Solar thermal plants utilize solar heat to warm water and boil it. Once the water is boiling, the steam that's created is channeled to turbines which are connected to generators that create the electricity. Most of the large-scale thermal plants exist in California. When it's dark out, natural gas is used to facilitate the process. Geothermal energy is energy produced from heat contained within the earth.
Geothermal plants use natural hot water and steam from the earth to run turbine generators.
You may recognize geothermal energy as geysers, like Old Faithful in Yellowstone National Park. Well, the leaves, stems and bark of organic compounds are burned and used to ignite the process of producing electricity. Agriculture plays a large part in the production of biomass power. Certain crops can be grown and harvested specifically for the purpose of producing electricity. Currently there are about 350 biomass power plants in the country.