This document discusses renewable energy and hydropower. It defines renewable energy as energy from natural resources like sunlight, wind, rain, tides and geothermal heat. Hydropower is generated from water flow and is captured using dams, turbines and generators. Large hydropower dams can power cities but require large initial investments, and have social costs from relocating residents and environmental impacts from flooding land. Smaller run-of-river hydropower projects have fewer impacts. Hydropower is a significant renewable source that produces clean energy without pollution.