Small-scale hydropower harnesses the energy in flowing water. Unfortunately, large-scale hydropower causes severe environmental impacts. Large dams displace local inhabitants, destroy habitat, and prevent fish from reaching their spawning grounds. Natural gas is the cleanest of the fossil fuels. Still, it is a significant source of carbon dioxide, the main cause of global warming.
Natural gas is non-renewable, meaning that supplies are limited.
Nuclear energy is fueled by uranium, also a non-renewable resource. Along with the risk of catastrophic accidents, nuclear power plants produce toxic radiation that will remain dangerous for many thousands of years. A fuel-cell powered bus. Hydrogen fuel cells can run cars and power homes and businesses. They cause little or no pollution, depending on how the hydrogen is created.