As early as the nineteenth century, a number of scientists recognized that fossil fuels like coal and oil are in limited supply and that burning them to produce energy cannot be sustained forever. In the decades that followed, new generations of researchers steadily perfected alternative, renewable energy sources intended to eventually replace fossil fuels. Today, those sustainable sources including solar, wind, and geothermal are rapidly changing the face of energy production around the globe.

A world filled with renewables -- Harnessing sunlight's vast energies -- Clean, inexpensive wind power -- Exploiting the planet's inexhaustible heat -- Hydrogen's potentially limitless power.