Understanding Geothermal Energy | A Quick Study

Understanding Geothermal Energy

by | Educational, Energy

Humans have been using geothermal energy for millennia, be it bathing in hot springs to using it as a renewable energy source in homes. Humans have been using geothermal energy for millennia, be it bathing in hot springs to using it as a renewable energy source in homes.   

High-pressure geysers are highlighted in many travelers’ holiday photos from Iceland to Chile — and more than 83 countries now exploit their geothermal resources.  

Let’s look at how geothermal technologies work, the history of geothermal energy, and how energy below the Earth’s crust can help tackle climate change by reducing fossil fuel emissions.  

What Is Geothermal Energy and How Does It Work? 

According to the Cambridge Dictionary, geothermal means “of or connected with the heat inside the Earth.” If you were to dig a deep hole into the Earth, the further down you go, the hotter it would become. That natural heat is what we call geothermal energy.  

Some areas below the crust are full of water that gets heated up by this thermal energy. Geothermal power plants dig wells 1-2 miles deep and pump hot water to the surface to power turbines for electricity generation. Geothermal heat pumps use this hot water to warm homes and businesses. It’s common to find geothermal power plants close to areas with geysers, volcanic activity, and hot springs.  

To understand geothermal energy, we must understand that thermal energy, or heat, is produced by rises in temperature.  

At an atomic level, electrons move around the nucleus of an atom. When pressure is applied to the atom — in this case, heat caused by a rise in temperature — the electrons move more quickly, crashing into each other and emitting thermal energy as heat. If we think about a boiling kettle, the water starts to heat up and move around, eventually boiling and releasing steam.   

The Earth’s core is the energy source for the heat and movement that provides us with geothermal energy. 

What Does Geothermal Mean?  

The word geothermal stems from Greek, from Earth (geo) and heat (therme). Geothermal energy is all the Earth’s stored heat energy.  

Geothermal energy is a renewable energy that comes from the Earth’s core, a solid iron core some 4,000 miles below the surface of the Earth. The core is estimated to be between 5,000 to 11,000 degrees Fahrenheit (2,760-6,093 Celsius), producing continual heat because of the radioactive decay of particles in rocks.  

Around this core is a molten iron core called magma. Then comes the mantle, with the Earth’s crust covering the mantle. Atop the crust is the surface as we know it.   

Molten rock, or magma, comes close to the Earth’s surface where the crust is thin, reaching temperatures of around 700 degrees Fahrenheit (370 Celsius). We see magma when volcanoes erupt as tectonic plates move.  

When magma heat is transferred to water that humans can access — some close to the surface and some many miles down — we can use the hot water as a geothermal resource. Magma can be called a geothermal fluid because it is something that transfers heat to the surface. 

Where Does Geothermal Energy Come From? 

Origins Geothermal Energy | Usage Globe-image

The Earth’s core is always conducting its thermal energy from the center of the Earth to the Earth’s surface. The Earth’s core is always conducting its thermal energy from the center of the Earth to the Earth’s surface. 

The four layers of the Earth are:  

  • The inner core (solid iron) 
  • Outer core (molten iron) 
  • Mantle (magma and rocks) 
  • Crust (surface) 

The slow decay of the radioactive particles in these layers produces geothermal energy, which is coming from deep inside the Earth, and conducting out to the surface of the Earth. 

How Is Geothermal Energy Used and What Is It Used For? 

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Geothermal energy has many modern and historical applications, with its first uses being for bathing, cooking, and heating. Our modern understanding of geothermal energy is more about energy production.  

There are many geothermal projects around the world. We use geothermal to produce electricity, district heating, and more. Your energy supplier can provide information about clean energy in your area.  

We can define the use of the Earth’s geothermal resources into four main types, and all require water and heat. The most common is hydrothermal. The other three — geo-pressurized, hot dry rock, and magma — are all in developmental stages. Hydrothermal resources are all used differently, depending on how deep the water is and its temperature. 

Low Temperature, Direct Use, or Heating 

Spas, district heating, crop growth, and other industrial processes like heating greenhouses can start with a hydrothermal resource as low as 50 degrees Fahrenheit (10 Celsius). These hydrothermal resources exist in almost every country in the world. About 45 states in the United States heat and cool some of their homes this way, as does nearly every home in Iceland with its geothermal heating systems 

High-Temperature Electricity Production 

Electricity can be generated once the hydrothermal resources hit 220 degrees Fahrenheit (104 Celsius), albeit most geothermal electricity plants’ temperatures range from 300-700 degrees Fahrenheit (149-371 Celsius). Geothermal reservoirs are known to reach 1,000 degrees Fahrenheit (538 Celsius).  

Dry steam, or vapor-dominated reservoirs, draw steam from underground geothermal reservoirs up to geothermal power plants to drive turbines that produce electricity. The Geysers geothermal field complex in Northern California is an example of a dry steam source. Old Faithful in Yellowstone National Park is another, but it’s not used to produce electricity.  

Hot water or flash steam power plants are the most common power plants. Typically, they draw from geothermal reservoirs of water whose temperatures exceed 360 degrees Fahrenheit (182 Celsius). Very hot water flows upwards, eventually turning, or flashing, into steam as the pressure that forced the water upwards reduces. This steam powers turbines to create electricity.   

Any leftover water and condensed steam return to the reservoir. It will be reheated and repeat its journey, making hot water (flash steam) a sustainable resource and renewable energy.  

Binary cycle power plants use water at lower temperatures in a slightly different manner, albeit the principle is the same. At binary cycle plants, the water temperature is more typically 225-360 degrees Fahrenheit (107-182 Celsius).  

Instead of using the steam directly, the hot water heats another compound with a lower boiling point, usually isobutane, pentane, or ammonia. This compound is called a working fluid. It’s vaporized in a heat exchanger, which turns a turbine to create electricity. All the water and fluids are kept separate. The water is injected back underground, where it’s reheated and used again in a closed-loop system.  

Geothermal is a useful addition to national grid managers handling their baseload the minimum electrical demand on a grid — because they offer consistent electricity generation. This reliability is important for any business looking for an energy supplier offering geothermal energy as part of its supply package.  

A new branch of energy is also being explored, called Enhanced Geothermal Systems, or EGS. The U.S. Department of Energy recently announced $25 million in funding to examine the potential of EGS. Enhanced Geothermal Systems aims to create artificial geothermal reservoirs by injecting water into “dry” cracks and gaps underground, creating water-based heat resources, or reservoirs, that can then house a binary cycle power plant at the surface. 

Where Is Geothermal Energy Being Used in the World? 

Geothermal Energy | Where is Renewable Energy used - geo city image 

The Italians built the very first geothermal energy plant in 1904 in Larderello, Italy.   

Geothermal is still not a massive player in the renewables market, lagging behind solar, wind, and hydro. It attracts nowhere near as much investment as other renewables. However, the continual availability of geothermal energy coupled with its affordability and small carbon footprint make it an increasingly popular green energy option.  

Geothermal plants are usually found along a geological fault line. The United States is the leading producer of geothermal energy globally, with an installed capacity of 3,639 megawatts in 2018, closely followed by Indonesia. The Philippines, Kenya, Turkey, New Zealand, Italy, and Iceland are all major players that are increasing their capabilities.  

California accounts for more than 71% of the United State’s total geothermal energy production; Nevada is the other big producer at 23%. However, only 5% of all California’s entire state electricity generation is from geothermal. 

Where Was Geothermal Energy First Used? 

Geothermal energy first came into industrial use at the start of the 20th century in Tuscany, Italy.  

Prince Piero Ginori Conti of Trevignano managed to power five light bulbs using the world’s first geothermal energy generator in 1904 at Larderello, a dry steam field. Various expansions took place, and by 1913 another world first was completed — a working geothermal power plant was built. It powered the local railway and towns or Larderello and Volterra.  

Power is still created in the same area as the 1904 plant. There are now 34 modern plants generating 800 megawatts of power which is around 2% of Italy’s power needs. 

How Does a Geothermal Power Plant Work? 

Geothermal Power Plant | Illustration How it Works

A geothermal power plant is often found near the boundaries of the Earth’s tectonic plates and near underground reservoirs of hot water. There are two types — a geothermal power plant and a geothermal heat pump.  

At a geothermal power plant, hot water is pumped, under high pressure, from deep underground. As it reaches the surface, its pressure drops. The water turns to steam, spinning a turbine that, via a generator, creates electricity. The steam eventually cools — most plants use cooling towers for their cooling systems — and the condensed water is injected back into the ground via injection wells, and the heating process is repeated.  

A geothermal heat pump is usually used as a heating system for homes, swimming pools, industry and more. A circuit of pipes, filled with water or a mixture of fluids, are buried underground. These pipes warm up thanks to the underground geothermal energy.   

A pump then pushes this warm water into buildings’ radiators. The structures warm up and as the warm water cools and the pump injects the cooled water back underground where it reheats before returning once more to the buildings. 

Why Is Geothermal Considered a Renewable Energy Resource? 

Geothermal is considered renewable energy because its power source — the Earth’s core — is almost unlimited when compared to human timescales. Also, there’s no need to burn fossil fuels to extract geothermal energy. As a result, there are fewer harmful emissions, classifying it as a sustainable energy form too.  

Some carbon dioxide — a greenhouse gas but not a pollutant — is released as part of the power plant’s processes. Many power plants reinject any released carbon dioxide into its underground reservoirs, reducing further any carbon dioxide emissions. It’s important to stress that geothermal processes do not create the CO2. It’s a natural gas present in the rocks and water. 

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Where Does the Heat for Geothermal Energy Come From? 

Geothermal energy comes from the Earth’s core, 4,000 miles below the surface of the Earth. Scientists estimate its temperature to be between 5,000 to 11,000 degrees Fahrenheit (2,760 to 6,093 Celsius).  

This heat transfers to a molten iron outer core then to the mantle. The final step for the heat is to the Earth’s crust. Once near the surface, fissures and underground water channels touch the mantle, heating the water.  

It is this super-heated water that we tap into to provide the steam and heat for geothermal energy. 

Where Is the World’s Largest Geothermal Field? 

Even though the hot water (flash) geothermal power plants are the most common type, it is a dry steam plant that’s the world’s largest plant.  

The Geysers Geothermal Complex in the United States features 22 power plants lined up around 30 square miles to the north of San Francisco. Their combined capacity is 1,571 megawatts. 

How Do Geothermal Wells Work? 

Geothermal wells work by tapping into the heat below the Earth’s surface. In simple terms, holes are drilled, and then the heat is extracted.  

A small well, for a home or business premise, would see holes drilled and pipes placed around 100-300 feet below the ground, where it is warmer than above ground. Water or a mixed solution passes through the pipes, heating up underground. A heat pump system then brings it into a building and pumps the cooler liquids back underground to be reheated.  

On an industrial scale, holes are drilled up to several kilometers deep. Geothermal plants are looking to tap into the heat and bring that heat to the surface as hot water or steam to drive turbines and create electricity. 

Geothermal Energy Efficiency 

Geothermal Energy Efficiency | - couple thermal-water image

Energy use is a hot topic due to climate change. Geothermal is clean energy that offers a lot of the renewable energy field, energy efficiency, a stable base load to grids, and the ability to warm homes and generate electricity..  

Always ask your energy supplier about sourcing your electricity from renewable sources, and ask if geothermal is an option. 

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