How is energy being used inefficiently?

Answer 1

The scientific answer is that energy is being used inefficiently in most mechanical power generating systems on Earth, including all forms of vehicle propulsion and heating. The reason for this is the second law of thermodynamics, which specifies that energy will not move from a colder mass to a warmer one, or alternatively that no system can be designed whose only effect is the total conversion of a specific quantity of thermal energy into and equal quantity of physical work. This means that for maximun efficiency, real systems must reject heat into a reservoir at absolute zero, -459 degrees Fahrenheit. Real reservoirs are much warmer: the atmosphere or ocean. The result is that propulsion systems have thermodynamic efficiencies of less than 50 per cent.