Consume energy, wasting resource ultimately that's valuable (6)
I believe the answer is:
useful
'that's valuable' is the definition.
(similar in meaning)
'consume energy wasting resource ultimately' is the wordplay.
I cannot quite see how this works, but
'consume' could be 'use' (use can mean to consume or get through) and 'use' is found in the answer.
The remaining letters 'ful' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for useful that I've seen before include "Utilitarian" , "Convenient" , "Functional, handy" , "Handy, serviceable" , "profitable" .)