Turning tap to conserve key non-renewable fuel (4)
I believe the answer is:
peat
'non-renewable fuel' is the definition.
'peat' can be an answer for 'fuel' (peat is a kind of fuel). I am not sure about the 'non-renewable' bit.
'turning tap to conserve key' is the wordplay.
'turning' shows that the letters should be reversed in order.
'to conserve' indicates putting letters inside.
'key' becomes 'e' (a musical key).
'tap' going around 'e' is 'taep'.
'taep' reversed gives 'PEAT'.
Can you help me to learn more?
(Other definitions for peat that I've seen before include "load of stuff in the garden?" , "Natural solid fuel" , "Fuel from marsh" , "Fuel cut from bog" , "Dried turf" .)