This document discusses four renewable energy sources: solar, wind, hydro, and geothermal. It provides details on each type of energy, including how it works, pros and cons, technologies involved, and future outlook. For solar, it describes concentrating solar power systems and thermal storage. For wind, it explains how turbines convert wind energy and wind classification in the US. Hydrogen is discussed as a secondary energy source that can be produced from various primary energies. Geothermal utilizes heat from the earth through closed loop systems. Overall, the document provides a high-level overview of these four renewable energy types.