A system to have an excess of energy?

Since we only preserve forces not energy itself... In order for a system to be called a source of energy, that system would consume a low input and would release and excess energy that's been stored as potential converted to kinetic energy right?

Pretty much like all the energy source we have present.
Now, imagine this:

If a system has in input of 5N within 0.05m and a stored energy that had applied 30N within 0.05m total energy = 1.8 Joules. over 1 second = 1.8Watts.

Where the input is equal to 0.25 J's = 0.25W

Question

A system to have an excess of energy?

Since we only preserve forces not energy itself... In order for a system to be called a source of energy, that system would consume a low input and would release and excess energy that's been stored as potential converted to kinetic energy right?

Pretty much like all the energy source we have present.
Now, imagine this:

If a system has in input of 5N within 0.05m and a stored energy that had applied 30N within 0.05m total energy = 1.8 Joules. over 1 second = 1.8Watts.

Where the input is equal to 0.25 J's = 0.25W

anonymous · Answer

Generally, in a system. How can we know there is a stored excess of energy? Or how do we know if there was an excess anyways! The input was less than output due to that stored energy?

anonymous · Answer

@Jemurray3  @Shane_B  @ghazi

anonymous · Answer

@Vincent-Lyon.Fr @Carl_Pham

anonymous · Answer

How would anyone notices a excess of energy? Is it the increase of KE from the input?
More force has been added than inputted? 

I believe those are the key factors to determine a energy source...