Which renewable energy source comes from Earth's interior?

Answer 1

Geothermal energy is heat derived below the earth's surface which can be harnessed to generate clean, renewable energy. This energy source may supply renewable power around the clock and emits little or no greenhouse gases -- all while (supposedly) requiring a small environmental footprint to develop.

Geothermal technologies use the naturally occurring heat located in shallow ground, hot water and rock below the earth's surface to generate electricity. Geothermal is considered a renewable source of energy because the earth's core generates nearly unlimited heat. The United States generates more electricity through geothermal energy than any other country in the world; 79% of the energy generated in the USA comes from California. Not all areas are suitable for geothermal energy utilization. With current geothermal technologies, electricity can be generated only where three key conditions are met: heat, fluid and natural permeability at depth. Small underground pathways conduct fluids through the hot rocks, carrying energy in the form of heat through wells to Earth's surface, driving turbines and generating electricity.

A new technology called Enhanced Geothermal Systems -- or EGS -- may be able to generate electricity anywhere there is hot rock at depth, greatly expanding the potential for geothermal power. EGS are man-made reservoirs created by drilling wells thousands of feet below the earth to access hot rock at the earth's crust. Highly pressurized cold water is pumped through the wells to cause pre-existing fractures of the hot rock to open up, increasing permeability - similar to the "fracking" technique used for enhanced oil recovery. This enables the water to flow through the cracked rock and pick up heat. The resulting hot water pumps back to the surface where it is depressurized to make steam, which spins a turbine to generate electricity. The water is then cooled and pumped through the wells again, repeating the same process and creating a closed-loop system.