Biomass can be converted into liquid or gaseous fuels, or it can be burned to generate electricity. Geothermal power is a form of renewable energy that uses natural heat from the Earth's core to warm buildings and generate electricity. 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.