I used to play with an idea of a science fiction novel, where the united Earth's currency is essentially kcal/kJ. The problem is that if you have a flammable and radioactive material, do you count the energy you get from it by burning it, or the energy from throwing it into a nuclear fission reactor, or the energy of throwing it into a black hole in a particular angle[1]?

[1]: https://www.youtube.com/watch?v=ulCdoCfw-bY