Change the narration: The teacher said, "The wind is a renewable energy source."
Answer: The teacher said that the wind is a renewable energy source.
Explanation
This is a universal truth (wind as a renewable energy source), so the present tense "is" remains unchanged in indirect speech.
The reporting verb "said" does not require "told" unless followed by an object.
So the correct narration: The teacher said that the wind is a renewable energy source.
