Geothermal energy is heat that is generated from within the earth. It is a source of energy that is clean, reliable and renewable. It utilizes the nearly limitless heat emanating from the earth's core as a source of power to generate electricity or, mechanically, to heat and cool structure. This energy can be accessed naturally through surface reservoirs or geysers; however, proximity to geysers and steam vents is not required for a geothermal project. Geothermal can also be supplied by drilling wells, ranging from 10-300 feet, into the ground. Currently, geothermal energy supplies more than 10,000 MW to 24 countries worldwide.
Types of Geothermal Energy
- Direct Use refers to producing heat directly from hot water within the earth. Geothermal reservoirs of hot water, which are found a few miles or more beneath the earth's surface, can be used to provide heat directly. Geothermal energy has been used for centuries to heat and cool structures as well as bathing and cooking. For this purpose, a well is drilled into a geothermal reservoir and a mechanical system consisting of piping and a heat exchanger delivers the heat. Once, cooled, water is either injected back into the reservoir or disposed of on the ground's surface. This usage can be applied to heating of individual buildings or entire neighborhoods and towns, known as district heating. Direct use geothermal heat is also used in greenhouses, fish farms and some industrial processes such as milk pasteurization. Most geothermal reservoirs are located in the western states and Alaska and Hawaii.
- Heating and Cooling can be supplied by using the earth's shallow ground temperature. Geothermal heat pumps, also known as ground source heat pumps, utilize energy resources located just 10 feet below the earth's surface to heat and cool buildings. This shallow ground maintains a constant temperature of between 50-60 degrees Fahrenheit. Because the earth's temperature range is typically warmer than winter temperatures and cooler than summer temperatures, this resource can be used to condition indoor air. A geothermal heat pump system is substantially more energy-efficient than a conventional heating and cooling system. It saves energy and money and prevents pollution. The Geothermal Energy Association estimates that 50,000-60,000 heat pumps are installed on an annual basis.
How Geothermal Heating and Cooling Works
Geothermal heat pumps consist of several basic parts. The heat exchanger is a system of pips in the shape of a loop which is buried in the ground near the structure to be served. A fluid, usually a mixture of water and antifreeze, is circulated through the pipes and the heat pump unit is used to extract heat from the water and provide it to the building in the winter. During the summer, the process is literally reversed, and the pump is used to remove heat from the building. This heat can either be returned underground or used to heat the building's water.
Costs of Geothermal Heating and Cooling
An average residential heat pump costs approximately $7,500 (about a 3 ton geothermal unit), while installation costs including drilling are between $10,000 and $30,000 depending on the system. The EPA estimates that homeowners can save 30-70 percent in heating costs and 20-50 percent in cooling costs when compared to conventional systems. The average payback of a geothermal installation ranges from three to ten years. However, systems can be paid back in as little as two years for a heating and cooling system.
- Geothermal Electricity generates electricity from the earth's heat. To generate electricity from geothermal energy, wells are drilled into geothermal reservoirs to obtain hot water found several miles or more below the earth's surface. This hot water is used to drive turbines that create electricity. Power plants feed this energy into the electrical grid. Current geothermal electricity generation in the U.S. is estimated at 3,000 MW connected to the grid. The U.S. continues to produce more geothermal electricity than any other country in the world, comprising approximately 30 percent of the world total geothermal electricity. Geothermal energy now produces enough electricity to meet the needs of 60 million people worldwide.
Benefits of Geothermal Energy
- Cost Effective: Geothermal systems save money in operating and costs. The return on investment for geothermal systems has an average of two to ten years, depending on the size of the project. Low utility bills help building owners see a monthly savings; geothermal systems use 25-50 percent less electricity than conventional heating and cooling systems. Financial incentives are also provides to lower the costs of geothermal and increase savings.
- Durability: Geothermal systems last on average for about 25 years for interior components and 50+ years for the ground loop. They have few mechanical components. Because the system is sheltered from exterior threats such as vandalism and debris build up, geothermal is quite reliable. Also, most geothermal units have warranties ranging from 25-50 years.
- Environmentally Friendly: Geothermal wells do not emit pollutants into the air. They also reduce the demand for coal powered plants to produce electricity. According to the EPA, geothermal systems can reduce energy consumption and emissions up to 44% when compared to air-source heat pumps and up to 72% when compared to electric resistance heating with standard air-conditioning equipment.
- Flexibility: Heat pumps allow a flexible design for new construction or renovation projects. Less hardware is associated with these systems when compared with conventional HVAC units. Equipment rooms can be greatly sized down to allow for more functional space. Geothermal systems also allow zone conditioning, allowing to heat and cool different spaces of a building based on use.
- Low Maintenance: Geothermal pumps are virtually maintenance free. When properly installed, maintenance costs are usually reduced and operation is similar to conventional systems. The components of geothermal systems are located in easily accessible areas of the building, which increases ease for upkeep.
- Storage: Unlike solar and wind power, geothermal energy is constantly available and does not need to be stored. The only limitation to its large-scale implementation is the location of reservoirs. Since these storage facilities are limited to the Western United States, major electrical power plants cannot be developed in the states without reserves. However, EGS research and development is expected to change this in the near future and open up areas that have not previously has access to significant geothermal electricity. Because they utilize a shallow heat source, geothermal heat pumps can be installed nearly anywhere.
- Year-Round Comfort: Geothermal systems uses duct work to supply warm and cool air into a building depending on the time of year. They also provide humidity control naturally by maintaining about 50% relative indoor humidity.
- Quiet Operation: Geothermal heat pumps use no outside condensing units. No noise is exposed when for operation. Even indoors, the system cannot be heard.