It has been estimated that fossil fuels will completely run out within the next 50 to 100 years. The world has already started to look to sustainable alternatives such as wind and solar power, but some researchers are looking further ahead to even more efficient and cleaner alternatives.
The team over at Futurism.com have compiled a list of some of the most promising & exciting alternative energy sources.
One day, we could be collecting solar power from space and beaming the energy back down to earth, or digging deep below the ground to harness geothermal energy from magma. Some of these ideas are already being developed, whilst other are still firmly in science fiction territory.
You can check out the full list in the infographic below. (click or tap on the image to view the full-size version).