Take a capacitor arrangement...the capacitor having 2 plates which are square shaped. Assuming one of the plates as A and the other as B. If A has been given a static charge, it can be said that the all energy possessed by A can be computed when A is discharged...overall discharging will release all the energy possessed by A...let this energy be x. Now, since B is in front of A and A has been given a charge, if B is earthed it will gain a charge equal and opposite to A (let's assume it be equal, it will be a bit less actually cause of E.F losses). Cause of this gained charge, a charge has to flow from B to earth; now energy can be harvested from this charge flow and it will be almost equal to x (assume it to be equal to x for simplicity, the difference will be very less if the right dielectric is used); thus it can be said that energy used for charging A has been recovered though this discharge. But still there can be one more discharge which will result in an energy output of 2x...joining of plates A and B; this energy is extra...where did it come from? There's another way by which this can be explained. Have a look at the 2 attached images. There are 2 curves, a red one and a blue one; the red one is fixed while the blue one has the ability to rotate along the surface of the yellow transparent cylinder (or the blue curve forms the locus of the yellow transparent cylinder.). Both the curves are metallic and the red curve is charged while the blue one is grounded all the time. If the blue curve is made to rotate continuously, it will charge and discharge cause of the red charged conductor depending on it's location on the yellow cylinder; energy can be harvested though these charge/discharge cycle. Now, assuming the blue curve has an angular momentum (large enough), under ideal conditions it will continue to rotate forever since the force of attraction between both the curves will be conservative, i.e at certain location of the blue curve, it's motion will get aided while at the remaining places it will get a resistance; overall, both equal out and it won't matter in a complete rotation of the blue curve...there will be ups and downs in it's angular velocity, that's all. But still we can harvest energy from the blue curve...where did this energy come from? This thing has screwed me up for ~2 years and I'm not getting any answers.