Nothing can put energy in a vast expanse (5)
I believe the answer is:
ocean
'a vast expanse' is the definition.
(I've seen this in another clue)
'nothing can put energy in' is the wordplay.
'nothing' becomes 'o' (O resembles 0).
'put' means one lot of letters go next to another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'in' indicates putting letters inside.
'o'+'can'='ocan'
'ocan' enclosing 'e' is 'OCEAN'.
(Other definitions for ocean that I've seen before include "Indian, for example" , "A mighty sea" , "Big sea" , "Major sea" , "Large stretch of water" .)