Because there's no way to convert energy from heat to mechanical, electrical, or chemical but they inevitably lose some of themselves to heat energy (through re

Because there's no way to convert energy from heat to mechanical, electrical, or chemical but they inevitably lose some of themselves to heat energy (through resistance, friction, and exothermic reactions). Note that you can use a difference in temperatures to generate mechanical/electrical energy, but that's also an increase in entropy as the nicely sorted temperatures get muddled and weakened, and there's no way to undo that either (at least not without suffering a loss of efficiency). Also note that you can always "cheat" by expanding your reference frame to include objects and energy you don't care about. That's why the first law of thermodynamics states that you can't get energy for free, but we can, for all intents and purposes, get "unlimited" "free" energy from the sun, and that a solar-powered machine could have what is effectively perpetual motion from our perspective. I don't know about you, but I'm not going to worry about the machine failing in five billion years when the sun dies.