What Is Geothermal Energy and How Does It Work?
Geothermal energy uses the internal heat of the Earth to harness power, including, but not limited to, electricity generation and heating. This heat is called geothermal energy. Geothermal energy is captured mainly through power plants, which utilize the heat from deep inside the Earth, in the form of steam, to generate electricity.
What Does Geothermal Mean?
The official definition of the term geothermal is “of or relating to the internal heat of the Earth.” The term “geothermal” borrows from the Greek words “geo,” which refers to the Earth, and “therme” or “thermos,” which mean heat. The term geothermal has been used since 1875, though humans have been using geothermal energy for longer than the English language has been around — perhaps even thousands of years.
Where Does Geothermal Energy Come From?
Geothermal energy is created deep in the bowels of the Earth — but it is harnessed at or near the Earth’s surface. The energy provided is contained in the heat, in the form of thermal energy. It comes up from the planet’s core and, if captured correctly, can provide energy for a variety of human activities in the modern world, such as electricity and heating.
How Is Geothermal Energy Generated?
Geothermal energy is generated by the thermal energy from the magma deep below the Earth’s surface. The magma heats rocks and parts of the Earth’s crust, as well as underground aquifers. Hot water can be released through geysers, hot springs, steam vents, underwater hydrothermal vents, and mud pots, all of which are all sources of geothermal energy. All these sources of heat, which come indirectly from the core of the planet, can be captured and used to generate energy for human consumption.
What Is Geothermal Energy Used For?
Currently, geothermal energy is used mainly for smaller-scale electricity generation and heating homes and hot water tanks. It can be used directly for heat, including structures such as buildings, parking lots, and sidewalks, or captured thermal steam can be used to generate electricity.
Dozens of countries around the world have developed methods of tapping into geothermal energy, and different types of geothermal energy are available in different areas of the world. In Iceland, for example, abundant geothermal resources have made this form of energy a reliable and inexpensive source of heat and power, while countries such as the United States must drill for geothermal energy, which is more expensive.
Low-temperature geothermal energy can be used for lower-energy applications, such as operating greenhouses, heating homes, running fisheries, and limited industrial production needs. While not as useful as high-temperature geothermal projects, this lower-temperature form of geothermal energy is most efficient when used as a passive heat source as it’s still possible to harness it for electricity generation.
There is also something known as a geothermal heat pump (GHP) that can tap into the planet’s interior heat nearly anywhere in the world. GHPs are drilled into the ground, somewhere between 15 to 350 feet (5 to 100 meters) deep, which is easily shallower than a typical oil and natural gas well. Plus, GHPs do not require bedrock fracturing (fracking) to get to the energy source.
The U.S. Environmental Protection Agency (EPA) and Energy Information Administration (EIA) have called geothermal heating “the most energy-efficient and environmentally safe heating and cooling system.”
Where Is Geothermal Energy Being Used in the World?
The first documented industrial use of geothermal energy was in the late 18th century in Italy, where steam coming from natural vents was utilized in the area now known as the Larderello fields.
By 2015, over 80 countries were using geothermal energy in some form, with the leading adopters located in China, Turkey, Iceland, Japan, Hungary, and the United States. The total worldwide installed capacity for direct use in 2015 was about 73,290 megawatts thermal (MWt), utilizing about 163,273 gigawatt-hours per year.
Geothermal energy is beginning to gain popularity as a source for electricity production as well — 24 countries now have installed geothermal electrical generation capacity, with the largest producers being the United States, Philippines, Indonesia, Mexico, New Zealand, and Italy. In 2016, the total worldwide installed capacity for electrical power generation was about 13,400 MW.
When it comes to utilization factors, geothermal fields run at about 95% efficiency, making it the highest for any form of renewable energy in the world.
How Does a Geothermal Power Plant Work?
Geothermal power plants are some of the smaller power generating facilities (by volume) currently operating in the world. However, there’s growing interest in tapping into the abundant natural energy of the Earth. Several countries are trying to bring geothermal power to places that were unable to take advantage of this incredible form of energy in the past.
There are three main types of geothermal power plants: dry-steam, flash-steam, and binary cycle.
Dry-Steam Power Plants
Dry-steam power plants are the most simple and straightforward: they take advantage of natural underground sources of steam, allowing the gas to travel directly to a turbine, which drives a generator to produce electricity.
The geothermal steam does not require any fossil fuels to propel the turbine. This not only cuts greenhouse gas emissions but it also cuts the need to transport and store fuels. Dry-steam plants emit steam rather than carbon dioxide.
Dry-steam power plants were the first type of geothermal plants built. They were used in Lardarello, Italy, in the early 20th century. Steam technology is still effective today — it’s currently in use at the world’s largest single source of geothermal power, known as The Geysers in Northern California.
The dry-steam power plants in Larderello still supply electricity to over a million people in the nearby region!
Flash-Steam Power Plants
Flash-steam power plants are a bit more complicated. They take high-pressure hot water found deep underground and convert the water to steam. This converted steam is then used to drive generator turbines. When the steam cools and returns to its liquid state, it’s sent back underground to heat up again for use in the near future. Most modern geothermal power plants are of the flash-steam variety.
Iceland famously uses this form of geothermal power plant to supply nearly all of its electrical needs, with the excess warm water produced by the flash-steam process used to heat icy sidewalks and roadways in the freezing winter.
Binary Cycle Power Plants
Binary cycle power plants differ from both the dry-steam and flash-steam plants in one major way: the water or steam from the geothermal reservoir never comes in contact with the turbine generator units. Lower temperature geothermal fluid is mixed with a secondary fluid, which has a lower boiling point than water, and the mixture is run through a heat exchanger. The heated initial fluid causes the secondary fluid to become vapor — this vapor is what drives the turbines and generates electricity, hence the applicable “binary” term.
These power plants are closed-loop systems. Like the other forms of geothermal energy, only water vapor is emitted into the atmosphere. They are not commonly used at present, but future geothermal electricity could come in large part from binary cycle power plants.
As of now, the most notable binary cycle plant in operation is the Beowawe Geothermal Facility in Nevada.
Is Geothermal Energy Renewable?
Yes, geothermal power is a completely renewable energy source. In fact, it is one of the most reliable forms of renewable energy and possibly the least invasive to the natural environment.
Why Is Geothermal Considered a Renewable Energy Resource?
Geothermal is considered renewable because the heat from the Earth is a constant source of energy — it is not finite or limited. Harnessing this energy is possible at all times and will continue to be possible as long as the access point to the thermal energy is open. Furthermore, geothermal energy production is not only renewable, it is a model form of clean energy and energy efficiency.
Where Does the Heat for Geothermal Energy Come From?
The heat for geothermal energy comes from the Earth’s core. Nuclear processes cause extreme temperatures deep in the core. This is mainly due to radioactive decay of isotopes, which are forms of an element that have a different number of neutrons than regular versions of the element’s atom, squeezing out of the high-pressure nucleus of the planet.
Radioactive decay has been a continual process in the core since the formation of the Earth. Temperatures at the Earth’s core are estimated to be more than 10,800 degrees Fahrenheit (about 6,000 degrees Centigrade), which is about as hot as the surface of the sun.
Where Is the World’s Largest Geothermal Field?
The largest geothermal field is in the United States. It is known as the Geysers Geothermal Complex, and has a capacity of 1,517 megawatts. It’s made up of 22 power plants in Northern California. It sits on top of a deep chamber of molten rock that spans more than 30 square miles.
The United States also has one of the highest installed geothermal capacities in the world. Though the efficiency of the country’s plants is relatively low, the capacity factor is high because geothermal is such a stable source of renewable energy unlike the more intermittent wind or solar.
The world’s largest utilized geothermal field per capita is in Iceland, where the small country runs almost exclusively on geothermal power.
How Do Geothermal Wells Work?
Geothermal wells work much like all other wells: deep holes are drilled to access resources buried underground. While other wells, such as water wells or oil wells, are designed to access liquids, geothermal wells are designed to access heat, or, more specifically, heated gas. This heated gas is harnessed in the form of spinning turbines for electricity generation or diverted directly to homes or hot water tanks if used as a heating system.
The Future of Geothermal Energy
While geothermal energy has been around since the beginning of time and used for thousands of years, it is only going to become more pronounced as the world’s energy demands more.
From the first industrial usage in Italy more than a century ago to the massive geothermal projects in China and the United States, it’s clear that our ability to harness the energy of the Earth itself is improving. And given its carbon-free makeup and limitless abundance, it will undoubtedly become an ever-increasing form of energy in the modern world.
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