Energy is the ability to do work. There are several types of energies such as heat, light and electric energies.Energy conservation is one of the most fundamental ideas in engineering. Energy can be converted from one form to another. Energy cannot be created or destroyed. Engineers use that to improve our life standards such as producing electricity. For example, some energy-conversion systems that the engineers use, take the raw energy from fossil fuels and nuclear fuels to generate electrical power. There are four types of energy in producing electricity from nuclear fuels. First of all, nuclear energy is converted into thermal energy, thermal energy is converted into mechanical energy, and mechanical energy is converted into electric energy. Also, there is a specific engineering branch for this called Energy Engineering. They design, develop, or evaluate energy-related projects or programs to reduce energy costs or improve energy efficiency during the designing and building. Electricity is indispensable in this era so an energy engineer may work in the efficiency of hydro-electric power systems. In hydroelectric power systems, a hydroelectric dam converts the potential energy stored in a water reservoir behind a dam to mechanical energy—mechanical energy is also known as kinetic energy. As the water flows down through the dam its kinetic energy is used to turn a turbine. The generator converts the turbine’s mechanical energy into electricity. In those systems energy is transformed but never created or lost. It just turns to another type of energy which helps engineers to use energy more efficiently in order to improve the welfare of the society.