The most common definition of sustainability comes from the Brundtland Commission which says:
"Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs."
Green energy is defined as any form of energy that is environmentally friendly or nonpolluting and renewable.
Forms of green energy include solar, wind, hydro, and geothermal.
Solar panels capture and convert the suns energy into electricity or can use the energy from the sun for heating or many other applications.
Wind energy is best harnessed using a wind turbine which can convert the mechanical energy created by the wind turning the blades of the turbine into electricity.
Hydroelectric power or hydropower works basically the same way as wind energy. Flowing water creates its own energy that flows through a turbine by turning the blades of the turbine which creates mechanical energy that can be converted into electrical energy.
Geothermal energy comes from the ground either from vents close to fault lines for large power plant applications to generate electricity or from only a few feet below ground level for smaller applications like heating and cooling your home.