Throughout recorded history, humans have searched for ways of putting energy to work for them. Humans have found ways of growing food instead of foraging for it out in the wild.
Sunlight is an energy source that is available to varying degrees every single day. Sunlight has been used in various ways since the beginning of human history.
Throughout history the wind has been used by humans as an energy source for such things as transportation and food production. Energy released by the trade winds—winds that almost always blow in the same direction—was first captured in the sails of ships and used to transport the ship and its cargo across oceans.
Water, a substance almost as old as the earth itself, covers about three quarters of the planet's surface. It is a very simple molecule, composed of two hydrogen atoms and one oxygen atom, but vital to life on the planet.
Scientists theorize that 15 billion years ago, when the universe was first forming, all matter exploded and released huge amounts of energy. It is this energy that still fuels the sun.
Solar, wind, hydro, and geothermal power have long been explored by humans as a means for harnessing the energy produced by the natural systems of the earth. Advances in these technologies have started to make each of them a viable alternative to fossil-fuel use.