Which power source has been least consumed?

Wind is the source of power which is least consumed.

Explanation:

Wind is least consumed source of power because the supply of wind is continuous and free of cost. No matter how much wind you used to convert it into energy but the supply will always be much more than its conversation into energy.

In the United States, the wind power resources are marked by wind a power density class which is ranges from class 1 to class 7. The higher class means strong winds which also mean more wind power.

explanation:

may i ask what challenges?

if you are on the computer you can not take a picture but you can upload one but i am not sure about phones but i'm pretty sure it's the but to upload one just click the paper clip looking thing/ link thingy thing and upload a pic