Nuclear energy is released during nuclear fission and fusion. In fission reaction, a heavy uranium atom splits into two relatively lighter nuclei when it is bombarded with low energy neutrons. In fusion reaction, lighter nuclei fuse together to form a relatively heavier nucleus. On the other hand, hydroelectricity is obtained from the stored potential energy of water when it falls below from a certain height. Thus, nuclear energy and energy from hydel plant are not derived from the sun’s energy.