Geothermal Energy and Its Uses
Utility-scale geothermal energy facilities generate electricity that is sent to energy consumers via electric transmission systems. On a smaller scale, geothermal energy can be used to deliver heat directly for commercial, residential, agricultural, or public facilities, or energy needs other than the commercial production of electricity.
What Is Geothermal Energy?
Geothermal energy is energy derived from the natural heat of the Earth. Geothermal resources are typically underground reservoirs of hot water or steam created by heat from the Earth, but also include subsurface areas of dry hot rock. Geothermal energy is considered a renewable resource because the heat emanating from the interior of the Earth is essentially limitless.
How Can We Use Energy from the Earth?
Geothermal hot water and steam can naturally reach the Earth's surface in the form of hot springs, geysers, mud pots, or steam vents. Geothermal reservoirs of hot water and steam are also found at various depths below the Earth's surface. Geothermal resources can be accessed by wells and used to provide heat directly. The heat can also be captured and used to commercially generate electricity.
How Is a Geothermal Reservoir Formed?
A geothermal system requires heat, water, and permeable host rock (called a reservoir). Heat from the Earth's interior flows continuously outward. In some places, heat flow causes the partial melting of crustal rock creating magma (molten rock), which rises to the Earth's surface. Magma that reaches the Earth's surface and issues from volcanoes is called lava. Magma remaining below the Earth's surface heats nearby rock and water, sometimes to levels as hot as 700°F (371°C). As a result, hot water and steam become trapped in the permeable and porous rocks underlying impermeable rock layers, forming a geothermal reservoir.
How Is Electricity from Geothermal Energy Sent to Users?
Electricity generated from geothermal energy is sent to users through a transmission system consisting of electric transmission lines, towers, substations, and other components (see Energy Transmission section to learn more). The integration of geothermal energy into a transmission system requires careful planning to balance the mix of geothermal energy with other sources of energy generation.