Electrical power unit (8)
I believe the answer is:
kilowatt
'electrical power unit' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for kilowatt that I've seen before include "Power used by one bar of the average electric fire" , "Unit of electrical power" , "Unit of electric power" , "measure of power" , "kW" .)