Earth's one source of electricity consumed by factory (6)
I believe the answer is:
planet
'earth's one' is the definition.
(Earth is a planet)
'source of electricity consumed by factory' is the wordplay.
'source of' suggests taking the first letters.
'consumed by' is an insertion indicator (inserted letters get consumed).
'factory' becomes 'plant' (I've seen this in other clues).
The first letter of 'electricity' is 'e'.
'e' inserted into 'plant' is 'PLANET'.
(Other definitions for planet that I've seen before include "Orbiting heavenly body" , "Is Pluto one?" , "Celestial body that revolves around the sun" , "Earth, for instance" , "Earth, for example" .)