Geothermal energy is heat energy from the earth—Geo (earth) + thermal (heat). Geothermal resources are reservoirs of hot water that exist or are human-made at varying temperatures and depths below the Earth’s surface.
The word geothermal comes from the Greek words geo (earth) and therme (heat). Geothermal energy is a renewable energy source because heat is continuously produced inside the earth. People use geothermal heat for bathing, heating buildings, and generating electricity.
Geothermal energy is the heat that comes from the sub-surface of the earth. It is contained in the rocks and fluids beneath the earth’s crust and can be found as far down as the earth’s hot molten rock, magma.
To produce power from geothermal energy, wells are dug a mile deep into underground reservoirs to access the steam and hot water there, which can then be used to drive turbines connected to electricity generators. There are three types of geothermal power plants; dry steam, flash, and binary.
Dry steam is the oldest form of geothermal technology and takes the steam out of the ground and uses it to directly drive a turbine. Flash plants use high-pressure hot water into cool, low-pressure water whilst binary plants pass hot water through a second liquid with a lower boiling point, which turns to vapor to drive the turbine.
Examples of Geothermal Energy
The heat of the Earth used to produce geothermal energy stems from impressive and spectacular natural phenomena that are intrinsic to our planet. The best-known examples of geothermal energy are volcanoes, fumaroles, boric-acid fumaroles, and geysers.
Volcanoes
Volcanoes are the most famous natural display of geothermal energy on the planet. Extremely complex geological structures, they have been generated within the earth’s crust since the beginning of time by the rising – following eruptive activity – of molten rock mass, magma, formed below or inside the earth’s crust. The temperature of magma outflow is usually between 650 and 1200 °C.
About 91% of Earth’s volcanoes are underwater, while there are about 1500 that are active on land. The land around volcanoes has great geothermal potential, which can be used to produce renewable energy, like at the Cerro Pabellón plant in Chile.
Fumaroles
Fumaroles are secondary volcanic phenomena. These small but deep cracks in the ground release gas at temperatures that can range from 100 to 900 °C. The drop in temperature when the gas comes in contact with the air causes it to condense and create fumes, which is where the phenomenon gets its name.
Fumaroles are generally located near craters or active volcanoes, as well as in areas where volcanic activity has stopped, but minor geothermal, or even hydrothermal, events still happen. Their complex chemical composition features a very strong acidity (with a pH almost at zero) and profoundly alters the surrounding soil, where the yellow coloring of sulfur often stands out.
Boric-acid Fumaroles and Geysers
Boric-acid fumaroles are violent emissions of water vapor from the subsoil, at temperatures between 150 and 230 °C. They feature constant emissions and very high pressure (up to 20 atmospheres). Boric-acid fumaroles are the main feature of the Larderello area.
Geysers
Geysers are very rare sources of boiling water, as they require geological and climate conditions that are found in very few areas of the planet. Iceland and Yellowstone National Park (in Wyoming, USA) are the two most famous areas featuring geysers: in both, a large quantity of geothermal energy is produced.
Geysers are powerful jets of water and steam, usually erupting at regular intervals. The duration of the jet can vary from a few seconds to several minutes. The name comes from the Icelandic verb gjósa, meaning to erupt, or to release in jets. And Geysir is the name of the most famous Icelandic geyser, which, in its most active periods, was able to emit jets up to 60 meters high.
Geothermal energy comes from deep inside the earth
The slow decay of radioactive particles in the earth’s core, a process that happens in all rocks, produces geothermal energy.
The earth has four major parts or layers:
- An inner core of solid iron that is about 1,500 miles in diameter.
- An outer core of hot molten rock called magma that is about 1,500 miles thick.
- A mantle of magma and rock surrounds the outer core which is about 1,800 miles thick.
- A crust of solid rock forms the continents and ocean floors that is 15 to 35 miles thick under the continents and 3 to 5 miles thick under the oceans.
Scientists have discovered that the temperature of the earth’s inner core is about 10,800 degrees Fahrenheit (°F), which is as hot as the surface of the sun. Temperatures in the mantle range from about 392°F at the upper boundary with the earth’s crust to approximately 7,230°F at the mantle-core boundary.
The earth’s crust is broken into pieces called tectonic plates. Magma comes close to the earth’s surface near the edges of these plates, which is where many volcanoes occur. The lava that erupts from volcanoes is partly magma. Rocks and water absorb heat from magma deep underground. The rocks and water found deeper underground have the highest temperatures.
Is geothermal energy renewable?
Yes, Because its source is the almost unlimited amount of heat generated by the Earth’s core. Even in geothermal areas dependent on a reservoir of hot water, the volume taken out can be reinjected, making it a sustainable energy source.
Geothermal Power Plant
Geothermal power plant (flash steam, combined cycle) in Iceland. Geothermal power plants are used in order to generate electricity by the use of geothermal energy (the Earth’s internal thermal energy). They essentially work the same as coal or nuclear power plant, the main difference being the heat source.
Geothermal power plants use hydrothermal resources that have both water (hydro) and heat (thermal). Geothermal power plants require high-temperature (300°F to 700°F) hydrothermal resources that come from either dry steam wells or hot water wells.
People use these resources by drilling wells into the earth and then piping steam or hot water to the surface. The hot water or steam powers a turbine that generates electricity. Some geothermal wells are as many as two miles deep.
Types of geothermal power plants
There are three basic types of geothermal power plants:
- Dry steam plants use steam directly from a geothermal reservoir to turn generator turbines. The first geothermal power plant was built in 1904 in Tuscany, Italy, where natural steam erupted from the earth.
- Flash steam plants take high-pressure hot water from deep inside the earth and convert it to steam to drive generator turbines. When the steam cools, it condenses to water and is injected back into the ground to be used again. Most geothermal power plants are flash steam plants.
- Binary cycle power plants transfer the heat from geothermal hot water to another liquid. The heat causes the second liquid to turn to steam, which is used to drive a generator turbine.
Use of geothermal energy
Some applications of geothermal energy use the earth’s temperatures near the surface, while others require drilling miles into the earth. There are three main types of geothermal energy systems:
- Direct use and district heating systems
- Geothermal power plants
- Geothermal heat pumps
1. Direct use and district heating systems
Direct use and district heating systems use hot water from springs or reservoirs located near the surface of the earth. Ancient Roman, Chinese, and Native American cultures used hot mineral springs for bathing, cooking, and heating.
Today, many hot springs are still used for bathing, and many people believe the hot, mineral-rich waters have health benefits.
Geothermal energy is also used to directly heat individual buildings and to heat multiple buildings with district heating systems. Hot water near the earth’s surface is piped into buildings for heat. A district heating system provides heat for most of the buildings in Reykjavik, Iceland.
Industrial applications of geothermal energy include food dehydration (drying), gold mining, and milk pasteurizing.
2. Geothermal electricity generation
Geothermal electricity generation requires water or steam at high temperatures (300° to 700°F). Geothermal power plants are generally built where geothermal reservoirs are located, within a mile or two of the earth’s surface.
3. Geothermal heat pumps
Geothermal heat pumps use the constant temperatures near the surface of the earth to heat and cool buildings. Geothermal heat pumps transfer heat from the ground (or water) into buildings during the winter and reverse the process in the summer.
Pros and Cons of Geothermal Energy
| Pros | Cons |
| This energy source is more environmentally friendly than conventional fuel sources. | An expensive resource to tap into, with high upfront costs ranging from around $2-$7 million for a plant with a 1-megawatt capacity. |
| A source of renewable energy. | Gases are released into the atmosphere during digging. |
| The number of exploitable geothermal resources will increase with ongoing research and development in the industry. | Geothermal energy runs the risk of triggering earthquakes. |
| A sustainable source of energy as its always available unlike wind and solar. | Expensive resource to tap into, with high upfront costs ranging from around $2-$7 million for a plant with a 1-megawatt capacity. |
| A reliable source as its easier to predict the power output from a geothermal plant with a high degree of accuracy. | Energy fluid needs to be pumped back into the underground reservoirs faster than it is depleted. Management is required to maintain sustainability. |
| No fuel is required. | |
| Increase in exploration meaning that new technologies are being created to improve the energy process. | |
| Pollution levels are much lower compared to fossil fuels. |
Advantages of geothermal energy
There are many advantages of geothermal energy:
- Geothermal Energy is a Renewable source of Energy.
- It is Environment Friendly
- No Fuel Needed
- Geothermal Energy is Available in Abundant Supply
- Significant Savings for Homeowners
- Smallest Land Footprint
- Innovation in Technology
- Almost No Noise Pollution
- Free Hot Water Production
Disadvantages of geothermal energy
- Suitable to Particular Region
- Geothermal Power Has High Initial Costs
- Cost of Powering the Pump
- Geothermal Power May Cause Surface Instability
- Environmental Concerns
- High Temperatures Needed
- May Run Out of Steam
- Sustainability Issues
- Distribution Costs