What is Geothermal Energy?

Geothermal, or Earth energy, is created from sources of heat deep under the Earth’s foremost layer. As the Earth’s core exudes heat to the surrounding rock, magma is created and flows under the planet’s surface. Since the liquid magma is less dense than the surrounding solid rock, the rocks begin to shift and the magma manifests itself on the Earth’s surface as lava.

Furthermore, the energy from the Earth’s core also heats water underground, which is then stored in porous layers of rock. Hot water from the Earth’s deeper layers can be found above ground in geothermal reservoirs, commonly referred to as hot springs or geysers. This water can reach temperatures up to 7000º F and can be harvested to use for daily processes such as heating homes and office buildings or providing hot water.

How is Geothermal Energy Taken from the Earth?
The process of harvesting heat energy from below the Earth’s surface was observed as a practice of the Romans in the first century. They used geysers extensively for bathing, for medicine, and to heat buildings. Some Native American populations also used geothermal energy for cooking and medicine over 10,000 years ago as well as the Maoris of New Zealand who have used geothermal energy for the past few centuries. Currently, geothermal energy is more commonly used in Canada and parts of Europe; specifically, Italy, several Scandinavian countries, and France, which currently heats over 200,000 homes using geothermal energy. Earth energy is also commonly used in Japan, the Philippines, Mexico, China, Indonesia, and Iceland.

To use geothermal energy, engineers design production wells that extract hot water from rock, or pumps that extract heat from where it is stored in the Earth’s interior layers. The raw energy is harvested in the form of heat, water, or steam and used like in any conventional power plant: to turn turbines that produce electricity. The water or steam is then returned to the Earth through injection wells where it can be heated again.

Converting Heat from the Earth’s Crust into Electricity
There are three main types of geothermal power plants. Each is dependent upon the nature of the geothermal reservoir from which the energy is taken. “Dry” or “steam” power plants use steam to power turbine engines that generate electricity. “Hot water” reservoirs yield water with temperatures ranging from 300-700 degrees Fahrenheit. Water in this temperature range can be used in “flash” power plants where the water is flashed into steam through a separator. The steam is then used to turn turbine heads and produce electricity. A third method is to use a heat exchanger. In binary power plants, a heat exchanger is used to pass heat from water in the temperature range of 250-360º F to a second substance that boils at a lower temperature than water. The steam created by the boiling substance is then used to power turbine engines for electricity production. In a binary power plant, the vapor is condensed into a liquid and used repeatedly, preventing the release of any harmful emissions into the air.

The Benefits of Using Geothermal Energy
The current global geothermal infrastructure is about 7,000 megawatts of electricity across 21 countries: the equivalent of almost 30 large coal power plants. Like other alternative energy sources, such as wind and solar energy, methods of using geothermal energy do not pollute the air or surrounding environment. Geothermal power plants are also smaller than other types of plant. These two factors enable geothermal power plants to be built directly on top of their power source, wherever it might be. Furthermore, weather conditions or fuel shocks have no effect on the operation of geothermal plants. Not only does this ensure reliability, it also means that geothermal capital and operational costs are reinvested back into a producer’s own national economy, which is good news for developing and industrialized countries alike. Additionally, geothermal power plants operate in increments and can be expanded as necessary. Lastly, building a geothermal power plants does not require the harvesting of forests, the construction of dams, strip-mines, dangerous oil pipelines, or risky off-shore platforms.

Additional Uses of Geothermal Energy
Geothermal waters are used in agriculture in the pasteurization of milk or to protect vegetables from snow buildup and frost during cold seasons. In urban developments geothermal waters are converted into heat with heat exchangers and used to heat office buildings, residences, or entire districts. Space heating was practiced first in Boise, Idaho and currently is used in over 271 communities in the United States as well as in France, Hungary, Romania, Germany, and Japan. The uses of geothermal waters are various and are specific to the needs of a particular region. In some parts of Ohio, for example, geothermal waters are piped underground to prevent sidewalks and streets from icing over.

The Future of Geothermal Energy
Earth energy exists in more than just hydrothermal reservoirs. Geothermal heat is also produced in the dry rock of the Earth’s layers. Currently, however, the technology has not been developed to harvest energy from layers of dry rock. Should the technology be developed in the near future, we could harvest enormous amounts of heat energy and augment what the United States Environmental Protection Agency has cited among its list of best heating and cooling technologies.

Briana Floyd hails from Springdale, Maryland. She is an engineering major who enjoys literature and nature.