Question

how is energy produced

Answer 1

According to the law of conservation of energy, the total energy of an isolated system remains constant - it is said to be conserved overtime. Energy can neither be created nor destroyed; rather it can be transformed from one from to another. Yes, but energy can be stored in some form or other. For example, In human beings, the energy obtained by the process of respiration is stored in cells in form of Adenosine Triphosphate (ATP) molecules. Another example can be that Solar energy obtained from the Sun can be stored in Photovoltaic cells.