Which power source has been least developed?

wood

wind

biofuel

hydroelectric

On the question, there should be a graph.  On the graph, you'll have various lines colored blue, red, yellow, turquoise, and dark green.  You basically just wanna look for the line that is the lowest, which should be the dark green line.  Which is the wind line.

So simply put, the answer is Wind.

This is also the answer for "Which power source has been least consumed?".  It's basically the same thing, and same answer.