Geothermal energy uses the Earth's natural internal heat to generate clean, reliable electricity. Three types of power plants, dry steam, flash steam, & binary cycle, each extract this heat differently depending on underground conditions. Companies like Toshiba, Mitsubishi, & Fuji Electric lead the supply of turbines & generators for these plants. Drilling costs remain the biggest expense, but advances in technology are expected to cut overall geothermal energy costs significantly in the coming decades.