Extracts energy, legal up to a point (7)
I believe the answer is:
elicits
'extracts' is the definition.
('elicit' can be a synonym of 'extract')
'energy legal up to a point' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'legal' becomes 'licit' (similar in meaning).
'up to a point' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'e'+'licit'+'s'='ELICITS'
Can you help me to learn more?
(Another definition for elicits that I've seen is " Draws out, response or information".)