Ok, I took a minute of my life of listening to music, and thought about different types of energy available to us.
I quickly got straight to the point, and thought about using gravity to create energy.
Obviously, If you just get a big on mill, and put some weight on the ends of it, you're not going to gain anything, because you have to lift the weights to start with.
Then I thought again, and how would you be able to not lift a weight, and still get energy?
Well, if you think about a landfill site, there are huge holes in the ground. If you put the waste onto a spinnable largish structure, and made it drop it at the bottom, then you would only gain energy, whilst putting the waste on the floor.
I drew a very quick diagram to help you understand.
Do you think this kind of thing is possible, or it not going to produce as much energy as creating the mill to actually do it in the first place. You could have more arms than in my drawing obviously...