes 'gust' (as in a gust of wind).
'top' indicates taking the first letters (in a down clue, the first letter is top).
The initial letter of 'ones' is 'o'.
'gust'+'o'='GUSTO'
'making one' is the link.
(Other definitions for gusto that I've seen before include "Hearty enjoyment" , "Relish - zest" , "Vigorous and enthusiastic enjoyment" , "Spirit" , "Great relish" .)