Project on energy in fibre (4)
I believe the answer is:
jute
'fibre' is the definition.
(jute is a kind of fibre)
'project on energy' is the wordplay.
'project' becomes 'jut' (I've seen this before).
'on' is a charade indicator (letters next to each other).
'energy' becomes 'e' (physics symbol as in E=mc2).
'jut'+'e'='JUTE'
'in' is the link.
(Other definitions for jute that I've seen before include "Rough plant fibre" , "Sacking plant; old tribesman" , "Fibre used for ropes and sacks" , "Fibre for ropes and mats - member of ancient Germanic tribe" , "Coarse fibre used in making sacks etc" .)