Is possible to generate energy from gravity? When the wind goes through the vanes of an wind turbine, that energy is harnessed to generate electricity. 
When the water goes through the water turbines, that energy is harnessed to generate electricity.
So my question is short and simple, is possible to harness gravitational potential energy?
 A: Is it possible to generate energy using gravity?
Yes and no. It depends what you mean by generate. What gravity does, is convert energy from one form to another. When you lift a bucket of water you do work on it. You add energy to it - we call it potential energy. Then when you upend the bucket, the water pours out, and gravity converts potential energy into kinetic energy. This can drive a turbine and generate electricity. 
We commonly talk of electricity as energy, so "gravity has generated energy". But it hasn't created any energy, or added any energy. Conservation of energy applies. It's merely converted potential energy into kinetic energy. In the world at large the input energy comes from the Sun which evaporates the water. It lifts it up and does work on it, like you did with the bucket.  
A: As per userTLK's comments, there are two ways we harness gravitational potential energy:


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*Hydro systems are systems where water is given gravitational potential energy by being evaporated by the sun's radiant energy. That gravitational potential energy then converts to kinetic energy - the falling of the water - which is then converted to electricity by the hydro turbine. Pumped hydro storage systems are very similar: the only difference is that the gravitational potential energy comes from the electricity used to pump the water uphill, rather than directly from the sun.

*Tidal systems are systems where energy in the sun/moon/earth system is converted to gravitational potential energy at the surface of oceans, creating a high tide: this is then converted to kinetic energy through a turbine at the base of a tidal barrage, which then is converted to electricity.
The energy has to come from somewhere. Gravity alone isn't enough - that's just a force. You need that force to act on some mass through a distance: the force times the distance gives you the energy.
A: Yes, it "Is possible to generate energy from gravity".
Gravity affects the orbit of the moon.
The moon affects the level of tide waters.
The movement & mass of tide waters can be captured & converted into electrical energy using energy harvesting technologies.
e.g.:  https://www.youtube.com/watch?v=7jsOerwz4Z8
