Of the following forms of energy, which one are humans exploiting at the largest fraction of its potential to supply us with electricity? This is not which one provides us the most, or which one could provide us the most, but which one are we using the greatest fraction of what is available? For example, if we are using 10% of all possible solar energy but only 1% of all possible wind and 3% of all possible hydroelectric power, the answer would be solar, regardless of the absolute amount of energy derived from each.