Crow about getting energy to shrink (5)
I believe the answer is:
cower
'shrink' is the definition.
(shrink can mean to cower from something)
'crow about getting energy' is the wordplay.
'about' indicates an anagram.
'getting' indicates putting letters inside.
'energy' becomes 'e' (physics symbol as in E=mc2).
'crow' is an anagram of 'cowr'.
'cowr' enclosing 'e' is 'COWER'.
'to' is the link.
(Other definitions for cower that I've seen before include "intimidating person?" , "Cringe, crouch" , "Quail" , "Grovel in fear" , "Cringe, grovel" .)