A generator for converting mechanical energy or hydropower or wind energy into electrical energy is disclosed. The generator includes a first member and a second member in contact with the first member to generate triboelectric charges. The second member rolls against the first member to generate a flow of electrons between two electrodes. Another embodiment of the generator includes two electrodes, and a member in contact with the two electrodes to generate triboelectric charges. The member rolls against the electrodes to generate a flow of electrons between the two electrodes.