Nuclear energy is the energy stored in the nucleus of an atom. Releasing this energy from the atom is what gives way to usable nuclear energy. The main way this is done is through nuclear fission. Nuclear power plants use nuclear fission to split apart atoms to form smaller atoms, which, in turn, releases energy and generates heat that typically turns a turbine. Solar energy, on the other hand, harnesses power from the sun. We can take radiation in the form of light from the sun and convert it into electricity. This is typically done through photovoltaic, or PV cells, which are made of semi-conductive materials like silicon. When sunlight is absorbed by PV cells, photons of light transfer that energy to electrons, which, in turn, creates energy in the form of an electric current as the electrons flow through the material. As such, solar energy is classified as a renewable energy source, since it is a source of energy that can theoretically regenerate and replenish itself indefinitely. While some argue that nuclear energy should also be classified as renewable, most agree that it is, more accurately, a sustainable energy source. This means that while nuclear power may not be seen as infinite, the rate that it is consumed is insignificant compared to the amount of the supply. It's like the kale of energy sources. Sure, there is only a finite amount of the stuff, but who would ever eat so much of it that the world would run out?