Geothermal energy harnesses heat from within the Earth's crust to generate electricity in power plants. It provides a renewable energy source that is available almost anywhere and produces energy with less pollution than other sources. California generates 5% of its electricity from geothermal energy, and the heat contained in just the upper 33,000 feet of Earth's crust contains 50,000 times more energy than all the planet's oil and natural gas reserves combined.