Energy is a system's ability to complete work, but because energy comes in so many forms, it's difficult to come up with a comprehensive definition. In a nutshell, energy is a system's power to make things happen. It is an object's property that can be transferred from one object to another or changed into different forms, but it cannot be created or destroyed. Energy is then stored in sources of energy in forms that cannot be directly utilized, but living beings require energy to stay alive. A renewable energy source is made up of natural resources that have no negative impact on the environment. Renewable energy sources are abundant in nature and are long-term sustainable. These energy supplies can be renewed naturally and are environmentally friendly. Nonrenewable energy sources pollute the environment and have a finite supply. Nonrenewable resources can be extracted from the earth, but they will deplete over time.