To reduce consumption is of no avail (7)
I believe the answer is:
useless
'to reduce consumption is' is the definition.
I can't tell whether this defines the answer.
'no avail' is the wordplay.
I cannot quite see how this works, but
'avail' could be 'use' (I've seen this in another clue) and 'use' is present in the answer.
The remaining letters 'less' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'of' is the link.
Can you help me to learn more?
(Other definitions for useless that I've seen before include "Without purpose" , "Futile and unavailing" , "Lacking in purpose" , "Of no benefit" , "Good for nothing" .)