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 photovoltaic cells convert sunlight directly into electricity. The document discusses the two types of solar energy and provides details on the composition and output of the sun. It also outlines the history of solar energy technology, practical applications of solar power today, advantages like lowered costs over time and environmental benefits, and challenges such as high initial installation expenses.