Begin again, competent, having a perpetual supply (9)

I believe the answer is:

renewable

I'm a little stuck... Click here to teach me more about this clue!

'having a perpetual supply' is the definition.
I can't judge whether this defines the answer.

'begin again competent' is the wordplay.
'begin again' becomes 'renew' (I've seen this before).
'competent' becomes 'able' (similar in meaning).
'renew'+'able'='RENEWABLE'

Can you help me to learn more?

(Other definitions for renewable that I've seen before include "As green energy sources" , "Never running out" .)

I've seen this clue in The Irish Times.

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