The 2nd Law of Thermodynamics tells us that the amount of useful energy degrades. The total amount of energy may not change, but the amount which can be converted to useful work is decreasing.
The Laws of Thermodynamics can be summarized as:
Zeroth Law: You get what you pay for.
First Law: You’re lucky if you break even.
Second Law: You can’t break even.
The Zeroth Law is the Law of Conservation of Energy.
Zeroth Law: You get what you pay for.
First Law: You’re lucky if you break even.
Second Law: You can’t break even.
~~~
Hence why (partly) perpetual motion machines are an impossibility. The other reason being that if they rely on matter as well as energy, then you cannot 100% insulate the energy within the system