Solar energy is energy from the sun that can be converted into thermal or electric energy. Thermal energy from the sun is used for heating while electric energy uses photovoltaic cells to produce electricity. The document discusses the history of solar energy development and provides examples of practical solar energy applications today such as solar panels, vehicles, street lights, and water pumps. It also outlines the advantages of solar energy being renewable, sustainable, and reducing environmental impacts compared to fossil fuels. The high upfront costs of solar energy systems and dependence on sunlight availability are mentioned as disadvantages.