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Did67, to recall the first principle of thermodynamics!
There is frequent confusion between energy and useful energy; the latter involves the energy level, from the richest in potentiality to the most degraded form.
This is why, for example, the heat pump that passes, often for the
nec plus ultra efficiency and technology, at best, only recover losses from nuclear power plants, to produce a degraded form of energy from high level energy ...
The machines which transform the potential energy of fuels into useful energy * have a very low efficiency since it involves a flow from a hot pole to a cold pole, just as the water drop causes an alternator due to the passage of 'a high point to a low point.
We can risk comparing energy and money (water?), Although in the first case it is a natural phenomenon while the second arises from a human creation: the respective theoretical units of these two concepts seem easy to compare, but this is not the case in practice: the "power to act" (to use a formula dear to
Spinoza) a 50 € note is not equal to another of the same value, it differs profoundly according to its holder.
Likewise, with a joule of electricity it is possible to do many things, while a joule of heat is much more limited and may be of no use, depending on the context.
The same goes for water which can have very great utility in small quantities and be in abundance without any "utility".
* Utility is used here in its physical sense and does not prejudge in any way the practical application ...