Nuclear

To get one ton of uranium requires mining 350,000 tons of earth. Once the uranium is mined it is composed of two types. The first and most abundant is U238 at 99.3% while the useful part is U235 at only .7%. The next step is to enrich the uranium to the point where the U235 is up to 4% and this takes considerable time and energy. Once the enriched uranium is in the reactor only the U235 is producing energy but the free neutrons are hitting the U238 atoms and changing them into new atoms that will be dangerous for 100,000 years. These are in small amounts but must be stored in a safe place. Thorium is a different animal. First off it is three times more abundant than uranium and does not require any enriching since the entire amount is used as fuel. The result is that one ton of thorium produces as much energy as 220 tons of uranium. As a point of comparison to illustrate why nuclear is the answer one ton of thorium yields as much energy as 250,000 tons of coal. In addition thorium reactors can use up the bad elements produce in the uranium plants and long term storage is no longer needed.