Energy is defined as the capacity of a system to perform work. This quantity can be assigned to any particle, object, or system of objects as a consequence of its physical state. Scientifically, energy is classified according to its nature (potential, kinetic, thermal…) or source (solar, wind, nuclear…). However, in this site we would like to classify it into the nature of its source, renewable energy or non-renewable energy. This classification keeps the awareness to the impact of these sources of energy on the environment. We have also reserved a topic for saving energy.