Energy that is derived from resources that can be regenerated naturally over time and are therefore considered to be renewable. It includes energy sources like sunlight, wind, water currents, and geothermal heat. Despite the fact that the majority of renewable energy sources are sustainable, some are not. For instance, certain biomass sources are deemed unsustainable at the rate at which they are being used. Renewable energy is frequently used to power stand-alone power systems, air and water heating and cooling systems, and electricity generation for a grid.