Western firm and new supplier of energy (4,4)
I believe the answer is:
wind farm
'supplier of energy' is the definition.
'western firm and new' is the wordplay.
'western' becomes 'w'.
'new' indicates anagramming the letters.
'firm'+'and'='firmand'
'firmand' anagrammed gives 'indfarm'.
'w'+'indfarm'='WIND FARM'
(Other definitions for wind farm that I've seen before include "Power plant that uses moving air to generate electricity" , "energy producer" , "Area of power turbines" , "generator" , "source of energy" .)