Geothermal energy is thermal energy stored beneath the earth’s surface.
It is clean, renewable, and popular because it can be harnessed from almost anywhere in the world to produce heat and electricity. Historically recognized as hot springs, geothermal energy is commonly used today for residential heating and cooling, and electricity generation. Although geothermal is not the most widely used source of energy, it is by far one of the most efficient and sustainable systems today.
Geothermal Energy Today
The United States is currently the world leader in geothermal energy production. According to the National Renewable Energy Laboratory, approximately 3.6 GW of geothermal energy capacity is installed and multiple projects are proposed for the future¹. Since geothermal energy is most commonly found on plate boundaries, it is popular in western states such as California, Hawaii, and Alaska. Smaller projects can also be seen in Idaho, Nevada, New Mexico, Oregon, Utah, and Wyoming. California is the state leader with 2,730 MW of geothermal energy currently installed².
Besides the US, Iceland is another leader of geothermal energy. Geothermal power facilities generate 25% of Iceland’s total energy production! Refer to this link to learn more about Iceland’s geothermal production.
How to Use Geothermal Energy
Geothermal energy is used in three main ways: direct use, power generation, and ground source heating and cooling:
- Direct Use: The hot water in geothermal reservoirs produces heat and steam, which can be directly used for multiple purposes. In the past, hot springs were directly used for bathing and cleaning purposes. Today, this hot water is extracted by a well and then delivered though piping, a heat exchanger, and controls for its intended purpose. Geothermal hot water has a variety of direct uses, ranging from melting ice on roads and sidewalks to warming fishing farms.
- Power Generation: Aside from being used directly, geothermal energy can be used to produce power (similar to solar and wind energy). Geothermal power plants capture deep deposits of geothermal energy, whether steam or hot water, and use this to drive turbines that sequentially produce electricity. There are three different types of geothermal power plants:
- Dry Steam Power Plants are the oldest geothermal plant design. Steam from underground is used to operate the turbine, which produces power. The steam is then either pumped back underground or released into the atmosphere.
- Flash Steam Power Plants are a more sophisticated steam power plant design. Highly pressurized water ranging from 300°-700°F is pumped from the earth’s surface and the pressure is then reduced, causing the water to immediately turn to steam. This sudden sporadic change of water “flashing” into steam essentially drives the turbine. The water is then cooled and pumped back underground.
- Binary Power Plants use a different approach than the previous two. Like a flash steam power plant, a binary power plant pumps pressurized hot water to the earth’s surface. The tube that does this, however, connects to a second tube that contains water at a lower pressure. Water from the first tube flows into the second one, boiling the water, which sequentially drives the turbine. Water from the first tube is then pumped back underground to restart the process.
- Ground Source Heating and Cooling is the most common use for geothermal energy today. As opposed to generally heating an area using heat found in the outside air, a ground source heat pump, or GSHP, taps into the constant temperature found within the earth’s surface. The fact that this constant temperature can be captured from almost anywhere in the world allows GSHPs to be one of the most sustainable and efficient technologies used today. This system specifically transfers heat from the earth into a building during the winter season and then transfers heat back into the ground during the summer. The temperature can be controlled with the use of heat from the earth.
How Geothermal Heating and Cooling Works
Geothermal heat pumps use a connection of pipes to transfer heat from the ground into a home. These pipes are filled with a water solution and properly welded to form a continuous loop between the home and the earth. During colder times, the water solution in the pipes is cooler than the surrounding ground; therefore, it absorbs the energy from underground and carries it to a heat exchanger where a refrigerant (a substance used for transitioning liquid to gas) absorbs the heat. This refrigerant gas then enters a compressor, where it is pressurized and increased to around 160°F. Next, it travels to an air heat exchanger. The heat pump’s blower circulates this air, allowing it to increase even more in temperature before being released as heat through a home’s air ducts. Finally, this cooled refrigerant recycles to begin the process again. For cooling purposes, the process is literally reversed. Since the water solution in the pipes is now warmer than the surrounding ground, heat is released back into the earth.
Benefits of Geothermal Energy
- Cost Savings: Geothermal systems have become a very economical choice for residential and commercial sectors over time. Their return on investment averages two to 10 years (depending on the size of the project) with utility costs for the installation of a residential geothermal heat pump typically 40%-60% lower than traditional costs. Furthermore, financial incentives are also provided to lower initial costs and increase savings over time.
- Durability: Geothermal heat pumps are not only efficient, but durable as well. They often last 20 years or more, while the underground piping carries warranties of 25 to 50 years. Because the system is sheltered from exterior threats such as damage or debris build-up, geothermal is quite reliable overall.
- Clean Energy: Since geothermal energy comes directly from the earth’s interior, no pollutants are emitted when capturing it. Also, the use of geothermal lessens the demand for coal-powered plants. According to Energy.gov, geothermal heat pumping systems use 25%-50% less electricity than conventional heating or cooling systems. Moreover, the plants that produce electricity from geothermal energy are just as environmentally friendly as the energy itself.
- Low Maintenance: Geothermal pumps are virtually maintenance-free. When properly installed, maintenance costs are usually reduced and operation is similar to conventional systems. Also, since a geothermal heat pump system is conveniently located in one’s home, the unit can be accessed at any time.
- Year-Round Comfort: Geothermal heat pumps work in two ways: by cooling an area during warmer times and heating an area during cooler times. Occupants are therefore generally comfortable year-round.
- Quiet Operation: Geothermal heat pumps make almost no noise at all. Since they are located inside, they are constructed for silent and efficient operation. Energy.gov states that a GHP system can be so quiet that users may even not know it is operating!
- Choosing and Installing Geothermal Heat Pumps
- EPA: Geothermal Energy
- Geothermal Heat Pump
- The Uses of Geothermal Energy
- Geothermal 101
- How Do Geothermal Power Plants Work?
- How Does Geothermal Heating and Cooling Work?
- Geothermal or Ground Source Heat Pumps
- Geothermal Heat Pump Consortium, Inc.
- International Geothermal Association
- International Ground Source Heat Pump Association
- National Renewable Energy Laboratory
- Initial Results from the 2020 U.S. Thermal Power Production and District Heating Market Report. (2020, October). National Renewable Energy Laboratory. https://www.nrel.gov/docs/fy21osti/77774.pdf
- Michael Nyberg. (n.d.). California Geothermal Energy Statistics and Data. California Energy Commission. https://ww2.energy.ca.gov/almanac/renewables_data/geothermal/index_cms.php