10. Charles Fritts
1883 — Charles Fritts, an American inventor, was the first to conceive the idea of solar energy. In 1883, he coated the semiconductor selenium with an extremely thin layer of gold. The resulting cell had a conversion efficiency of only about 1%. Additionally, the hefty cost of the materials prevented the cells from being made in large quantities. Today, however, Fritts’ discovery has led to solar cells that are over 20% efficient.