What is Energy? Energy is the ability to do work. The law of conservation of energy states that "Energy can be converted from one form to another, but can neither be created nor destroyed." The SI unit of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of 1 metre against a force of 1 newton. Common forms of energy include the Kinetic Energy of a moving object, the Potential Energy stored by an object's position in a force field (gravitational, electric or magnetic), the Elastic Energy stored by stretching solid objects, the Chemical Energy released when a fuel burns, the Radiant Energy carried by light, the Electrical Energy and the Thermal Energy due to an object's temperature. Energy Transformation Devices lists some of the important devices used for converting the energy from one form to the other.
Energy Transformation, also termed as energy conversion, is the process of changing energy from one of its forms into another. In physics, energy is a quantity that provides the capacity to perform many actions—think of lifting or warming an object. In addition to being convertible, energy is transferable to a different location or object, but it cannot be created or destroyed.
Sources from which energy can be produced are known as Energy Sources. Energy sources are divided into two groups:

Renewable Energy Source (an energy source that can be easily replenished) - Solar energy from the sun, Geothermal energy from heat inside the earth, Wind energy, Biomass from plants, Hydropower from flowing water.

Nonrenewable Energy Source:(an energy source that cannot be easily replenished) - Petroleum products, Hydrocarbon gas liquids, Natural gas, Coal, Nuclear energy. Most of the energy consumed in the United States is from nonrenewable energy sources

Energy Transformation Devices - Equipments used to Transform Energy. Renewable and nonrenewable energy sources can be used as primary energy sources to produce energy such as heat or to produce secondary energy such as electricity.