Crossword Genius

Zero energy? Source of hydroelectricity (4)

Ross

I believe the answer is:

nile

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

'hydroelectricity' is the definition.
Both the answer and definition are singular nouns.
Maybe there's an association between them I don't understand?

'zero energy? source' is the wordplay.
'zero' becomes 'nil' (synonyms).
'source' says to take the initial letters (source can mean a beginning or origin).
The initial letter of 'energy' is 'e'.
'nil'+'e'='NILE'

'of' is the link.

Can you help me to learn more?

(Other definitions for nile that I've seen before include "long-distance runner in Africa" , "Cairo's river" , "Egyptian river" , "River of Egypt" , "Egypt's river" .)

I've seen this clue in The Guardian.
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