An electrical generator is driven by gravitational force provided by a plurality of pairs of water tanks. Each pair of water tanks is suspended by an elongated chain supported by a series of pulleys. The water tanks in each pair of water tanks move between an upper position and a lower position alternately by filling selected ones of the water tanks with water and draining from the other selected ones of the water tanks. The vertical movement of the water tanks alternately filled with water is translated by ratchet wheels and bevel gear wheels to rotate the electrical generator in the same direction for generating the electrical power.