At this moment around the world, billions of lights, computer, TVs, and fridges are turned on. At any moment of any day, 25 million cars are driving on roads and nearly 700,000 people are flying somewhere in a plane. Most of the energy that we use for these things comes from fuels like coal, oil, and natural gas. One day soon, we will not have any more of these fuels. Where will our energy come from in the future, and how will this change our world?