This document discusses renewable sources of energy. It defines renewable energy as energy from sources that are naturally replenished, such as sunlight, geothermal heat, wind, tides, water, and biomass. Some key renewable energy sources covered include solar, wind, hydro, and bioenergy. The document outlines technologies for harnessing these sources, such as photovoltaic cells, solar balloons, and wind turbines. It also discusses emerging technologies that harvest energy from natural resources like plants, bacteria, and trees. In conclusion, the document emphasizes that renewable energy can provide clean energy for the world in a sustainable way.