Is it possible to convert gravitational energy directly into electrical energy? It is possible to produce strong gravitational accelerations on the free electrons of a conductor in order to obtain electrical current. This allows the conversion of gravitational energy directly into electrical energy.
Considering that there is formal analogy between gravitational theory and electromagnetic theory, then it seems like that such a proposition is possible, at least theoretically.
And if it is indeed possible to convert gravitational energy into electrical energy, will it imply potential destruction of natural gravitational field?
 A: Suppose you have a charged parallel plate capacitor, with fixed equal and opposite charges on the plates. Both plates are parallel to the ground (i.e. perpendicular to the gravitational field). The upper plate is fixed, and the lower plate can be released to fall a certain distance under the influence of gravity. You release the lower plate, and the plate spacing gets bigger as it falls. Neglecting fringe fields, the electric field between the capacitor plates stays the same, but now occupies a greater volume, so more energy is stored in the electric field. You have converted gravitational potential energy directly into electrical energy. You have not destroyed the gravitational field in the process.
A: Electromagnetic interaction is about $10^{35}$ times stronger than gravitational interaction, which is why e.g. a television cathode ray tube (yes, I'm old) would work all the same on the Moon as on Earth, even though the Moon's gravitation on the surface is only a fraction of the Earth's. The electrons are so fast that they have left the apparatus before they even notice they are in a gravity well: At 3000V in a  CRT they are apparently accelerated to 1/10 c, or 30,000,000 m/s, giving them 33 nanoseconds or so within a 1 m CRT. During that time they fall $s = 1/2 a t^2 = 1/2 * 9.81m/s^2 * (33*10^{-9}s)^2 \approx 5.3*10^{-15}m$.
Electrons are also very light, hundreds of times lighter than the neutrons and protons, and therefore are heavily accelerated by electric fields but don't gain much energy from gravitational fields. Even the capacitor experiment suggested by Puk doesn't use the gravitational force on the electrons (much) — those would go wherever the electrostatic field wants them to. Instead, he converted the gravitational energy of the much heavier protons and neutrons. It is also noteworthy that the vast majority of atoms in a normal metal plate capacitor is electrically neutral. The charge is measured in Coulomb, which is $6.24*10^{18}$ electrons, as opposed to about $10^{25}$ atoms in a kg of copper. At a charge of 1 Coulomb in a one kg capacitor there are about a million neutral copper atoms before you are finding a lacking or excess electron. If all of the atoms were ionized the electrostatic force would be much stronger than the gravitation.
A: If you have two objects that are charged with the same polarity, but the electrical force between them is slightly less than the gravitational pull, then they will accelerate towards each other, but this acceleration will be partially counteracted by the repulsion between them. The gravitational field goes work on the objects, the objects do work on the electrical field, and so part of the gravitational potential energy is converted to electrical potential energy.
