Renewable energy is a term used to refer to forms of energy that are naturally obtained from the environment and from sources that can be replenished naturally. These include solar energy, wind energy, geothermal energy, hydropower, and biomass. This tutorial explains the basic concepts of each form of renewable energy and the efficiency of each form.

•  Solar energy − Energy from the Sun is referred to as solar energy. Solar energy could be used as either active solar or passive solar. Active solar is directly consumed in activities such as drying clothes and warming of air. Technology has provided a number of ways to utilize this abundant resource.
•  Geothermal energy − This refers to heat energy stored under the ground for millions of years through the earth formation. It utilizes a rich storage of unutilized thermal energy that exists under the earth’s crust.
• Hydro-power − This is a major renewable energy source used all over the world today to produce electricity.
• Wind energy − In ancient times, wind energy was used to move ships by impacting on the sails.
• Biomass energy − In energy generation, it refers to waste plants that are utilized to generate energy by combustion.