Aptly, energy in boom starting to turn up as a fuel source (4-3)
I believe the answer is:
peat-bog
'aptly energy in boom starting to turn up' is the definition.
I know nothing about this answer so I can't tell whether this works.
'a fuel source' is the wordplay.
'a fuel' becomes 'peat' (peat is a kind of fuel).
'source' becomes 'bog' (I can't explain this - if you can you should believe this answer much more).
'peat'+'bog'='PEAT-BOG'
'as' acts as a link.
Can you help me to learn more?
(Other definitions for peat-bog that I've seen before include "Boat peg (anag.)" , "Source of vegetable fuel" , "Wet spongy ground, cut and dried for fuel" .)