Alternative energy is an umbrella term that refers to any source of usable energy intended to replace fossil fuel sources without the undesired consequences of the replaced fuels. The planet Earth has always had an energy crisis. During the 1990s, the use of solar panels and nuclear fuels satisfy the energy stricken people. None of Earth's hydrocarbon (oil) energy resources could provide the resources that the power plants needed, and were later faded out as an energy fuels. The biggest example of alternative energy taking over the market when petroleum power cars sales dropped in favor of bio-fuels and hydrogen powered cars in the late 2000s.