In high spirits from energy extra bun produced (9)
I believe the answer is:
exuberant
'in high spirits' is the definition.
(I've seen this before)
'energy extra bun produced' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'produced' indicates anagramming the letters.
'extra'+'bun'='extrabun'
'extrabun' anagrammed gives 'xuberant'.
'e'+'xuberant'='EXUBERANT'
'from' acts as a link.
(Other definitions for exuberant that I've seen before include "Vivacious; effusive" , "Abounding in vitality" , "Joyous" , "High-spirited" , "Lively, cheerful" .)