Glycogen, which is a long chain carbohydrate made by polymerising glucose molecules together, is stored in the liver and, in small amounts, in the muscles. It provides a fast boost of energy for short intense exercise. When your glycogen reserves run out, the body switches to using fat, which takes longer to turn into glucose. This is known by athletes as “hitting the wall”. You feel really tired about 20-30 minutes into your run, when your body switches over to fat catabolism.

Fat is the other main group of molecules which the body uses to store energy. It is very energy dense, because fat doesn’t need to be stabilised with water, whereas carbohydrates do. Therefore fat uses less volume to store the same amount of calories. The down-side as I’ve already mentioned, is the time it takes your adipose (fat storing) tissues to respond to a lowered blood sugar level.

Edit – Yertle, ATP is a short term energy transfer molecule, not a storage molecule. It’s too labile.

reppDOTorg/discussion/green-power/200205/msg00011.html

In 1943 he had proposed to FDR…we can get all the energy we need from any space we happen to be in.

He didnt show up … He was found dead in his apartment, Natural causes. but when I spoke at the 1981 Conference a detective from New York, approached me afterward and said…he was involved with the investigation.
National Security reasons, that nobody was to know Coroners report had indicated he had been poisoned.