How Heat From Inside The Earth Is Tapped As A Source Of Geothermal Energy?
What is Geothermal Energy?
Geothermal energy is thermal energy generated and stored inside the Earth. The word “geothermal” comes from the Greek words geo (earth) and therme (heat). Geothermal energy is a renewable source of energy because heat is continuously produced inside the Earth by the slow decay of radioactive particles, such as potassium-40 and thorium-232, in the Earth’s core (EIA).
The Earth has a molten core surrounded by a thick viscous mantle. This internal heat from radioactive decay and friction is carried to the surface by thermal conduction through the Earth’s crust. Where the geothermal gradient is high near the Earth’s surface, there are geothermal reservoirs of hot water and steam. These reservoirs can occur naturally, where magma comes close to the surface, or can be human-made repositories accessed through drilling (DOE).
Geothermal energy is considered a renewable source because the heat emanating from the interior of the Earth is constantly being produced and replenished (TWI). The Earth will continuously produce heat as long as radioactive elements are present in its core. Unlike fossil fuels which take millions of years to form, the heat generated inside the Earth is constantly regenerated.
How is Heat Generated Inside the Earth?
The Earth’s internal heat comes from two main sources: radioactive decay of minerals and residual heat from planetary formation.
Radioactive decay involves the gradual breakdown of unstable radioactive elements like uranium, thorium, and potassium. As these elements decay, they release heat. This accounts for about half of the heat in the Earth’s interior.
The other half of the heat comes from primordial heat left over from the formation of the planet about 4.5 billion years ago. Intense collisions and friction between rock particles generated tremendous heat as the Earth formed from accretion of cosmic debris. Some of this ancient heat still persists today.
This internal heat warms the core and mantle of our planet. It drives important geological processes like tectonic plate movements, volcanism, and the planet’s magnetic field. Understanding the origins and mechanisms of the Earth’s internal heat gives insight into these dynamic systems shaping our world.
Types of Geothermal Resources
There are three main types of geothermal resources that can be used to generate electricity:
Hydrothermal Resources
Hydrothermal resources contain hot water or steam and are the most common type of geothermal resource. They occur where groundwater has seeped deep underground and been heated by hot rocks. The heated water then rises back up, sometimes erupting as hot springs or geysers Types of Geothermal Power Plants. Hydrothermal resources have the highest energy content and are the easiest to harness for electricity generation.
Geo-Pressured Resources
Geo-pressured resources contain hot water under pressure. They are found in places where high temperature and pressure have trapped water between layers of impermeable rock. Drilling into these resources releases hot water that can be converted into electricity Geothermal Energy.
Hot Dry Rock Resources
Hot dry rock resources consist of hot rock with limited water content. They are accessed by drilling wells into the hot rock and pumping water through the space between the wells. As the injected water passes through the hot rock, it heats up and can be extracted as hot water or steam to generate electricity Geothermal Energy.
Locations of Geothermal Activity
Geothermal energy can be found in areas where heat from the Earth’s core rises close enough to the surface to be tapped for energy production. The key locations for geothermal activity are:
Plate Boundaries
Places where tectonic plates meet tend to have high geothermal activity as the plates shift and collide, allowing magma and heat to rise up. Notable plate boundaries with geothermal potential include the Pacific Ring of Fire around the rim of the Pacific Ocean. EIA
Hot Spots
Hot spots like Yellowstone National Park in the United States often have significant geothermal resources as magma chambers heat water which rises to the surface as hot springs and geysers. The islands of Hawaii were also formed by geothermal hot spots.
Volcanically Active Areas
Any region with active or geologically young volcanoes tend to have accessible geothermal resources, as seen at famous volcanic sites like Mount Vesuvius in Italy and Mount Fuji in Japan.
Technologies to Harness Geothermal
There are several ways geothermal energy is harnessed and used for electricity production and heating/cooling applications.
Geothermal Power Plants
Geothermal power plants use the heat from geothermal reservoirs to produce electricity. There are three main types of geothermal power plant technologies:
- Dry steam plants that use steam directly from a geothermal reservoir to turn generator turbines. The first geothermal power plant was opened at Larderello in Italy in 1911 and was a dry steam plant (Electricity Generation, 2022).
- Flash steam plants that pull deep, high-pressure hot water into lower pressure tanks and use the resulting flashed steam to drive turbine generators.
- Binary cycle plants that pass geothermal fluid through heat exchangers to heat a secondary fluid with a lower boiling point that vaporizes and drives turbine generators.
Binary cycle plants are the most common geothermal power plants today because they are suitable for lower temperature reservoirs (IRENA, 2022).
Geothermal Heating/Cooling Systems
Geothermal heat pumps use stable ground or water temperatures near the Earth’s surface to control building temperatures above ground. In winter, heat is extracted and concentrated indoors; in summer, heat is extracted from buildings and dispersed into cooler ground. Geothermal heat pumps use 25-50% less electricity than conventional heating/cooling systems (Geothermal Basics, 2022).
Direct Use Applications
Geothermal reservoirs can provide direct heating for applications like greenhouse heating, industrial processing, aquaculture, and district heating. Hot geothermal fluid can also be used directly for therapeutic baths and spas. Direct use of geothermal heat does not require converting heat into electricity.
Advantages of Geothermal
Geothermal energy has several notable advantages that make it an attractive renewable energy source. First, geothermal is a renewable energy source. The heat within the earth is constantly being replenished and will never run out, making geothermal a sustainable long-term energy solution (1).
Geothermal plants also provide reliable baseload power that is available 24/7, regardless of weather conditions or time of day. Geothermal energy has high capacity factors of 90-95%, compared to the typical 30% capacity factors of other renewables like solar and wind power (2). This means geothermal power plants can operate continuously with excellent availability.
In addition, geothermal energy helps reduce greenhouse gas emissions when displacing fossil fuel electricity generation. Geothermal power plants emit little to no greenhouse gases because no fuel is combusted. The geothermal working fluid is usually reinjected back into the reservoir after producing electricity (1). This makes geothermal an environmentally friendly energy option.
(1) https://www.enelgreenpower.com/learning-hub/renewable-energies/geothermal-energy/advantages
(2) https://www.twi-global.com/technical-knowledge/faqs/geothermal-energy/pros-and-cons
Disadvantages of Geothermal
While geothermal energy has several advantages, there are some drawbacks to consider as well:
High upfront costs. Drilling geothermal wells and building power plants requires significant capital investment upfront before any energy can be generated. This can make geothermal projects cost prohibitive, with development costs ranging from $2-5 million per MW of installed capacity.1
Limited to certain geographic locations. Geothermal energy is only feasible in areas with suitable hydrothermal resources, such as along tectonic plate boundaries, volcanic hot spots, and some subduction zones. This limits where geothermal plants can be built.2
Potential emissions of toxins. Geothermal reservoirs can contain gases like hydrogen sulfide, ammonia, methane, and carbon dioxide which may be released into the atmosphere during drilling and energy generation. Proper containment systems are needed to limit these emissions.3
Notable Geothermal Projects
There are several notable large-scale geothermal projects operating around the world today:
The Geysers, California
Located in the Mayacamas Mountains north of San Francisco, The Geysers is the largest complex of geothermal power plants in the world. It consists of 22 power plants with an installed capacity of over 2,000 megawatts, making it one of the largest electricity producing geothermal fields globally. The Geysers produces enough electricity to meet the needs of more than 1 million homes.
Wairakei, New Zealand
The Wairakei geothermal power station located near Taupo, New Zealand was the first wet steam power station in the world. Commissioned in 1958, Wairakei was the prototype for large-scale wet steam plants at the Geysers and around the world. At its peak, Wairakei produced 185 megawatts of electricity from steam and hot water extracted from underground wells.
Iceland’s Geothermal Use
Iceland is a global leader in geothermal energy, with five major geothermal power plants producing over 665 megawatts of electricity. Nearly 90% of Iceland’s homes are heated using geothermal energy. Iceland is also working on using geothermal energy for industrial purposes such as aluminum smelting. Geothermal provides about 25% of Iceland’s total primary energy supply.
Future of Geothermal
The future of geothermal energy looks bright, with new technologies unlocking greater potential. One major area of development is enhanced geothermal systems (EGS). EGS can access heat buried deeper underground through techniques like hydraulic fracturing. By fracturing hot rock and circulating water through it, EGS can extract heat for power generation even where natural reservoirs are lacking.
Co-production of geothermal energy with oil drilling also offers promise. Water brought to the surface during oil and gas operations can be used for geothermal heating and power. This approach reduces drilling costs and maximizes resource use.
Floating geothermal plants present another opportunity to expand geothermal capabilities. Floating power stations can be located offshore, giving access to geothermal resources under the seafloor. Experimental projects are underway, including a floating plant off the coast of Iceland.
With such innovations on the horizon, geothermal is poised to play an even greater role in the global shift toward renewable energy.
Conclusions
We’ve discussed the unique nature of geothermal energy as a renewable resource that taps into the immense heat generated within the Earth’s core. Unlike wind or solar, geothermal provides constant baseline power, regardless of weather or time of day. Technologies like enhanced geothermal systems demonstrate the large scale potential of advanced geothermal plants, while smaller scale direct use applications provide heating and cooling in over 80 countries already.
With the urgent need to transition away from fossil fuels, geothermal stands out as a promising green energy source. It offers a substantial, reliable energy supply without carbon emissions, air pollution or resource depletion. While geothermal has some geographical limitations and upfront costs, its ability to provide constant clean power gives it major advantages. With further research and investment, geothermal can play an increasingly vital role in a sustainable energy future.
