Internal heat from the Earth, or geothermal — Geo (Earth) + Thermal (heat) — energy is an enormous, underused heat and power resource. Geothermal energy uses heat from the Earth. It provides continuous, 24-hour a day, clean, sustainable energy. It is considered a renewable resource because the heat emanating from the interior of the Earth is essentially limitless. The heat continuously flowing from the Earth’s interior, which travels primarily by conduction, is estimated to be equivalent to 42 million megawatts (MW) of power, and is expected to remain so for billions of years to come, ensuring an inexhaustible supply of energy. According to the International Geothermal Association, Geothermal energy has been established as a reliable and environmentally friendly source of power.