eli5: To make fusion energy viable, we need to get out more energy than it takes to actually run the process. But doesn’t that contradict the laws of thermodynamics (getting more energy out then you put in)?

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eli5: To make fusion energy viable, we need to get out more energy than it takes to actually run the process. But doesn’t that contradict the laws of thermodynamics (getting more energy out then you put in)?

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No, because E=MCC (C squared). It’s that trick of squatting the speed of light that makes converting mass into energy so appealing. Once we get the physics right to contain the plasma in a fusion reactor, we’ll have boundless energy available with minimum radioactive byproducts to deal with.

There was a podcast last week on BBC that explained this and why it doesn’t Curious Cases of Rutherford and Fry

You’re neglecting the fuel that’s consumed. In the case of fusion the fuel is hydrogen, and mass of the fuel is consumed. Energy input is needed to maintain pressure and to start it up in the first place, and that’s what is being talked about when talking about energy input.

Think of like a regular fire. You need to put energy in to start with a match, you need to recycle some of that energy to keep it warm (which is why blowing a fire puts it out, it blows away the residual heat which is needed to gassify the solid fuel and maintain the fire) and you get energy out.

It’s like with a fire: You put in fuel and you get heat out which you can then use to make electricity or whatever. All of the energy was already present in the fuel, so we are not violating any laws. But we are getting more *usable* energy out than we put in.

Technically, we aren’t getting more energy out. We are just getting energy out in a different form.

That energy starts stored in fuel, and (ideally) ends up as electrical energy. Fusion is the process we use to convert it from fuel to electricity. We’ve got loads of fuel, and want electricity instead.