English novelist using ecofriendly energy (6)
I believe the answer is:
greene
'english novelist' is the definition.
(I've seen this before)
'ecofriendly energy' is the wordplay.
'ecofriendly' becomes 'green' (I've seen this before).
'energy' becomes 'e' (physics symbol as in E=mc2).
'green'+'e'='GREENE'
'using' acts as a link.
(Other definitions for greene that I've seen before include "The Quiet American author" , "Graham --, British author" , "Graham -, English novelist" , "Graham -, English author (Brighton Rock)" , "Graham -, twentieth century English author" .)