What is geothermal energy?
Geothermal energy uses heat from the center of the earth to produce energy. Readily accessible sources are usually found in areas where plate tectonics are at work, causing the earth’s crust to move and fracture, allowing molten rock to move upward and heat water in the ground. While it is a lesser-known source of energy and electricity than other renewables like wind and solar, chances are you already know some forms of geothermal energy. If you’ve ever heard of geysers which eject columns of hot water and steam into the air or seen natural hot springs and heated pools, then you’ve seen geothermal energy at work!
Geothermal technology captures the heat from the earth’s core and uses it to power generators and to heat and cool buildings. Since the earth's core is constantly producing energy in the form of heat, geothermal energy is consistently available. It is this consistency that differentiates it from other renewable sources; it does not carry the same inherent variability associated with sun or wind, which is one of its most important advantages.
How is geothermal energy used?
There are a couple ways in which this heat can be used. The first kind is a geothermal heat pump, used to heat and cool buildings by taking advantage of the heat in the 10 feet of earth below the surface, which remains at 50-60 degrees Fahrenheit year round. A system of pipes in the ground by the building carries a fluid (usually water or a water and antifreeze mixture), which is heated by the surrounding ground. A heat pump removes the heat from this fluid and pumps it into the air duct system of the building, circulating warm air. In the summer, the system can work in reverse; removing warm air from the building’s interior heats up the fluid in the pipes which then transfers heat into the ground and circulates the cooler air.
When geothermal energy is used to produce electricity, it is done at power plants that tap into large reservoirs of hot water miles beneath the surface. Flash steam plants, which are the most common, use pools at temperatures greater than 360 degrees Fahrenheit. At these temperatures, the water naturally rises as a result of pressure and produces steam as it moves upwards. The steam is separated from the water and used to power a turbine, which in turn powers a generator. Excess steam and water are recycled back into the reservoir, creating a replenishing and sustainable resource while emitting few greenhouse gasses.
Other less common forms of geothermal energy production include dry steam plants and binary cycle power plants. Dry steam plants use steam directly from natural reservoirs to power generators while binary use the hot water from reservoirs to turn another liquid into steam in order to power a generator. For each type of power plant, after the water and steam are extracted, the water is filtered and injected back into the ground to replenish the source.
The United States is the top producer of geothermal energy world-wide, with sources of production mainly located in the western states, Alaska, and Hawaii. In areas where geothermal is not as readily available, enhanced geothermal systems (EGS) could rapidly expand generation by creating engineered systems as opposed to those naturally found in the ground. With these EGS, geothermal energy would not be geographically limited to natural hot springs, and the benefits of this clean source of energy would be far-reaching.