What is Geothermal Energy?
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.
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.
Advantages of geothermal energy
There are many advantages of geothermal energy but also some challenges that need to be overcome in order to fully exploit this natural resource.
1. Environmentally Friendly
Geothermal energy is more environmentally friendly than conventional fuels like coal and other fossil fuels. In addition, the CO2 footprint of a geothermal power plant is small. Geothermal energy is associated with a certain amount of pollution, but it is relatively low compared to fossil fuels.
2. Renewable
Geothermal energy is a renewable energy source that will last until the earth is destroyed by the sun in around 5 billion years. The hot reservoirs on earth are replenished naturally, making them both renewable and sustainable.
3. Huge Potential
Worldwide energy consumption is currently around 15 terawatts, a far cry from the total potential energy available from geothermal sources.
While we are currently unable to use most of the reservoirs, there is hope that the number of usable geothermal resources will increase with the ongoing research and development in the industry.
It is currently estimated that geothermal power plants could deliver between 0.0035 and 2 terawatts of power.
4. Sustainable/Stable
Geothermal energy is a reliable source of energy compared to other renewable resources such as wind and solar power. This is because, unlike wind or solar energy, the resource is always available to be tapped.
5. Heating and Cooling
For the effective use of geothermal energy to generate electricity, water temperatures of over 150 ° C are required to drive turbines. Alternatively, the temperature difference between the surface and a soil source can be used.
Since the ground is more resistant to seasonal heat changes than the air, it can act as a heat sink/source with a geothermal heat pump just two meters below the surface.
6. Reliable
The energy generated from this resource is easy to calculate as it does not fluctuate like other energy sources such as the sun and wind. This means that we can predict the performance of a geothermal system with a high degree of accuracy.
7. No Fuel Required
Because geothermal energy is a naturally occurring resource, no fuel is required, such as fossil fuels, which are finite resources that must be mined or otherwise extracted from the earth.
8. Rapid Evolution
A lot of geothermal research is currently underway, which means that new technologies are being created to improve the energy process. There are more and more projects to improve and expand this industrial sector. With this rapid development, many of the current disadvantages of geothermal energy are being alleviated.
Disadvantages of Geothermal Energy
1. Location Restricted
The single biggest disadvantage of geothermal energy is that it is site-specific. Geothermal plants need to be built in places where the energy is accessible, which means that some areas cannot use this resource.
Of course, this is not a problem if you live in a place where geothermal energy is easily accessible, for example in Iceland.
2. Environmental Side Effects
Although geothermal energy does not normally emit greenhouse gases, many of these gases are stored underground and released into the atmosphere when digging. While these gases are also naturally released into the atmosphere, the rate increases near geothermal facilities. However, these gas emissions are still far lower than those associated with fossil fuels.
3. Earthquakes
Geothermal energy also runs the risk of causing earthquakes. This is due to changes in the structure of the earth as a result of the trench. This problem is more common with improved geothermal power plants that push water into the earth’s crust to open cracks for greater exploitation of the resource.
However, since most geothermal systems are not located in population centers, the impact of these earthquakes is relatively minor.
4. High Costs
Geothermal energy is an expensive resource. The prices for a system with a capacity of 1 megawatt are between 2 and 7 million US dollars. However, if the upfront costs are high, the expense can be amortized as a long-term investment.
5. Sustainability
In order to maintain the sustainability of geothermal energy, the liquid must be pumped back into the underground reservoirs faster than it is depleted. This means that geothermal energy must be properly managed in order to maintain its sustainability.
